Wild et al. argue that the evolution of reduced virulence can be understood from the perspective of inclusive fitness, obviating the need to evoke group selection as a contributing causal factor. Although they acknowledge the mathematical equivalence of the inclusive fitness and multilevel selection approaches, they conclude that reduced virulence can be viewed entirely as an individual-level adaptation by the parasite. Here we show that their model is a well- known special case of the more general theory of multilevel selection, and that the cause of reduced virulence resides in the opposition of two processes: within-group and among-group selection. This distinction is important in light of the current controversy among evolutionary biologists in which some continue to affirm that natural selection centres only and always at the level of the individual organism or gene, despite mathematical demonstrations that evolutionary dynamics must be described by selection at various levels in the hierarchy of biological organization.
How does altruism arise when organisms are competing for survival? This question underlies the decades-long debate between those who argue in favor of "kin selection," in which individuals are altruistic to those who share their genes, and those who argue in favor of "group selection," in which altruism arises from being part of a group.
In this week's issue of Nature, a team of 18 scientists, including four from the New England Complex Systems Institute (NECSI), show that the two traditional approaches are actually mathematically equivalent.
How can this be? In order for kin selection to be important, the related kin have to be in groups that preferentially confer altruistic behaviors on each other. In order for group selection to operate, the members of a group have to be closer kin than they are to other groups. The two ideas are close enough that they can actually be converted to each other mathematically. This understanding has been stated in research articles in the past, but the broader biological and scientific community has not recognized it.
According to principal author Professor Michael Wade "It is remarkable that kin selection has been widely accepted and group selection widely disparaged when, for simple genetic models, they are actually equivalent mathematically." Moreover, according to Professor Charles Goodnight, "Experiments have shown the effect of group selection. For example, selecting whole coops of chickens improves egg-laying over selecting individuals, because the socially better behaved chickens are more successful when groups are selected."
The article in Nature also points to key research by scientists of the New England Complex Systems Institute, in which the kin selection and group selection ideas are shown to be insufficient to describe the origins of altruism in all cases. According to NECSI President Professor Yaneer Bar-Yam, "When there are self-organized groups, the dynamics of group formation change the dynamics of evolution and make it much easier for altruism to arise." Professor Marcus de Aguiar explains "We showed that spatial systems, in which local selection occurs, create altruism without need for the limited conditions in which kin or group selection hold."
The article represents a cooperative effort of many scientists to clarify longstanding confusions about the evolutionary origins of altruism.
Please click here to read more on Nature's website.
The New England Complex Systems Institute (NECSI) is an independent non-profit research and education institute developing new scientific methods, and applying them to the challenges of society. Based in Cambridge, MA, NECSI engages in original research, education, and community development. To find out more, visit www.necsi.edu.