They say having a family changes a man forever. But it may not just be a sense of duty that drives new dads to swap evenings in the pub for quiet nights at home。

　　A study has found that when men become fathers, their bodies suppress production of the sex hormone, making them more interested in parenting than mating。

　　The researchers measured testosterone levels in saliva from a group of 21-year-old men from the Philippines with no children. Testosterone boosts behaviors that help a male compete for a mate。

　　Over the next five years, childless men saw an average age-related testosterone decline of 14 percent, but for those who became fathers, the typical drop was 34 percent。

　　The men who reported caring for their child for between one and three hours per day saw the greatest decline, which the authors said was not accounted for by stress or sleep deprivation。

　　Co-author Lee Gettler, an anthropologist at Northwestern, said: "I think it is reasonable to predict that the men’s testosterone could remain low for a number of years if they remained heavily involved in providing care to their children."

　　This is the first to suggest that settling down and having children actually causes the fall。

　　据英国《每日邮报》9月12日报道，人们说，家庭常常会改变一个男人。但是，刚刚成为爸爸的男性们之所以不再光顾酒吧，而是选择回到家中宁静度日，这不仅仅是因为他们受到了责任感的驱使。

　　研究发现，男人在成为父亲之后，他们的身体就会抑制性激素的产生，这使其对养育子女比对性生活的兴趣更大。

　　研究人员对一组来自菲律宾的尚未成为父亲的21岁男性唾液中的睾丸素水平进行了测量。睾丸素促使男性追求配偶。

　　在接下来的5年中，无子女的男性由于年龄原因，睾丸素平均减少了14%，而那些成为父亲的男性，他们的睾丸素锐减了34%。

　　根据报告显示，那些每天花一至三小时时间来照顾小孩的男性，他们的性激素减少的最多。研究人员认为，这一现象并不能归咎于压力大或是缺乏睡眠这些因素。

　　美国西北大学的研究员雷?盖图说：“我认为，这个判断较为合理，即如果男性照顾小孩的负担较重，那么他们的睾丸素将会在数年内都保持在一个较低水平上。”

　　该研究首次证实了成家和生子确实会导致睾丸素减少。