Evolution now : a century after Darwin / edited by John Maynard Smith.

Date:
1982
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Evolution now : a century after Darwin / edited by John Maynard Smith. Source: Wellcome Collection.

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    THE EVOLUTION OF BEHAVIOUR 213 mutant strategy can invade the population. But other strategies may be evolutionarily stable as well. In fact, when w is sufficiently great, there is no single best strategy regardless of the behavior of the others in the populahon^'. Just because there is no single best strategy, it does not follow that analysis is hopeless. On the contrary, we demonstrate not only the stability of a given strategy, but also its robustness and initial viability. Before turning to the development of the theory, let us consider the range of biological reality that is encompassed by the game theoretic approach. To start with, an organism does not need a brain to employ a strategy. Bacteria, for example, have a basic capacity to play games in that (i) bacteria are highly responsive to selected aspects of their environment, especially their chemical environment; (ii) this implies that they can respond differentially to what other organisms around them are doing; (iii) these conditional strategies of behavior can certainly be inherited; and (iv) the behavior of a bacterium can affect the fitness of other organisms around it, just as the behavior of other organisms can affect the fitness of a bacterium. While the strategies can easily include differenrial responsiveness to recent changes in the environment or to cumulative averages over time, in other ways their range of responsiveness is limited. Bacteria cannot 'remember' or 'interpret' a complex past sequence of changes, and they probably cannot distinguish alternative origins of adverse or beneficial changes. Some bacteria, for example, produce their own antibiotics, bacteriocins; those are harmless to bacteria of the producing strain, but destructive to others. A bacterium might easily have production of its own bacteriocin dependent on the perceived presence of like hostile products in its environment, but it could not aim the toxin produced toward an offending initiator. From existing evidence, so far from an individual level, discrimination seems to be by species rather even than variety. For example, a Rhizobium strain may occur in nodules which it causes on the roots of many species of leguminous plants, but it may fix nitrogen for the benefit of the plant in only a few of these species^. Thus, in many legumes the Rhizobium seems to be a pure parasite. In the light of theory to follow, it would be interesting to know whether these parasitized legumes are perhaps less beneficial to free living Rhizobium in the sur¬ rounding soil than are those in which the full symbiosis is established. But the main point of concern here is that such discrimination by a Rhizobium seems not to be known even at the level of varieties within a species. As one moves up the evolutionary ladder in neural complexity, game- playing behavior becomes richer. The intelligence of primates, including humans, allows a number of relevant improvements: a more complex memory, more complex processing of information to determine the next action as a function of the interaction so far, a better estimate of the probability of future interaction with the same individual, and a better ability to distinguish between different individuals. The discrimination of others may be among the most important of abilities because it allows one to handle interactions with many individuals without having to treat