4.11: Curbing runaway selection

Sexual selection can lead to what has been termed, but is not really, runaway selection. For example, the more prominent the peacock male's tail the more likely he will find a mate even though larger and larger tails can have significant negative effects of survival. All of which is to say that there are both positive and negative selection pressures for tail size, influencing the probability that a particular male mates successfully. Selection never really runs away, but settles down when the positive benefit(s), in terms of sexual success, and the negative cost(s) of a trait come to be (roughly) equal to each other. In the wild, there will be reproductively successful male peacocks with large tails, even if those tails may make them more susceptible to predators.

For another example, consider the evolution of extremely large antlers associated with male dominance and mate accessibility, such as occurred in Megaloceros giganteous (↓). Large antlers influence the animal’s ability to move through heavily wooded areas or to run fast. In a stable environment, the costs and benefits of antlers are expected to balance out. Selection will produce an optimal solution. If the environment changes however, this balance may be disrupted; pre-existing behaviors and phenotypes may influence the impact of selective pressures. Organism’s may not be able to adapt fast enough to avoid extinction. There is a balance between costs and benefits, particularly within a changing environment.

Social and ecological interactions apply to all organisms, from bacteria to humans. They serve as a counter-balance to the common caricature of evolution as a ruthless and never ceasing competition between organisms. This hyper-competitive view, often known as the struggle for existence or Social Darwinism, may be appealing to ruthless (anti-union / anti-social) capitalists but is not supported by scientifically-established evolutionary scenarios. It has been promulgated by a number of pundits who have used it to justify various political and inherently non-scientific positions, arguing against social programs that help the poor, often characterized as the unfit ,at the “expense” of the wealthy (who might be viewed as parasites). Assuming that certain organisms are inherently less fit, and that they could be identified, this view of the world gave rise to eugenics, the view that genetically inferior people should be removed from the population or sterilized, before their "bad" traits overwhelmed a particular culture. Eugenics was an influential ideology in the United States during the early part of the 20^th century and inspired the genocidal programs of the Nazis in Germany. It re-emerges periodically for various reasons. What is particularly odd about this pseudo-evolutionary perspective is that it is actually anti-evolutionary, since if the unfit really were unfit, they could not possibly take over a population. In addition, it completely ignores the deeply social (cooperative) aspect of the human species.

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