Maternal Influence and Sex of the Infant

• Sex and Evolution: Bateman, Trivers-Willard, Coolidge, and Their Effects by James Brody, 6/20/97
  
  

There was a news bit citing "Nature" that if the female was older than the male, then a female child was more likely. The reverse was true if the male was older than the female.

This is pretty interesting because the mother, in addition to the father, influences the sex of the child.

This latest piece is similar to the Trivers-Willard Effect in which it is in the genetic interests of younger mothers to produce sons (because they will be healthier and more likely to mate more often than the same number of healthy daughters) and older mothers to produce daughters (because even an unhealthy female from an older mother has a greater chance of mating than an unhealthy male). The effect has been verified with a couple of species, including my own.

As David Hume and others tried to tell us, there are no universal generalizations in science. Instead, we use them in the dogged pursuit of knowledge by finding the exceptions. Thus, the former absolute rule that the father determines the sex of the child has been modified. People such as Brian Goodwin who discuss "Excitable Fields" as key influences on genetic expression are not surprised by this conceptual enrichment.

Weissmann's Principle and the Central Dogma is still in place so far as I know. Weissmann described the separation between reproductive DNA which is largely impervious to environmental tinkering and somatic DNA which adjusts its output of RNA and proteins to adjust to environmental demands. Thus, large muscles can be grown but not inherited.

The Central Dogma is that DNA produces RNA which produces proteins. There is no feedback loop from proteins or RNA to modify the structure of DNA. However, there is some nibbling at the Central Dogma. Certain bacteria will shift their DNA structure in response to the kinds of nutrients in their bath. This kind of process is one more intriguing, possible mechanism of speciation if it were more generally true. It has the advantage of allowing multiple, non-sibling male and female creatures to be made who could probably mate with each other but perhaps not with members of their parents' species. Mutation and genetic drift all have the disadvantage of producing only children (who share the change in genotype) from the same mother. Such children then have to mate with each other, increasing all the negative things that routinely occur with inbreeding. Speciation, to avoid inbreeding, ought to produce variations from several different parents and at about the same time.

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