5 ms·
> this is commonly attributed to the fact that human babies have immature brains that cannot mature due to birth canal constraints, which is constrained by pelv
by jacinda 5y ago
> this is commonly attributed to the fact that human babies have immature brains that cannot mature due to birth canal constraints, which is constrained by pelvis size which is constrained by the need to walk upright
Interestingly, the EGG hypothesis postulates that the constraining factor is not pelvis size, but rather that neonates consume so much energy that we give birth just before a women's metabolic limits would otherwise be overrun (leading to both maternal and infant death). Based on this, the increased energy demands of our larger brains mean that we have to sacrifice neonatal motor skills or drastically improve the metabolic efficiency of adult women.
https://www.pnas.org/content/109/38/15212 https://www.pnas.org/content/109/38/15212
> In humans, maximum sustained metabolic rate is thought to be 2.0–2.5× basal metabolic rate (BMR).
> By 9 mo, metabolic demands of the fetus threaten to push maternal energy requirements beyond 2.1× BMR. Extending gestation by even one month would likely require metabolic investment beyond the mother’s capacity. Instead, the mother delivers and the neonate’s growth rate slows relative to its fetal growth rate, keeping both the offspring’s and the mother’s energy requirements in check.
- Nition 5y ago> Instead, the mother delivers and the neonate’s growth rate slows relative to its fetal growth rate. Worth noting how massive the growth rate is I think: Even after birth, the baby gains weight faster than it ever will again in its life. In absolute terms! In relative terms it's even more insane. A 12-year-old boy going through puberty will go from 90lb to 100lb over a year, an increase of 10lb or ~10%. The average baby boy will be born at 7.5lb and weigh 20lb at one year old, an increase of 12.5lb or ~270%. Nearly triple the size!
- techrat 5y agoDiminishing returns as the numbers of scale increase. The growth might seem impressive when you do percentages of a very small number, but it's still a very small number overall.
- Nition 5y agoIt's not though, that's my point. Even in absolute terms, weight gain from growth in the first year is still more than any other time in the average person's life.
- agent008t 5y agoPutting on 6kg in a year is not that fast, people do sometimes gain weight faster than that in adulthood.
- FartyMcFarter 5y agoThat's not growth, just fat accumulation which is a much simpler process.
- agent008t 5y agoAnd a child puts on 100% bone and muscle?
- FartyMcFarter 5y agoNo, but I'm not sure what point you're trying to make?
- agent008t 5y agoI was just pointing out that a baby does not gain weight faster than it ever will again in its life, in absolute terms. That's all. Not sure why I got the downvotes and no-true-scotsman arguments in return.
- tk75x 5y agoPlus fat and some water, yes. And furthermore, to go from a 10 pound baby to a 100 pound adult, I will make the claim that a baby has to gain 900% body mass.
- Naracion 5y agoHow are you defining growth? Are you defining it by volume? Ie assuming the body mass density remains the same, how much does the weight increase (which means the body is volumetrically growing)? If not--I am very lightweight right now, and I'm trying to put on body mass by eating more and exercising. While my volume will increase, my main growth is in density. My growth is not in fat, but actual muscle mass. Is this growth? If so, I have gone from 125lb to 140lb in ~2 months, which in absolute terms is obviously more than the baby (my goal is 160lb by the end of the year). A few years ago, I went from ~130lb to 165 lb in three months--blame the free food at FAANG cafes during an internship. But this might be closer to what you were saying earlier--putting on fat. Edit. I guess in the original statement saying that a person will never gain weight at this rate again there should be the explicit assumption that we're talking about natural growth, not growth due to external factors (ie more eating--intentional or not). In that case, that statement would be true.
- MoreenDichele 5y agoThat's obvious bullshit because then any woman giving birth to twins would die. Use your fucking brain please.
- eru 5y ago> Interestingly, the EGG hypothesis postulates that the constraining factor is not pelvis size, but rather that neonates consume so much energy that we give birth just before a women's metabolic limits would otherwise be overrun (leading to both maternal and infant death). Based on this, the increased energy demands of our larger brains mean that we have to sacrifice neonatal motor skills or drastically improve the metabolic efficiency of adult women. This seems weird. Fully breastfed babies require even more calories from the mother. (They are bigger than unborn babies, and they lose more heat.)
- mandelken 5y agoPerhaps it’s more than just calories or energy intake, but as well doing the breathing, immuno responses, digesting, filtering blood etc. for both mother and baby?
- eru 5y agoMaybe. But now we are just speculating.
- TheGeminon 5y ago> Instead, the mother delivers and the neonate’s growth rate slows relative to its fetal growth rate, keeping both the offspring’s and the mother’s energy requirements in check. Growth rate slows after birth, so that would account for some of that. Mother’s also would not need to carry around the weight of the baby, and would be more able to provide for the child.
- watwut 5y ago> constraining factor is not pelvis size I kind of doubt that, because if baby is after term, the risk is supposed to be childbirth itself being too dangerous. And they induce birth if the baby is too big too. Large baby is considered a risk on itself.
- eru 5y agoYes. And for even larger babies, c-sections are common.
- l33t2328 5y ago> consume so much energy that we give birth just before a women's metabolic limits would otherwise be overrun Since babies traditionally breast feed and thus survive solely on the mother’s energy after birth, this explanation doesn’t seem to hold water.
- slickrick216 5y agoBreast feeding is quite hard on women and many women struggle to sustain the child on the breast alone. There’s a history of communal feeding which adds new energy into the equation and also mixed feeding once the child is old enough. I would say it’s probably a continuation at the peak metabolic rate described in the parent post.
- eidelweissflow 5y agoMost women I know who struggled with breastfeeding were due to inability to have the baby correctly latched. Once the baby is latched, women shouldn’t have a problem with supply. Mother spends at most 500 calories extra when breastfeeding which most of the time comes from the weight that’s gained during pregnancy. I myself was able to exclusively breastfeed for 6 months after which we started introducing solids.
- minitoar 5y agoThe truncated gestation is sort of taking that into account, at least according to this paper https://www.pnas.org/content/109/38/15212 https://www.pnas.org/content/109/38/15212