Scientism

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Scientism 

Scientism is the belief that science and the scientific method are the best or only way to render truth about the world and reality.

While the term was defined originally to mean "methods and attitudes typical of or attributed to natural scientists", some scholars, as well as political and religious leaders, have also adopted it as a pejorative term with the meaning "an exaggerated trust in the efficacy of the methods of natural science applied to all areas of investigation (as in philosophy, the social sciences, and the humanities)".

Overview

Francis Bacon has been viewed by some scholars as an early proponent of scientism, but this is a modern assertion as Bacon was a devout Anglican, writing in his Essays, "a little philosophy inclineth man's mind to atheism, but depth in philosophy bringeth men's minds about to religion."

With respect to the philosophy of science, the term scientism frequently implies a critique of the more extreme expressions of logical positivism and has been used by social scientists such as Friedrich Hayek, philosophers of science such as Karl Popper, and philosophers such as Mary Midgley, the later Hilary Putnam, and Tzvetan Todorov to describe (for example) the dogmatic endorsement of scientific methods and the reduction of all knowledge to only that which is measured or confirmatory.

More generally, scientism is often interpreted as science applied "in excess". This use of the term scientism has two senses:

• The improper use of science or scientific claims. This usage applies equally in contexts where science might not apply, such as when the topic is perceived as beyond the scope of scientific inquiry, and in contexts where there is insufficient empirical evidence to justify a scientific conclusion. It includes an excessive deference to the claims of scientists or an uncritical eagerness to accept any result described as scientific. This can be a counterargument to appeals to scientific authority. It can also address attempts to apply natural science methods and claims of certainty to the social sciences, which Friedrich Hayek described in The Counter-Revolution of Science (1952) as being impossible, because those methods attempt to eliminate the "human factor", while social sciences (including his own topic of economics) mainly concern the study of human action.
• "The belief that the methods of natural science, or the categories and things recognized in natural science, form the only proper elements in any philosophical or other inquiry", or that "science, and only science, describes the world as it is in itself, independent of perspective" with a concomitant "elimination of the psychological [and spiritual] dimensions of experience". Tom Sorell provides this definition: "Scientism is a matter of putting too high a value on natural science in comparison with other branches of learning or culture." Philosophers such as Alexander Rosenberg have also adopted "scientism" as a name for the opinion that science is the only reliable source of knowledge.

It is also sometimes used to describe the universal applicability of the scientific method, and the opinion that empirical science constitutes the most authoritative worldview or the most valuable part of human learning, sometimes to the complete exclusion of other opinions, such as historical, philosophical, economic or cultural opinions. It has been defined as "the view that the characteristic inductive methods of the natural sciences are the only source of genuine factual knowledge and, in particular, that they alone can yield true knowledge about man and society". The term scientism is also used by historians, philosophers, and cultural critics to highlight the possible dangers of lapses towards excessive reductionism with respect to all topics of human knowledge.

For social theorists practising the tradition of Max Weber, such as Jürgen Habermas and Max Horkheimer, the concept of scientism relates significantly to the philosophy of positivism, but also to the cultural rationalization for modern Western civilization. Ernesto Sabato, physicist and essayist, wrote in his 1951 essay Hombres y engranajes ("Man and mechanism") of the "superstition of science" as the most contradictory of all superstitions, since this would be the "superstition that one should not be superstitious". He wrote: "science had become a new magic and the man in the street believed in it the more the less he understood it".

Definitions

Reviewing the references to scientism in the works of contemporary scholars in 2003, Gregory R. Peterson detected two main general themes:

• It is used to criticize a totalizing opinion of science as if it were capable of describing all reality and knowledge, or as if it were the only true method to acquire knowledge about reality and the nature of things;
• It is used, often pejoratively, to denote violations by which the theories and methods of one (scientific) discipline are applied inappropriately to another (scientific or non-scientific) discipline and its domain. An example of this second usage is to term as scientism any attempt to claim science as the only or primary source of human values (a traditional domain of ethics) or as the source of meaning and purpose (a traditional domain of religion and related worldviews).

The term scientism was popularized by F. A. Hayek, who defined it in 1942 as the "slavish imitation of the method and language of Science".

Mathematician Alexander Grothendieck, in his 1971 essay "The New Universal Church", characterized scientism as a religion-like ideology that advocates scientific reductionism, scientific authoritarianism, political technocracy and technological salvation, while denying the epistemological validity of feelings and experiences such as love, emotion, beauty and fulfillment. He predicted that "in coming years, the chief political dividing line will fall less and less among the traditional division between 'right' and 'left', but increasingly between the adherents of scientism, who advocate 'technological progress at any price', and their opponents, i.e., roughly speaking, those who regard the enhancement of life, in all its richness and variety, as being the supreme value".

E. F. Schumacher, in his A Guide for the Perplexed (1977), criticized scientism as an impoverished world view confined solely to what can be counted, measured and weighed. "The architects of the modern worldview, notably Galileo and Descartes, assumed that those things that could be weighed, measured, and counted were more true than those that could not be quantified. If it couldn't be counted, in other words, it didn't count."

In 1979, Karl Popper defined scientism as "the aping of what is widely mistaken for the method of science".

In 2003, Mikael Stenmark proposed the expression scientific expansionism as a synonym of scientism. In the Encyclopedia of Science and Religion, he wrote that, while the doctrines that are described as scientism have many possible forms and varying degrees of ambition, they share the idea that the boundaries of science (that is, typically the natural sciences) could and should be expanded so that something that has not been previously considered as a subject pertinent to science can now be understood as part of science (usually with science becoming the sole or the main arbiter regarding this area or dimension). According to Stenmark, the strongest form of scientism states that science does not have any boundaries and that all human problems and all aspects of human endeavor, with due time, will be dealt with and solved by science alone. This idea has also been termed the myth of progress.

Intellectual historian T. J. Jackson Lears argued in 2013 that there has been a recent reemergence of "nineteenth-century positivist faith that a reified 'science' has discovered (or is about to discover) all the important truths about human life. Precise measurement and rigorous calculation, in this view, are the basis for finally settling enduring metaphysical and moral controversies." Lears specifically identified Harvard psychologist Steven Pinker's work as falling in this category. Philosophers John N. Gray and Thomas Nagel have made similar criticisms against popular works by moral psychologist Jonathan Haidt, atheist author Sam Harris, and writer Malcolm Gladwell.

Strong and weak scientism

There are various ways of classifying kinds of scientism. Some authors distinguish between strong and weak scientism, as follows:

• Strong scientism: "of all the knowledge we have, scientific knowledge is the only 'real knowledge'" (Moti Mizrahi), or, "the view that some proposition or theory is true and/or rational to believe if and only if it is a scientific proposition or theory" (J. P. Moreland), or, "only science yields epistemically credible data" (Michael W. Austin)
• Weak scientism: "of all the knowledge we have, scientific knowledge is the best knowledge" (Moti Mizrahi), or, "science is the most valuable, most serious, and most authoritative sector of human learning" (J. P. Moreland), or, "scientific knowledge claims are the most credible knowledge claims" (Michael W. Austin)

A 2023 research article by Rik Peels in the journal Interdisciplinary Science Reviews explores the concept of scientism, defining it as the belief that science is the only means of obtaining knowledge and truth. Peels distinguishes between weak scientism, which limits the validity of science to specific areas, and strong scientism, which extends this validity to all fields of knowledge. The author argues that strong scientism is untenable and self-confuting because science itself is based on common sense assumptions and non-scientific principles. He proposes that scientism can be considered a form of fundamentalism, characterized by a Manichean narrative that is reactive against other sources of knowledge. The article suggests that science can learn from mainstream religion when it comes to scientific fundamentalism, by promoting a more open and tolerant approach to other forms of knowledge.

Relevance to debates about science and religion

Both religious and non-religious scholars have applied the term scientism to individuals associated with New Atheism. Theologian John Haught argued that philosopher Daniel Dennett and other New Atheists subscribe to a belief system of scientific naturalism, which includes the dogma that "only nature, including humans and our creations, is real: that God does not exist; and that science alone can give us complete and reliable knowledge of reality." Haught argued that this belief system is self-refuting since it requires its adherents to assent to beliefs that violate its own stated requirements for knowledge. Christian philosopher Peter Williams argued in 2013 that it is only by conflating science with scientism that New Atheists feel qualified to "pontificate on metaphysical issues". Daniel Dennett responded to religious criticism of his 2006 book Breaking the Spell: Religion as a Natural Phenomenon by saying that accusations of scientism "[are] an all-purpose, wild-card smear ... When someone puts forward a scientific theory that [religious critics] really don't like, they just try to discredit it as 'scientism'. But when it comes to facts, and explanations of facts, science is the only game in town".

Non-religious scholars have also associated New Atheist thought with scientism and/or with positivism. Atheist philosopher Thomas Nagel argued that philosopher Sam Harris conflated all empirical knowledge with scientific knowledge. Marxist literary critic Terry Eagleton argued that Christopher Hitchens possessed an "old-fashioned scientistic notion of what counts as evidence" that reduces knowledge to what can and cannot be proven by scientific procedure. Agnostic philosopher Anthony Kenny has also criticized New Atheist philosopher Alexander Rosenberg's The Atheist's Guide to Reality for resurrecting a self-refuting epistemology of logical positivism and reducing all knowledge of the universe to the discipline of physics.

Michael Shermer, founder of The Skeptics Society, discussed resemblances between scientism and traditional religions, indicating the cult of personality that develops for some scientists. He defined scientism as a worldview that encompasses natural explanations, eschews supernatural and paranormal speculations, and embraces empiricism and reason.

The Iranian scholar Seyyed Hossein Nasr has stated that in the Western world, many will accept the ideology of modern science, not as "simple ordinary science", but as a replacement for religion.

Gregory R. Peterson wrote that "for many theologians and philosophers, scientism is among the greatest of intellectual sins". Genetic biologist Austin L. Hughes wrote in the conservative journal The New Atlantis that scientism has much in common with superstition: "the stubborn insistence that something ... has powers which no evidence supports."

Repeating common criticisms of logical positivism and verificationism, philosopher of religion Keith Ward has said that scientism is philosophically inconsistent or even self-refuting, as the truth of the two statements "no statements are true unless they can be proven scientifically (or logically)" and "no statements are true unless they can be shown empirically to be true" cannot themselves be proven scientifically, logically, or empirically.

Philosophy of science

Main article: Philosophy of science

Anti-scientism

Philosopher Paul Feyerabend, who was an enthusiastic proponent of scientism during his youth, later came to characterize science as "an essentially anarchic enterprise" and argued emphatically that science merits no exclusive monopoly of "dealing in knowledge" and that scientists have never operated within a distinct and narrowly self-defined tradition. In his essay Against Method he depicted the process of contemporary scientific education as a mild form of indoctrination, intended for "making the history of science duller, simpler, more uniform, more 'objective' and more easily accessible to treatment by strict and unchanging rules".

[S]cience can stand on its own feet and does not need any help from rationalists, secular humanists, Marxists and similar religious movements; and ... non-scientific cultures, procedures and assumptions can also stand on their own feet and should be allowed to do so ... Science must be protected from ideologies; and societies, especially democratic societies, must be protected from science ... In a democracy scientific institutions, research programmes, and suggestions must therefore be subjected to public control, there must be a separation of state and science just as there is a separation between state and religious institutions, and science should be taught as one view among many and not as the one and only road to truth and reality.

— Paul Feyerabend, Against Method, p. viii

Pro-scientism

Physicist and philosopher Mario Bunge used the term scientism with a favorable rather than pejorative sense in numerous books published during several decades, and in articles with titles such as "In Defense of Realism and Scientism" and "In Defense of Scientism". Bunge said that scientism should not be equated with inappropriate reductionism, and he dismissed critics of science such as Hayek and Habermas as dogmatists and obscurantists:

To innovate in the young sciences it is necessary to adopt scientism. This is the methodological thesis that the best way of exploring reality is to adopt the scientific method, which may be boiled down to the rule "Check your guesses." Scientism has been explicitly opposed by dogmatists and obscurantists of all stripes, such as the neoliberal ideologist Friedrich von Hayek and the "critical theorist" Jürgen Habermas, a ponderous writer who managed to amalgamate Hegel, Marx, and Freud, and decreed that "science is the ideology of late capitalism."

— Mario Bunge, Evaluating Philosophies

In 2018, philosophers Maarten Boudry and Massimo Pigliucci co-edited a book titled Science Unlimited? The Challenges of Scientism in which a number of chapters by philosophers and scientists defended scientism. In his chapter "Two Cheers for Scientism", Taner Edis wrote:

It is defensible to claim that scientific, philosophical, and humanistic forms of knowledge are continuous, and that a broadly naturalistic description of our world centered on natural science is correct ... At the very least, such views are legitimate—they may be mistaken, but not because of an elementary error, a confusion of science with ideology, or an offhand dismissal of the humanities. Those of us who argue for such a view are entitled to have two cheers for an ambitious conception of science; and if that is scientism, so be it.

— Taner Edis, "Two Cheers for Scientism"

Rhetoric of science

Main article: Rhetoric of science

Thomas M. Lessl argued that religious themes persist in what he terms scientism, the public rhetoric of science. There are two methods of describing this idea of scientism: the epistemological method (the assumption that the scientific method trumps other ways of knowing) and the ontological method (that the rational mind represents the world and both operate in knowable ways). According to Lessl, the ontological method is an attempt to "resolve the conflict between rationalism and skepticism". Lessl also argued that without scientism, there would not be a scientific culture.

Rationalization and modernity

See also: Rationalization (sociology) and Antipositivism § Frankfurt School

In the introduction to his collected works on the sociology of religion, Max Weber asked why "the scientific, the artistic, the political, or the economic development [elsewhere] ... did not enter upon that path of rationalization which is peculiar to the Occident?" According to the German social theorist Jürgen Habermas, "For Weber, the intrinsic (that is, not merely contingent) relationship between modernity and what he called 'Occidental rationalism' was still self-evident." Weber described a process of rationalisation, disenchantment and the "disintegration of religious world views" that resulted in modern secular societies and capitalism.

"Modernization" was introduced as a technical term only in the 1950s. It is the mark of a theoretical approach that takes up Weber's problem but elaborates it with the tools of social-scientific functionalism ... The theory of modernization performs two abstractions on Weber's concept of "modernity". It dissociates "modernity" from its modern European origins and stylizes it into a spatio-temporally neutral model for processes of social development in general. Furthermore, it breaks the internal connections between modernity and the historical context of Western rationalism, so that processes of modernization ... [are] no longer burdened with the idea of a completion of modernity, that is to say, of a goal state after which "postmodern" developments would have to set in. ... Indeed it is precisely modernization research that has contributed to the currency of the expression "postmodern" even among social scientists.

— Jürgen Habermas, The Philosophical Discourse of Modernity

Habermas is critical of pure instrumental rationality, arguing that the "Social Life–World" of subjective experiencing is better suited to literary expression. Where the sciences select experiences that can be expressed in formal language using general definitions, the literary arts select private, unrepeatable experiences where definitions are generated through "intersubjectivity of mutual understanding in each concrete case". Habermas quoted writer Aldous Huxley in order to juxtapose the "social life-world" and the "worldless universe of facts" underscoring the duality of literature and science:

The world with which literature deals is the world in which human beings are born and live and finally die; the world in which they love and hate, in which they experience triumph and humiliation, hope and despair; the world of sufferings and enjoyments, of madness and common sense, of silliness, cunning and wisdom; the world of social pressures and individual impulses, of reason against passion, of instincts and conventions, of shared language and unsharable feelings and sensations.

[...]

[The scientist] is the inhabitant of a radically different universe--not the universe of given appearances, but the world of inferred fine structures, not the experienced world of unique events and diverse qualities, but the world of quantified regularities.

— Aldous Huxley, Literature and Science

Happiness economics

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Happiness_economics 

Richer countries tend to be happier than poorer countries (observations are lined up around an upward-sloping trend), and richer people within countries tend to be happier than poorer people in the same countries (arrows are consistently pointing northeast).

The economics of happiness or happiness economics is the theoretical, qualitative and quantitative study of happiness and quality of life, including positive and negative affects, well-being, life satisfaction and related concepts – typically tying economics more closely than usual with other social sciences, like sociology and psychology, as well as physical health. It typically treats subjective happiness-related measures, as well as more objective quality of life indices, rather than wealth, income or profit, as something to be maximized.

The field has grown substantially since the late 20th century, for example by the development of methods, surveys and indices to measure happiness and related concepts, as well as quality of life. Happiness findings have been described as a challenge to the theory and practice of economics. Nevertheless, furthering gross national happiness, as well as a specified Index to measure it, has been adopted explicitly in the Constitution of Bhutan in 2008, to guide its economic governance.

Subject classifications

The subject may be categorized in various ways, depending on specificity, intersection, and cross-classification. For example, within the Journal of Economic Literature classification codes, it has been categorized under:

• Welfare economics at JEL: D63 – Equity, Justice, Inequality, and Other Normative Criteria and Measurement
• Health, education, and welfare at JEL: I31 – General Welfare; Basic needs; Living standards; Quality of life; Happiness
• Demographic economics at JEL:J18 – Public policy.

Metrology

Given its very nature, reported happiness is subjective. It is difficult to compare one person's happiness with another's. It can be especially difficult to compare happiness across cultures. However, many happiness economists believe they have solved this comparison problem. Cross-sections of large data samples across nations and time demonstrate consistent patterns in the determinants of happiness.

Happiness is typically measured using subjective measures – e.g. self-reported surveys – and/or objective measures. One concern has always been the accuracy and reliability of people's responses to happiness surveys. Objective measures such as lifespan, income, and education are often used as well as or instead of subjectively reported happiness, though this assumes that they generally produce happiness, which while plausible may not necessarily be the case. The terms quality of life or well-being are often used to encompass these more objective measures.

Micro-econometric happiness equations have the standard form: ${\displaystyle W_{it}=\alpha +\beta x_{it}+{ϵ}_{it}}$. In this equation ${\displaystyle W}$ is the reported well-being of individual ${\displaystyle i}$ at time ${\displaystyle t}$, and ${\displaystyle x}$ is a vector of known variables, which include socio-demographic and socioeconomic characteristics.

Macro-econometric happiness has been gauged by some as Gross National Happiness, following Sicco Mansholt's 1972 introduction of the measure, and by others as a Genuine Wealth index. Anielski in 2008 wrote a reference definition on how to measure five types of capital: (1) human; (2) social; (3) natural; (4) built; and (5) financial.

Happiness, well-being, or satisfaction with life, was seen as unmeasurable in classical and neo-classical economics. Van Praag was the first person who organized large surveys in order to explicitly measure welfare derived from income. He did this with the Income Evaluation Question (IEQ). This approach is called the Leyden School. It is named after the Dutch university where this approach was developed. Other researchers included Arie Kapteyn and Aldi Hagenaars.

Some scientists claim that happiness can be measured both subjectively and objectively by observing the joy center of the brain lit up with advanced imaging, although this raises philosophical issues, for example about whether this can be treated as more reliable than reported subjective happiness.

Determinants

GDP and GNP

Typically national financial measures, such as gross domestic product (GDP) and gross national product (GNP), have been used as a measure of successful policy. There is a significant association between GDP and happiness, with citizens in wealthier nations being happier than those in poorer nations. In 2002, researchers argued that this relationship extends only to an average GDP per capita of about $15,000. In the 2000s, several studies have obtained the opposite result, so this Easterlin paradox is controversial.

Individual income

Historically, economists have said that well-being is a simple function of income. However, it has been found that once wealth reaches a subsistence level, its effectiveness as a generator of well-being is greatly diminished. Happiness economists hope to change the way governments view well-being and how to most effectively govern and allocate resources given this paradox.

In 2010, Daniel Kahneman and Angus Deaton found that higher earners generally reported better life satisfaction, but people's day-to-day emotional well-being only rose with earnings until a threshold annual household pre-tax income of $75,000. This particular study by Kahneman and Deaton showed the relationship between experienced happiness and the maximum amount of income at $75,000. Experienced happiness is the happiness received on a daily basis-"the frequency and intensity of experiences of joy, fascination, anxiety, sadness, anger, and affection that make one's life pleasant or unpleasant." The other finding from Kahneman and Deaton is there is no evidence supporting a maximum income to what is called reflective happiness. This data is supported by the use of the Cantrill Ladder, which revealed that there is a direct relationship between income and reflective happiness. This can conclude, to a point, that money does buy happiness.

Other factors have been suggested as making people happier than money. A short term course of psychological therapy is 32 times more cost effective at increasing happiness than simply increasing income.

Scholars at the University of Virginia, University of British Columbia and Harvard University released a study in 2011 after examining numerous academic papers in response to an apparent contradiction: "When asked to take stock of their lives, people with more money report being a good deal more satisfied. But when asked how happy they are at the moment, people with more money are barely different than those with less." The study included the following eight general recommendations:

• Spend money on "experiences" rather than goods.
• Donate money to others, including charities, rather than spending it solely on oneself.
• Spend small amounts of money on many small, temporary pleasures rather than less often on larger ones.
• Don't spend money on "extended warranties and other forms of overpriced insurance."
• Adjust one's mindset to "pay now, consume later," instead of "consume now, pay later."
• Exercise circumspection about the day-to-day consequences of a purchase beforehand.
• Rather than buying products that provide the "best deal," make purchases based on what will facilitate well-being.
• Seek out the opinions of other people who have prior experience of a product before purchasing it.

In their "Unhappy Cities" paper, Edward Glaeser, Joshua Gottlieb and Oren Ziv examined the self-reported subjective well-being of people living in American metropolitan areas, particularly in relation to the notion that "individuals make trade-offs among competing objectives, including but not limited to happiness." The researchers findings revealed that people living in metropolitan areas where lower levels of happiness are reported are receiving higher real wages, and they suggest in their conclusion that "humans are quite understandably willing to sacrifice both happiness and life satisfaction if the price is right."

Social security

Ruut Veenhoven claimed that social security payments do not seem to add to happiness. This may be due to the fact that non-self-earned income (e.g., from a lottery) does not add to happiness in general either. Happiness may be the mind's reward for a useful action. However, Johan Norberg of Centre for Independent Studies, a free enterprise economy think tank, presents a hypothesis that as people who think that they themselves control their lives are happier, paternalist institutions may decrease happiness.

An alternative perspective focuses on the role of the welfare state as an institution that improves quality of life not only by increasing the extent to which basic human needs are met, but also by promoting greater control of one's life by limiting the degree to which individuals find themselves at the mercy of impersonal market forces that are indifferent to the fate of individuals. This is the argument suggested by the U.S. political scientist Benjamin Radcliff, who has presented a series of papers in peer-reviewed scholarly journals demonstrating that a more generous welfare state contributes to higher levels of life satisfaction, and does so to rich and poor alike.

Employment

Generally, the well-being of those who are employed is higher than those who are unemployed. Employment itself may not increase subjective well-being, but facilitates activities that do (such as supporting a family, philanthropy, and education). While work does increase well-being through providing income, income level is not as indicative of subjective well-being as other benefits related to employment. Feelings of autonomy and mastery, found in higher levels in the employed than unemployed, are stronger predictors of subjective well-being than wealth.

When personal preference and the amount of time spent working do not align, both men and women experience a decrease in subjective well-being. The negative effect of working more or working less than preferred has been found across multiple studies, most finding that working more than preferred (over-employed) is more detrimental, but some found that working less (under-employed) is more detrimental. Most individuals' levels of subjective well-being returned to "normal" (level previous to time mismatch) within one year. Levels remained lower only when individuals worked more hours than preferred for a period of two years or more, which may indicate that it is more detrimental to be over-employed than under-employed in the long-term.

Employment status effects are not confined to the individual. Being unemployed can have detrimental effects on a spouse's subjective well-being, compared to being employed or not working (and not looking for work). Partner life satisfaction is inversely related to the number of hours their partner is underemployed. When both partners are underemployed, the life-satisfaction of men is more greatly diminished than women. However, just being in a relationship reduces the impact unemployment has on the subjective well-being of an individual. On a broad scale, high rates of unemployment negatively affect the subjective well-being of the employed.

Becoming self-employed can increase subjective well-being, given the right conditions. Those who leave work to become self-employed report greater life satisfaction than those who work for others or become self-employed after unemployment; this effect increases over time. Those who are self-employed and have employees of their own report higher life-satisfaction than those who are self-employed without employees, and women who are self-employed without employees report a higher life satisfaction than men in the same condition.

The effects of retirement on subjective well-being vary depending on personal and cultural factors. Subjective well-being can remain stable for those who retire from work voluntarily, but declines for those who are involuntarily retired. In countries with an average social norm to work, the well-being of men increases after retirement, and the well-being of retired women is at the same level as women who are homemakers or work outside the home. In countries with a strong social norm to work, retirement negatively impacts the well-being of men and women.

Relationships and children

In the 1970s, women typically reported higher subjective well-being than did men. By 2009, declines in reported female happiness had eroded a gender gap.

In rich societies, where a rise in income doesn't equate to an increase in levels of subjective well-being, personal relationships are the determining factors of happiness.

Glaeser, Gottlieb and Ziv suggest in their conclusion that the happiness trade-offs that individuals seem willing to make aligns with the tendency of parents to report less happiness, as they sacrifice their personal well-being for the "price" of having children.

Freedom and control

There is a significant correlation between feeling in control of one's own life and happiness levels.

A study conducted at the University of Zurich suggested that democracy and federalism bring well-being to individuals. It concluded that the more direct political participation possibilities available to citizens raises their subjective well-being. Two reasons were given for this finding. First, a more active role for citizens enables better monitoring of professional politicians by citizens, which leads to greater satisfaction with government output. Second, the ability for citizens to get involved in and have control over the political process, independently increases well-being.

American psychologist Barry Schwartz argues in his book The Paradox of Choice that too many consumer and lifestyle choices can produce anxiety and unhappiness due to analysis paralysis and raised expectations of satisfaction.

Religious diversity

National cross-sectional data suggest an inverse relationship between religious diversity and happiness, possibly by facilitating more bonding (and less bridging) social capital.

Happiness and leisure

See also: Happiness and Leisure

Much of the research regarding happiness and leisure relies on subjective well-being (SWB) as an appropriate measure of happiness. Research has demonstrated a wide variety of contributing and resulting factors in the relationship between leisure and happiness. These include psychological mechanisms, and the types and characteristics of leisure activities that result in the greatest levels of subjective happiness. Specifically, leisure may trigger five core psychological mechanisms including detachment-recovery from work, autonomy in leisure, mastery of leisure activities, meaning-making in leisure activities, and social affiliation in leisure (DRAMMA). Leisure activities that are physical, relational, and performed outdoors are correlated with greater feelings of satisfaction with free time. Research across 33 different countries shows that individuals who feel they strengthen social relationships and work on personal development during leisure time are happier than others. Furthermore, shopping, reading books, attending cultural events, getting together with relatives, listening to music and attending sporting events is associated with higher levels of happiness. Spending time on the internet or watching TV is not associated with higher levels of happiness as compared to these other activities.

Research has shown that culture influences how we measure happiness and leisure. While SWB is a commonly used measure of happiness in North America and Europe, this may not be the case internationally. Quality of life (QOL) may be a better measure of happiness and leisure in Asian countries, especially Korea. Countries such as China and Japan may require a different measurement of happiness, as societal differences may influence the concept of happiness (i.e. economic variables, cultural practices, and social networks) beyond what QOL is able to measure. There seem to be some differences in leisure preference cross-culturally. Within the Croatian culture, family related leisure activities may enhance SWB across a large spectrum of ages ranging from adolescent to older adults, in both women and men. Active socializing and visiting cultural events are also associated with high levels of SWB across varying age and gender. Italians seem to prefer social conceptions of leisure as opposed to individualistic conceptions. Although different groups of individuals may prefer varying types and amount of leisure activity, this variability is likely due to the differing motivations and goals that an individual intends to fulfill with their leisure time.

Research suggests that specific leisure interventions enhance feelings of SWB. This is both a top-down and bottom-up effect, in that leisure satisfaction causally affects SWB, and SWB causally affects leisure satisfaction. This bi-directional effect is stronger in retired individuals than in working individuals. Furthermore, it appears that satisfaction with our leisure at least partially explains the relationship between our engagement in leisure and our SWB. Broadly speaking, researchers classify leisure into active (e.g. volunteering, socializing, sports and fitness) and passive leisure (e.g. watching television and listening to the radio). Among older adults, passive leisure activities and personal leisure activities (e.g. sleeping, eating, and bathing) correlate with higher levels of SWB and feelings of relaxation than active leisure activities. Thus, although significant evidence has demonstrated that active leisure is associated with higher levels of SWB, or happiness, this may not be the case with older populations.

Both regular and irregular involvement in sports leisure can result in heightened SWB. Serious, or systematic involvement in certain leisure activities, such as taekwondo, correlates with personal growth and a sense of happiness. Additionally, more irregular (e.g. seasonal) sports activities, such as skiing, are also correlated with high SWB. Furthermore, the relationship between pleasure and skiing is thought to be caused in part by a sense of flow and involvement with the activity. Leisure activities, such as meeting with friends, participating in sports, and going on vacation trips, positively correlate with life satisfaction. It may also be true that going on a vacation makes our lives seem better, but does not necessarily make us happier in the long term. Research regarding vacationing or taking a holiday trip is mixed. Although the reported effects are mostly small, some evidence points to higher levels of SWB, or happiness, after taking a holiday.

Economic security

See also: Economic security

 Poverty alleviation is associated with happier populations. According to the latest systematic review of the economic literature on life satisfaction: Volatile or high inflation is bad for a population's well-being, particularly those with a right-wing political orientation. That suggests the impact of disruptions to economic security are in part mediated or modified by beliefs about economic security.

Political stability

The Voxeu analysis of the economic determinants of happiness found that life satisfaction explains the largest share of an existing government's vote share, followed by economic growth, which itself explains six times as much as employment and twice as much as inflation.

Economic freedom

Individualistic societies have happier populations. Institutes of economic freedom are associated with increases wealth inequality but does not necessarily contribute to decreases in aggregate well-being or subjective well-being at the population level. In fact, income inequality enhances global well-being. There is some debate over whether living in poor neighbours make one happier. And, living among rich neighbours can dull the happiness that comes from wealth. This is purported to work by way of an upward or downward comparison effect (Keeping up with the Joneses). The balance of evidenceis trending in favour of the hypothesis that living in poor neighbourhoods makes one less happy, and living in rich neighbourhoods actually makes one happier, in the United States. While social status matters, a balance of factors like amenities, safe areas, well maintained housing, turn the tide in favour of the argument that richer neighbours are happier neighbours.

Democracy

"The right to participate in the political process, measured by the extent of direct democratic rights across regions, is strongly correlated with subjective well-being (Frey and Stutzer, 2002) ... a potential mechanism that explains this relationship is the perception of procedural fairness and social mobility." Institutions and well-being, democracy and federalism are associated with a happier population. Correspondingly, political engagement and activism have associated health benefits. On the other hand, some non-democratic countries such as China and Saudi Arabia top the Ipsos list of countries where the citizenry is most happy with their government's direction. That suggests that voting preferences may not translate well into overall satisfaction with the government's direction. In any case, both of these factors revealed preference and domain specific satisfaction rather than overall subjective well being.

Economic development

Historically, economists thought economic growth was unrelated to population level well-being, a phenomenon labelled the Easterlin paradox. More robust research has identified that there is a link between economic development and the wellbeing of the population. A <2017 meta-analysis shows that the impact of infrastructure expenditure on economic growth varies considerably. So, one cannot assume an infrastructure project will yield welfare benefits. The paper doesn't investigate or elaborate on any modifiable variables that might predict the value of a project. However, government spending on roads and primary industries is the best value target for transport spending, according to a 2013 meta-analysis. 7%+/−3% per annum discount rates are typically applied as the discount rate on public infrastructure projects in Australia. Smaller real discount rates are used internationally to calculate the social return on investment by governments.

Alternative approach: economic consequences of happiness

While the mainstream happiness economics has focused on identifying the determinants of happiness, an alternative approach in the discipline examines instead what are the economic consequences of happiness. Happiness may act as a determinant of economic outcomes: it increases productivity, predicts one's future income and affects labour market performance. There is a growing number of studies justifying the so-called "happy-productive worker" thesis. The positive and causal impact of happiness on an individual's productivity has been established in experimental studies. Happiness can affect voting for the incumbent party. Research in political science and behavioral economics suggests that voters’ subjective well-being, or happiness, often influences their political decisions, including whether to support the incumbent party, independently from the effect mediated by the economic individual conditions.

Related studies

The Satisfaction with Life Index. Blue through red represent most to least happy respectively; grey areas have no reliable data available.

The Satisfaction with Life Index is an attempt to show the average self-reported happiness in different nations. This is an example of a recent trend to use direct measures of happiness, such as surveys asking people how happy they are, as an alternative to traditional measures of policy success such as GDP or GNP. Some studies suggest that happiness can be measured effectively. The Inter-American Development Bank (IDB), published in November 2008 a major study on happiness economics in Latin America and the Caribbean.

There are also several examples of measures that include self-reported happiness as one variable. Happy Life Years, a concept brought by Dutch sociologist Ruut Veenhoven, combines self-reported happiness with life expectancy. The Happy Planet Index combines it with life expectancy and ecological footprint.

Gross National Happiness (GNH) is a concept introduced by the King of Bhutan in 1972 as an alternative to GDP. Several countries have already developed or are in the process of developing such an index. Bhutan's index has led that country to limit the amount of deforestation it will allow and to require that all tourists to its nation must spend US$200.

After the military coup of 2006, Thailand also instituted an index. The stated promise of the new Prime Minister Surayud Chulanont is to make the Thai people not only richer but happier as well. Much like GDP results, Thailand releases monthly GNH data. The Thai GNH index is based on a 1–10 scale with 10 being the happiest. As of 13 May 2007, the Thai GNH measured 5.1 points. The index uses poll data from the population surveying various satisfaction factors such as security, public utilities, good governance, trade, social justice, allocation of resources, education and community problems.

Australia, China, France and the United Kingdom are also coming up with indexes to measure national happiness. The UK began to measure national wellbeing in 2012. North Korea also announced an international Happiness Index in 2011 through Korean Central Television. North Korea itself came in second, behind #1 China. Canada released the Canadian Index of Wellbeing (CIW) in 2011 to track changes in wellbeing. The CIW has adopted the following working definition of wellbeing: The presence of the highest possible quality of life in its full breadth of expression focused on but not necessarily exclusive to good living standards, robust health, a sustainable environment, vital communities, an educated populace, balanced time use, high levels of democratic participation, and access to and participation in leisure and culture

Ecuador's and Bolivia's new constitutions state the indigenous concept of "good life" ("buen vivir" in Spanish, "sumak kawsay" in Quichua, and "suma qamaña" in Aymara) as the goal of sustainable development.

Neoclassical economics

Neoclassical, as well as classical economics, are not subsumed under the term happiness economics although the original goal was to increase the happiness of the people. Classical and neoclassical economics are stages in the development of welfare economics and are characterized by mathematical modeling. Happiness economics represents a radical break with this tradition. The measurement of subjective happiness respectively life satisfaction by means of survey research across nations and time (in addition to objective measures like lifespan, wealth, security etc.) marks the beginning of happiness economics.

Criticism

Some have suggested that establishing happiness as a metric is only meant to serve political goals. Recently there has been concern that happiness research could be used to advance authoritarian aims. As a result, some participants at a happiness conference in Rome have suggested that happiness research should not be used as a matter of public policy but rather used to inform individuals.

Even on the individual level, there is discussion on how much effect external forces can have on happiness. Less than 3% of an individual's level of happiness comes from external sources such as employment, education level, marital status, and socioeconomic status. To go along with this, four of the Big Five Personality Traits are substantially associated with life satisfaction, openness to experience is not associated. Having high levels of internal locus of control leads to higher reported levels of happiness.

Even when happiness can be affected by external sources, it has high hedonic adaptation, some specific events such as an increase in income, disability, unemployment, and loss (bereavement) only have short-term (about a year) effects on a person's overall happiness and after a while happiness may return to levels similar to unaffected peers.

What has the most influence over happiness are internal factors such as genetics, personality traits, and internal locus of control. It is theorized that 50% of the variation in happiness levels is from genetic sources and is known as the genetic set point. The genetic set point is assumed to be stable over time, fixed, and immune to influence or control. This goes along with findings that well-being surveys have a naturally positive baseline.

With such strong internal forces on happiness, it is hard to have an effect on a person's happiness externally. This in turn lends itself back to the idea that establishing a happiness metric is only for political gain and has little other use. To support this even further it is believed that a country aggregate level of SWB can account for more variance in government vote share than standard macroeconomic variables, such as income and employment.

Technical issues

According to Bond and Lang (2018), the results are skewed due to the fact that the respondents have to "round" their true happiness to the scale of, e.g., 3 or 7 alternatives (e.g., very happy, pretty happy, not too happy). This "rounding error" may cause a less happy group seem happier, in the average. This would not be the case if the happiness of both groups would be normally distributed with the same variance, but that is usually not the case, based on their results. For some not-implausible log-normal assumptions on the scale, typical results can be reversed to the opposite results.

They also show that the "reporting function" seems to be different for different groups and even for the same individual at different times. For example, when a person becomes disabled, they soon start to lower their threshold for a given answer (e.g., "pretty happy"). That is, they give a higher answer than they would have given at the same happiness state before becoming disabled.

Last universal common ancestor

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Last_universal_common_ancestor

Phylogenetic tree linking all major groups of living organisms, namely the bacteria, archaea, and eukaryota, with the last universal common ancestor (LUCA) shown at the root

The last universal common ancestor (LUCA) is the hypothesized latest common ancestral cell population from which all subsequent life forms descend, including Bacteria, Archaea, and Eukarya. The cell had a lipid bilayer; it possessed the genetic code and ribosomes which translated from DNA or RNA to proteins. Although the timing of the LUCA cannot be definitively constrained, most studies suggest that the LUCA existed by 3.5 billion years ago, and possibly as early as 4.3 billion years ago or earlier. The nature of this point or stage of divergence remains a topic of research.

All earlier forms of life preceding this divergence and all extant organisms are generally thought to share common ancestry. On the basis of a formal statistical test, this theory of a universal common ancestry (UCA) is supported in preference to competing multiple-ancestry hypotheses. The first universal common ancestor (FUCA) is a hypothetical non-cellular ancestor to LUCA and other now-extinct sister lineages.

Whether the genesis of viruses falls before or after the LUCA–as well as the diversity of extant viruses and their hosts–remains a subject of investigation.

While no fossil evidence of the LUCA exists, the detailed biochemical similarity of all current life (divided into the three domains) makes its existence widely accepted by biochemists. Its characteristics can be inferred from shared features of modern genomes. These genes describe a complex life form with many co-adapted features, including transcription and translation mechanisms to convert information from DNA to mRNA to proteins.

Historical background

Further information: Tree of life (biology)

A tree of life, like this one from Charles Darwin's notebooks c. July 1837, implies a single common ancestor at its root (labelled "1").

A phylogenetic tree directly portrays the idea of evolution by descent from a single ancestor. An early tree of life was sketched by Jean-Baptiste Lamarck in his Philosophie zoologique in 1809. Charles Darwin more famously proposed the theory of universal common descent through an evolutionary process in his book On the Origin of Species in 1859: "Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed." The last sentence of the book begins with a restatement of the hypothesis:

There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one ...

By 1871, in another letter to Hooker, Darwin speculated on the natural origin of life itself, writing that life might have begun in a "warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc., present", an early expression of abiogenesis.

The term "last universal common ancestor" or "LUCA" was first used in the 1990s for such a primordial organism.

Inferring LUCA's features

Biochemical mechanisms

While the anatomy of LUCA cannot be reconstructed with certainty, its biochemical mechanisms can be deduced and described in some detail, based on properties shared by currently living organisms as well as genetic analysis.

LUCA certainly had genes and a genetic code. Its genetic material was most likely DNA, so that it lived after the RNA world. The DNA was kept double-stranded by an enzyme, DNA polymerase, which recognises the structure and directionality of DNA. The integrity of the DNA was maintained by a group of repair enzymes including DNA topoisomerase. If the genetic code was based on dual-stranded DNA, it was expressed by copying the information to single-stranded RNA. The RNA was produced by a DNA-dependent RNA polymerase using nucleotides similar to those of DNA. It had multiple DNA-binding proteins, such as histone-fold proteins. The genetic code was expressed into proteins. These were assembled from 20 free amino acids by translation of a messenger RNA via a mechanism of ribosomes, transfer RNAs, and a group of related proteins.

Although LUCA was likely not capable of sexual interaction, gene functions were present that promoted the transfer of DNA between individuals of the population to facilitate genetic recombination. Homologous gene products that promote genetic recombination are present in bacteria, archaea and eukaryota, such as the RecA protein in bacteria, the RadA protein in archaea, and the Rad51 and Dmc1 proteins in eukaryota.

LUCA's functionality, and evidence for the early evolution of membrane-dependent biological systems, together suggest that LUCA was a cell with membranes. It contained a water-based cytoplasm enclosed by a lipid bilayer membrane; it reproduced by cell division. It tended to exclude sodium and concentrate potassium by means of specific ion transporters (or ion pumps). The cell multiplied by duplicating all its contents followed by cellular division. The cell used chemiosmosis to produce energy. It also reduced CO₂ and oxidized H₂ (methanogenesis or acetogenesis) via acetyl-thioesters.

By phylogenetic bracketing, analysis of its offspring groups, LUCA appears to have been a small, single-celled organism. It likely had a ring-shaped coil of DNA floating freely within the cell. Morphologically, it would likely not have stood out within a mixed population of small modern-day bacteria. The originator of the three-domain system, Carl Woese, stated that in its genetic machinery, the LUCA would have been a "simpler, more rudimentary entity than the individual ancestors that spawned the three [domains] (and their descendants)".

Because bacteria and archaea differ in their structure of phospholipids and cell wall, ion pumping, most proteins involved in DNA replication, and glycolysis, it is inferred that LUCA had a permeable membrane without an ion pump. The emergence of Na⁺/H⁺ antiporters likely led to the later evolution of impermeable membranes in eukaryotes, archaea, and bacteria. This would accord with LUCA's having made use of the natural geochemical proton gradient in its environment across a leaky membrane to provide it with energy. Cell walls, too, would have evolved later. Although LUCA likely had DNA, it is unknown if it could replicate DNA: as Weiss et al write, it "might just have been a chemically stable repository for RNA-based replication". It is likely that LUCA's permeable membrane was composed of archaeal lipids (isoprenoids) and bacterial lipids (fatty acids). Isoprenoids would have helped to stabilize LUCA's membrane in the surrounding extreme habitat.

LUCA's genome was likely similar in size to that of modern prokaryotes, encoding around 2,600 proteins, based on statistical inference using the probabilistic gene- and species-tree reconciliation algorithm ALE. It may have been an acetogen, respiring anaerobically, and may have had an early CAS-based anti-viral immune system. The inferred metabolic features are consistent with the early Earth hydrothermal systems with high concentrations of CO₂ and H₂.

An anaerobic thermophile

Further information: Phylogenetic bracketing

 

A direct way to infer LUCA's genome would be to find genes common to all surviving descendants, but little can be learnt by this approach, as there are only about 30 such genes. They are mostly for ribosome proteins, proving that LUCA had the genetic code. Many other LUCA genes have been lost in later lineages over 4 billion years of evolution.

Three ways to infer genes present in LUCA: universal presence, presence in both the Bacterial and Archaean domains, and presence in two phyla in both domains. The first yields as stated only about 30 genes; the second, some 11,000 with lateral gene transfer (LGT) very likely; the third, 355 genes probably in LUCA, since they were found in at least two phyla in both domains, making LGT an unlikely explanation.

An alternative to the search for "universal" traits is to use genome analysis to identify phylogenetically ancient genes. This gives a picture of a LUCA that could live in a geochemically harsh environment and is like modern prokaryotes. Analysis of biochemical pathways implies the same sort of chemistry as does phylogenetic analysis.

LUCA systems and environment, including the Wood–Ljungdahl or reductive acetyl–CoA pathway to fix carbon, and most likely DNA complete with the genetic code and enzymes to replicate it, transcribe it to RNA, and translate it to proteins.

In 2016, Madeline C. Weiss and colleagues genetically analyzed 6.1 million protein-coding genes and 286,514 protein clusters from sequenced prokaryotic genomes representing many phylogenetic trees, and identified 355 protein clusters that were probably common to the LUCA. The results of their analysis are highly specific, though debated. They depict LUCA as "anaerobic, CO₂-fixing, H₂-dependent with a Wood–Ljungdahl pathway (the reductive acetyl-coenzyme A pathway), N₂-fixing and thermophilic. LUCA's biochemistry was replete with FeS clusters and radical reaction mechanisms." The cofactors indicate "dependence upon transition metals, flavins, S-adenosyl methionine, coenzyme A, ferredoxin, molybdopterin, corrins and selenium. Its genetic code required nucleoside modifications and S-adenosylmethionine-dependent methylations." They show that methanogens and clostridia were basal, near the root of the phylogenetic tree, in the 355 protein lineages examined, and that the LUCA may therefore have inhabited an anaerobic hydrothermal vent setting in a geochemically active environment rich in H₂, CO₂, and iron, where ocean water interacted with hot magma beneath the ocean floor. It is inferred that LUCA grew from H₂ and CO₂ via the reverse incomplete Krebs cycle. Other metabolic pathways inferred in LUCA are the pentose phosphate pathway, glycolysis, and gluconeogenesis. Even if phylogenetic evidence may point to a hydrothermal vent environment for a thermophilic LUCA, this does not constitute evidence that the origin of life took place at a hydrothermal vent since mass extinctions may have removed previously existing branches of life.

The LUCA used the Wood–Ljungdahl or reductive acetyl–CoA pathway to fix carbon, if it was an autotroph, or to respire anaerobically, if it was a heterotroph.

Weiss and colleagues write that "Experiments ... demonstrate that ... acetyl-CoA pathway [chemicals used in anaerobic respiration] formate, methanol, acetyl moieties, and even pyruvate arise spontaneously ... from CO₂, native metals, and water", a combination present in hydrothermal vents.

An experiment shows that Zn²⁺, Cr³⁺, and Fe can promote 6 of the 11 reactions of an ancient anabolic pathway called the reverse Krebs cycle in acidic conditions which implies that LUCA might have inhabited either hydrothermal vents or acidic metal-rich hydrothermal fields.

Undersampled protein families

Some other researchers have challenged Weiss et al.'s 2016 conclusions. Sarah Berkemer and Shawn McGlynn argue that Weiss et al. undersampled the families of proteins, so that the phylogenetic trees were not complete and failed to describe the evolution of proteins correctly. There are two risks in attempting to attribute LUCA's environment from near-universal gene distribution (as in Weiss et al. 2016). On the one hand, it risks misattributing convergence or horizontal gene transfer events to vertical descent; on the other hand, it risks misattributing potential LUCA gene families as horizontal gene transfer events. A phylogenomic and geochemical analysis of a set of proteins that probably traced to the LUCA show that it had K⁺-dependent GTPases and the ionic composition and concentration of its intracellular fluid was seemingly high K⁺/Na⁺ ratio, NH⁺
₄, Fe²⁺, CO²⁺, Ni²⁺, Mg²⁺, Mn²⁺, Zn²⁺, pyrophosphate, and PO³⁻
₄ which would imply a terrestrial hot spring habitat. It possibly had a phosphate-based metabolism. Further, these proteins were unrelated to autotrophy (the ability of an organism to create its own organic matter), suggesting that the LUCA had a Heterotrophic lifestyle (consuming organic matter) and that its growth was dependent on organic matter produced by the physical environment.

The presence of the energy-handling enzymes CODH/acetyl-coenzyme A synthase in LUCA could be compatible with being an autotroph and with life as a mixotroph or heterotroph. Weiss et al. in 2018 replied that no enzyme defines a trophic lifestyle, and that heterotrophs evolved from autotrophs.

A 2024 study directly estimated the order in which amino acids were added into the genetic code from early protein domain sequences. A total of 969 protein domains were classified as present in LUCA, including 101 domain sequences that dated back to the even-older pre-LUCA communities. 88% of the protein domains annotated as LUCA or pre-LUCA were confirmed by Moody et al. 2024, by being associated with proteins that are more than 50% likely to be present in LUCA. It found that amino acids that bind metals, and those that contain sulphur, came early in the genetic code. The study suggests that sulphur metabolism and catalysis involving metals were important elements of life at the time of LUCA.

Possibly a mesophile

Several lines of evidence suggest that LUCA was non-thermophilic. The content of G + C nucleotide pairs (compared to the occurrence of A + T pairs) can indicate an organism's thermal optimum as they are more thermally stable due to an additional hydrogen bond. As a result, they occur more frequently in the rRNA of thermophiles; however, this is not seen in LUCA's reconstructed rRNA.

The identification of thermophilic genes in the LUCA has been challenged, as they may instead represent genes that evolved later in archaea or bacteria, then migrated between these via horizontal gene transfer, as in Woese's 1998 hypothesis. For instance, the thermophile-specific topoisomerase, reverse gyrase, was initially attributed to LUCA before an exhaustive phylogenetic study revealed a more recent origin of this enzyme followed by extensive horizontal gene transfer. LUCA could have been a mesophile that fixed CO₂ and relied on H₂, and lived close to hydrothermal vents.

Further evidence that LUCA was mesophilic comes from the amino acid composition of its proteins. The abundance of I, V, Y, W, R, E, and L amino acids (denoted IVYWREL) in an organism's proteins is correlated with its optimal growth temperature. According to phylogenetic analysis, the IVYWREL content of LUCA's proteins suggests its ideal temperature was below 50°C.

Evidence that bacteria and archaea both independently underwent phases of increased and subsequently decreased thermo-tolerance suggests a dramatic post-LUCA climate shift that affected both populations, and would explain the seeming genetic pervasiveness of thermo-tolerant genetics.

Age

Further information: Abiogenesis

Studies from 2000 to 2018 have suggested an increasingly ancient time for the LUCA. In 2000, estimates of the LUCA's age ranged from 3.8 to 3.5 bya (billion years ago) in the Paleoarchean, a few hundred million years after the earliest fossil evidence of life, for which candidates range in age from 4.28 to 3.48 bya. This placed the origin of the first forms of life shortly after the Late Heavy Bombardment which was thought to have repeatedly sterilized Earth's surface. However, a 2018 study by Holly Betts and colleagues applied a molecular clock model to the genomic and fossil record (102 species, 29 common protein-coding genes, mostly ribosomal), concluding that LUCA preceded the Late Heavy Bombardment (making the LUCA over 3.9 bya). A 2022 study suggested an age of around 4.2–3.6 bya for the LUCA. A 2024 study suggested that the LUCA lived around 4.2 bya (with a confidence interval of 4.33–4.09 bya). This 2024 dating implies that the time gap between the origin of life and LUCA is only about 100-200 million years, as the first habitable environments likely formed around 4.3 or 4.4 bya.

Root of the tree of life

For branching of bacteria phyla, see Bacterial phyla.

2005 tree of life showing horizontal gene transfers between branches including (coloured lines) the symbiogenesis of plastids and mitochondria. "Horizontal gene transfer and how it has impacted the evolution of life is presented through a web connecting bifurcating branches that complicate, yet do not erase, the tree of life".

In 1990, a novel concept of the tree of life was presented, dividing the living world into three stems, classified as the domains Bacteria, Archaea, Eukarya. It is the first tree founded exclusively on molecular phylogenetics, and which includes the evolution of microorganisms. It has been called a "universal phylogenetic tree in rooted form". This tree and its rooting became the subject of debate.

In the meantime, numerous modifications of this tree, mainly concerning the role and importance of horizontal gene transfer for its rooting and early ramifications have been suggested. Since heredity occurs both vertically and horizontally, the tree of life may have been more weblike or netlike in its early phase and more treelike when it grew three-stemmed. Presumably horizontal gene transfer has decreased with growing cell stability.

A modified version of the tree, based on several molecular studies, has its root between a monophyletic domain Bacteria and a clade formed by Archaea and Eukaryota. A small minority of studies place the root in the domain bacteria, in the phylum Bacillota, or state that the phylum Chloroflexota (formerly Chloroflexi) is basal to a clade with Archaea and Eukaryotes and the rest of bacteria (as proposed by Thomas Cavalier-Smith). Metagenomic analyses recover a two-domain system with the domains Archaea and Bacteria; in this view of the tree of life, Eukaryotes are derived from Archaea. With the later gene pool of LUCA's descendants, sharing a common framework of the AT/GC rule and the standard twenty amino acids, horizontal gene transfer would have become feasible and could have been common.

The nature of LUCA remains disputed. In 1994, on the basis of primordial metabolism (as discussed by Wächtershäuser), Otto Kandler proposed a successive divergence of the three domains of life from a multiphenotypical population of pre-cells, reached by gradual evolutionary improvements (cellularization). The phenotypically diverse pre-cells of this population were metabolising, self-reproducing entities exhibiting frequent mutual exchange of genetic information. Thus, in this scenario there was no "first cell". It may explain the unity and, at the same time, the partition into three lines (the three domains) of life. Kandler's pre-cell theory is supported by Wächtershäuser. In 1998, Carl Woese, based on the RNA world concept, proposed that no individual organism could be considered a LUCA, and that the genetic heritage of all modern organisms derived through horizontal gene transfer among an ancient community of organisms. Other authors concur that there was a "complex collective genome" at the time of the LUCA, and that horizontal gene transfer was important in the evolution of later groups; Nicolas Glansdorff states that LUCA "was in a metabolically and morphologically heterogeneous community, constantly shuffling around genetic material" and "remained an evolutionary entity, though loosely defined and constantly changing, as long as this promiscuity lasted."

The theory of a universal common ancestry of life is widely accepted. In 2010, based on "the vast array of molecular sequences now available from all domains of life", D. L. Theobald published a "formal test" of universal common ancestry (UCA). This deals with the common descent of all extant terrestrial organisms, each being a genealogical descendant of a single species from the distant past. His formal test favoured the existence of a universal common ancestry over a wide class of alternative hypotheses that included horizontal gene transfer. Basic biochemical principles imply that all organisms do have a common ancestry.

A proposed non-cellular ancestor to LUCA is the first universal common ancestor (FUCA). FUCA would therefore be the ancestor to every modern cell as well as to ancient, now-extinct cellular lineages not descending from LUCA. FUCA is assumed to have had descendants other than LUCA, none of which have modern descendants. Some genes of these ancient now-extinct cell lineages are thought to have been horizontally transferred into the genome of early descendants of LUCA.

LUCA and viruses

The origin of viruses remains disputed. Since viruses need host cells for their replication, it is likely that they emerged after the formation of cells. Viruses may even have multiple origins and different types of viruses may have evolved independently over the history of life. There are different hypotheses for the origins of viruses, for instance an early viral origin from the RNA world or a later viral origin from selfish DNA.

Based on how viruses are currently distributed across the bacteria and archaea, the LUCA is suspected of having been prey to multiple viruses, ancestral to those that now have those two domains as their hosts. Furthermore, extensive virus evolution seems to have preceded the LUCA, since the jelly-roll structure of capsid proteins is shared by RNA and DNA viruses across all three domains of life. LUCA's viruses were probably mainly dsDNA viruses in the groups called Duplodnaviria and Varidnaviria. Two other single-stranded DNA virus groups within the Monodnaviria, the Microviridae and the Tubulavirales, likely infected the last bacterial common ancestor. The last archaeal common ancestor was probably host to spindle-shaped viruses. All of these could well have affected the LUCA, in which case each must since have been lost in the host domain where it is no longer extant. By contrast, RNA viruses do not appear to have been important parasites of LUCA, even though straightforward thinking might have envisaged viruses as beginning with RNA viruses directly derived from an RNA world. Instead, by the time the LUCA lived, RNA viruses had probably already been out-competed by DNA viruses.

LUCA might have been the ancestor of some viruses, with one of its descendants being the archaic virocell ancestor, the ancestor to large-to-medium-sized DNA viruses. The distribution pattern of DNA viruses in the tree of life also supports the hypothesis that DNA viruses originated from RNA-based LUCA. Viruses could equally have evolved before LUCA but after the first universal common ancestor (FUCA), according to the reduction hypothesis, where giant viruses evolved from primordial cells that became parasitic.