Tagged: evolutionary theory

Nesting and Spring-loaded Parasitism

While enjoying your eggs, you should consider what primitive social insects do with theirs. Why? Because it may be essential to our understanding of social behavior and, hence, the notion of moral and ethical behavior. I’m reading Nowak, Tarnita, and E.O. Wilson’s 2010 article (and 43 pages of supporting materials), “The evolution of eusociality” from Nature (466/doi:10.1038/nature09205).

This is a contentious paper, I should add, because it postulates “multilevel selection” that operate at the group or species level. It is remarkable in several ways. First, it uses mathematical terminology to explain aspects if the theory of eusociality (literally: “good sociality” but, theoretically, the highest levels of social interaction) that we rarely see in papers on evolutionary theory. Specifically, ideas like “global updating” are introduced to explain why traditional methods of explaining eusociality are plagued by false assumptions about the spatial distribution of mating opportunities. I’m reminded of my own critique of the microevolution versus macroevolution distinction that pervades anti-evolution arguments: why would nature (or God for that matter) prevent hybridization of species while making it easy for genetic drift within a species? We either have a failure of imagination, the deliberate introduction of barriers to hybridization just to fool all of us or maintain a prescribed order, or we have a continuous transition from micro to macro effects (hint: there is actually no real distinction).

But back to eggs. E.O. Wilson and colleagues suggest that the earliest forms of sociality were among the parasitic wasps, like the Tarantula Hawk. Accumulate prey, stuff eggs into them, and then move on. Next, icky stuff happens in the prey. One allele change can turn the move on behavior off when the local environment is sufficiently rich, however, and then moms and offspring hang around in colonies together. Not mathematical is the use of “spring-loaded pre-adaptations” to describe this transition. The loss of wings among worker ants is a spring-loaded trait, as is the inability of fire ants to recognize aliens from other colonies; they can’t go anywhere or accurately target others for attack.

The 43 pages of supporting materials demonstrates that modern scientific theories, like the “Dark Matter” work previously described, are just not very simple. They are, arguably, just simple enough and no more so. Still, the more than 130 evolutionary biologists who objected to the Wilson paper argue that the previous theory (kin selection) was a simple solution that demanded no additional complexity. The naked mole rat and termites may object, but perhaps a synthesis is forthcoming.

Multilevel Selection and Proximate Causation

A strong critique of On the Role of Males by Dawkins was, put simply, that it continues the wrongheaded pursuit of the notion of “multilevel selection” that confuses the vehicles and replicators in the selection process. In this case, selfish genetics precludes the application of a lossy filter for genetic defects because it becomes a species-level selective mechanism.

While largely a technical distinction in evolutionary theory, much remains to be explained if we presume that there are no selective pressures that operate at levels above the genetic. For instance, when human females are subject to environmental stressors, the sex ratio changes to favor boys.  From Valerie Grant’s Wartime sex ratios: Stress, male vulnerability and the interpretation of atypical sex ratio data:

At the end of war, and other times of both chronic and acute stress, remarkable changes occur in the human secondary (birth) sex ratio. At the end of a long war, significantly more boys are born; after a short war, or disaster, fewer boys than usual are born six to nine months later. Since it is commonly held that the sex of the offspring is a matter of chance, these data provide an intriguing problem; but new findings in reproductive physiology, and an increased understanding of male vulnerability, could help resolve it. It appears the sex ratio of offspring may be influenced by variations in the mother’s follicular testosterone. Under conditions of chronic stress, maternal testosterone rises, resulting in an increase in male conceptions; but these same stressful conditions also exacerbate differential male vulnerability, so more males are lost during pregnancy. At the end of war, improving conditions temper male vulnerability, leaving higher sex ratios at birth. Conversely, normal conditions at conception followed by a severe stressor during pregnancy result in lower secondary sex ratios.

Here we have evidence of a proximate cause (stress triggers hormone changes) that leads to a group-level change that has selective advantage.  How do we reconcile this with purist selfish genetics? We might be able to create a string of explanations that supports a selfish genetic interpretation, but it’s not clear why an immensely reticulated explanation helps improve on the interpretation.