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zoom RSS 男は父親になるとテストステロンのレベルが低下する

<<   作成日時 : 2011/09/13 20:10   >>

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 男は父親になると赤ん坊の世話をするように生物学的に仕向けられることが、テストステロンのレベルの研究による発見でわかった。
 624人の若者の調査で父親になる前後で検査をしたところ、赤ん坊が生まれると男のテストステロンレベルが大幅に低下することがわかった。1ヶ月以内の赤ん坊がいる父親のレベルが特に低かった。子どもの世話をする人で特に低下が大きかった。

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12 September 2011 Last updated at 22:09 GMT
Fatherhood 'lowers testosterone to keep men loyal'
http://www.bbc.co.uk/news/health-14880055

By Michelle Roberts Health reporter, BBC News

画像Men appear to be biologically wired to care for their babies, say researchers who have discovered levels of testosterone go down after fatherhood.

This drop in the male hormone presumably makes the dad more family-oriented and less likely to stray, say the Northwestern University team.
Testosterone increases a man's sex drive and helps him compete for a mate.
The Proceedings of the National Academy of Sciences work followed 624 young men before and after they became fathers.
This revealed that as soon as a man had a baby, his testosterone levels dropped substantially.
Men with newborn babies less than a month old had especially reduced levels of testosterone.
Larger falls were also seen in those who were more involved in childcare.

Biological driver

The lead investigator of the work carried out in the Philippines, Christopher Kuzawa, said: "Raising human offspring is such an effort that it is co-operative by necessity, and our study shows that human fathers are biologically wired to help with the job.
"Fatherhood and the demands of having a newborn baby require many emotional, psychological and physical adjustments. Our study indicates that a man's biology can change substantially to help meet those demands."
And the researchers believe lower testosterone levels might protect against certain chronic diseases, which could, in part, explain why married men and fathers often enjoy better health than single men of the same age.
Prof Ashley Grossman, spokesman for the Society for Endocrinology, said life and biology may be "much more subtle and adaptable than we had previously thought.
"This shows the hormonal and behavioural trade-off between mating and parenting, one requiring a high and the other a low testosterone level."
Dr Allan Pacey, senior lecturer in andrology at the University of Sheffield, said the findings were fascinating:
"Testosterone levels in men generally don't change that much. They can slowly decline as men get older and change in response to some medical conditions and treatment. But to see dramatic changes in response to family life is intriguing.
"The observations could make some evolutionary sense if we accept the idea that men with lower testosterone levels are more likely to be monogamous with their partner and care for children. However, it would be important to check that link between testosterone levels and behaviour before we could be certain."

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Longitudinal evidence that fatherhood decreases testosterone in human males

Lee T. Gettlera,b,1,2,
Thomas W. McDadea,b,
Alan B. Feranilc, and
Christopher W. Kuzawaa,b,1,2

+ Author Affiliations

aDepartment of Anthropology, and
bCells to Society, Center on Social Disparities and Health, Institute for Policy Research, Northwestern University, Evanston, IL 60208; and
cOffice of Population Studies Foundation, University of San Carlos, Cebu City 6000, Philippines

Edited by A. E. Storey, Department of Psychology, Memorial University of Newfoundland, St. John's, NF, Canada, and accepted by the Editorial Board July 28, 2011 (received for review May 10, 2011)

Abstract

In species in which males care for young, testosterone (T) is often high during mating periods but then declines to allow for caregiving of resulting offspring. This model may apply to human males, but past human studies of T and fatherhood have been cross-sectional, making it unclear whether fatherhood suppresses T or if men with lower T are more likely to become fathers. Here, we use a large representative study in the Philippines (n = 624) to show that among single nonfathers at baseline (2005) (21.5 ± 0.3 y), men with high waking T were more likely to become partnered fathers by the time of follow-up 4.5 y later (P < 0.05). Men who became partnered fathers then experienced large declines in waking (median: −26%) and evening (median: −34%) T, which were significantly greater than declines in single nonfathers (P < 0.001). Consistent with the hypothesis that child interaction suppresses T, fathers reporting 3 h or more of daily childcare had lower T at follow-up compared with fathers not involved in care (P < 0.05). Using longitudinal data, these findings show that T and reproductive strategy have bidirectional relationships in human males, with high T predicting subsequent mating success but then declining rapidly after men become fathers. Our findings suggest that T mediates tradeoffs between mating and parenting in humans, as seen in other species in which fathers care for young. They also highlight one likely explanation for previously observed health disparities between partnered fathers and single men.

Published online before print September 12, 2011, doi: 10.1073/pnas.1105403108 PNAS September 12, 2011

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