近期發表在美國《國家科學學會學報》上的一項研究報告顯示，在人類進化過程中，女性將會變矮、體重會增加、身體會更健康，而且生育周期會更長。如果按照這項研究的趨勢發展，到2409年的時候，女性的平均身高將會減少2厘米，體重增加1公斤，生育頭胎的年齡將會提前5個月，而停經期將會推后10個月。這項研究是由耶魯大學進化生物學教授史蒂芬？斯特恩斯組織進行的，他和他的研究小組對馬薩諸塞州弗雷明漢鎮1.4萬居民中2238名已過生育年齡的女性醫療史進行研究，并測量了她們的身高、體重、膽固醇、血壓以及其他指標。結果發現，身材矮小、體重較重的女性生的孩子比高個、苗條的女性要多；血壓和膽固醇指標較低的女性多育的幾率也較高。研究還發現，母親的這些身體特質都會遺傳給女兒，并由此影響到下一代的生育狀況。

    New research at Yale University has provided the strongest evidence yet that humans are evolving – and suggests that women of the future will be shorter, heavier, and healthier, and will have children for longer.

    As medicine has allowed people who would previously have died young to live to childbearing age and beyond, many have assumed that natural selection no longer works on our species.

    But Prof Stephen Stearns, the evolutionary biologist at Yale University behind the study, says: "That's just plain false."

    While survival to reproductive age is no longer such a hurdle for humans, other evolutionary pressures – including sexual selection and reproductive fitness – are still working away in full force.

    If the trends the research detected are representative and continue for another 10 generations, Prof Stearns says that the average woman in 2409AD will be 2cm （0.8in） shorter and 1kg （2lb 3oz） heavier, will bear her first child five months earlier, and enter the menopause 10 months later.

    Prof Stearns and his team studied the medical histories of 14,000 residents of the Massachusetts town of Framingham, using medical data from a study going back to 1948 and spanning three generations.

    It looked at 2,238 women past reproductive age – so that they had had all the children they were going to – and tested their height, weight, cholesterol, blood pressure, and other traits, to see if there was a correlation with the number of children they had borne.

    It found that shorter, heavier women had more children than lighter, taller ones. Women with lower blood pressure and cholesterol were also more likely to have large families.

    Women who gave birth early or had a late menopause were likely to have more children as well.

    More importantly, however, these traits were then passed on to their daughters, who also, on average, had more children.

    The study has not determined why these factors are linked to reproductive success, but it is likely that they indicate genetic, rather than environmental, effects. Prof Stearns' team controlled for other factors, including social and cultural change.

    He told New Scientist: "It's interesting that the underlying biological framework is still detectable beneath the culture."

    Research suggesting humans are evolving has been carried out before, but this is believed to be the first that directly compares reproductive success of individuals with physiological changes.

    The research is published in the Proceedings of the National Academy of Sciences journal.