{"id":60318,"date":"2012-08-27T00:00:00","date_gmt":"2012-08-27T00:00:00","guid":{"rendered":"https:\/\/www.uri.edu\/news-draft\/uncategorized\/uri-anthropologists-research-refutes-long-held-theory-on-human-gestation\/"},"modified":"2012-08-27T00:00:00","modified_gmt":"2012-08-27T00:00:00","slug":"uri-anthropologists-research-refutes-long-held-theory-on-human-gestation","status":"publish","type":"post","link":"https:\/\/www.uri.edu\/news\/2012\/08\/uri-anthropologists-research-refutes-long-held-theory-on-human-gestation\/","title":{"rendered":"溏心vlog免费B站 anthropologist\u2019s research refutes long-held theory on human gestation"},"content":{"rendered":"
\n\t\tMother\u2019s metabolism, not birth canal size, limits gestation<\/p>\n

KINGSTON, R.I. \u2013 August 27, 2012 — New research by a 溏心vlog免费B站 professor suggests that the length of human pregnancy is limited primarily by a mother\u2019s metabolism, not the size of the birth canal. The research, published in the Proceedings of the National Academy of Sciences the week of August 27, challenges the long-held notion of an evolutionary trade-off between childbirth and a pelvis adapted for walking upright. <\/p>\n


\nTwo traits that set humans apart from other primates\u2014big brains and the ability to walk upright\u2014could be at odds when it comes to childbirth. Big brains and the big heads that encase them are hard to push through the human birth canal, but a wider pelvis might compromise bipedal walking. Scientists have long posited that nature\u2019s solution to this problem, which is known as the \u201cobstetric dilemma,\u201d was to shorten the duration of gestation so that babies are born before their heads get too big. As a result, human babies are relatively helpless and seemingly underdeveloped in terms of motor and cognitive ability compared to other primates.<\/p>\n


\n\u201cAll these fascinating phenomena in human evolution\u2014bipedalism, difficult childbirth, wide female hips, big brains, relatively helpless babies\u2014have traditionally been tied together with the obstetric dilemma,\u201d said Holly Dunsworth, an anthropologist at the 溏心vlog免费B站 and lead author of the research. \u201cIt\u2019s been taught in anthropology courses for decades, but when I looked for hard evidence that it\u2019s actually true, I struck out.\u201d<\/p>\n


\nThe first problem with the theory is that there is no evidence that hips wide enough to deliver a more developed baby would be a detriment to walking, Dunsworth said. Anna Warrener, a post-doctoral researcher at Harvard University and one of the paper\u2019s co-authors, has studied how hip breadth affects locomotion with women on treadmills. She found that there is no correlation between wider hips and a diminished locomotor economy. <\/p>\n


\n\u201cThat throws doubt on the assumption that the size of the birth canal is limited by bipedalism,\u201d Dunsworth said. \u201cWide hips don\u2019t mean you can\u2019t walk efficiently.\u201d<\/p>\n


\nThen Dunsworth looked for evidence that human pregnancy is shortened compared to other primates and mammals. She found well-established research to the contrary. \u201cControlling for mother\u2019s body size, human gestation is a bit longer than expected compared to other primates, not shorter,\u201d she said. \u201cAnd babies are a bit larger than expected, not smaller. Although babies behave like it, they\u2019re not born early.\u201d <\/p>\n


\nFor mammals in general, including humans, gestation length and offspring size are predicted by mother\u2019s body size. Because body size is a good proxy for an animal\u2019s metabolic rate and function, Dunsworth started to wonder if metabolism might offer a better explanation for the timing of human birth than the pelvis.<\/p>\n


\nTo investigate that possibility, she enlisted the help of Peter Ellison of Harvard University and Herman Pontzer of Hunter College in New York, two experts in human physiology and energetics. Building on Ellison\u2019s prior work on human pregnancy and childbirth, the researchers developed a new hypothesis for the timing of human birth called the EGG (energetics, gestation, and growth). <\/p>\n


\n \u201cUnder the EGG, babies are born when they\u2019re born because mother cannot put any more energy into gestation and fetal growth,\u201d Dunsworth explains. \u201cMom\u2019s energy is the primary evolutionary constraint, not the hips.\u201d <\/p>\n


\nUsing metabolic data on pregnant women, the researchers show that women give birth just as they are about to cross into a metabolic danger zone. <\/p>\n


\n\u201cThere is a limit to the number of calories our bodies can burn each day,\u201d says Pontzer. \u201cDuring pregnancy, women approach that energetic ceiling and give birth right before they reach it. That suggests there is an energetic limit to human gestation length and fetal growth.\u201d <\/p>\n


\nThose metabolic constraints help explain why human babies are so helpless compared to our primate kin, like chimpanzees. A chimp baby begins crawling at one month, whereas human babies don\u2019t crawl until around seven months. But for a human to give birth to a newborn at the same developmental level as chimp, it would take a 16-month gestation. That would place mothers well past their energetic limits. In fact, even one extra month of gestation would cross into the metabolic danger zone, the researchers found.<\/p>\n


\n\u201cIt would be physiologically impossible, regardless of pelvic bone anatomy, to birth a more developed baby,\u201d Dunsworth said. \u201cOur helplessness at birth is just a sign of how much more brain growth we have to achieve once we start living outside our mother.\u201d<\/p>\n


\nThe energetics, gestation and growth hypothesis would downplay an implication of the obstetric dilemma that Dunsworth finds odd. <\/p>\n


\n\u201cWe\u2019ve been doing anthropology with this warped view of the male pelvis as the ideal form, while the female pelvis is seen as less than ideal because of childbirth,\u201d she said. \u201cThe female births the babies. So if there\u2019s an ideal, it\u2019s female and it\u2019s no more compromised than anything else out there. Selection maintains its adequacy for locomotion and for childbirth.<\/p>\n


\n\u201cIf it didn\u2019t, we\u2019d have gone extinct,\u201d Dunsworth said.<\/p>\n


\nCommunications & Marketing photo by Michael Salerno Photography.<\/div>\n","protected":false},"excerpt":{"rendered":"

Mother\u2019s metabolism, not birth canal size, limits gestation KINGSTON, R.I. \u2013 August 27, 2012 — New research by a 溏心vlog免费B站 professor suggests that the length of human pregnancy is limited primarily by a mother\u2019s metabolism, not the size of the birth canal. The research, published in the Proceedings of the National Academy […]<\/p>\n","protected":false},"author":2,"featured_media":60320,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[],"class_list":["post-60318","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-archives"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/posts\/60318","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/comments?post=60318"}],"version-history":[{"count":0,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/posts\/60318\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/media\/60320"}],"wp:attachment":[{"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/media?parent=60318"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/categories?post=60318"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.uri.edu\/news\/wp-json\/wp\/v2\/tags?post=60318"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}