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There have been numerous studies indicating that a woman's age and weight are key factors in determining infant survival rates and their physical and cognitive well-being. However, researchers have found that humans inherit the bulk of their genetic mutations from their fathers and that mutation rates increase with the father's age.

"Most mutations come from dad," affirms David Reich, professor of genetics at Harvard Medical School and a co-leader of the study.

In addition to finding 3.3 paternal germline mutations for each maternal mutation, the study also found that the mutation rate in fathers doubles from age 20 to 58 but that there is no association with age in mothers -- a finding that may shed light on conditions, such as autism, that correlate with the father's age.

Another study, published in the journal Nature, shows that older men are more likely than young ones to father a child who develops autism or schizophrenia, because of random mutations that become more numerous with advancing paternal age, however a mother's had no bearing on the risk for these disorders, the study found.

Reich's team identified 2,058 mutational changes, yielding a rate of mutation that suggests human and chimpanzee ancestral populations diverged between 3.7 million and 6.6 million years ago. More than this, it shows that the human genome could undergo drastic changes if current reproductive rates (the growing preference of adults to have kids later in life compared to earlier generations).

Reich explains that he and his colleagues offer the first proof and clear example of a new kind of human evolution for a specific trait.

"We provide a demonstration of how humans have been able to adapt rapidly without needing to wait for new mutations to happen, by drawing instead on the existing genetic diversity within the human population."