Fathering sons, daughters may be in man's genes

A UK researcher has a new explanation for how the human race manages to keep a fairly even balance of males and females. (File Photo)
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BEIJING, Jan. 3 -- A UK researcher has a new

explanation for how the human race manages to keep a fairly even balance of

males and females, despite massive deaths of young males in war and selective

abortion of female fetuses in certain parts of the world.

Corry Gellatly, a research scientist at Newcastle

University, proposes that there's a gene that determines whether a man will

father more sons, more daughters, or equal numbers of each. When females are in

short supply, they have a better chance of snagging a mate, and are thus more

likely to pass the gene for fathering daughters on to their offspring. And when

men are scarce, they have a better chance of mating and passing along the gene

for having sons.

"It's kind of a counter-balancing mechanism,"

Gellatly explained. "You can't get a population that becomes too skewed toward

males or too skewed toward females."

The ratio of male to female births jumped

significantly at the end of each of the world wars in countries involved in the

fighting. A number of hypotheses have been floated to explain why. One idea is

that returning soldiers have extra-frequent sex with their partners, which could

lead to fertilization earlier in the menstrual cycle, possibly making male

births more likely.

After sorting through 927 family trees from North

America and Europe, including 556,387 people in all, Gellatly proposes another

explanation.

In an article published online in the journal

Evolutionary Biology, the researcher suggests that men carry a gene that

controls their ratio of X to Y sperm, and thus the likelihood of their fathering

sons or daughters.

Gellatly made a computer model simulating how the

gene would act over 500 generations, and examined whether offspring sex ratios

in the real-life family trees supported his hypothesis. Both experiments bore

out his idea of a gene for gender.

Almost all of our genes come in pairs, with one being

inherited from each parent. Gellatly hypothesizes that the gender-controlling

gene comes in a "male" and "female" version, with three possible combinations of

the two.

A man could have a "male-male" gene, which would

promote the formation of Y sperm; a "male-female" gene, which would cause him to

produce about the same number of X and Y sperm; and a "female-female" gene,

which would cause him to make more X sperm.

"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 explains.

(Source: China Daily/Agencies)