Animal Behavior: Group selection sudeshrathod


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Group selection was used as a popular explanation for adaptations, especially by British zoologist Vero C. Wynne-Edwards in the 1960s. He provided a framework for understanding the balance between altruistic and self-interested adaptations, proposing that group-level adaptations for group-level survival were possible. Supported more recently by others including David Sloan Wilson, an evolutionary biologist and author at the State University of New York at Binghamton

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Animal Behavior: Group selection sudeshrathod

  1. 1. T Y B Sc. Zoology Notes: Paper IV –Animal BehaviorA model that examines the behaviour of parasites infecting their hosts renders the evolutionaryparadigm of group selection unnecessary, say scientists in Canada and the United Kingdom 1.Why organisms display behaviours or other adaptations that arent directly beneficial to them is aquestion that has intrigued biologists and caused conflict between different schools of thought forgenerations. Bees that spend their lives serving their queen, for example, and elephants that carefor the offspring of others in the herd are participating in cooperative acts that may underminetheir own chances of reproducing.Group selection was used as a popular explanation for adaptations, especially by British zoologistVero C. Wynne-Edwards in the 1960s. He provided a framework for understanding the balancebetween altruistic and self-interested adaptations, proposing that group-level adaptations forgroup-level survival were possible. Voiced more recently by others including David Sloan Wilson,an evolutionary biologist and author at the State University of New York at Binghamton, grouptheory has come to mean selection and adaptation at multiple levels: traits can confer benefits tothe individual, the family, the group or the society. (a) Group selection is a means by which cooperative behavior might evolve, though chances are that in the real world it makes little contribution except, perhaps, in the evolution of culturally learned behavior that is cooperative (b) The basic idea is that two groups are competing either over resources or directly fighting against each other; if in one group individuals cooperate whereas in the other they do not, then the overall fitness of the cooperating group will exceed that of the non-cooperating group, thus driving the latter, along with its non-cooperative behavior, to extinction (c) For example, humans even within large groups are very willing to put aside differences to fight against a common enemy.Williams presents a simple of model of biotic adaptation, and a more complicated model byWright which makes use of "drift". First, biotic adaptation is theoretically possible, as the followingfigure shows.By Prof. S D RathodDept. of ZoologyB N Bandodkar College of Science, Thane, India
  2. 2. T Y B Sc. Zoology Notes: Paper IV –Animal BehaviorSewall Wright is known for the notion of "drift". If a group is small and relatively isolated, apeculiar gene may become dominant within the group by genetic drift. The holder of such a genemay be disadvantageous for the holder but advantageous to the group (e.g., by altruisticbehavior), and the group may become larger (the group is successful vis-a-vis other groups). And ifthe group becomes large enough, some of the holders of this gene may move into other groups,and a similar process can begin within these new groups.A. Animals sometimes restrain their reproduction:Animals restraining from reproduction and allowing the counterparts to reproduce, is theindication of the group selection. Because doing this an individual looses its own geneticrelationship but help the other individuals with different genotypes to enhance the group andtheir co-evolution. But doing this even though the individual is at lost it benefits group as a hole tocarry their generations in future successfully. Spatial populations of predators and prey have alsoBy Prof. S D RathodDept. of ZoologyB N Bandodkar College of Science, Thane, India
  3. 3. T Y B Sc. Zoology Notes: Paper IV –Animal Behaviorbeen shown to show restraint of reproduction at equilibrium, both individually and through socialcommunicationB. The haystack model and trait groupsMaynard Smith can be credited with what has become known as the "haystack model" of groupselection. As a non-mathematical introduction to the idea, imagine a group of animals that spendmost of their time living and breeding in haystacks but that occasionally all come out of theirhaystacks simultaneously, mix together and then separate into equal groups, which once again gooff to inhabit separate haystacks.Each of these two traits works on a different level of selection. Within the individual haystacks theselfish organisms benefit in terms of evolutionary fitness. This is because the selfish organismsbenefit from the actions of the altruistic organisms but do not pay any of the evolutionary costsfor being altruistic (sacrificing some good for that of others). Thus, in each generation the numberof altruists in the group would shrink compared to the number of selfish organisms. As a resultone might first think that a group beneficial trait, especially an altruistic one, would be doomed toeventually die out. But we must remember the strange nature of these hypothetical organisms.Every so often, at the same time, all the members of all the haystacks form one large group,randomly assort into equal groups, and then move back into the haystacks. Because of this analtruistic behavior can take hold by the following reasoning. While the number of selfishorganisms in each haystack increases in percentage every generation, the total population ofhaystacks that contain altruists produce more offspring over all than those that do not. This meansthat populations with altruists are going to be over-represented when all the haystacks areabandoned to form a larger group. So long as the number of generations spent in each haystack isnot so long as to dramatically reduce the number of altruists, and so long as the group benefit ofthe altruistic trait is significant enough, the number of altruists in all the haystack populations canrise.C. Multilevel selection theoryDavid Sloan Wilson, the developer of Multilevel Selection Theory (MLS) compares the many layersof competition and evolution to the "Russian Matryoska Dolls" within one another. The lowestlevel is the genes, next come the cells, and then the organism level and finally the groups. Thedifferent levels function cohesively to maximize fitness, or reproductive success. After establishingthese levels, MLS goes further by saying that selection for the group level, which is competitionbetween groups, must outweigh the individual level, which is individuals competing within agroup, for a group-beneficiating trait to spread. MLS theory focuses on the phenotype this waybecause it looks at the levels that selection directly acts uponExperimental results starting in the late 1970s demonstrated that group selection was far moreeffective than the then-current theoretical models had predicted. A review of this experimentalwork has shown that the early group selection models were flawed because they assumed thatgenes acted independently, whereas in the experimental work it was apparent that geneBy Prof. S D RathodDept. of ZoologyB N Bandodkar College of Science, Thane, India
  4. 4. T Y B Sc. Zoology Notes: Paper IV –Animal Behaviorinteraction, and more importantly, genetically based interactions among individuals, were animportant source of the response to group selection (e.g.). As a result many are beginning torecognize that group selection, or more appropriately multilevel selection, is potentially animportant force in evolution.For humans, a highly pro-social, cognitive thinking species, social norms can be seen as a means ofreducing the individual level variation and competition and shift selection in humans to the grouplevel. Wilson ties the MLS theory regarding humans to another upcoming theory known as gene-culture evolution by acknowledging that culture seems to characterize a group-level mechanismfor human groups to adapt to environmental changes. Methods of testing MLS include socialpsychological experimentation and multilevel modeling equations.D. Group selection due to differing ESSsThe problem with group selection is that for a whole group to get a single trait, it must spreadthrough the whole group first by regular evolution. But, as J. L. Mackie suggested, when there aremany different groups, each with a different Evolutionarily Stable Strategy (ESS), there is selectionbetween the different ESSs, since some are worse than others. For example, a group wherealtruism arose would outcompete a group where every creature acted in its own interest (see, forinstance, the ESSs created by Koinophilia).E. Some examples: 1. In cooperative breeding, not only the parents but related and sometimes unrelated individuals of the same species help in looking after the nest, eggs and offspring, i.e. appear to show altruistic behavior. Some studies have shown that environmental factors, such as shortage of territories or unpredictability of resources, predispose birds to cooperative breeding, although environment is only one of the factors involved. Numerous studies deal with the genetic basis of cooperative breeding. Kinship (inclusive fitness) may often give a satisfactory explanation, but is less satisfactory when non-related individuals act as “helpers”, and there is increasing evidence that non-related helpers are indeed quite common. Therefore, explanations based on group augmentation (increase in the density and size of the population) are attempted, because it seems obvious that the size of a group enhances its genetic diversity and thereby its evolutionary survivability. 2. In eusociality (formation of ‘superorganisms’, ‘states’), as found for example in bees, ants and termites, the ‘altruistic’ behaviour is far more advanced than in cooperative breeding. Most of the individuals of an insect ‘state’ have lost their ability to reproduce altogether and devote their entire energy to supporting the colony. Until recently, the commonly accepted explanation.By Prof. S D RathodDept. of ZoologyB N Bandodkar College of Science, Thane, India
  5. 5. T Y B Sc. Zoology Notes: Paper IV –Animal Behavior 3. Humans differ from other animals in possessing a huge and complex brain that has permitted development of culture. Ethical convictions usually involving altruistic principles are part of culture and transmitted by tradition. Although genes certainly provide the general basis for culture formation in being responsible for development of the brain in the first place, it is unlikely that they are solely (if at all) responsible for each cultural trait. Dawkins, for example, claims that genes are not significant in the formation of human cultural traits, some sociobiologists at least attribute a greater role to them. Is it possible that only humans can truly act in an altruistic way, for example because they are able to arrive at ethical philosophical principles as in Buddhism, Hinduism.F. Critisism :Group selection isn’t widely accepted by evolutionists for several reasons. 1. First, it’s not an efficient way to select for traits, like altruistic behavior, that are supposed to be detrimental to the individual but good for the group. Groups divide to form other groups much less often than organisms reproduce to form other organisms, so group selection for altruism would be unlikely to override the tendency of each group to quickly lose its altruists through natural selection favoring cheaters. 2. Further, we simply have little evidence that selection on groups has promoted the evolution of any trait. 3. Finally, other, more plausible evolutionary forces, like direct selection on individuals for reciprocal support, could have made us prosocial. These reasons explain why only a few biologists, like [David Sloan] Wilson and E. O. Wilson (no relation), advocate group selection as the evolutionary source of cooperation. Group selection describes natural selection operating between groups of organisms, rather than between individuals. This would produce adaptations that benefit the group, rather than the individual. Darwins theory of evolution was based upon individual selection, and he rejected the idea of group selection.By Prof. S D RathodDept. of ZoologyB N Bandodkar College of Science, Thane, India