Dawkins, Richard. The Extended Phenotype. Oxford: Oxford University Press, 1982.

If society systematically trains children without penises to knit and play with dolls, and trains children with penises to play with guns and toy soldiers, any resulting differences in male and female preferences are strictly speaking genetically determined differences! They are determined, through the medium of societal custom, by the fact of possession or non-possession of a penis, and that is determined (in a normal environment and in the absence of ingenious plastic surgery or hormone therapy) by sex chromosomes. (p. 12)

Undoubtedly genetic variance is a significant cause of much phenotypic variance in observed populations, but its effects may be overridden, modified, enhanced or reversed by other causes. Genes may modify the effects of other genes, and may modify the effects of the environment. Environmental events, both internal and external, may modify the effects of genes, and may modify the effects of other environmental events. (p. 13)

The important point is that there is no general reason for expecting genetic influences to be any more irreversible than environmental ones. (p. 13)

If I am homozygous for a gene G, nothing save mutation can prevent my passing G on to all my children. So much is inexorable. But whether or not I, or my children, show the phenotypic effect normally associated with possession of G may depend very much on how we are brought up, what diet or education we experience, and what other genes we happen to possess. So, of the two effects that genes have on the world – manufacturing copies of themselves, and influencing phenotypes – the first is inflexible apart from the rare possibility of mutation; the second may be exceedingly flexible. I think a confusion between evolution and development is, then, partly responsible for the myth of genetic determinism. (p. 14)

Genes do not control behaviour in the sense of programming the machine in the sense of interfering with its performance. They only control behaviour in the sense of programming the machine in advance of performance. (p. 16) cf Dennett’s design space

Reading is a learned skill of prodigious complexity, but this provides no reason in itself for skepticism about the possible existence of a gene for reading. All we would need in order to establish the existence of a gene for reading is to discover a gene for not reading, say a gene which induced a brain lesion causing specific dyslexia. Such a dyslexic person might be normal and intelligent in all respects except that he could not read. No geneticist would be particularly surprised if this type of dyslexia turned out to breed true in some Mendelian fashion. (p. 23)

“it still does not follow that there is any genetic variation in mental abilities left in the human population today: the genetic variance might all have been used up by selection. (p. 26)

It is always possible to talk about the natural selection of a behaviour pattern in two ways. We can either talk about how individuals with a tendency to perform the behaviour pattern being ‘fitter’ than individuals with a less strongly developed tendency. This is the now fashionable phraseology, within the paradigm of the ‘selfish organism’ and the ‘central theorem of sociobiology’. Alternatively, and equivalently, we can talk directly of genes for performing the behaviour pattern surviving better than their alleles. (p. 27)

The phenotypic effect of any gene (versus its alleles) is not a property of the gene alone, but also of the embryological context in which it acts. (p. 34)

Adoption and contraception, like reading, mathematics, and stress-induced illness, are products of an animal that is living in an environment radically different from the one in which its genes were naturally selected. The question, about the adaptive significance of behaviour in an artificial world, should never have been put; and although a silly question may deserve a silly answer, it is wiser to give no answer at all and to explain why. (p. 36)

A gene ‘for’ A in environment X may well turn out to be a gene for B in environment Y. It is simply meaningless to speak of an absolute, context-free, phenotypic effect of a given gene. (p. 38)

One of the main messages of this book is that, for many purposes, it is better to regard at the level at which selection acts as neither the organism, nor the group or any larger unit, but the gene or small genetic fragment. (p. 52)

The genome of an individual organism in a sexual population is the product of a more or less random shuffling of the genes in the population. Genes are selected over their alleles because of their phenotypic effects, averaged over all the individual bodies in which they are distributed, over the whole population, and through many generations. (p. 52)

The more static attributes of an animal, its anatomical structure for instance, are obviously adapted only to long-range average conditions. (p. 53)

It is convenient to use the metaphor of an arms race whenever we have progressive improvements in adaptations in one lineage, as an evolutionary response to progressive counter-improvements in an enemy lineage. (p. 61)

I am, indeed, quite sympathetic towards the idea that human culture provides a new milieu in which an entirely different kind of replicator selection can go. (p. 87)

The whole purpose of our search for a ‘unit of selection’ is to discover a suitable actor to play the leading role in our metaphors of purpose. (p. 91)

An active replicator is a chunk of genome that, when compared to its alleles, exerts phenotypic power over its world, such that its frequency increases or decreases relative to that of its alleles. (p. 91)

For my purposes a genetic replicator is defined by reference to its alleles, but this is not a weakness of the concept. Or, if it is deemed to be a weakness, it is a weakness that afflicts the whole science of population genetics, not just the particular idea of genetic units of selection. (p. 92)

Both geneticists and natural selection are concerned with differences! However complex the genetic basis of features that all members of a species have in common, natural selection is concerned with differences. Evolutionary change is a limited set of substitutions at identifiable loci. (p. 93)

Germ-line replicators, then, are units that actually survive or fail to survive, the difference constituting natural selection. Active replicators have some effect on the world, which influences their chances of surviving. It is the effects on the world of successful active germ-line replicators that we see as adaptations. (p. 95)

The phenotypic effects of a meme may be in the form of words, music, visual images, styles of clothing, facial or hand gestures, skills such as opening milk bottles in tits, or panning wheat in Japanese macaques. They are the outward and visible (audible, etc.) manifestations of the memes within the brain. They may e perceived by the sense organs of other individuals, and they may so imprint themselves on the brains of the receiving individuals that a copy (not necessarily exact) of the original meme is graven in the receiving brain. The new copy of the meme is then in a position to broadcast its phenotypic effects, with the result that further copies of itself may be made in yet other brains. (p. 109)

How do a meme’s phenotypic effects contribute to its success or failure in being replicated? The answer is the same as for the genetic replicator. Any effect that a meme has on the behavior of a body bearing it may influence that meme’s chance of surviving. (p. 110)

A meme that made its bodies run over cliffs would have a fate like that of a gene fore making its bodies run over cliffs. It would tend to be eliminated from the meme-pool. But just as promoting bodily survival is only a part of what constitutes success in genetic replicators, so there are many other ways in which memes may work phenotypically for their own preservation. If the phenotypic effect of a meme is a tune, the catchier it is the more likely it is to be copied. (p. 110)

If it is a scientific idea, its chances of spreading through the world’s scientific brains will be influenced by its compatibility with the already established corpus of ideas. If it is a political or religious idea, it may assist its own survival if one of its phenotypic effects is to make its bodies violently intolerant to new and unfamiliar ideas. A meme has its own opportunities for replication, and its own phenotypic effects, and there is no reason why success in a meme should have any connection whatever to genetic success. (p. 110)

Genes are favoured or disfavoured relative to their alleles as a consequence of their phenotypic effects on the world. (p. 206)

Phenotypic effects of genes, whether at the level of intracellular biochemistry, gross bodily morphology or extended phenotype, are potentially devices by which genes level themselves into the next generation, or barriers to their doing so. (p. 207)

genes that bear upon any given extended phenotypic trait may be in conflict rather than in concert with one another. (p. 221)

An animal’s behaviour tends to maximize the survival of the genes ‘for’ that behaviour, whether or not those genes happen to be in the body of the particular animal performing it. (p. 233)

Two genes may be said to be complementary if the survival of each, relative to its alleles, is enhanced when the other is abundant in the population. (p. 240).