Female infanticide

From Wikipedia, the free encyclopedia

 

Female infanticide is the deliberate killing of newborn female children. In countries with a history of female infanticide, the modern practice of sex-selective abortion is often discussed as a closely related issue. Female infanticide is a major cause of concern in several nations such as China, India and Pakistan. It has been argued that the low status in which women are viewed in patriarchal societies creates a bias against females.

In 1978, anthropologist Laila Williamson, in a summary of data she had collated on how widespread infanticide was, found that infanticide had occurred on every continent and was carried out by groups ranging from hunter gatherers to highly developed societies, and that, rather than this practice being an exception, it has been commonplace. The practice has been well documented among the indigenous peoples of Australia, Northern Alaska and South Asia, and Barbara Miller argues the practice to be "almost universal," even in the West. Miller contends that female infanticide is commonplace in regions where women are not employed in agriculture and regions in which dowries are the norm. In 1871 in The Descent of Man, and Selection in Relation to Sex, Charles Darwin wrote that the practice was commonplace among the aboriginal tribes of Australia.

In 1990, Amartya Sen writing in the New York Review of Books estimated that there were 100 million fewer women in Asia than would be expected, and that this amount of "missing" women "tell[s] us, quietly, a terrible story of inequality and neglect leading to the excess mortality of women." Initially Sen's suggestion of gender bias was contested and it was suggested that hepatitis B was the cause of the alteration in the natural sex ratio. However it is now widely accepted that the numerical worldwide deficit in women is due to gender specific abortions, infanticide and neglect.

In seventh-century Arabia, before Islamic culture became established, female infanticide was widely practiced. This is attributed by scholars to the fact that women were deemed "property" within those societies. Others have speculated that to prevent their daughters from a life of misery, the mothers would kill the child. With the arrival of Islamic rule the practice was made illegal.

China

Matteo Ricci

China has a history of female infanticide spanning 2,000 years. With the arrival of Christian missionaries in the late sixteenth century, the missionaries discovered female infanticide was being practiced – newborns were seen thrown into rivers or onto rubbish piles. In the seventeenth century, Matteo Ricci documented that the practice occurred in several of China's provinces and that the primary reason for the practice was poverty.

In 19th-century China, female infanticide was widespread. Readings from Qing texts show a prevalence of the term ni nü ("to drown girls"), and drowning was the common method used to kill female children. Other methods used were suffocation and starvation. Leaving a child exposed to the elements was another method of killing an infant: the child would be placed in a basket which was then placed in a tree. Buddhist nunneries created "baby towers" for people to leave a child; it is however unclear as to whether the child was being left for adoption or if it had already died and was being left for burial. In 1845 in the province of Jiangxi, a missionary wrote that these children survived for up to two days while exposed to the elements, and that those passing by would pay no attention.

The majority of China's provinces practiced female infanticide during the 19th century. In 1878, French Jesuit missionary Gabriel Palatre collected documents from 13 provinces, and the Annales de la Sainte-Enfance (Annals of the Holy Childhood) also found evidence of infanticide in Shanxi and Sichuan. According to the information collected by Palatre, the practice was more widely spread in the southeastern provinces and in the Lower Yangzi River region.

Chinese anti infanticide tract circa 1800.

 

In China, the practice of female infanticide was not wholly condoned. Buddhism in particular was quite forceful in its condemnation of it. Buddhists wrote that the killing of young girls would bring bad karma; conversely, those who saved a young girl's life either through intervening or through presents of money or food would earn good karma, leading to a prosperous life, a long life and success for their sons. However the Buddhist belief in reincarnation meant that the death of an infant was not final, as the child would be reborn; this belief eased the guilt felt over female infanticide.

The Confucian attitude towards female infanticide was conflicted. By placing value on age over youth, Confucian filial piety lessened the value of children. The Confucian emphasis on the family led to increasing dowries which in turn led to a girl being far more expensive to raise than a boy, causing families to feel they could not afford as many daughters. The Confucian custom of keeping the male within the family meant that the money spent on a daughter's upbringing along with the dowry would be lost when she married, and as such girls were called "money-losing merchandise". Conversely the Confucian belief of Ren led Confucian intellectuals to support the idea that female infanticide was wrong and that the practice would upset the balance between yin and yang.

A white paper published by the Chinese government in 1980 stated that the practice of female infanticide was a "feudalistic evil". The state's official position on the practice is that it is a carryover from feudal times, and is not a result of the states one-child policy. Jing-Bao Nie argues however that it would be "inconceivable" to believe there is no link between the state's family planning policies and female infanticide.

India

A map of India's child sex ratio, 2011.

 

The dowry system in India is one given reason for female infanticide; over a time period spanning centuries it has become embedded within Indian culture. Although the state has taken steps^[c] to abolish the dowry system, the practice persists, and for poorer families in rural regions female infanticide and gender selective abortion is attributed to the fear of being unable to raise a suitable dowry and then being socially ostracized.

In 1789 during British colonial rule in India the British discovered that female infanticide in Uttar Pradesh was openly acknowledged. A letter from a magistrate who was stationed in the North West of India during this period spoke of the fact that for several hundred years no daughter had ever been raised in the strongholds of the Rajahs of Mynpoorie. In 1845 however the ruler at that time did keep a daughter alive after a district collector named Unwin intervened. A review of scholarship has shown that the majority of female infanticides in India during the colonial period occurred for the most part in the North West, and that although not all groups carried out this practice, it was indeed widespread. In 1870, after an investigation by the colonial authorities the practice was made illegal, with the Female Infanticide Prevention Act, 1870. 

According to women's rights activist Donna Fernandes, some practices are so deeply embedded within Indian culture it is "almost impossible to do away with them", and she has said that India is undergoing a type of "female genocide". The United Nations has declared that India is the most deadly country for female children, and that in 2012 female children aged between 1 and 5 were 75 percent more likely to die as opposed to boys. The children's rights group CRY has estimated that of the 12 million females born yearly in India, 1 million will have died within their first year of life. During British rule, the practice of female infanticide in the Indian state of Tamil Nadu among the Kallars and the Todas was reported. More recently in June 1986 it was reported by India Today in a cover story Born to Die that female infanticide was still in practice in Usilampatti in southern Tamil Nadu. The practice was mostly prevalent among the dominant caste of the region, Kallars.

Pakistan

In Pakistan female infanticide is practiced as female children are seen as a financial burden due to the dowry the parents have to pay when their daughter reaches a marriageable age. Pakistan is still a male-dominated nation and remains a patriarchal society. In addition, the boys in the family are given preferential treatment, receiving food and medical care before the girls do.

Socio-economics

Eliminating females poses an issue, as this reduces the number of females that will be able to bear children. It also poses an issue with feelings of female worth, as families wanting to eradicate female babies teach the young girls in their society that they are inferior to the opposite sex, making it more likely that they face oppression and have reduced access to jobs. The dowry system has an effect on the families and poverty line, as some families struggle to pay a dowry while earning below the minimum wage.

As of 2017 Pakistani women earn less than their male counterparts, earning under a hundred rupees a month, and are often unable to receive an education that would allow them to have better working hours and pay. Some are also restricted to only working within the home, while men are allowed to do the majority of crop work and herding.

Solutions/Programs

There are Non-Government Developmental Organizations (NGDOS) which have gender awareness policies that are designed to prevent female discrimination all over the world. For instance, these NGDOS, starting off in small groups, go to corporations to educate the staff about gender discrimination. The organization mostly sees the importance of educating the men who are in the work force on the issues of women within society. Therefore, the men are able to sympathize with the women in terms of how being a women in society may make you feel inferior. Another solution would be to eradicate the dowry system so that families will not have pay such a heavy price for their daughters. Also, with the eradication of the system it will eliminate the idea that females are seen as financial burdens. Thus will allow females to become individuals being able to raise their social status in terms of women being provided with a better salary.

The Girl Child Protection Scheme is an organization that is designed to set up cradles near stores so that families who have mostly daughters may leave them in a safe place, instead of engaging in the practice of killing the female. Therefore, this allows the government to take over and place the female child up for adoption. Educating young girls and women about the purpose of female infanticide will help them to become aware of how important women are in society being able to become independent. Also, with more women being able to contribute to the work force, society will be able to move above the poverty line.

Reactions

The Geneva Centre for the Democratic Control of Armed Forces (DCAF) wrote in their 2005 report, Women in an Insecure World, that at a time when the number of casualties in war had fallen, a "secret genocide" was being carried out against women. According to DCAF the demographic shortfall of women who have died for gender related issues is in the same range as the 191 million estimated dead from all conflicts in the twentieth century. In 2012, the documentary It's a Girl: The Three Deadliest Words in the World was released, and in one interview, an Indian woman claimed she had killed eight of her daughters.

Why Apocalyptic Claims About Climate Change Are Wrong

Written by Michael Shellenberger on Nov 26, 2019. 

Original link:  https://climatechangedispatch.com/apocalyptic-claims-climate-wrong/?fbclid=IwAR3aqV6NoVS6KF6RJWKAoTIcwLO7EM_Ox5xm7Wb4Gd1I2WtezyqJg3QCrxQ

Environmental journalists and advocates have in recent weeks made a number of apocalyptic predictions about the impact of climate change.

Bill McKibben suggested climate-driven fires in Australia had made koalas “functionally extinct.”

Extinction Rebellion said: “Billions will die” and “Life on Earth is dying.” Vice claimed the “collapse of civilization may have already begun.”

Few have underscored the threat more than student climate activist Greta Thunberg and Green New Deal sponsor Rep. Alexandria Ocasio-Cortez.

The latter said, “The world is going to end in 12 years if we don’t address climate change.” Says Thunberg in her new book, “Around 2030 we will be in a position to set off an irreversible chain reaction beyond human control that will lead to the end of our civilization as we know it.”

Sometimes, scientists themselves make apocalyptic claims. “It’s difficult to see how we could accommodate a billion people or even half of that,” if Earth warms four degrees, said one earlier this year.

“The potential for multi-breadbasket failure is increasing,” said another. If sea levels rise as much as the Intergovernmental Panel on Climate Change predicts, another scientist said, “It will be an unmanageable problem.”

Apocalyptic statements like these have real-world impacts. In September, a group of British psychologists said children are increasingly suffering from anxiety from the frightening discourse around climate change.

In October, an activist with Extinction Rebellion (”XR”) — an environmental group founded in 2018 to commit civil disobedience to draw awareness to the threat its founders and supporters say climate change poses to human existence — and a videographer, were kicked and beaten in a London Tube station by angry commuters.

And last week, an XR co-founder said a genocide like the Holocaust was “happening again, on a far greater scale, and in plain sight” from climate change.

Climate change is an issue I care passionately about and have dedicated a significant portion of my life to addressing. I have been politically active on the issue for over 20 years and have researched and written about it for 17 years.

Over the last four years, my organization, Environmental Progress, has worked with some of the world’s leading climate scientists to prevent carbon emissions from rising. So far, we’ve helped prevent emissions from increasing the equivalent of adding 24 million cars to the road.

I also care about getting the facts and science right and have in recent months corrected inaccurate and apocalyptic news media coverage of fires in the Amazon and fires in California, both of which have been improperly presented as resulting primarily from climate change.

Journalists and activists alike have an obligation to describe environmental problems honestly and accurately, even if they fear doing so will reduce their news value or salience with the public.

There is good evidence that the catastrophist framing of climate change is self-defeating because it alienates and polarizes many people.

And exaggerating climate change risks is distracting us from other important issues including ones we might have more near-term control over.

I feel the need to say this up-front because I want the issues I’m about to raise to be taken seriously and not dismissed by those who label anyone as “climate deniers” or “climate delayers” who push back against exaggeration.

With that out of the way, let’s look at whether the science supports what’s being said.

First, no credible scientific body has ever said climate change threatens the collapse of civilization much less the extinction of the human species. “‘Our children are going to die in the next 10 to 20 years.’

What’s the scientific basis for these claims?” BBC’s Andrew Neil asked a visibly uncomfortable XR spokesperson last month.

“These claims have been disputed, admittedly,” she said. “There are some scientists who are agreeing and some who are saying it’s not true. But the overall issue is that these deaths are going to happen.”

“But most scientists don’t agree with this,” said Neil. “I looked through IPCC reports and see no reference to billions of people going to die, or children in 20 years. How would they die?”

“Mass migration around the world already taking place due to prolonged drought in countries, particularly in South Asia. There are wildfires in Indonesia, the Amazon rainforest, Siberia, the Arctic,” she said.

But in saying so, the XR spokesperson had grossly misrepresented the science. “There is robust evidence of disasters displacing people worldwide,” notes IPCC, “but limited evidence that climate change or sea-level rise is the direct cause.”

What about “mass migration”? “The majority of resultant population movements tend to occur within the borders of affected countries,” says IPCC.

It’s not like climate doesn’t matter. It’s that climate change is outweighed by other factors.

Earlier this year, researchers found that climate “has affected organized armed conflict within countries. However, other drivers, such as low socioeconomic development and low capabilities of the state, are judged to be substantially more influential.”

Last January, after climate scientists criticized Rep. Ocasio-Cortez for saying the world would end in 12 years, her spokesperson said: “We can quibble about the phraseology, whether it’s existential or cataclysmic.” He added, “We’re seeing lots of [climate change-related] problems that are already impacting lives.”

That last part may be true, but it’s also true that economic development has made us less vulnerable, which is why there was a 99.7% decline in the death toll from natural disasters since its peak in 1931.

In 1931, 3.7 million people died from natural disasters. In 2018, just 11,000 did.  And that decline occurred over a period when the global population quadrupled.

What about sea-level rise? IPCC estimates sea level could rise two feet (0.6 meters) by 2100. Does that sound apocalyptic or even “unmanageable”?

Consider that one-third of the Netherlands is below sea level, and some areas are seven meters below sea level. You might object that the Netherlands is rich while Bangladesh is poor.

But the Netherlands adapted to living below sea level 400 years ago. Technology has improved a bit since then.

What about claims of crop failure, famine, and mass death? That’s science fiction, not science. Humans today produce enough food for 10 billion people or 25% more than we need, and scientific bodies predict increases in that share, not declines.

The United Nations Food and Agriculture Organization (FAO) forecasts crop yields increasing by 30% by 2050. And the poorest parts of the world, like sub-Saharan Africa, are expected to see increases of 80 to 90%.

Nobody is suggesting climate change won’t negatively impact crop yields. It could. But such declines should be put in perspective.

Wheat yields increased 100 to 300% around the world since the 1960s, while a study of 30 models found that yields would decline by 6% for every one degree Celsius increase in temperature.

Rates of future yield growth depend far more on whether poor nations get access to tractors, irrigation, and fertilizer than on climate change, says FAO.

All of this helps explain why IPCC anticipates climate change will have a modest impact on economic growth. By 2100, IPCC projects the global economy will be 300 to 500% larger than it is today.

Both IPCC and the Nobel-winning Yale economist, William Nordhaus, predict that warming of 2.5°C and 4°C would reduce gross domestic product (GDP) by 2% and 5% over that same period.

Does this mean we shouldn’t worry about climate change? Not at all.

One of the reasons I work on climate change is because I worry about the impact it could have on endangered species.

Climate change may threaten one million species globally and half of all mammals, reptiles, and amphibians in diverse places like the Albertine Rift in central Africa, home to the endangered mountain gorilla.

But it’s not the case that “we’re putting our own survival in danger” through extinctions, as Elizabeth Kolbert claimed in her book, Sixth Extinction. As tragic as animal extinctions are, they do not threaten human civilization.

If we want to save endangered species, we need to do so because we care about wildlife for spiritual, ethical, or aesthetic reasons, not survival ones.

And exaggerating the risk and suggesting climate change is more important than things like habitat destruction is counterproductive.

For example, Australia’s fires are not driving koalas ‘extinct,’ as Bill McKibben suggested.

The main scientific body that tracks the species, the International Union for the Conservation of Nature, or IUCN, labels the koala “vulnerable,” which is one level less threatened than “endangered,” two levels less than “critically endangered,” and three less than “extinct” in the wild.

Should we worry about koalas? Absolutely! They are amazing animals and their numbers have declined to around 300,000. But they face far bigger threats such as the destruction of habitat, disease, bushfires, and invasive species.

Think of it this way. The climate could change dramatically — and we could still save koalas. Conversely, the climate could change only modestly — and koalas could still go extinct.

The monomaniacal focus on climate distracts our attention from other threats to koalas and opportunities for protecting them, like protecting and expanding their habitat.

As for fire, one of Australia’s leading scientists on the issue says,

“Bushfire losses can be explained by the increasing exposure of dwellings to fire-prone bushlands. No other influences need to be invoked. So even if climate change had played some small role in modulating recent bushfires, and we cannot rule this out, any such effects on risk to the property are clearly swamped by the changes in exposure.”

Nor are the fires solely due to drought, which is common in Australia, and exceptional this year. “Climate change is playing its role here,” said Richard Thornton of the Bushfire and Natural Hazards Cooperative Research Centre in Australia, “but it’s not the cause of these fires.”

The same is true for fires in the United States. In 2017, scientists modeled 37 different regions and found “humans may not only influence fire regimes but their presence can actually override, or swamp out, the effects of climate.”

Of the 10 variables that influence fire, “none were as significant… as the anthropogenic variables,” such as building homes near, and managing fires and wood fuel growth within, forests.

Climate scientists are starting to push back against exaggerations by activists, journalists, and other scientists.

“While many species are threatened with extinction,” said Stanford’s Ken Caldeira, “climate change does not threaten human extinction… I would not like to see us motivating people to do the right thing by making them believe something that is false.”

I asked the Australian climate scientist Tom Wigley what he thought of the claim that climate change threatens civilization. “It really does bother me because it’s wrong,” he said. “All these young people have been misinformed. And partly it’s Greta Thunberg’s fault. Not deliberately. But she’s wrong.”

But don’t scientists and activists need to exaggerate in order to get the public’s attention?

“I’m reminded of what [late Stanford University climate scientist] Steve Schneider used to say,” Wigley replied. “He used to say that as a scientist, we shouldn’t really be concerned about the way we slant things in communicating with people out on the street who might need a little push in a certain direction to realize that this is a serious problem. Steve didn’t have any qualms about speaking in that biased way. I don’t quite agree with that.”

Wigley started working on climate science full-time in 1975 and created one of the first climate models (MAGICC) in 1987. It remains one of the main climate models in use today.

“When I talk to the general public,” he said, “I point out some of the things that might make projections of warming less and the things that might make them more. I always try to present both sides.”

Part of what bothers me about the apocalyptic rhetoric by climate activists is that it is often accompanied by demands that poor nations be denied the cheap sources of energy they need to develop. I have found that many scientists share my concerns.

“If you want to minimize carbon dioxide in the atmosphere in 2070  you might want to accelerate the burning of coal in India today,” MIT climate scientist Kerry Emanuel said.

“It doesn’t sound like it makes sense. Coal is terrible for carbon. But it’s by burning a lot of coal that they make themselves wealthier, and by making themselves wealthier they have fewer children, and you don’t have as many people burning carbon, you might be better off in 2070.”

Emanuel and Wigley say the extreme rhetoric is making any political agreement on climate change harder.

“You’ve got to come up with some kind of middle ground where you do reasonable things to mitigate the risk and try at the same time to lift people out of poverty and make them more resilient,” said Emanuel. “We shouldn’t be forced to choose between lifting people out of poverty and doing something for the climate.”

Happily, there is plenty of middle ground between climate apocalypse and climate denial.

---

Michael Shellenberger was Time Magazine’s “Hero of the Environment,” Green Book Award Winner, and President of Environmental Progress, a research and policy organization. He is also the author of several bestselling books.

Read more at Forbes

Cinderella effect

From Wikipedia, the free encyclopedia

 

In evolutionary psychology, the Cinderella effect is the phenomenon of higher incidence of different forms of child abuse and mistreatment by stepparents than by biological parents. It takes its name from the fairy tale character Cinderella, which is about a girl who is mistreated by her stepsisters. Evolutionary psychologists describe the effect as a byproduct of a bias towards kin, and a conflict between reproductive partners of investing in young that are unrelated to one partner. There is both supporting evidence for this theory and criticism against it.

Background

In the early 1970s, a theory arose on the connection between stepparents and child maltreatment. "In 1973, forensic psychiatrist P. D. Scott summarized information on a sample of "fatal battered-baby cases" perpetrated in anger ... 15 of the 29 killers – 52% – were stepfathers." Although initially there was no analysis of this raw data, empirical evidence has since been collected on what is now called the Cinderella effect through official records, reports, and census.

For over 30 years, data has been collected regarding the validity of the Cinderella effect, with a wealth of evidence indicating a direct relationship between step-relationships and abuse. This evidence of child abuse and homicide comes from a variety of sources including official reports of child abuse, clinical data, victim reports, and official homicide data. Studies have concluded that "stepchildren in Canada, Great Britain, and the United States indeed incur greatly elevated risk of child maltreatment of various sorts, especially lethal beatings".

Powerful evidence in support of the Cinderella effect comes from the finding that when abusive parents have both step and genetic children, they generally spare their genetic children. In such families, stepchildren were exclusively targeted 9 out of 10 times in one study and in 19 of 22 in another. In addition to displaying higher rates of negative behaviors (e.g., abuse) toward stepchildren, stepparents display fewer positive behaviors toward stepchildren than do the genetic parents. For example, on average, stepparents invest less in education, play with stepchildren less, take stepchildren to the doctor less, etc. This discrimination against stepchildren is unusual compared with abuse statistics involving the overall population given "the following additional facts: (1) when child abuse is detected, it is often found that all the children in the home have been victimized; and (2) stepchildren are almost always the eldest children in the home, whereas the general ... tendency in families of uniform parentage is for the youngest to be most frequent victims."

Evolutionary psychology theory

Evolutionary psychologists Martin Daly and Margo Wilson propose that the Cinderella effect is a direct consequence of the modern evolutionary theory of inclusive fitness, especially parental investment theory. They argue that human child rearing is so prolonged and costly that "a parental psychology shaped by natural selection is unlikely to be indiscriminate". According to them, "research concerning animal social behaviour provide a rationale for expecting parents to be discriminative in their care and affection, and more specifically, to discriminate in favour of their own young". Inclusive fitness theory proposes a selective criterion for the evolution of social traits, where social behavior that is costly to an individual organism can nevertheless emerge when there is a statistical likelihood that significant benefits of that social behavior accrue to (the survival and reproduction of) other organisms whom also carry the social trait (most straightforwardly, accrue to close genetic relatives). Under such conditions, a net overall increase in reproduction of the social trait in future generations can result. 

The initial presentation of inclusive fitness theory (in the mid 1960s) focused on making the mathematical case for the possibility of social evolution, but also speculated about possible mechanisms whereby a social trait could effectively achieve this necessary statistical correlation between its likely bearers. Two possibilities were considered: One that a social trait might reliably operate straightforwardly via social context in species where genetic relatives are usually concentrated in a local home area where they were born ('viscous populations'); The other, that genetic detection mechanisms ('supergenes') might emerge that go beyond statistical correlations, and reliably detect actual genetic relatedness between the social actors using direct 'kin recognition'. The relative place of these two broad types of social mechanisms has been debated, but many biologists consider 'kin recognition' to be an important possible mechanism. Martin Daly and Margo Wilson follow this second mechanism, and expect that parents "discriminate in favour of their own young", i.e. their actual genetic relatives.

Daly and Wilson research

The most abundant data on stepchild mistreatment has been collected and interpreted by psychologists Martin Daly and Margo Wilson, who study with an emphasis in Neuroscience and Behavior at McMaster University. Their first measure of the validity of the Cinderella effect was based on data from the American Humane Association (AHA), an archive of child abuse reports in the United States holding over twenty thousand reports. These records led Wilson and Daly to conclude that "a child under three years of age who lived with one genetic parent and one stepparent in the United States in 1976 was about seven times more likely to become a validated child-abuse case in the records than one who dwelt with two genetic parents". Their overall findings demonstrate that children residing with stepparents have a higher risk of abuse even when other factors are considered.

Explanation

All organisms face trade-offs as to how to invest their time, energy, risk, and other resources, so investment in one domain (e.g., parental investment) generally takes away from their ability to invest in other domains (e.g. mating effort, growth, or investment in other offspring). Investment in non-genetic children therefore reduces an individual's ability to invest in itself or its genetic children, without directly bringing reproductive benefits. Thus, from an evolutionary biology perspective, one would not expect organisms to regularly and deliberately care for unrelated offspring.

Daly and Wilson point out that infanticide is an extreme form of biasing parental investment that is widely practiced in the animal world. For example, when an immigrant male lion enters a pride, it is not uncommon for him to kill the cubs fathered by other males. Since the pride can only provide support for a limited number of cubs to survive to adulthood, the killing of the cubs in competition with the new male's potential offspring increases the chances of his progeny surviving to maturity. In addition, the act of infanticide speeds the return to sexual receptivity in the females, allowing for the male to father his own offspring in a timelier manner. These observations indicate that in the animal world, males employ certain measures in order to ensure that parental investment is geared specifically toward their own offspring.

Unlike the lion, however, humans in a stepparenting situation face a more complicated tradeoff since they cannot completely disown their partner's offspring from a previous relationship, as they would risk losing sexual access to their partner and any chance of producing potential offspring. Thus, according to Daly and Wilson, stepparental investment can be viewed as mating effort to ensure the possibility of future reproduction with the parent of their stepchild. This mating effort hypothesis suggests that humans will tend to invest more in their genetic offspring and invest just enough in their stepchildren. It is from this theoretical framework that Daly and Wilson argue that instances of child abuse towards non-biological offspring should be more frequent than towards biological offspring.

One would therefore expect greater parental responsiveness towards one's own offspring than towards unrelated children, and this will result in more positive outcomes and fewer negative outcomes towards one's own children than towards other children in which one is expected to invest (i.e., stepchildren). "If child abuse is a behavioral response influenced by natural selection, then it is more likely to occur when there are reduced inclusive fitness payoffs owing to uncertain or low relatedness". Owing to these adaptations from natural selection, child abuse is more likely to be committed by stepparents than genetic parents—both are expected to invest heavily in the children, but genetic parents will have greater child-specific parental love that promotes positive caretaking and inhibits maltreatment.

Daly and Wilson report that this parental love can explain why genetic offspring are more immune to lashing out by parents. They assert that, "Child-specific parental love is the emotional mechanism that permits people to tolerate—even to rejoice in—those long years of expensive, unreciprocated parental investment". They point to a study comparing natural father and stepfather families as support for the notion that stepparents do not view their stepchildren the same as their biological children, and likewise, children do not view their stepparents the same as their biological parents. This study, based on a series of questionnaires which were then subjected to statistical analyses, reports that children are less likely to go to their stepfathers for guidance and that stepfathers rate their stepchildren less positively than do natural fathers.

Daly and Wilson's reports on the overrepresentation of stepparents in child homicide and abuse statistics support the evolutionary principle of maximizing one's inclusive fitness, formalized under Hamilton's Rule, which helps to explain why humans will preferentially invest in close kin. Adoption statistics also substantiate this principle, in that non-kin adoptions represent a minority of worldwide adoptions. Research into the high adoption rates of Oceania shows that childlessness is the most common reason for adopting, and that in the eleven populations for which data was available, a large majority of adoptions involved a relative with a coefficient of relatedness greater than or equal to 0.125 (e.g., genetic cousins). It is also observed that parents with both biological and adopted children bias the partitioning of their estates in favor of the biological children, demonstrating again that parental behavior corresponds to the principles of kin selection.

Methods

In their 1985 Canadian sample, Daly and Wilson classify the frequencies of different living arrangements (two natural parents, one natural parent, one natural parent with one stepparent, or other) according to child age. This was accomplished by administering a randomized telephone survey.

Records of child abuse from children's aid organizations as well as police reports on runaways and juvenile offenders were then used to determine whether children from stepparental living situations were overrepresented as abuse victims when compared to the demographic data gathered from the telephone survey data. The results indicate that the only living situation that has a significant correlation to increased child abuse is one natural parent and one stepparent in the same household. While rates of running away and crime were comparable for children living with stepparents and children of single-parents, abuse rates for children living with stepparents were much higher.

Daly and Wilson examined several potentially confounding variables in their research, including socioeconomic status, family size, and maternal age at childbirth, however only minor differences between natural-parent and stepparent families with respect to these factors were found, indicating that none of these are major contributing factors to the observed Cinderella effect.

Attachment theory

Evolutionary psychologists have also suggested that one of the causes of stepchild abuse may be the lack of a parental attachment bond that the mother would normally form with her own child. An attachment bond will, in general, be more secure if formed before the age of two, and adoption can often disrupt the development of this bond. An infant who is fed by the primary parental figure, usually the mother, and has the mother present during severely physically painful events will have form a stronger parental attachment bond, and either a consistent omission of the mother from this process or an alteration between two people (the original mother and the adoptive mother) can cause either an insecure attachment or disorganized attachment from the parent to the child. As a result, it is highly recommended by most psychologists that the adoptive mother be present very early in the infant's life, preferably immediately after its birth, in order to avoid attachment disruptions and attachment disorders. This theory cannot be a whole explanation for the Cinderella effect, as psychological research has shown that secure attachment bonds can be developed between a parent and adopted child, and the quality of the relationship between parent and child will more often depend on the child's pre-adoption experiences, such as length of time in social care and previous trauma, more than characteristics of the parents.

Misunderstandings

It is sometimes argued that this evolutionary psychological account does not explain why the majority of stepparents do not abuse their partners' children, or why a significant minority of genetic parents do abuse their own offspring. However, their argument is based on a misunderstanding: the evolutionary psychological account is that (all else equal) parents will love their own children more than other people's children – it does not argue that stepparents will "want" to abuse their partner's children, or that genetic parenthood is absolute proof against abuse. Under this account, stepparental care is seen as "mating effort" towards the genetic parent, such that most interactions between stepparent and stepchildren will be generally positive or at least neutral, just usually not as positive as interactions between the genetic parent and the child would be.

Supportive evidence

Strong support for the Cinderella effect as described by Daly and Wilson comes from a study of unintentional childhood fatal injuries in Australia. Tooley et al. follow the argument of Daly and Wilson to extend the Cinderella effect from cases of abuse to incidences of unintentional fatalities. Children are not only vulnerable to abuse by their parents, but they are also dependent on their parents for supervision and protection from a variety of other harms. Given that parental supervision is fundamentally correlated to incidences of unintentional childhood injury as shown by Wadsworth et al. and Peterson & Stern, Tooley et al. posit that selective pressures would favor an inclination towards parental vigilance against threats to offspring well-being. Tooley et al. further argue that parental vigilance is not as highly engaged in stepparents as genetic parents, therefore placing stepchildren at greater risk for unintentional injury.

Based on data gathered from the Australia National Coroners' Information System, stepchildren under five years of age are two to fifteen times more likely to experience an unintentional fatal injury, especially drowning, than genetic children. Additionally, the study finds that the risks of unintentional fatal injury are not significantly higher for genetic children in single parent homes versus two-parent homes. This difference suggests that removing one biological parent from the home does not significantly increase risk to the children, but that adding a nonbiological parent to the home results in a drastic increase in the risk of unintentional fatal injury. Despite the fact that adding a stepparent to the home increases the available resources in terms of supervision in comparison to a single-parent home, risk of unintentional fatal injury still significantly rises. This higher risk of injury for stepchildren can be attributed to the fact that stepparents occupy the same supervisory role as a genetic parent, yet they have a lower intrinsic commitment to protecting the child and therefore are less likely to be adequately vigilant. The authors conclude that the Cinderella effect applies not only to purposeful abuse by stepparents, but is also relevant to explaining increased rates of accidental fatalities among stepchildren.

Furthermore, a study of parental investment behaviors among American men living in Albuquerque, New Mexico, reveals a trend of increasing financial expenditures on genetic offspring in comparison to step-offspring, which also suggests that parents are less inclined to preserve the well-being of stepchildren. The study assesses paternal investment based on four measures: the probability that a child attends college, the probability that the child receives money for college, the total money spent on children, and the amount of time per week spent with children. Four different classifications of father-child relationships are examined and compared, including fathers living with their genetic children and stepfathers living with the stepchildren of their current mates. Though the study finds a clear trend of increasing investment in genetic children, the data also shows that stepfathers do still invest substantially in stepchildren. The authors explain the parental investment exhibited by stepfathers towards stepchildren as possibly motivated by the potential to improve the quality or increase the duration of the man's relationship with the stepchildren's mother. This studied corroborates the findings of Lynn White, that stepparents in general provide less social support to stepchildren than their genetic children.

Though the general trend of the data from this study supports the Cinderella effect, Anderson and colleagues note that the observed differences between investment in children and stepchildren might be slightly reduced by a few confounding factors. For example, the authors point out that stepparenting is a self-selective process, and that when all else is equal, men who bond with unrelated children are more likely to become stepfathers, a factor that is likely to be a confounding variable in efforts to study the Cinderella effect. Anderson and colleagues also conducted a similar study of Xhosa students in South Africa that analyzes the same four classifications of adult-child relationships, and this study offers similar results to those observed among men in Albuquerque.

Additionally, a study of Hadza foragers in Tanzania by Marlowe also finds evidence of decreased care provided by men to stepchildren when compared with genetic children. The author uses the Mann-Whitney U-tests to evaluate most of the observed differences in care exhibited towards children and stepchildren, and finds that Hadza men spend less time with (U=96), communicate less with (U=94.5), nurture less, and never play with their stepchildren. Marlowe further argues that any care that is provided towards stepchildren is likely attributable to the man's mating efforts and not parental interest in the well-being of the stepchildren.

In further support of the Cinderella effect as elaborated by Daly and Wilson, a study conducted in a rural village in Trinidad demonstrates that in households containing both genetic children and stepchildren, fathers devote approximately twice as much time to interaction with genetic offspring in comparison to stepchildren. Additionally, this study finds that the duration of the relationship between the stepfather and stepchildren is negatively correlated with the relative proportion of interaction time and positively correlated with the relative proportion of antagonistic interactions between the two. As a proportion of total time spent interacting with genetic and stepchildren, stepfathers are shown to have approximately 75 percent more antagonistic interactions with stepchildren. In this study, antagonistic interactions are defined as involving physical or verbal combat or an expression of injury. This includes, for example, spanking, screaming, crying, and arguing. The duration of the relationship between genetic fathers and children shows a positive correlation with both relative proportion of interaction time and antagonistic interaction. The author argues that these results show that in terms of time invested, men favor their children over stepchildren, and this preference is not attributable to the duration of the adult-child relationship, a factor which is sometimes believed to be a confounding variable in the Cinderella effect. Though this study does claim a significant increase in antagonistic behavior between stepparents and stepchildren and therefore supports the Cinderella effect, it also notes that only six percent of all the observed parent-child interactions were considered antagonistic, and that the researchers never noticed any blatant physical child abuse.

Criticism

David Buller

Philosopher of science David Buller, as a part of his general critique of evolutionary psychology  has reviewed Daly and Wilson's data. He argues that evolutionary psychology (EP) mistakenly attempts to discover human psychological adaptations rather than "the evolutionary causes of psychological traits." Buller also argues that Daly and Wilson's 1985 Canadian sample included cases of sexual abuse as well as cases of unintentional omission, such as not buckling a child's seatbelt in the car. Buller asserts that unintentional omission does not fall under the realm of dangerous acts, and rather should be designated "maltreatment". He argues that since sexual abuse is not often accompanied by physical abuse, it is unreasonable to assume that it is motivated by the same kind of psychological mechanism as child homicide. Buller also points out that the conclusion that non-biological parents are more likely to abuse children is contradicted by the fact that even if the rate of abuse among stepparents was disproportionate, most child abuse is in fact committed by biological parents, and that the lowest rate of child abuse is found among adoptive parents. Daly and Wilson respond to Buller's criticism by stating that Buller confuses the empirical statistical findings, which define the Cinderella effect, with the proposed theoretical framework, which offers an evolutionary explanation for the data.

Buller also argues that Daly and Wilson's findings are inherently biased since they use data from official documents, and the officials collecting that data are trained to take special notice of stepparents versus biological parents. Furthermore, Buller states that since Daly and Wilson rely on official reports (such as death certificates) for their data, and that this data is inherently biased against stepparents. He cites a Colorado study, in which it was found that maltreatment fatalities were more likely to be correctly reported on death certificates when an unrelated individual was the perpetrator rather than when a parent was the perpetrator, suggesting that the data is empirically skewed to support the Cinderella effect. According to this study, by Crume et al., when the perpetrator of the murder was a parent, maltreatment was correctly noted on the death certificate only 46 percent of the time. Furthermore, they found that when the perpetrator was an "Other unrelated (including boyfriend)" individual, maltreatment was reported on the death certificate 86 percent of the time, significantly higher than for parents. Although these statistics seem to provide evidence of bias against stepparents, further review of the data undermines this conclusion. As Crume et al. and Daly and Wilson note, maltreatment was only likely to be reported on the death certificates 47 percent of the time in the case of "Other relatives (including step-parents)," which represents a marginal increase from the amount of parental maltreatment. Therefore, as Daly and Wilson respond to Buller's critique, this does not seem to be a significant source of error in studying the Cinderella effect and does not provide evidence for inherent bias in their data.

Temrin et al. Sweden study

The findings of Daly and Wilson have been called into question by one study of child homicides in Sweden between 1975 and 1995, which found that children living in households with a non-genetic parent were not at an increased risk of homicide when compared to children living with both genetic parents. The study, published in 2000 and conducted by Temrin and colleagues argued that when Daly and Wilson classified homicides according to family situation, they did not account for the genetic relatedness of the parent who actually committed the crime. In the Swedish sample, in two out of the seven homicides with a genetic and non-genetic parent, the offender was actually the genetic parent and thus these homicides do not support Daly and Wilson's definition of the Cinderella effect.

Daly and Wilson attribute the contrasting findings of the Swedish study to an analytical oversight. Temrin and colleagues neglect to consider the fact that the proportion of children in living situations with a stepparent is not constant for all child age groups, but rather increases with age. After correcting for age differences, the Swedish data set produces results in accordance with the previous findings of Daly and Wilson. The Swedish sample does show, however, decreased risk to children living with a stepparent compared to the North American samples collected by Daly and Wilson, suggesting that there is some degree of cross-cultural variation in the Cinderella effect.

Alternative hypotheses

It has been noted by multiple researchers that child abuse is an intricate issue and is affected by other factors. Daly and Wilson state, however, that even if evolutionary psychology cannot account for every instance of stepparental abuse, this does not invalidate their empirical findings.

Burgess and Drais propose that child maltreatment is too complex to be explained fully by genetic relatedness alone and cite other reasons for child maltreatment, such as social factors, ecological factors and child traits such as disability and age. However, they also note that these traits are simply indicative, and do not inevitably lead to child maltreatment. Temrin and colleagues also suggest that there may be other factors involved with child homicide, such as prior convictions, drug abuse problems, lost custody battles and mental health problems.

In 1984, Giles-Sims and David Finkelhor categorized and evaluated five possible hypotheses that could explain the Cinderella effect: "social-evolutionary theory", "normative theory", "stress theory", "selection factors", and "resource theory". The social-evolutionary theory is based on the proposal that non-genetically related parents will invest less in costly parental duties, due to the fact that their genes are not being passed on by that individual. The normative theory proposes that, due to genetic repercussions, incest among genetically related individuals is a widespread taboo and would thus be less common among biological relatives. They propose that incest among stepfamilies would be less taboo, since there is no risk of genetic degradation. The stress theory proposes that increased stressors, which are inherently more common among stepfamilies, cause an increased risk of abuse. The selection factors theory proposes that individuals who are likely to be stepparents (divorcees) are likely to be inherently more violent due to emotional disturbances, aggressive impulses, and self-esteem issues. Due to this, stepparents as a group would have a higher proportion of individuals with violent-prone characteristics, which would suggest that the abuse is happening due to personality factors, rather than the stepparental relationship directly. Finally, according to resource theory, individuals who contribute resources are granted authority, while individuals that lack resources are denied authority and more likely to resort to violence to obtain authority. It is therefore hypothesized that stepparents who are able to contribute resources to a family and have those resources be accepted by the family are less likely to be abusive. However, this hypothesis had yet to be tested directly on stepfamilies. This paper of Giles-Sims and Finkelhor predates however practically all empirical studies on the Cinderella effect.

Ethical issues

Discussing the implications of this line of research, Australian psychologist Greg Tooley, author of a 2006 study confirming the existence of the effect, confessed that "it is certainly difficult to talk about because it is such a hot issue".

Parental investment

From Wikipedia, the free encyclopedia

 

A female calliope hummingbird feeding her chicks

 

A human mother feeding her child

 

Parental investment, in evolutionary biology and evolutionary psychology, is any parental expenditure (e.g. time, energy, resources) that benefits offspring. Parental investment may be performed by both males and females (biparental care), females alone (exclusive maternal care) or males alone (exclusive paternal care). Care can be provided at any stage of the offspring's life, from pre-natal (e.g. egg guarding and incubation in birds, and placental nourishment in mammals) to post-natal (e.g. food provisioning and protection of offspring).

Parental investment theory, a term coined by Robert Trivers in 1972, predicts that the sex that invests more in its offspring will be more selective when choosing a mate, and the less-investing sex will have intra-sexual competition for access to mates. This theory has been influential in explaining sex differences in sexual selection and mate preferences, throughout the animal kingdom and in humans.

History

In 1859, Charles Darwin published On the Origin of Species. This introduced the concept of natural selection to the world, as well as related theories such as sexual selection. For the first time, evolutionary theory was used to explain why females are "coy" and males are "ardent" and compete with each other for females' attention. In 1930, Ronald Fisher wrote The Genetical Theory of Natural Selection, in which he introduced the modern concept of parental investment, introduced the sexy son hypothesis, and introduced Fisher's principle. In 1948, Angus John Bateman published an influential study of fruit flies in which he concluded that because female gametes are more costly to produce than male gametes, the reproductive success of females was limited by the ability to produce ovum, and the reproductive success of males was limited by access to females. In 1972, Trivers continued this line of thinking with his proposal of parental investment theory, which describes how parental investment affects sexual behavior. He concludes that the sex that has higher parental investment will be more selective when choosing a mate, and the sex with lower investment will compete intra-sexually for mating opportunities. In 1974, Trivers extended parental investment theory to explain parent-offspring conflict, the conflict between investment that is optimal from the parent's versus the offspring's perspective.

Parental care

Parental investment theory is a branch of life history theory. The earliest consideration of parental investment is given by Ronald Fisher in his 1930 book The Genetical Theory of Natural Selection, wherein Fisher argued that parental expenditure on both sexes of offspring should be equal. Clutton-Brock expanded the concept of parental investment to include costs to any other component of parental fitness.

Male dunnocks tend to not discriminate between their own young and those of another male in polyandrous or polygynandrous systems. They increase their own reproductive success through feeding the offspring in relation to their own access to the female throughout the mating period, which is generally a good predictor of paternity. This indiscriminative parental care by males is also observed in redlip blennies.

A cellar spider defending spiderlings.

 

In some insects, male parental investment is given in the form of a nuptial gift. For instance, ornate moth females receive a spermatophore containing nutrients, sperm and defensive toxins from the male during copulation. This gift, which can account for up to 10% of the male's body mass, constitutes the total parental investment the male provides.

In some species, such as humans and many birds, the offspring are altricial and unable to fend for themselves for an extended period of time after birth. In these species, males invest more in their offspring than do the male parents of precocial species, since reproductive success would otherwise suffer.

The benefits of parental investment to the offspring are large and are associated with the effects on condition, growth, survival, and ultimately on reproductive success of the offspring. For example, in the cichlid fish Tropheus moorii, a female has very high parental investment in her young because she mouthbroods the young and while mouthbrooding, all nourishment she takes in goes to feed the young and she effectively starves herself. In doing this, her young are larger, heavier, and faster than they would have been without it. These benefits are very advantageous since it lowers their risk of being eaten by predators and size is usually the determining factor in conflicts over resources. However, such benefits can come at the cost of parent's ability to reproduce in the future e.g., through increased risk of injury when defending offspring against predators, loss of mating opportunities whilst rearing offspring, and an increase in the time interval until the next reproduction. 

A special case of parental investment is when young do need nourishment and protection, but the genetic parents do not actually contribute in the effort to raise their own offspring. For example, in Bombus terrestris, oftentimes sterile female workers will not reproduce on their own, but will raise their mother's brood instead. This is common in social Hymenoptera due to haplodiploidy, whereby males are haploid and females are diploid. This ensures that sisters are more related to each other than they ever would be to their own offspring, incentivizing them to help raise their mother's young over their own.

Overall, parents are selected to maximize the difference between the benefits and the costs, and parental care will be likely to evolve when the benefits exceed the costs.

Parent-offspring conflict

Reproduction is costly. Individuals are limited in the degree to which they can devote time and resources to producing and raising their young, and such expenditure may also be detrimental to their future condition, survival, and further reproductive output. However, such expenditure is typically beneficial to the offspring, enhancing their condition, survival, and reproductive success. These differences may lead to parent-offspring conflict. Parents are naturally selected to maximize the difference between the benefits and the costs, and parental care will tend to exist when the benefits are substantially greater than the costs. 

Parents are equally related to all offspring, and so in order to optimize their fitness and chance of reproducing their genes, they should distribute their investment equally among current and future offspring. However, any single offspring is more related to themselves (they have 100% of their DNA in common with themselves) than they are to their siblings (siblings usually share 50% of their DNA), it is best for the offspring's fitness if the parent(s) invest more in them. To optimize fitness, a parent would want to invest in each offspring equally, but each offspring would want a larger share of parental investment. The parent is selected to invest in the offspring up until the point at which investing in the current offspring is costlier than investing in future offspring.

In iteroparous species, where individuals may go through several reproductive bouts during their lifetime, a tradeoff may exist between investment in current offspring and future reproduction. Parents need to balance their offspring's demands against their own self-maintenance. This potential negative effect of parental care was explicitly formalized by Trivers in 1972, who originally defined the term parental investment to mean any investment by the parent in an individual offspring that increases the offspring's chance of surviving (and hence reproductive success) at the cost of the parent's ability to invest in other offspring.

King penguin and a chick

 

Penguins are a prime example of a species that drastically sacrifices their own health and well-being in exchange for the survival of their offspring. This behavior, one that does not necessarily benefit the individual, but the genetic code from which the individual arises, can be seen in the King Penguin. Although some animals do exhibit altruistic behaviors towards individuals that are not of direct relation, many of these behaviors appear mostly in parent-offspring relationships. While breeding, males remain in a fasting-period at the breeding site for five weeks, waiting for the female to return for her own incubation shift. However, during this time period, males may decide to abandon their egg if the female is delayed in her return to the breeding grounds.

It shows that these penguins initially show a trade-off of their own health, in hopes of increasing the survivorship of their egg. But there comes a point where the male penguin's costs become too high in comparison to the gain of a successful breeding season. Olof Olsson investigated the correlation between how many experiences in breeding an individual has and the duration an individual will wait until abandoning his egg. He proposed that the more experienced the individual, the better that individual will be at replenishing his exhausted body reserves, allowing him to remain at the egg for a longer period of time.

The males' sacrifice of their body weight and possible survivorship, in order to increase their offspring's chance of survival is a trade-off between current reproductive success and the parents' future survival. This trade-off makes sense with other examples of kin-based altruism and is a clear example of the use of altruism in an attempt to increase overall fitness of an individual's genetic material at the expense of the individual's future survival.

Maternal-offspring conflict in investment

The maternal-offspring conflict has also been studied in animals species and humans. One such case has been documented in the mid-1970s by ethologist Wulf Schiefenhövel. Eipo women of West New Guinea engage in a cultural practice in which they give birth just outside the village. Following the birth of their child, each woman weighed whether or not she should keep the child or leave the child in the brush nearby, inevitably ending in the death of the child. Likelihood of survival and availability of resources within the village were factors that played into this decision of whether or not to keep the baby. During one illustrated birth, the mother felt the child was too ill and would not survive, so she wrapped the child up, preparing to leave the child in the brush; however, upon seeing the child moving, the mother unwrapped the child and brought it into the village, demonstrating a shift of life and death. This conflict between the mother and the child resulted in detachment behaviors in Brazil, seen in Scheper-Hughes work as "many Alto babies remain[ed] not only unchristened but unnamed until they begin to walk or talk", or if a medical crisis arose and the baby needed an emergency baptism. This conflict between survival, both emotional and physical, prompted a shift in cultural practices, thus resulting in new forms of investment from the mother towards the child.

Alloparental care

Alloparental care also referred to as 'Allomothering,' is when a member of a community, apart from the biological parents of the infant, partake in offspring care provision. A range of behaviors fall under the term alloparental care, some of which are: carrying, feeding, watching over, protecting, and grooming. Through alloparental care stress on parents, especially the mother, can be reduced, therefore reducing the negative effects of the parent-offspring conflict on the mother. In While the apparent altruistic nature of the behavior may seem at odds with Darwin's theory of natural selection, as taking care of offspring which are not one's own would not increase one's direct fitness, while taking time, energy and resources away from raising one's own offspring, the behavior can be explained evolutionarily as increasing indirect fitness, as the offspring is likely to be non-descendent kin, therefore carrying some of the genetics of the alloparent.

Offspring and situation direction

Parental investment behavior enhances the chances of survival of offspring, and it does not require underlying mechanisms to be compatible with empathy applicable to adults, or situations involving unrelated offspring, and it does not require the offspring to reciprocate the altruistic behavior in any way. Parentally investing individuals are not more vulnerable to being exploited by other adults.

Trivers' parental investment theory

Parental investment as defined by Trivers in 1972 is the investment in offspring by the parent that increases the offspring's chances of surviving and hence reproductive success at the expense of the parent's ability to invest in other offspring. A large parental investment largely decreases the parents' chances of investing in other offspring. Parental investment can be split into two main categories: mating investment and rearing investment. Mating investment consist of the sexual act and the sex cells invested. The rearing investment is the time and energy expended to raise the offspring after conception. Women's parental investment in both mating and rearing efforts greatly surpasses that of the male. In terms of sex cells (egg and sperms cells), the female's investment is a lot larger, while males produce thousands of sperm cells which are supplied at a rate of twelve million per hour.

Women have a fixed supply of around 400 ova. Also, the acts of fertilization and gestation occur in the women, which compared to the male's investment of just one cell outweighs it. Furthermore, each intercourse could result in a nine-month commitment such as gestation (the act of breastfeeding) for the woman. From Trivers' theory of parental investment several implications follow. The first is that women are often but not always the more investing sex. The fact that they are the more investing sex has meant that evolution has favored females who are more selective of their mates to ensure that intercourse would not result in unnecessary costs. The third implication is that because women invest more and are essential for the reproductive success of their offspring they are a valuable resource for men; as a result, males often compete for sexual access to them.

Males as the more investing sex

For many species the only type of male investment received is that of sex cells. In those terms, the female investment greatly exceeds that of male investment as previously mentioned. However, there are other ways in which males invest in their offspring. For example, the male can find food as in the example of balloon flies. He may find a safe environment for the female to feed or lay her eggs as exemplified in many birds.

He may also protect the young and provide them with opportunities to learn as in many young as in wolves. Overall, the main role that males overtake is that of protection of the female and their young. That often can decrease the discrepancy of investment caused by the initial investment of sex cells. There are some species such as the Mormon cricket, pipefish seahorse and Panamanian poison arrow frog males invest more. Among the species where the male invests more, the male is also the pickier sex, placing higher demands on their selected female. For example, the female that they often choose usually contain 60% more eggs than rejected females.

This links Parental Investment Theory (PIT) with sexual selection: where parental investment is bigger for a male than a female, it's usually the female who competes for a mate, as shown by Phalaropidae and polyandrous bird species. In these species females are usually more aggressive, brightly colored, and larger than males, suggesting the more investing sex has more choice while selecting a mate compared to the sex engaged in intra-sexual selection.

Females as a valuable resource for males

The second prediction that follows from Trivers' theory is that the fact that women invest more heavily in offspring makes them a valuable resource for males as it ensures the survival of their offspring which is the driving force of natural selection. Therefore, the sex that invests less in offspring will compete among themselves to breed with the more heavily investing sex. In other words, males will compete for females. It has been argued that jealousy has developed to avert the risk of potential loss of parental investment in offspring.

If a male redirects his resources to another female it is a costly loss of time, energy and resources for her offspring. However, the risks for males are higher because although women invest more in their offspring, they have bigger maternity certainty because they themselves have carried out the child. However, males can never have 100% paternal certainty and therefore risk investing resources and time in offspring that is genetically unrelated. Evolutionary psychology views jealousy as an adaptive response to this problem.

Application of Trivers' theory in real life

Trivers' theory has been very influential as the predictions it makes correspond to differences in sexual behaviors of men and women, as demonstrated by a variety of research. Cross-cultural study from Buss (1989) shows that males are tuned into physical attractiveness as it signals youth and fertility and ensures male reproductive success, which is increased by copulating with as many fertile females as possible. Women on the other hand are tuned into resources provided by potential mates, as their reproductive success is increased by ensuring their offspring will survive, and one way they do so is by getting resources for them. Alternatively, another study shows that men are more promiscuous than women, giving further support to this theory. Clark and Hatfield found that 75% of men were willing to have sex with a female stranger when propositioned, compared to 0% of women. On the other hand, 50% of women agreed to a date with a male stranger. This suggests males seek short term relationships, while women show a strong preference for long-term relationships.

However, these preferences (male promiscuity and female choosiness) can be explained in other ways. In Western cultures, male promiscuity is encouraged through the availability of pornographic magazines and videos targeted to the male audience. Alternatively, both Western and Eastern cultures discourage female promiscuity through social checks such as slut-shaming.

PIT (Parental Investment Theory) also explains patterns of sexual jealousy. Males are more likely to show a stress response when imagining their partners showing sexual infidelity (having sexual relations with someone else), and women showed more stress when imagining their partner being emotionally unfaithful (being in love with another woman). PIT explains this, as woman's sexual infidelity decreases the male's paternal certainty, thus he will show more stress due to fear of cuckoldry. On the other hand, the woman fears losing the resources her partner provides. If her partner has an emotional attachment to another female it's likely that he won't invest into their offspring as much, thus a greater stress response is shown in this circumstance.

A heavy criticism of the theory comes from Thornhill and Palmer's analysis of it in A Natural History of Rape: Biological Bases of Sexual Coercion, as it seems to rationalise rape and sexual coercion of females. Thornhill and Palmer claimed rape is an evolved technique for obtaining mates in an environment where women choose mates. As PIT claims males seek to copulate with as many fertile females as possible, the choice women have could result in a negative effect on the male's reproductive success. If women didn't choose their mates, Thornhill and Palmer claim there would be no rape. This ignores a variety of sociocultural factors, such as the fact that not only fertile females are raped – 34% of underage rape victims are under 12, which means they are not of fertile age, thus there is no evolutionary advantage in raping them. 14% of rapes in England are committed on males, who cannot increase a man's reproductive success as there will be no conception. Thus, what Thornhill and Palmer called an 'evolved machinery' might not be very advantageous.

Versus sexual strategies

Trivers' theory overlooks that women do have short-term relationships such as one-night stands, while not all men behave promiscuously. An alternative explanation to PIT (Parental Investment Theory) and mate preferences would be Buss and Schmitt's sexual strategies theory. SST argues that both sexes pursue short-term and long-term relationships, but seek different qualities in their short- and long-term partners. For a short-term relationship women will prefer an attractive partner, but in a long-term relationship they might be willing to trade-off that attractiveness for resources and commitment. On the other hand, men might be accepting of a sexually willing partner in a short-term relationships, but to ensure their paternal certainty they will seek a faithful partner instead.

International politics

Parental investment theory is not only used to explain evolutionary phenomena and human behavior but describes recurrences in international politics as well. Specifically, parental investment is referred to when describing competitive behaviors between states and determining aggressive nature of foreign policies. The parental investment hypothesis states that the size of coalitions and the physical strengths of its male members determines whether its activities with its foreign neighbors are aggressive or amiable. According to Trivers, men have had relatively low parental investments, and were therefore forced into fiercer competitive situations over limited reproductive resources. Sexual selection naturally took place and men have evolved to address its unique reproductive problems. Among other adaptations, men's psychology has also developed to directly aid men in such intra-sexual competition.

One essential psychological developments involved decision-making of whether to take flight or actively engage in warfare with another rivalry group. The two main factors that men referred to in such situations were (1) whether the coalition they are a part of is larger than its opposition and (2) whether the men in their coalition have greater physical strength than the other. The male psychology conveyed in the ancient past has been passed on to modern times causing men to partly think and behave as they have during ancestral wars. According to this theory, leaders of international politics were not an exception. For example, the United States expected to win the Vietnam war due to its greater military capacity when compared to its enemies. Yet victory, according to the traditional rule of greater coalition size, did not come about because the U.S. did not take enough consideration to other factors, such as the perseverance of the local population.

The parental investment hypothesis contends that male physical strength of a coalition still determines the aggressiveness of modern conflicts between states. While this idea may seem unreasonable upon considering that male physical strength is one of the least determining aspects of today's warfare, human psychology has nevertheless evolved to operate on this basis. Moreover, although it may seem that mate seeking motivation is no longer a determinant, in modern wars sexuality, such as rape, is undeniably evident in conflicts even to this day.

Pair of crested auklets

Sexual selection

In many species, males can produce a larger number of offspring over the course of their lives by minimizing parental investment in favor of investing time impregnating any reproductive-age female who is fertile. In contrast, a female can have a much smaller number of offspring during her reproductive life, partly due to higher obligate parental investment. Females will be more selective ("choosy") of mates than males will be, choosing males with good fitness (e.g., genes, high status, resources, etc.), so as to help offset any lack of direct parental investment from the male, and therefore increase reproductive success. Robert Trivers' theory of parental investment predicts that the sex making the largest investment in lactation, nurturing, and protecting offspring will be more discriminating in mating; and that the sex that invests less in offspring will compete via intrasexual selection for access to the higher-investing sex.

In species where both sexes invest highly in parental care, mutual choosiness is expected to arise. An example of this is seen in crested auklets, where parents share equal responsibility in incubating their single egg and raising the chick. In crested auklets both sexes are ornamented.

Parental investment in humans

Humans have evolved increasing levels of parental investment, both biologically and behaviorally. The fetus requires high investment from the mother, and the altricial newborn requires high investment from a community. Species whose newborn young are unable to move on their own and require parental care have a high degree of altriciality. Human children are born unable to care for themselves and require additional parental investment post-birth in order to survive.

Maternal investment

Trivers (1972) hypothesized that greater biologically obligated investment will predict greater voluntary investment. Mothers invest an impressive amount in their children before they are even born. The time and nutrients required to develop the fetus, and the risks associated with both giving these nutrients and undergoing childbirth, are a sizable investment. To ensure that this investment is not for nothing, mothers are likely to invest in their children after they are born, to be sure that they survive and are successful. Relative to most other species, human mothers give more resources to their offspring at a higher risk to their own health, even before the child is born. This is associated with the evolution of a slower life history, in which fewer, larger offspring are born after longer intervals, requiring increased parental investment.

The placenta attaches to the uterine wall, and the umbilical cord connects it to the fetus.

 

The developing human fetus––and especially the brain––requires nutrients to grow. In the later weeks of gestation, the fetus requires increasing nutrients as the growth of the brain increases. Rodents and primates have the most invasive placenta phenotype, the hemochorial placenta, in which the chorion erodes the uterine epithelium and has direct contact with maternal blood. The other placental phenotypes are separated from the maternal bloodstream by at least one layer of tissue. The more invasive placenta allows for a more efficient transfer of nutrients between the mother and fetus, but it comes with risks as well. The fetus is able to release hormones directly into the mother’s bloodstream to “demand” increased resources. This can result in health problems for the mother, such as pre-eclampsia. During childbirth, the detachment of the placental chorion can cause excessive bleeding.

The obstetrical dilemma also makes birth more difficult and results in increased maternal investment. Humans have evolved both bipedalism and large brain size. The evolution of bipedalism altered the shape of the pelvis, and shrunk the birth canal at the same time brains were evolving to be larger. The decreasing birth canal size meant that babies are born earlier in development, when they have smaller brains. Humans give birth to babies with brains 25% developed, while other primates give birth to offspring with brains 45-50% developed. A second possible explanation for the early birth in humans is the energy required to grow and sustain a larger brain. Supporting a larger brain gestationally requires energy the mother may be unable to invest.

The obstetrical dilemma makes birth challenging, and a distinguishing trait of humans is the need for assistance during childbirth. The altered shape of the bipedal pelvis requires that babies leave the birth canal facing away from the mother, contrary to all other primate species. This makes it more difficult for the mother to clear the baby’s breathing passageways, to make sure the umbilical cord isn’t wrapped around the neck, and to pull the baby free without bending its body the wrong way.

The human need to have a birth attendant also requires sociality. In order to guarantee the presence of a birth attendant, humans must aggregate in groups. It has been controversially claimed that humans have eusociality, like ants and bees, in which there is relatively high parental investment, cooperative care of young, and division of labor. It is unclear which evolved first; sociality, bipedalism, or birth attendance. Bonobos, our closest living relatives alongside chimpanzees, have high female sociality and births among bonobos are also social events. Sociality may have been a prerequisite for birth attendance, and bipedalism and birth attendance could have evolved as long as five million years ago.

A baby, mother, grandmother, and great-grandmother. In humans, grandparents often help to raise a child.

 

As female primates age, their ability to reproduce decreases. The grandmother hypothesis describes the evolution of menopause, which may or may not be unique to humans among primates. As women age, the costs of investing in additional reproduction increase and the benefits decrease. At menopause, it is more beneficial to stop reproduction and begin investing in grandchildren. Grandmothers are certain of their genetic relation to their grandchildren, especially the children of their daughters, because maternal certainty of their own children is high, and their daughters are certain of their maternity to their children as well. It has also been theorized that grandmothers preferentially invest in the daughters of their daughters because X chromosomes carry more DNA and their granddaughters are most closely related to them.

Paternal investment

As altriciality increased, investment from individuals other than the mother became more necessary. High sociality meant that female relatives were present to help the mother, but paternal investment increased as well. Paternal investment increases as it becomes more difficult to have additional children, and as the effects of investment on offspring fitness increase.

Men are more likely than women to give no parental investment to their children, and the children of low-investing fathers are more likely to give less parental investment to their own children. Father absence is a risk factor for both early sexual activity and teenage pregnancy. Father absence raises children's stress levels, which are linked to earlier onset of sexual activity and increased short-term mating orientation. Daughters of absent fathers are more likely to seek short-term partners, and one theory explains this as a preference for outside (non-partner) social support because of the perceived uncertain future and uncertain availability of committing partners in a high-stress environment.

Investment as predictor of mating strategies

Chance of fertilization by menstrual cycle day relative to ovulation, with data from two different studies.

Concealed ovulation

Women can only get pregnant while ovulating. Human ovulation is concealed, or not signaled externally. Concealed ovulation decreases paternity certainty because men are unsure when women ovulate. The evolution of concealed ovulation has been theorized to be a result of altriciality and increased need for paternal investment. There are two ways this could be true. First, if men are unsure of the time of ovulation, the best way to successfully reproduce would be to repeatedly mate with a woman throughout her cycle, which requires pair bonding, which in turn increases paternal investment. The second theory states that decreased paternity certainty would increase paternal investment in polygamous groups, because more men may invest in the offspring. The second theory is better regarded today, because all mammals with concealed ovulation are promiscuous, and men display relatively low mate-guarding behavior, as monogamy and the first theory require.

Mating orientations

Sociosexuality was first described by Alfred Kinsey as a willingness to engage in casual and uncommitted sexual relationships. Sociosexual orientation describes sociosexuality on a scale from unrestricted to restricted. Individuals with an unrestricted sociosexual orientation have higher openness to sex in less committed relationships, and individuals with a restricted sociosexual orientation have lower openness to casual sexual relationships. However, today it is acknowledged that sociosexuality does not in reality exist on a one-dimensional scale. Individuals who are less open to casual relationships are not always seeking committed relationships, and individuals who are less interested in committed relationships are not always interested in casual relationships. Short- and long-term mating orientations are the modern descriptors of openness to uncommitted and committed relationships, respectively.

Parental investment theory, as proposed by Trivers, argues that the sex with higher obligatory investment will be more selective in choosing sex partners, and the sex with lower obligatory investment will be less selective and more interested in "casual" mating opportunities. The more investing sex cannot reproduce as frequently, causing the less investing sex to compete for mating opportunities. In humans, women have higher obligatory investment (pregnancy and childbirth), than men (sperm production). Women are more likely to have higher long-term mating orientations, and men are more likely to have higher short-term mating orientations.

Short- and long-term mating orientations influence women's preferences in men. Studies have found that women put great emphasis on career-orientation, ambition and devotion only when considering a long-term partner. When marriage is not involved, women put greater emphasis on physical attractiveness. Generally, women prefer men who are likely to perform high parental investment and have good genes. Women prefer men with good financial status, who are more committed, who are more athletic, and who are healthier.

Some inaccurate theories have been inspired by parental investment theory. The "structural powerlessness hypothesis" proposes that women strive to find mates with access to high levels of resources because as women, they are excluded from these resources directly. However, this hypothesis has been disproved by studies which found that financially successful women place an even greater importance on financial status, social status, and possession of professional degrees.

Humans are sexually dimorphic; the average man is taller than the average woman.

Sexual dimorphism

Sexual dimorphism is the difference in body size between male and female members of a species as a result of intrasexual selection, which is sexual selection that acts within a sex. High sexual dimorphism and larger body size in males is a result of male-male competition for females. Primate species in which groups are formed of many females and one male have higher sexual dimorphism than species that have both multiple females and males, or one female and one male. Polygynous primates have the highest sexual dimorphism, and polygamous and monogamous primates have less. Humans have the lowest levels of sexual dimorphism of any primate species, indicating that we have evolved decreasing levels of polygyny. Decreased polygyny is associated with increased paternal investment.

The demographic transition

The demographic transition describes the modern decrease in both birth and death rates. From a Darwinian perspective, it does not make sense that families with more resources are having fewer children. One explanation for the demographic transition is the increased parental investment required to raise children who will be able to maintain the same level of resources as their parents.