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Archive for March, 2013

This week’s reading was an excerpt from Major Transitions in Evolution by Maynard Smith and Szathmary. The particular “major transitions” emphasized in the reading and relevant to discussions of altruism deal with situations where the complexity of a group of organisms increases due to high levels of cooperation and specialization among their constituent members. For example, the evolution of multi-cellularity could be viewed as one such event. In particular, the examples highlighted in the reading included the evolution of eusociality in social insects, as well as the evolution of complex human societies.

We began by discussing social insects. A typical explanation for the evolution of eusociality in insects is some variant of kin selection. Most of the individuals in a colony are highly related (sisters), and hence have an average relatedness to other colony members that is the same as their relatedness to their own offspring (r =1/2 in both cases). This high level of relatedness between colony members is consistent with kin selection-based explanations for the high levels of cooperation and altruistic behavior in these insect species. Haplodiploidy has also been invoked as a potential explanation for the evolution of eusociality in some social insects, such as bees and ants. Haplodiploidy appears to be somewhat correlated with eusociality across several species, in particular hymenopterans (ants, bees, sawflies, and wasps). In hymenopterans, the males are haploid, while the females are diploid. This means that the average relatedness between sisters is 0.75, making it appear to be even more beneficial for a worker to invest resources in her siblings than in her offspring. However, one can refute this argument simply by considering that the average relatedness of workers to the male offspring of the queen is only 0.25, meaning that (assuming a 1:1 sex ratio) the average relatedness to all siblings is still 0.5. Furthermore, many bee species are solitary rather than eusocial, despite being haplodiploid. Nonetheless, it is possible that sex ratios are important for the evolution of eusociality, and thus haplodiploidy may play a role, albeit a much less clear-cut one than originally proposed.

We next discussed the concept of “division of labor”. Broadly speaking, division of labor refers to situations in which the individual units of a system (such as cells in a multicellular organism, individual insects in a colony, or humans in a complex society) take on different functional roles with respect to their behavior and their individual contributions to the activity of the system as a whole. For example, individual cells in a multicellular organism differentiate into different cell types, and termites in a colony take on distinct roles (worker, soldier, etc.). Division of labor typically involves a dramatic increase in the overall complexity of a system, and often allows for a new type of resource to be used, or a new ecological niche to be filled. In this case, the concept of absolute fitness vs. relative fitness becomes important. Absolute fitness (unlike relative fitness) is not defined relative to other individuals in a population, and could increase when a new ecological niche or a new set of resources suddenly becomes available, allowing for (at least temporary) increases in overall reproduction. One could even make the argument that such increases in absolute fitness may be a fundamental driver of increased complexity, although alternative explanations have also been proposed.

Near the end of the meeting we returned to a list of the various definitions or “cases” of altruism discussed at the previous meeting (see the table in blog entry from Feb 13 for definitions, in particular cases 1-4). These cases are distinct from one another primarily because they involve different types of costs (perceived, intended or actual) on the part of the individual performing the altruistic act. One can also approach different notions of altruism with respect to different ways in which the benefits of an altruistic act can be distributed. This is particularly relevant in discussing the evolution of social cooperation. To this end, two additional concepts were introduced:

1) “Loyalty”, which refers to altruistic behavior that benefits members of the in-group more than members of the out-group. One can construct how this might have evolved biologically.

2) What we decided (after some debate) to call “Full Altruism”. “Full Altruism” refers to the case where altruistic behavior benefits the out-group more than the in-group. Unlike loyalty, this type of behavior is much more difficult to explain biologically. Furthermore, the distinction between loyalty and full altruism is especially important for discussions surrounding the ethical and theological dimensions of altruism.

-David Lyttle

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