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Sunday, January 26, 2020

The Selfish Gene

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/The_Selfish_Gene

The Selfish Gene
The Selfish Gene3.jpg
Original cover, with detail from the painting The Expectant Valley by the zoologist Desmond Morris
AuthorRichard Dawkins
CountryUnited Kingdom
LanguageEnglish
SubjectEvolutionary biology
PublisherOxford University Press
Publication date
  • 1976
  • Second edition in 1989
  • Third edition in 2006
  • Fourth edition in 2016
Media typePrint
Pages224
ISBN0-19-857519-X
OCLC2681149
Followed byThe Extended Phenotype 

The Selfish Gene is a 1976 book on evolution by the biologist Richard Dawkins, in which the author builds upon the principal theory of George C. Williams's Adaptation and Natural Selection (1966). Dawkins uses the term "selfish gene" as a way of expressing the gene-centred view of evolution (as opposed to the views focused on the organism and the group), popularising ideas developed during the 1960s by W. D. Hamilton and others. From the gene-centred view, it follows that the more two individuals are genetically related, the more sense (at the level of the genes) it makes for them to behave selflessly with each other.

A lineage is expected to evolve to maximise its inclusive fitness—the number of copies of its genes passed on globally (rather than by a particular individual). As a result, populations will tend towards an evolutionarily stable strategy. The book also introduces the term meme for a unit of human cultural evolution analogous to the gene, suggesting that such "selfish" replication may also model human culture, in a different sense. Memetics has become the subject of many studies since the publication of the book. In raising awareness of Hamilton's ideas, as well as making its own valuable contributions to the field, the book has also stimulated research on human inclusive fitness.

In the foreword to the book's 30th-anniversary edition, Dawkins said he "can readily see that [the book's title] might give an inadequate impression of its contents" and in retrospect thinks he should have taken Tom Maschler's advice and called the book The Immortal Gene.

In July 2017 a poll to celebrate the 30th anniversary of the Royal Society science book prize listed The Selfish Gene as the most influential science book of all time.

Background

Dawkins builds upon George C. Williams's book Adaptation and Natural Selection (1966), which argued that altruism is not based upon group benefit per se, but is a result of selection that occurs "at the level of the gene mediated by the phenotype" and any selection at the group level occurred only under rare circumstances. This approach was developed further during the 1960s by W. D. Hamilton and others who opposed group selection and selection aimed directly at benefit to the individual organism:
Despite the principle of 'survival of the fittest' the ultimate criterion which determines whether [a gene] G will spread is not whether the behavior is to the benefit of the behaver, but whether it is to the benefit of the gene G ...With altruism this will happen only if the affected individual is a relative of the altruist, therefore having an increased chance of carrying the gene.
— W. D. Hamilton, The Evolution of Altruistic Behavior, pp. 354–355
An extended discussion of Dawkins' views and his book The Selfish Gene is provided by Wilkins and Hull.

Book


Contents

Dawkins begins by discussing the altruism that people display, indicating that he will argue it is explained by gene selfishness, and attacking group selection as an explanation. He considers the origin of life with the arrival of molecules able to replicate themselves. From there, he looks at DNA's role in evolution, and its organisation into chromosomes and genes, which in his view behave selfishly. He describes organisms as apparently purposive but fundamentally simple survival machines, which use negative feedback to achieve control. This extends, he argues, to the brain's ability to simulate the world with subjective consciousness, and signalling between species. He then introduces the idea of the evolutionarily stable strategy, and uses it to explain why alternative competitive strategies like bullying and retaliating exist. This allows him to consider what selfishness in a gene might actually mean, describing W. D. Hamilton's argument for kin selection, that genes for behaviour that improves the survival chances of close relatives can spread in a population, because those relatives carry the same genes. 

Dawkins examines childbearing and raising children as evolutionary strategies. He attacks the idea of group selection for the good of the species as proposed by V. C. Wynne-Edwards, arguing instead that each parent necessarily behaves selfishly. A question is whether parents should invest in their offspring equally or should favour some of them, and explains that what is best for the survival of the parents' genes is not always best for individual children. Similarly, Dawkins argues, there are conflicts of interest between males and females, but he notes that R. A. Fisher showed that the optimal sex ratio is 50:50. He explains that this is true even in an extreme case like the harem-keeping elephant seal, where 4% of the males get 88% of copulations. In that case, the strategy of having a female offspring is safe, as she'll have a pup, but the strategy of having a male can bring a large return (dozens of pups), even though many males live out their lives as bachelors. Amotz Zahavi's theory of honest signalling explains stotting as a selfish act, he argues, improving the springbok's chances of escaping from a predator by indicating how difficult the chase would be.

Dawkins discusses why many species live in groups, achieving mutual benefits through mechanisms such as Hamilton's selfish herd model: each individual behaves selfishly but the result is herd behaviour. Altruism too can evolve, as in the social insects such as ants and bees, where workers give up the right to reproduce in favour of a sister, the queen; in their case, the unusual (haplodiploid) system of sex determination may have helped to bring this about, as females in a nest are exceptionally closely related. 

The final chapter of the first edition introduced the idea of the meme, a culturally-transmitted entity such as a hummable tune, by analogy to genetic transmission. Dawkins describes God as an old idea which probably arose many times, and which has sufficient psychological appeal to survive effectively in the meme pool. The second edition (1989) added two more chapters.

Themes


"Selfish" genes

In describing genes as being "selfish", Dawkins states unequivocally that he does not intend to imply that they are driven by any motives or will, but merely that their effects can be metaphorically and pedagogically described as if they were. His contention is that the genes that are passed on are the ones whose evolutionary consequences serve their own implicit interest (to continue the anthropomorphism) in being replicated, not necessarily those of the organism. In later work, Dawkins brings evolutionary "selfishness" down to creation of a widely proliferated extended phenotype.

For some, the metaphor of "selfishness" is entirely clear, while to others it is confusing, misleading, or simply silly to ascribe mental attributes to something that is mindless. For example, Andrew Brown has written:
""Selfish", when applied to genes, doesn't mean "selfish" at all. It means, instead, an extremely important quality for which there is no good word in the English language: "the quality of being copied by a Darwinian selection process." This is a complicated mouthful. There ought to be a better, shorter word—but "selfish" isn't it."
Donald Symons also finds it inappropriate to use anthropomorphism in conveying scientific meaning in general, and particularly for the present instance. He writes in The Evolution of Human Sexuality (1979):
"In summary, the rhetoric of The Selfish Gene exactly reverses the real situation: through [the use of] metaphor genes are endowed with properties only sentient beings can possess, such as selfishness, while sentient beings are stripped of these properties and called machines...The anthropomorphism of genes...obscures the deepest mystery in the life sciences: the origin and nature of mind."
 

"Replicators"

Dawkins proposes the idea of the "replicator":
"It is finally time to return to the problem with which we started, to the tension between individual organism and gene as rival candidates for the central role in natural selection...One way of sorting this whole matter out is to use the terms ‘replicator’ and ‘vehicle’. The fundamental units of natural selection, the basic things that survive or fail to survive, that form lineages of identical copies with occasional random mutations, are called replicators. DNA molecules are replicators. They generally, for reasons that we shall come to, gang together into large communal survival machines or 'vehicles'."
— Richard Dawkins, The Selfish Gene, p. 253 (Anniversary Edition)
The original replicator (Dawkins' Replicator) was the initial molecule which first managed to reproduce itself and thus gained an advantage over other molecules within the primordial soup. As replicating molecules became more complex, Dawkins postulates, the replicators became the genes within organisms, with each organism's body serving the purpose of a 'survival machine' for its genes.
Dawkins writes that gene combinations which help an organism to survive and reproduce tend to also improve the gene's own chances of being replicated, and, as a result, "successful" genes frequently provide a benefit to the organism. An example of this might be a gene that protects the organism against a disease. This helps the gene spread, and also helps the organism. 

Genes vs organisms

There are other times when the implicit interests of the vehicle and replicator are in conflict, such as the genes behind certain male spiders' instinctive mating behaviour, which increase the organism's inclusive fitness by allowing it to reproduce, but shorten its life by exposing it to the risk of being eaten by the cannibalistic female. Another example is the existence of segregation distorter genes that are detrimental to their host, but nonetheless propagate themselves at its expense. Likewise, the persistence of junk DNA that [Dawkins believed at that time] provides no benefit to its host can be explained on the basis that it is not subject to selection. These unselected for but transmitted DNA variations connect the individual genetically to its parents, but confer no survival benefit.

These examples might suggest that there is a power struggle between genes and their interactor. In fact, the claim is that there isn't much of a struggle because the genes usually win without a fight. However, the claim is made that if the organism becomes intelligent enough to understand its own interests, as distinct from those of its genes, there can be true conflict.

An example of such a conflict might be a person using birth control to prevent fertilisation, thereby inhibiting the replication of his or her genes. But this action might not be a conflict of the 'self-interest' of the organism with his or her genes, since a person using birth control might also be enhancing the survival chances of their genes by limiting family size to conform with available resources, thus avoiding extinction as predicted under the Malthusian model of population growth.

Altruism

Dawkins says that his "purpose" in writing The Selfish Gene is "to examine the biology of selfishness and altruism." He does this by supporting the claim that "gene selfishness will usually give rise to selfishness in individual behaviour. However, as we shall see, there are special circumstances in which a gene can achieve its own selfish goals best by fostering a limited form of altruism at the level of individual animals." Gene selection provides one explanation for kin selection and eusociality, where organisms act altruistically, against their individual interests (in the sense of health, safety or personal reproduction), namely the argument that by helping related organisms reproduce, a gene succeeds in "helping" copies of themselves (or sequences with the same phenotypic effect) in other bodies to replicate. The claim is made that these "selfish" actions of genes lead to unselfish actions by organisms. A requirement upon this claim, supported by Dawkins in Chapter 10: "You scratch my back, I'll ride on yours" by examples from nature, is the need to explain how genes achieve kin recognition, or manage to orchestrate mutualism and coevolution. Although Dawkins (and biologists in general) recognize these phenomena result in more copies of a gene, evidence is inconclusive whether this success is selected for at a group or individual level. In fact, Dawkins has proposed that it is at the level of the extended phenotype:
"We agree [referring to Wilson and Sober's book Unto others: The evolution and psychology of unselfish behavior] that genes are replicators, organisms and groups are not. We agree that the group selection controversy ought to be a controversy about groups as vehicles, and we could easily agree to differ on the answer...I coined the [term] vehicle not to praise it but to bury it....Darwinism can work on replicators whose phenotypic effects (interactors) are too diffuse, too multi-levelled, too incoherent to deserve the accolade of vehicle...Extended phenotypes can include inanimate artifacts like beaver dams...But the vehicle is not something fundamental...Ask rather 'Is there a vehicle in this situation and, if so, why?'"
—Richard Dawkins, Burying the Vehicle
Although Dawkins agrees that groups can assist survival, they rank as a "vehicle" for survival only if the group activity is replicated in descendants, recorded in the gene, the gene being the only true replicator. An improvement in the survival lottery for the group must improve that for the gene for sufficient replication to occur. Dawkins argues qualitatively that the lottery for the gene is based upon a very long and broad record of events, and group advantages are usually too specific, too brief, and too fortuitous to change the gene lottery.
"We can now see that the organism and the group of organisms are true rivals for the vehicle role in the story, but neither of them is even a candidate for the replicator role. The controversy between ‘individual selection’ and ‘group selection’ is a real controversy between alternative vehicles...As it happens the outcome, in my view, is a decisive victory for the individual organism. The group is too wishy-washy an entity."
—Richard Dawkins, The Selfish Gene, pp. 254-255
Prior to the 1960s, it was common for altruism to be explained in terms of group selection, where the benefits to the organism or even population were supposed to account for the popularity of the genes responsible for the tendency towards that behaviour. Modern versions of "multilevel selection" claim to have overcome the original objections, namely, that at that time no known form of group selection led to an evolutionarily stable strategy. The claim still is made by some that it would take only a single individual with a tendency towards more selfish behaviour to undermine a population otherwise filled only with the gene for altruism towards non-kin.

Reception

The Selfish Gene was extremely popular when first published, causing "a silent and almost immediate revolution in biology", and it continues to be widely read. It has sold over a million copies, and has been translated into more than 25 languages. Proponents argue that the central point, that replicating the gene is the object of selection, usefully completes and extends the explanation of evolution given by Charles Darwin before the basic mechanisms of genetics were understood.

According to the ethologist Alan Grafen, acceptance of adaptionist theories is hampered by a lack of a mathematical unifying theory and a belief that anything in words alone must be suspect. According to Grafen, these difficulties along with an initial conflict with population genetics models at the time of its introduction "explains why within biology the considerable scientific contributions it [The Selfish Gene] makes are seriously underestimated, and why it is viewed mainly as a work of exposition." According to comparative psychologist Nicky Hayes, "Dawkins presented a version of sociobiology that rested heavily on metaphors drawn from animal behavior, and extrapolated these...One of the weaknesses of the sociological approach is that it tends only to seek confirmatory examples from among the huge diversity of animal behavior. Dawkins did not deviate from this tradition." More generally, critics argue that The Selfish Gene oversimplifies the relationship between genes and the organism. (As an example, see Thompson.)

The Selfish Gene further popularised sociobiology in Japan after its translation in 1980.

With the addition of Dawkins's book to the country's consciousness, the term "meme" entered popular culture. Yuzuru Tanaka of Hokkaido University wrote a book, Meme Media and Meme Market Architectures, while the psychologist Susan Blackmore wrote The Meme Machine (2000), with a foreword by Dawkins. The information scientist Osamu Sakura has published a book in Japanese and several papers in English on the topic. Nippon Animation produced an educational television program titled The Many Journeys of Meme

In 1976, the ecologist Arthur Cain, one of Dawkins's tutors at Oxford in the 1960s, called it a "young man's book" (which Dawkins points out was a deliberate quote of a commentator on the New College, Oxford philosopher A. J. Ayer's Language, Truth, and Logic (1936)). Dawkins noted that he had been "flattered by the comparison, [but] knew that Ayer had recanted much of his first book and [he] could hardly miss Cain's pointed implication that [he] should, in the fullness of time, do the same." This point also was made by the philosopher Mary Midgley: "The same thing happened to AJ Ayer, she says, but he spent the rest of his career taking back what he'd written in Language, Truth and Logic. "This hasn't occurred to Dawkins", she says. "He goes on saying the same thing."" However, according to Wilkins and Hull, Dawkins' thinking has developed, although perhaps not defusing this criticism:
"In Dawkins' early writings, replicators and vehicles played different but complementary and equally important roles in selection, but as Dawkins honed his view of the evolutionary process, vehicles became less and less fundamental... In later writings Dawkins goes even further and argues that phenotypic traits are what really matter in selection and that they can be treated independently of their being organized into vehicles....Thus, it comes as no surprise when Dawkins proclaims that he "coined the term ‘vehicle’ not to praise it but to bury it." As prevalent as organisms might be, as determinate as the causal roles that they play in selection are, reference to them can and must be omitted from any perspicuous characterization of selection in the evolutionary process. Dawkins is far from a genetic determinist, but he is certainly a genetic reductionist."
— John S Wilkins, David Hull, Dawkins on Replicators and Vehicles, The Stanford Encyclopedia of Philosophy
 

Units of selection

As to the unit of selection: "One internally consistent logical picture is that the unit of replication is the gene,...and the organism is one kind of ...entity on which selection acts directly." Dawkins proposed the matter without a distinction between 'unit of replication' and 'unit of selection' that he made elsewhere: "the fundamental unit of selection, and therefore of self-interest, is not the species, nor the group, nor even strictly the individual. It is the gene, the unit of heredity." However, he continues in a later chapter:
"On any sensible view of the matter Darwinian selection does not work on genes directly. ...The important differences between genes emerge only in their effects. The technical word phenotype is used for the bodily manifestation of a gene, the effect that a gene has on the body...Natural selection favours some genes rather than others not because of the nature of the genes themselves, but because of their consequences—their phenotypic effects...But we shall now see that the phenotypic effects of a gene need to be thought of as all the effects that it has on the world. ...The phenotypic effects of a gene are the tools by which it levers itself into the next generation. All I am going to add is that the tools may reach outside the individual body wall...Examples that spring to mind are artefacts like beaver dams, bird nests, and caddis houses."
— Richard Dawkins, The Selfish Gene, Chapter 13, pp. 234, 235, 238
Dawkins' later formulation is in his book The Extended Phenotype (1982), where the process of selection is taken to involve every possible phenotypical effect of a gene. 

Stephen Jay Gould finds Dawkins' position tries to have it both ways:
"Dawkins claims to prefer genes and to find greater insight in this formulation. But he allows that you or I might prefer organisms—and it really doesn't matter."
— Stephen Jay Gould, The Structure of Evolutionary Theory, pp. 640-641
The view of The Selfish Gene is that selection based upon groups and populations is rare compared to selection on individuals. Although supported by Dawkins and by many others, this claim continues to be disputed. While naïve versions of group selectionism have been disproved, more sophisticated formulations make accurate predictions in some cases while positing selection at higher levels. Both sides agree that very favourable genes are likely to prosper and replicate if they arise and both sides agree that living in groups can be an advantage to the group members. The conflict arises in part over defining concepts:
"Cultural evolutionary theory, however, has suffered from an overemphasis on the experiences and behaviors of individuals at the expense of acknowledging complex group organization...Many important behaviors related to the success and function of human societies are only properly defined at the level of groups".
In The Social Conquest of Earth (2012), the entomologist E. O. Wilson contends that although the selfish-gene approach was accepted "until 2010 [when] Martin Nowak, Corina Tarnita, and I demonstrated that inclusive fitness theory, often called kin selection theory, is both mathematically and biologically incorrect." Chapter 18 of The Social Conquest of Earth describes the deficiencies of kin selection and outlines group selection, which Wilson argues is a more realistic model of social evolution. He criticises earlier approaches to social evolution, saying: "...unwarranted faith in the central role of kinship in social evolution has led to the reversal of the usual order in which biological research is conducted. The proven best way in evolutionary biology, as in most of science, is to define a problem arising during empirical research, then select or devise the theory that is needed to solve it. Almost all research in inclusive-fitness theory has been the opposite: hypothesize the key roles of kinship and kin selection, then look for evidence to test that hypothesis." According to Wilson: "People must have a tribe...Experiments conducted over many years by social psychologists have revealed how swiftly and decisively people divide into groups, and then discriminate in favor of the one to which they belong." (pp. 57, 59) According to Wilson: "Different parts of the brain have evolved by group selection to create groupishness." (p. 61)

Some authors consider facets of this debate between Dawkins and his critics about the level of selection to be blather:
"The particularly frustrating aspects of these constantly renewed debates is that, even though they seemed to be sparked by rival theories about how evolution works, in fact they often involve only rival metaphors for the very same evolutionary logic and [the debates over these aspects] are thus empirically empty."
— Laurent Keller, Levels of Selection in Evolution, p.4
Other authors say Dawkins has failed to make some critical distinctions, in particular, the difference between group selection for group advantage and group selection conveying individual advantage.

Choice of words

A good deal of objection to The Selfish Gene stemmed from its failure to be always clear about "selection" and "replication". Dawkins says the gene is the fundamental unit of selection, and then points out that selection doesn't act directly upon the gene, but upon "vehicles" or '"extended phenotypes". Stephen Jay Gould took exception to calling the gene a 'unit of selection' because selection acted only upon phenotypes. Summarizing the Dawkins-Gould difference of view, Sterelny says:
"Gould thinks gene differences do not cause evolutionary changes in populations, they register those changes."
—Kim Sterelny: Dawkins vs. Gould, p. 83
The word "cause" here is somewhat tricky: does a change in lottery rules (for example, inheriting a defective gene "responsible" for a disorder) "cause" differences in outcome that might or might not occur? It certainly alters the likelihood of events, but a concatenation of contingencies decides what actually occurs. Dawkins thinks the use of "cause" as a statistical weighting is acceptable in common usage. Like Gould, Gabriel Dover in criticizing The Selfish Gene says:
"It is illegitimate to give 'powers' to genes, as Dawkins would have it, to control the outcome of selection...There are no genes for interactions, as such: rather, each unique set of inherited genes contributes interactively to one unique phenotype...the true determinants of selection".
— Gabriel Dover: Dear Mr. Darwin, p. 56
However, from a comparison with Dawkins' discussion of this very same point, it would seem both Gould's and Dover's comments are more a critique of his sloppy usage than a difference of views. Hull suggested a resolution based upon a distinction between replicators and interactors. The term "replicator" includes genes as the most fundamental replicators but possibly other agents, and interactor includes organisms but maybe other agents, much as do Dawkins' 'vehicles'. The distinction is as follows:
replicator: an entity that passes on its structure largely intact in successive replications.
interactor: an entity that interacts as a cohesive whole with its environment in such a way that this interaction causes replication to be differential.
selection: a process in which the differential extinction or proliferation of interactors causes the differential perpetuation of the replicators that produced them.
Hull suggests that, despite some similarities, Dawkins takes too narrow a view of these terms, engendering some of the objections to his views. According to Godfrey-Smith, this more careful vocabulary has cleared up "misunderstandings in the "units of selection" debates."

Enactive arguments

Behavioural genetics entertains the view:
"that genes are dynamic contributors to behavioral organization and are sensitive to feedback systems from the internal and external environments." "Technically behavior is not inherited; only DNA molecules are inherited. From that point on behavioral formation is a problem of constant interplay between genetic potential and environmental shaping."
—D.D. Thiessen, Mechanism specific approaches in behavior genetics, p. 91
This view from 1970 is still espoused today, and conflicts with Dawkins' view of "the gene as a form of "information [that] passes through bodies and affects them, but is not affected by them on its way through"". The philosophical/biological field of enactivism stresses the interaction of the living agent with its environment and the relation of probing the environment to cognition and adaptation. Gene activation depends upon the cellular milieu. An extended discussion of the contrasts between enactivism and Dawkins' views, and with their support by Dennett, is provided by Thompson.

In Mind in Life, the philosopher Evan Thompson has assembled a multi-sourced objection to the "selfish gene" idea. Thompson takes issue with Dawkin's reduction of "life" to "genes" and "information":
"Life is just bytes and bytes and bytes of digital information"[50]
— Richard Dawkins: River out of Eden: A Darwinian View of Life, p. 19
"On the bank of the Oxford canal...is a large willow tree, and it is pumping downy seeds into the air...It is raining instructions out there; it's raining programs; it's raining tree-growing, fluff-spreading algorithms. That is not a metaphor, it is the plain truth"
— Richard Dawkins: The Blind Watchmaker, p. 111
Thompson objects that the gene cannot operate by itself, since it requires an environment such as a cell, and life is "the creative outcome of highly structured contingencies". Thompson quotes Sarkar:
"there is no clear technical notion of "information" in molecular biology. It is little more than a metaphor that masquerades as a theoretical concept and ...leads to a misleading picture of the nature of possible explanations in molecular biology."
— Sahotra Sarkar Biological information: a skeptical look at some central dogmas of molecular biology, p. 187
Thompson follows with a detailed examination of the concept of DNA as a look-up-table and the role of the cell in orchestrating the DNA-to-RNA transcription, indicating that by anyone's account the DNA is hardly the whole story. Thompson goes on to suggest that the cell-environment interrelationship has much to do with reproduction and inheritance, and a focus on the gene as a form of "information [that] passes through bodies and affects them, but is not affected by them on its way through" is tantamount to adoption of a form of material-informational dualism that has no explanatory value and no scientific basis. (Thomson, p. 187) The enactivist view, however, is that information results from the probing and experimentation of the agent with the agent's environment subject to the limitations of the agent's abilities to probe and process the result of probing, and DNA is simply one mechanism the agent brings to bear upon its activity.

Moral arguments

Another criticism of the book is its treatment of morality, and more particularly altruism, as existing only as a form of selfishness:
"It is important to realize that the above definitions of altruism and selfishness are behavioural, not subjective. I am not concerned here with the psychology of motives...My definition is concerned only with whether the effect of an act is to lower or raise the survival prospects of the presumed altruist and the survival prospects of the presumed beneficiary."
— Richard Dawkins, The Selfish Gene, p. 12
"We can even discuss ways of cultivating and nurturing pure, disinterested altruism, something that has no place in nature, something that has never existed before in the whole history of the world."
— Richard Dawkins, The Selfish Gene, p. 179
The philosopher Mary Midgley has suggested this position is a variant of Hobbes' explanation of altruism as enlightened self-interest, and that Dawkins goes a step further to suggest that our genetic programming can be overcome by what amounts to an extreme version of free will. Part of Mary Midgley's concern is that Richard Dawkins' account of The Selfish Gene serves as a moral and ideological justification for selfishness to be adopted by modern human societies as simply following "nature", providing an excuse for behavior with bad consequences for future human society.

Dawkins' major concluding theme, that humanity is finally gaining power over the "selfish replicators" by virtue of their intelligence, is criticized also by primatologist Frans de Waal, who refers to it as an example of a "veneer theory" (the idea that morality is not fundamental, but is laid over a brutal foundation). Dawkins claims he merely describes how things are under evolution, and makes no moral arguments. On BBC-2 TV, Dawkins pointed to evidence for a "Tit-for-Tat" strategy (shown to be successful in game theory) as the most common, simple, and profitable choice.

More generally, the objection has been made that The Selfish Gene discusses philosophical and moral questions that go beyond biological arguments, relying upon anthropomorphisms and careless analogies.

Publication

The Selfish Gene was first published by Oxford University Press in 1976 in eleven chapters with a preface by the author and a foreword by Robert Trivers. A second edition was published in 1989. This edition added two extra chapters, and substantial endnotes to the preceding chapters, reflecting new findings and thoughts. It also added a second preface by the author, but the original foreword by Trivers was dropped. The book contains no illustrations.

The book has been translated into at least 23 languages including Arabic, Thai and Turkish.

In 2006, a 30th-anniversary edition was published with the Trivers foreword and a new introduction by the author. It was accompanied by a festschrift entitled Richard Dawkins: How a Scientist Changed the Way We Think (2006). In March 2006, a special event entitled The Selfish Gene: Thirty Years On was held at the London School of Economics. In March 2011, Audible Inc published an audiobook edition narrated by Richard Dawkins and Lalla Ward.

In 2016, Oxford University Press published a 40th anniversary edition with a new epilogue, in which Dawkins describes the continued relevance of the gene's eye view of evolution and states that it, along with coalescence analysis "illuminates the deep past in ways of which I had no inkling when I first wrote The Selfish Gene...."

Spider web

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Spider_web
 
A classic circular form spider's web
 
Opadometa fastigata weaving the web. See the silk coming from the spinneret glands located at the tip of the abdomen.
 
Spiral orb webs in Karijini, Western Australia
 
Garden Orbweaver with beetle prey caught in its web

A spider web, spiderweb, spider's web, or cobweb (from the archaic word coppe, meaning "spider") is a structure created by a spider out of proteinaceous spider silk extruded from its spinnerets, generally meant to catch its prey.

Spider webs have existed for at least 100 million years, as witnessed in a rare find of Early Cretaceous amber from Sussex, southern England. Many spiders build webs specifically to catch insects to eat. However, not all spiders catch their prey in webs, and some do not build webs at all. "Spider web" is typically used to refer to a web that is apparently still in use (i.e. clean), whereas "cobweb" refers to abandoned (i.e. dusty) webs. However, the word "cobweb" is also used by biologists to describe the tangled three-dimensional web of some spiders of the Theridiidae family. While this large family is known as the cobweb spiders, they actually have a huge range of web architectures; other names for this spider family include tangle-web spiders and comb-footed spiders.

Silk production

Clearly visible spider silk production
 
Zygiella orb web
 
Infographic illustrating the process of constructing an orb web
 
Spider web covered in hoar frost

When spiders moved from the water to the land in the Early Devonian period, they started making silk to protect their bodies and their eggs. Spiders gradually started using silk for hunting purposes, first as guide lines and signal lines, then as ground or bush webs, and eventually as the aerial webs that are familiar today.

Spiders produce silk from their spinneret glands located at the tip of their abdomen. Each gland produces a thread for a special purpose – for example a trailed safety line, sticky silk for trapping prey or fine silk for wrapping it. Spiders use different gland types to produce different silks, and some spiders are capable of producing up to eight different silks during their lifetime.

Most spiders have three pairs of spinnerets, each having its own function – there are also spiders with just one pair and others with as many as four pairs.

Webs allow a spider to catch prey without having to expend energy by running it down. Thus it is an efficient method of gathering food. However, constructing the web is in itself an energetically costly process because of the large amount of protein required, in the form of silk. In addition, after a time the silk will lose its stickiness and thus become inefficient at capturing prey. It is common for spiders to eat their own web daily to recoup some of the energy used in spinning. The silk proteins are thus recycled.

The tensile strength of spider silk is greater than the same weight of steel and has much greater elasticity. Its microstructure is under investigation for potential applications in industry, including bullet-proof vests and artificial tendons. Researchers have used genetically modified mammals to produce the proteins needed to make this material.

Types

Argiope sp. sitting on web decorations at the center of the web
 
There are a few types of spider webs found in the wild, and many spiders are classified by the webs they weave. Different types of spider webs include:
  • Spiral orb webs, associated primarily with the family Araneidae, as well as Tetragnathidae and Uloboridae
  • Tangle webs or cobwebs, associated with the family Theridiidae
  • Funnel webs, with associations divided into primitive and modern
  • Tubular webs, which run up the bases of trees or along the ground
  • Sheet webs
Several different types of silk may be used in web construction, including a "sticky" capture silk and "fluffy" capture silk, depending on the type of spider. Webs may be in a vertical plane (most orb webs), a horizontal plane (sheet webs), or at any angle in between. It is hypothesized that these types of aerial webs co-evolved with the evolution of winged insects. As insects are spiders' main prey, it is likely that they would impose strong selectional forces on the foraging behavior of spiders. Most commonly found in the sheet-web spider families, some webs will have loose, irregular tangles of silk above them. These tangled obstacle courses serve to disorient and knock down flying insects, making them more vulnerable to being trapped on the web below. They may also help to protect the spider from predators such as birds and wasps.

Orb web construction

A typical orb web constructed by an Araneus (family Araneidae) spider.
 
Most orb weavers construct webs in a vertical plane, although there are exceptions, such as Uloborus diversus, which builds a horizontal web. During the process of making an orb web, the spider will use its own body for measurements. 

Many webs span gaps between objects which the spider could not cross by crawling. This is done by first producing a fine adhesive thread to drift on a faint breeze across a gap. When it sticks to a surface at the far end, the spider feels the change in the vibration. The spider reels in and tightens the first strand, then carefully walks along it and strengthens it with a second thread. This process is repeated until the thread is strong enough to support the rest of the web.

After strengthening the first thread, the spider continues to make a Y-shaped netting. The first three radials of the web are now constructed. More radials are added, making sure that the distance between each radial and the next is small enough to cross. This means that the number of radials in a web directly depends on the size of the spider plus the size of the web. It is common for a web to be about 20 times the size of the spider building it. 
 
After the radials are complete, the spider fortifies the center of the web with about five circular threads. It makes a spiral of non-sticky, widely spaced threads to enable it to move easily around its own web during construction, working from the inside outward. Then, beginning from the outside and moving inward, the spider methodically replaces this spiral with a more closely spaced one made of adhesive threads. It uses the initial radiating lines as well as the non-sticky spirals as guide lines. The spaces between each spiral and the next are directly proportional to the distance from the tip of its back legs to its spinners. This is one way the spider uses its own body as a measuring/spacing device. While the sticky spirals are formed, the non-adhesive spirals are removed as there is no need for them any more.

Australian garden orb weaver spider, after having captured prey

After the spider has completed its web, it chews off the initial three center spiral threads then sits and waits. If the web is broken without any structural damage during the construction, the spider does not make any initial attempts to rectify the problem.

The spider, after spinning its web, then waits on or near the web for a prey animal to become trapped. The spider senses the impact and struggle of a prey animal by vibrations transmitted through the web. A spider positioned in the middle of the web makes for a highly visible prey for birds and other predators, even without web decorations; many day-hunting orb-web spinners reduce this risk by hiding at the edge of the web with one foot on a signal line from the hub or by appearing to be inedible or unappetizing. 

Spiders do not usually adhere to their own webs, because they are able to spin both sticky and non-sticky types of silk, and are careful to travel across only non-sticky portions of the web. However, they are not immune to their own glue. Some of the strands of the web are sticky, and others are not. For example, if a spider has chosen to wait along the outer edges of its web, it may spin a non-sticky prey or signal line to the web hub to monitor web movement. However, in the course of spinning sticky strands, spiders have to touch these sticky strands. They do this without sticking by using careful movements, dense hairs and nonstick coatings on their feet to prevent adhesion.

Uses

A soldier ant finds itself entangled in the web of a garden spider.

Some species of spider do not use webs for capturing prey directly, instead pouncing from concealment (e.g. trapdoor spiders) or running them down in open chase (e.g. wolf spiders). The net-casting spider balances the two methods of running and web spinning in its feeding habits. This spider weaves a small net which it attaches to its front legs. It then lurks in wait for potential prey and, when such prey arrives, lunges forward to wrap its victim in the net, bite and paralyze it. Hence, this spider expends less energy catching prey than a primitive hunter such as the wolf spider. It also avoids the energy loss of weaving a large orb web. 

Some spiders manage to use the signaling-snare technique of a web without spinning a web at all. Several types of water-dwelling spiders rest their feet on the water's surface in much the same manner as an orb-web user. When an insect falls onto the water and is ensnared by surface tension, the spider can detect the vibrations and run out to capture the prey.

Uses by humans

Cobweb paintings, which began during the 16th century in a remote valley of the Austrian Tyrolean Alps, were created on fabrics consisting of layered and wound cobwebs, stretched over cardboard to make a mat, and strengthened by brushing with milk diluted in water. A small brush was then used to apply watercolor to the cobwebs, or custom tools to create engravings. Fewer than a hundred cobweb paintings survive today, most of which are held in private collections.

In traditional European medicine, cobwebs were used on wounds and cuts and seem to help healing and reduce bleeding. Spider webs are rich in vitamin K, which can be effective in clotting blood. Webs were used several hundred years ago as pads to stop an injured person's bleeding. The effects of some drugs can be measured by examining their effects on a spider's web-building.

Spider web strands have been used for crosshairs or reticles in telescopes.

Development of technologies to mass-produce spider silk has led to manufacturing of prototype military protection, medical devices, and consumer goods.

Adhesive properties

 
The figure on the left is an optical microscope image of glue balls. The second figure from left is a scanning ion secondary electron image of the glue balls. The two figures on the right are the scanning ion secondary electron images before and after adhesion of the substrate to the glue ball.
 
The stickiness of spiders' webs is courtesy of droplets of glue suspended on the silk threads. This glue is multifunctional – that is, its behavior depends on how quickly something touching it attempts to withdraw. At high velocities, they function as an elastic solid, resembling rubber; at lower velocities, they simply act as a sticky glue. This allows them to retain a grip on attached food particles. The web is electrically conductive which causes the silk threads to spring out to trap their quarry, as flying insects tend to gain a static charge which attracts the silk.

Communal spider webs

After severe, extensive flooding in Sindh, Pakistan, many trees were covered with spider webs.

Occasionally, a group of spiders may build webs together in the same area.

Massive flooding in Pakistan during the 2010 monsoon drove spiders above the waterline, into trees. The result was trees covered with spider webs.

The communal spider web at Lake Tawakoni State Park

One such web, reported in 2007 at Lake Tawakoni State Park in Texas, measured 200 yards (180 m) across. Entomologists believe it may be the result of social cobweb spiders or of spiders building webs to spread out from one another. There is no consensus on how common this occurrence is.

In Brazil, there have been two instances of a phenomenon that became known as "raining spiders"; communal webs that cover such wide gaps and which strings are so difficult to see that hundreds of spiders seem to be floating in the air. The first occurred in Santo Antônio da Platina, Paraná, in 2013, and involved Anelosimus eximius individuals; the second was registered in Espírito Santo do Dourado, Minas Gerais, in January 2019, and involved Parawixia bistriata individuals.

Outside influences

Certain drugs, including caffeine, affect the way spiders build webs.

Administering certain drugs to spiders affects the structure of the webs they build. It has been proposed by some that this could be used as a method of documenting and measuring the toxicity of various substances.

Low gravity

It has been observed that being in Earth's orbit has an effect on the structure of spider webs in space.

Spider webs were spun in low earth orbit in 1973 aboard Skylab, involving two female European garden spiders (cross spiders) called Arabella and Anita, as part of an experiment on the Skylab 3 mission. The aim of the experiment was to test whether the two spiders would spin webs in space, and, if so, whether these webs would be the same as those that spiders produced on Earth. The experiment was a student project of Judy Miles of Lexington, Massachusetts.

After the launch on July 28, 1973, and entering Skylab, the spiders were released by astronaut Owen Garriott into a box that resembled a window frame. The spiders proceeded to construct their web while a camera took photographs and examined the spiders' behavior in a zero-gravity environment. Both spiders took a long time to adapt to their weightless existence. However, after a day, Arabella spun the first web in the experimental cage, although it was initially incomplete. 

The first web spun by the spider Arabella in orbit

The web was completed the following day. The crew members were prompted to expand the initial protocol. They fed and watered the spiders, giving them a house fly. The first web was removed on August 13 to allow the spider to construct a second web. At first, the spider failed to construct a new web. When given more water, it built a second web. This time, it was more elaborate than the first. Both spiders died during the mission, possibly from dehydration.

When scientists were given the opportunity to study the webs, they discovered that the space webs were finer than normal Earth webs, and although the patterns of the web were not totally dissimilar, variations were spotted, and there was a definite difference in the characteristics of the web. Additionally, while the webs were finer overall, the space web had variations in thickness in places: some places were slightly thinner, and others slightly thicker. This was unusual, because Earth webs have been observed to have uniform thickness.

In popular culture

Spider webs play a crucial role in the children's novel Charlotte's Web. Webs are also featured in many other cultural depictions of spiders. In films, illustration, and other visual arts, spider webs may be used to readily suggest a "spooky" atmosphere, or imply neglect or the passage of time. Artificial "spider webs" are a common element of Halloween decorations. Spider webs are a common image in tattoo art, often symbolizing long periods of time spent in prison, or used simply to fill gaps between other images. 

Some observers believe that a small spider is depicted on the United States one-dollar bill, in the upper-right corner of the front side (obverse), perched on the shield surrounding the number "1". This perception is enhanced by the resemblance of the background image of intertwining fine lines to a stylized spider web. However, other observers believe the figure is an owl.

Artificial spider webs are used by the superhero Spider-Man to restrain enemies and to make ropes on which to swing between buildings as quick transportation.

The World Wide Web is thus named because of its tangled and interlaced structure, said to resemble that of a spider web.

The notable tensile strength of spider webs is often exaggerated in science fiction, often as a plot device to justify the presence of artificially giant spiders.

Equality (mathematics)

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