Group Selection - Multilevel Selection Theory

Multilevel Selection Theory

In recent years, the limitations of earlier models have been addressed, and newer models suggest that selection may sometimes act above the gene level. Recently David Sloan Wilson and Elliot Sober have argued that the case against group selection has been overstated. They focus their argument on whether groups can have functional organization in the same way individuals do and, consequently, whether groups can also be "vehicles" for selection. For example, groups that cooperate better may have out-reproduced those that did not. Resurrected in this way, Wilson & Sober's new group selection is usually called multilevel selection theory.

David Sloan Wilson, the developer of Multilevel Selection Theory (MLS) compares the many layers of competition and evolution to the "Russian Matryoska Dolls" within one another. The lowest level is the genes, next come the cells, and then the organism level and finally the groups. The different levels function cohesively to maximize fitness, or reproductive success. After establishing these levels, MLS goes further by saying that selection for the group level, which is competition between groups, must outweigh the individual level, which is individuals competing within a group, for a group-beneficiating trait to spread. MLS theory focuses on the phenotype this way because it looks at the levels that selection directly acts upon.

MLS theory does not lean towards individual or group selection but can be used to evaluate the balance between group selection and individual selection on a case-by-case scenario. Some experiments done imply that group selection can prevail, such as the experiment conducted by William Muir of Purdue University comparing egg productivity in hens. In the experiment, he demonstrates the existence of group selection by showing that in individual selection, a hyper-aggressive strain had been produced that led to many fatal attacks only after six generations. Group selection has been most often postulated in humans and, notably, social insects that make cooperation a driving force of their adaptations over time.

For humans, a highly pro-social, cognitive thinking species, social norms can be seen as a means of reducing the individual level variation and competition and shift selection in humans to the group level. 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 mechanism for human groups to adapt to environmental changes. Methods of testing MLS include social psychological experimentation and multilevel modeling equations.

Wilson & Sober's work has been part of a revival of interest in multilevel selection as an explanation for evolutionary phenomena. Indeed, in a 2005 article, E. O. Wilson argued that kin selection could no longer be thought of as underlying the evolution of extreme sociality, for two reasons. First, some authors have shown that the argument that haplodiploid inheritance, characteristic of the Hymenoptera, creates a strong selection pressure towards nonreproductive castes is mathematically flawed. Second, eusociality no longer seems to be confined to the hymenopterans; increasing numbers of highly social taxa have been found in the years since Wilson's foundational text on sociobiology was published in 1975, including a variety of insect species, as well as a rodent species (the naked mole rat). Wilson suggests the equation for Hamilton's rule:

rb > c

(where b represents the benefit to the recipient of altruism, c the cost to the altruist, and r their degree of relatedness) should be replaced by the more general equation

(rb_k + b_e) > c

in which b_k is the benefit to kin (b in the original equation) and b_e is the benefit accruing to the group as a whole. He then argues that, in the present state of the evidence in relation to social insects, it appears that b_e>rb_k, so that altruism needs to be explained in terms of selection at the colony level rather than at the kin level. However, it is well understood in social evolution theory that kin selection and group selection are not distinct processes, and that the effects of multi-level selection are already fully accounted for in Hamilton's original rule, rb>c.