A father’s age when conceiving a child may help shape and speed the rate of human evolution, with older men more likely to pass genetic mutations to the next generation.

Schizophrenia and autism spectrum disorder have long been linked to advanced paternal age, as more Westernized people delay parenthood later into their thirties, forties, and beyond. The 70 or so genetic mutations resident within an unborn child — a zygote — come from both the father and mother. However, the share of mutations is strongly influenced by paternal age with an average of two additional genetic mutations for every “extra year” of age, Oxford University geneticists reported Thursday in the journal Science.

Thus, aging fathers may shape possible futures with a strong male bias in the evolutionary force of sexual selection. “In humans, a father’s age is known to affect how many mutations he passes on to his children, and is also an established risk factor in a number of mental health disorders,” study author Gil McVean said in a press statement.

Discovered within the sequenced genomes of nine western chimpanzees in captivity in the Netherlands was an even stronger male influence over evolution, with paternal age making the difference in how sexual selection shapes evolution. A greater share of the mutations found within the DNA of chimpanzee offspring was found to come from fathers, supporting past study findings on the subject. The geneticists sequenced the genomes of parents and offspring within a three-generation family of chimpanzees, identifying mutations as any DNA changes not also present in either the father or mother.

"This study finds that in chimpanzees the father's age has a much stronger effect on mutation rate — about one and a half times that in humans,” McVean said. “As a consequence, a greater fraction of new mutations enter the population through males, around 90 per cent, compared to humans, where fathers account for 75 per cent of new mutations."

The explanation for the stronger male influence over sexual selection in chimpanzees might come down to simple testicle size, McVean and his colleagues said in the paper. But the principle works similarly in both species. Whereas the female primate reproductive system does not produce new genetic mutations after a mother’s birth, the male’s biology continually produces sperm throughout a lifetime, remixing possible futures for better or worse.

On the positive side, Northwestern University anthropologist Dan Eisenberg says advanced paternal age confers children and grandchildren with longer chromatic telomeres, protecting genes from dangerous nucleotide losses during cellular replication. In a 2012 study published in the Proceedings of the National Academy of Sciences, Eisenberg and his colleagues found that “the lengthening of telomeres predicted by each year that the father’s or grandfather’s reproduction are delayed is equal to the yearly shortening of [telomeres] seen in middle-age to elderly women in this sample.”

That Northwestern team said the data suggested a biological mechanism ripe for exploitation: Delayed reproduction by humans might slow the aging of tissues dependent on cellular replication, and thus grant humanity a reprieve from the gallows.

Yet a higher rate of genetic mutations increasing relative to older paternal ages across Westernized societies may also bring increased chances of developing serious mental illnesses such as schizophrenia and autism spectrum disorder. Geneticists in Iceland published a study in Nature, also in 2012, describing a “deleterious” decline as fathers age into their thirties, forties, and even older at the time of conception.

“The older we are as fathers, the more likely we will pass on our mutations,” lead author Kári Stefánsson, chief executive of deCODE Genetics in Reykjavik, told Nature. “The more mutations we pass on, the more likely that one of them is going to be deleterious.”

 

Source: McVean G, Father's age influences rate of evolution. Science. 2014.