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macroevolution

Размер семенников отрицательно коррелирует со склонностью заботиться о своих детях

Статья в PNAS.
Теоретически, самец должен как-то распределять свои лимитированные ресурсы между заботой об уже имеющихся детях и попытками заиметь новых. Обе стратегии по-своему эволюционно выгодны (т.е. могут повысить ваш репродуктивный успех). Но за двумя зайцами сразу не угонишься. Должен быть какой-то баланс, компромисс (trade-off) между этими альтернативными стратегиями. Кто-то делает ставку на заботу о потомстве, кто-то - на максимизацию его количества.
Авторы обнаружили отрицательную корреляцию между размером семенников (и уровнем тестостерона) у молодых отцов и рядом признаков, указывающих на любовь к своему ребенку и желание вкладываться в заботу о нем (напр., такой признак, как возбуждение VTA - вентральной области покрышки среднего мозга - при виде фотографии своего ребенка). Короче говоря, папаши с большими семенниками в среднем спокойнее относятся к своим детям и менее склонны тратить свои ресурсы на заботу о них.

Men’s testes size negatively tied to parenting involvement

Testes size tied to parenting involvement. Image courtesy of Patrik Hägglund/Wikimedia Commons.

Testes size tied to parenting involvement. Image courtesy of Patrik Hägglund/Wikimedia Commons.

An evolutionary hypothesis called Life History Theory holds that mating and parenting compete for the limited energy animals expend on reproduction. Previous studies have suggested that decreases in testosterone may suppress mating efforts, potentially channeling resources toward paternal care of infants. Jennifer Mascaro et al. investigated the link between testes size and parenting investment among men, given that testes volume is associated with sperm production and testosterone levels. The authors recruited 70 biological fathers in and around Atlanta who were 21–43 years of age and had 1–2-year-old children, and used MRI to measure the men’s testes volumes and monitor brain activity in a region implicated in parental motivation, while the men viewed photographs of their own child, a stranger’s child, or an adult stranger. The men’s partners also answered a parenting questionnaire that queried the fathers’ involvement in tasks such as taking children to health care visits and attending to children at night. The authors report that fathers’ testes size was negatively tied to nurturing-related brain activity triggered while they viewed pictures of their own child. In particular, fathers who were more responsive than others to their child’s emotional faces tended to have smaller testes and be more involved in infant care. According to the authors, the link between testes size and parenting-related brain activity suggests a trade-off between begetting and rearing offspring. — P.N.

"Testicular volume is inversely correlated with nurturing-related brain activity in human fathers," by Jennifer S. Mascaro, Patrick D. Hackett, and James K. Rilling
[Abstract]

http://www.pnas.org/content/early/2013/09/04/1305579110
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