Journal and Proceedings of The Royal Society of New South Wales Volume 120 Parts 1 and 2 [Issued September, 1987]




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SELECTION AND SOCIAL BEHAVIOR: THE EMERGENCE OF NON-GENETIC EVOLUTION


The realisation that selection can take place at many levels helps a great deal in understanding the evolution of cooperation. While much cooperation involves reciprocity, what has been called “social compensation” (“you scratch my back and I’ll scratch yours”), there remains the large and important category of altruistic behavior. Altruistic behavior is defined biologically as behavior in which one individual reduces its reproductive capacity in favor of that of another (this differs from the everyday definition of altruism, in which intention and not effect is all that matters (Stent, 1978), but then we cannot really be sure of the intentions of other humans, let alone of non-humans). Social insects provide an extreme example of altruism: in many species, the workers are sterile and labor solely to aid their mother in producing some reproductive individuals to perpetuate the colony (E.O. Wilson, 1971).

The problem of altruism, as was seen by Darwin, is that it is hard to understand at first glance how reproductive restraint and, especially, sterility can be selected for! Darwin also glimpsed the process which was later explored quite fully by Bill Hamilton (e.g. 1963, 1964, 1972) and named kin-selection by John Maynard Smith (1964). Quite simply, kin-selection is group selection in which the groups are made up of relatives (Wade, 1980a). Reproductive self-sacrifice can be selected for if the result is to increase the overall frequency of the genes responsible for the behavior through their increased replication via relatives of the altruist. This approach provides a framework not only for understanding the evolution of groups such as the social insects (e.g. Crozier, 1982), but also for framing laboratory tests (Wade, 1980b).

No treatment of the evolution of social behavior would be complete without at least a brief mention of Maynard Smith’s Evolutionary Stable Strategy approach (Maynard Smith, 1982). Briefly, an ESS is a phenotype that, if present alone in a population, successfully excludes any other. The inclusion of the word “strategy” belies the generality of this approach, which of course is applicable to more than just behavioral differences. Furthermore, the ESS approach is a largely successful attempt to model evolution quantitatively without needing the precision in specifying parameters that bedevils efforts to apply population genetics to long-term evolutionary change.

As an example of the ESS approach we can take the explanation afforded by it to one of the puzzles of animal contests: owners of resources often fight fiercely for the resource whereas challengers are timid. This asymmetry can be shown in many cases to be uncorrelated with the fighting ability of the contestants. Maynard Smith pointed out that a strategy following the rule “If owner fight hard, if challenger retreat quickly” would replace either of the unconditional approaches of fighting hard every time (“hawk”) or of always giving up easily (“dove”). This replacement is expected because the followers of this bourgeois strategy would never fight each other hard, whereas the “hawks” would fight each other hard each time they met, and the “doves” would easily lose whatever resources they had acquired.

Behavior leads us to consider the emergence of non-genetic evolution. Culture, defined biologically, is the transmission of learned behavior patterns. Evolution now becomes rather complex, because in organisms which are social, and these include most higher animals (Wilson, 1975; Wittenberger 1981; Trivers, 1985), there is the passing on of genes (of course), and, potentially, of environment (a result of parental activities) and learned behaviors as well (Cavalli-Sforza and Feldman, 1981). Only genes show obligatory and exclusive vertical transmission; behavior can be passed horizontally (such as between non-relatives) and its transmission thus resembles the typical infective transmission of microorganisms (Cavalli-Sforza and Feldman, 1981; Lumsden and Wilson, 1981; Boyd and Richerson, 1985).

We expect our own species to be the champion at culture, but cultural transmission certainly occurs in other species too. Bonner (1980) considers examples, such as the occurrences of birds learning from others to pierce the caps of milk bottles, of chimpanzees passing on termite-hunting skills, and of the transfer between individual Japanese macaque monkeys of skills in processing new foods (such as paper-wrapped toffees supplied by scientists!).

Clearly, genetic and cultural evolution are both “biological”, and we would expect them to interact, and the theory of this interaction is now a healthy field of study. Some authors, such as Lumsden and Wilson (1981) have stressed cases, such as tendencies to avoid incest, in which cultural biases reinforce genetic ones, but the two need not agree. Dawkins (1976) pointed out that cultural patterns may reduce the genetic fitness of carriers, and Boyd and Richerson (1985) provide a strong beginning to understanding this phenomenon quantitatively (celibacy is a possible example -assuming that by adopting their calling priests and nuns are not somehow preferentially helping their non-celibate relatives!)

Wyles et al. (1983) point out that cultural evolution should tend to increase the rate of genetic evolution, because the acquisition of new behaviors will change the environment and hence the selective milieu of the creatures involved. They use the example of the distribution of the ability to digest lactose as adults: human groups which keep dairy cattle have this ability, and those which don’t keep cattle lack it, suggesting that drinking milk as an adult (a cultural trait) selects for adult lactase secretion. In agreement with this suggestion is the quite close concordance observed between relative brain size and morphological evolutionary rate seen in Table 2, on the assumption that larger brains confer a greater ability to support culture. Of course, as stressed by Lumsden and Wilson (1981), it is possible that cultural evolution in our own species could become so rapid as to lead to a rate of environmental change that genetic change cannot keep up with!




TABLE 2
BRAINSIZE AND EVOLUTIONARY RATE

Relative brain size (as a proportion of body weight) compared with anatomical evolutionary rate, as calculated by Wyles et al. (1983)

Taxonomic group

Relative Brain Size

Evolutionary rate

Homo (humans)

114

>10

All hominoids

26

2.5

Songbirds

23

1.6

Other mammals

12

0.7

Other birds

4.3

0.7

Lizards

1.2

0.25

Frogs

0.9

0.23

Salamanders

0.8

0.26
Findings such as those of the occurrence of cultural transmission in species other than our own give a new twist to the Darwinian revolution. Darwin showed that humans have a heritage derived from that of other animals, and indeed rooted in the whole living world. This insight was greeted with antagonism by many fearing that it demonstrated that humans have an “animal nature”. The recent studies on social behavior in other species complete Darwin’s revolution by turning this popular understanding on its head. Rather than evolutionary biology saying that humans share unpleasant characteristics with other creatures, we can now see that other creatures are really quite like us in many of the things that we pride ourselves on!
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