Home > Work > The Extended Phenotype: The Long Reach of the Gene
41 " If replicators exist that are active, variants of them with certain phenotypic effects tend to out-replicate those with other phenotypic effects. If they are also germ-line replicators, these changes in relative frequency can have long-term, evolutionary impact. "
― Richard Dawkins , The Extended Phenotype: The Long Reach of the Gene
42 " It is these phenotypic effects that we see as adaptations to survival. When we ask whose survival they are adapted to ensure, the fundamental answer has to be not the group, nor the individual organism, but the relevant replicators themselves. "
43 " Replicators need not last forever. They need only last long enough to produce additional replicators [fecundity] that retain their structure largely intact [fidelity]. The relevant longevity concerns the retention of structure through descent. Some entities, though structurally similar, are not copies because they are not related by descent. "
44 " A replicator may be said to ‘benefit’ from anything that increases the number of its descendant (‘germ-line’) copies. "
45 " To the extent that active germ-line replicators benefit from the survival of the bodies in which they sit, we may expect to see adaptations that can be interpreted as for bodily survival. "
46 " To the extent that active germ-line replicators benefit from the survival of bodies other than those in which they sit, we may expect to see ‘altruism’, parental care, etc. "
47 " Most of the replicators in the world have won their place in it by defeating all available alternative alleles. The weapons with which they won, and the weapons with which their rivals lost, are their respective phenotypic consequences "
48 " These phenotypic consequences are conventionally thought of as being restricted to a small field around the replicator itself, its boundaries being defined by the body wall of the individual organism in whose cells the replicator sits. But the nature of the causal influence of gene on phenotype is such that it makes no sense to think of the field of influence as being limited in this arbitrary way, any more than it makes sense to think of it as limited to intracellular biochemistry. We must think of each replicator as the centre of a field of influence on the world at large. "
49 " Just as every gene is the centre of a radiating field of influence on the world, so every phenotypic character is the centre of converging influences from many genes, both within and outside the body of the individual organism. "
50 " An extended phenotypic character is the product of the interaction of many genes whose influence impinges from both inside and outside the organism. The interaction is not necessarily harmonious—but then nor are gene interactions within bodies necessarily harmonious, "
51 " The genotype may be a ‘physiological team’, but we do not have to believe that that team was necessarily selected as a harmonious unit in comparison with less harmonious rival units. Rather, each gene was selected because it prospered in its environment, and its environment necessarily included the other genes which were simultaneously prospering in the gene-pool. Genes with complementary ‘skills’ prosper in each others’ presence. "
52 " What does complementariness mean for genes? 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. "
53 " To the extent that active germ-line replicators benefit from the survival of the group of individuals in which they sit, over and above the two effects just mentioned, we may expect to see adaptations for the preservation of the group. "
54 " It is fundamental to the idea of a replicator that when a mistake or ‘mutation’ does occur it is passed on to future copies: the mutation brings into existence a new kind of replicator which ‘breeds true’ until there is a further mutation "
55 " Genes manipulate the world and shape it to assist their replication. "
56 " The word replicator is purposely defined in a general way, so that it does not even have to refer to DNA. "
57 " 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 on. "
58 " From the viewpoint of this book an animal artefact, like any other phenotypic product whose variation is influenced by a gene, can be regarded as a phenotypic tool by which that gene could potentially lever itself into the next generation. "
59 " In principle, we may consider any portion of chromosome as a potential candidate for the title of replicator. "
60 " To the extent that active germ-line replicators benefit from the survival of the bodies in which they sit, we may expect to see adaptations that can be interpreted as for bodily survival. A large number of adaptations are of this type. To the extent that active germ-line replicators benefit from the survival of bodies other than those in which they sit, we may expect to see ‘altruism’, parental care, etc. To the extent that active germ-line replicators benefit from the survival of the group of individuals in which they sit, over and above the two effects just mentioned, we may expect to see adaptations for the preservation of the group. "