UK researcher Corry Gellatly believes he has a new explanation for how the human race keeps a balance of males and females.
The research scientist from Newcastle University proposes that a gene determines whether a man will father more sons or daughters.
According to Gellatly, when the female population is low, women have a better chance of finding a mate, which makes them more likely to pass the gene for fathering daughters to their children. When men are scarce, they also have a better chance of finding a mate and passing along the gene for more sons to their offspring.
“It’s kind of a counterbalancing mechanism,” Gellatly told Reuters. “You can’t get a population that becomes too skewed toward males or too skewed toward females.”
At the end of each world war, the ratio of male to female births jumped in countries involved in the fighting. Many hypotheses have been made to explain why. One says that returning soldiers have extra sex with their partners, leading to fertilization earlier in the menstrual cycle which could lead to more male births.
Another hypothesis says that larger males are more likely to survive battles, and to have male offspring.
Gellatly devised his hypothesis after sorting through 927 family trees from North America and Europe.
The researcher suggests that men carry a gene controlling their ratio of X to Y sperm.
Gellatly made a computer model to simulate how the gene would work over 500 generations, and studied whether offspring sex ratios in real family trees could support his idea.
Both experiments supported his hypothesis.
Gellatly believes the gene is very ancient, and is probably carried by any species that produces sexually. He also believes the gene comes in twos in a male (X) and female (Y) version with three combinations of the pair: XX to produce more male sperm, YY to produce more female sperm, and XY to remain neutral.
“The structure of the proposed gene is essentially very basic, and its function is simply to say ‘produce more boys’ or ‘produce more girls,'” Gellatly added.
Gellatly’s theory explains why male births increased after the world wars. Families with many sons are more likely to have surviving male children who can pass along genes. Families with fewer male offspring would be less to likely to have sons who survived the wars.
Academic paper: Trends in Population Sex Ratios May be Explained by Changes in the Frequencies of Polymorphic Alleles of a Sex Ratio Gene. Corry Gellatly. Published in: Evolutionary Biology, DOI 10.1007/s11692-008-9046-3
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