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Why Do Humans Grow Up So Slowly? Blame the Brain

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  • not so fast (Score:5, Insightful)

    by arth1 (260657) on Monday August 25, 2014 @10:17PM (#47753549) Homepage Journal

    That there is an inverse correlation between brain glucose use and body growth does not imply that the brain's use of glucose stymies the growth until later.
    If that were the case, kids who are overfed carbohydrates would be smarter and taller, not fatter and dumber.

    My guess is that slow growth is selected for because children who look like children enjoy special care and protection by adults. Growing to adult size by age 7 might be detrimental to survival.

    • by Anonymous Coward

      What utter fucking rubbish. Getting to the point you can run / fight according to Darwin and thence eventually able to breed is more beneficial. Being a walking target for disease and predators is from a Darwin perspective really bad, growing up fast is what should have been selected.

      • Re:not so fast (Score:5, Interesting)

        by Beck_Neard (3612467) on Monday August 25, 2014 @10:40PM (#47753639)

        Yup, and what makes it even more rubbish is the idea that simply feeding someone more food is enough to change their biochemistry, metabolism, and energy distribution budget towards diverting more energy towards growth and less towards the brain, and that blood glucose levels are determined by dietary carbohydrates.

        But I do enjoy reading the pseudo-intellectual armchair philosophizing that we see so often.

        • Re:not so fast (Score:4, Interesting)

          by Anonymous Coward on Monday August 25, 2014 @11:20PM (#47753797)

          Nobody should be allowed to comment on genetics or evolution until they've read The Selfish Gene. While some small parts of it are arguably out-dated, it really helps orient one's mindset regarding evolutionary genetics. The Selfish Gene will survive as an extant and useful work much longer than Darwin's On the Origin of Species.

          Even many biologists should read it. Too many biologists lack rigor when they hypothesize about evolutionary behavior. The Selfish Gene really lays out not only what has been effectively proven about evolutionary genetics, but provides examples of the complex but elegant mechanisms that _new_ evolutionary processes (e.g. group selection) will probably also look like if they can ever be proven.

          • Re: (Score:3, Informative)

            by Half-pint HAL (718102)
            No-one should be allowed to comment on anything if they have read The Selfish Gene. Dawkins is a dangerous hack and a terrible writer. His pop-science books never educate the state-of-the-art, but instead indocrtrinate his view to the exclusion of all others.
      • Re:not so fast (Score:5, Insightful)

        by ShanghaiBill (739463) on Monday August 25, 2014 @11:24PM (#47753821)

        growing up fast is what should have been selected.

        Not necessarily. The major threat to children in primitive hunter gatherer societies is not predators but hunger. By staying smaller during their formative years, they reduce the amount of calories need to survive. But the selection pressures are different on boys and girls. Girls are generally able to procreate as soon as they reach puberty. But boys need to wait till they are older, and have built up social status. So it makes sense for girls to mature faster, and that is what happens. Look at a group of kids in 4th or 5th grade, and the girls are several inches taller than the boys.

        • Re:not so fast (Score:5, Interesting)

          by Jane Q. Public (1010737) on Tuesday August 26, 2014 @12:20AM (#47754043)

          Not necessarily. The major threat to children in primitive hunter gatherer societies is not predators but hunger. By staying smaller during their formative years, they reduce the amount of calories need to survive.

          This. Also, it takes time to learn the vast amount of information that it takes for a human being to really be smart enough to manipulate its environment... which evolution has obviously selected for. Chimps, for example, often actually outpace human learning for up to 2 years, but then humans continue to learn while the chimp rapidly levels off. Keeping resource use to a low level during this long learning phase is likely a long-term survival trait.

          Also it should be noted that another factor in humans' slow growth is already known: humans can only have babies with brains so big, before birth becomes a very big problem. So a longer period is needed for the human brain to grow to its adult size.

          But the selection pressures are different on boys and girls. Girls are generally able to procreate as soon as they reach puberty. But boys need to wait till they are older, and have built up social status. So it makes sense for girls to mature faster, and that is what happens. Look at a group of kids in 4th or 5th grade, and the girls are several inches taller than the boys.

          It is more accurate to say that boys and girls mature at different rates.

          If you adjust for the probable influence of estrogen mimics in our current environment, human females start to mature sexually before males do, but actually finish their sexual maturation later. You are referring more to social factors than genetic: often males need to be older to establish themselves in order to semi-permanently mate, but that is not the same things as physical sexual maturity needed to procreate.

          • Re:not so fast (Score:4, Interesting)

            by ShanghaiBill (739463) on Tuesday August 26, 2014 @01:20AM (#47754211)

            You are referring more to social factors than genetic

            These are not separate factors. Genes influence social behavior, and social behavior influences which genes are selected. In ALL human societies, men prefer women younger than themselves that are physically attractive, which correlates with fertility. In ALL human societies, women prefer men with high social status, and greater resources. It is unlikely that such universally pervasive preferences are purely "social" rather than genetically innate. Chimpanzee males have no preference for younger females, and when given a choice of mates, will prefer older females. Female chimps do not have the same decline in fertility with age that women have, and more mature and experienced females have a greater chance of successfully rearing offspring.

            • In ALL human societies, men prefer women younger than themselves that are physically attractive, which correlates with fertility. In ALL human societies, women prefer men with high social status, and greater resources.

              As a generalization, this is true enough. So, I will amend my comment. They might be genetic factors, but they aren't overt physical factors. The fact that males tend to be older when they mate is not a matter of sexual maturity, which generally comes long before then.

            • by Prien715 (251944)

              In ALLpatriarchal human societies, men prefer women younger than themselves

              FTFY.

              • by arth1 (260657)

                In ALLpatriarchal human societies, men prefer women younger than themselves

                FTFY.

                Do you have an example of a matriarchal society where men do not overall prefer women younger than themselves? It only takes one counter-example to topple his claim, but you need to provide one.

          • It takes a long time to teach our kids because the system we have for teaching them is horribly inefficient and has been for thousands of years at this point.

            But it carries on not because it's good but instead because it is so indoctrinated and there is no allowance to try anything radically different. If you try even things like "new math" parents freak out because that's not what they learned.

            In fact, the entire schooling process we have, from primary schools to colleges and post-graduate should be reexa

            • It takes a long time to teach our kids because the system we have for teaching them is horribly inefficient and has been for thousands of years at this point.

              Until around 1900, within the working class (which generally included lower middle class back then), education was reading, basic writing and arithmetic. A 12 year old - whether boy or girl - was expected to be a productive member of working class society and was often married (12 for girls and 14 or so for boys). Education beyond that was for the upper class (and upper middle class), especially university level education. Extending education through grade 12 (typically age 17 or 18) for (nominally) all you

          • It's interesting how for most of human history people were partnering up and and having babies around 14/15 yrs old and being grandparents at 30 yrs old and great grandparents at 45 yrs for the few that were lucky enough to live that long.

            Now in our highly specialized society, people are commonly having babies in the mid-30s.

      • by Anonymous Coward
        My son is 5. In dog years he would be running/fighting/making Darwin happy by now. In reality he is very clumsy and unprepared to run/fight. If he were adult-sized by now it would be a major disaster, which would make Darwin very unhappy. On the plus side his intelligence surpassed the smartest of dogs by now, making Darwin very happy. Cut the BS and learn to apply Darwin correctly.
      • Try behaving like a seven-year-old in grown man's body (on the webs doesn't count), see how that works for you. Your older peers will be a bigger threat to you (and you to them) than disesase and predators.

    • by Dutch Gun (899105)

      Growing to adult size by age 7 might be detrimental to survival.

      Really? That hypothesis doesn't make a lot of sense to me. Larger and stronger at a younger age would seem to be a good survival trait, not a bad one. It doesn't seem like the benefits of parental protection instincts for young children would outweigh the negatives of being weaker and smaller, purely on the basis of survival traits. Besides which, I don't think parental protection instincts necessarily disappear when a child reaches adulthood. Talk to my mother if you're not convinced.

      Still, it doesn't

      • Re:not so fast (Score:5, Insightful)

        by Dahamma (304068) on Monday August 25, 2014 @11:13PM (#47753769)

        The evolutionary reality is even simpler that that (though the achievement of those is clearly not). The three main factors are:

        1. be able to reproduce
        2. be able to attract/acquire a mate
        3. be able to care for/protect offspring long enough for them to reach #1

        Clearly if it was just up #1 we would still be living alongside the rest of the primates. #2 can be a fairly complex social interaction - but insects are just as capable of it as humans. #3 is where the whole thing explodes, and is the key to investing all of those resources into the brain (and is what made it more evolutionarily advantageous to extend the time to #1 and #2).

        Though of course in modern human society, social and technological advancement in #3 has so outpaced the first two that they barely seem to matter, and is why we are basically blowing past any "natural" population control. Our brains are letting us find clever ways of surviving and stripping the planet of resources, but unless we figure out a way to expand beyond the planet or stop using its finite resources we'll go through the same collapse seen in any other species going through a population explosion...

      • Larger and stronger at a younger age would seem to be a good survival trait, not a bad one. It doesn't seem like the benefits of parental protection instincts for young children would outweigh the negatives of being weaker and smaller, purely on the basis of survival traits.

        It is axiomatic that, as far as Homo sapiens is concerned, evolution disagrees with you. I believe the reason is you limit what survival traits are to less than what they truly are.

      • by ultranova (717540)

        Larger and stronger at a younger age would seem to be a good survival trait, not a bad one.

        Too inexperienced to make good decisions + too strong to be easily controlled = excellent chances of dying young.

    • by wvmarle (1070040)

      Humans are by far the most intelligent creatures on this world, and thanks to that intelligence can learn a lot.

      Learning primarily takes place in the childhood stage, when parents directly teach their children all they need to know to survive (which until not so long ago, was indeed mostly survival skills: how to grow your own food and so). A long childhood (and with that, long parental care) may for this reason be an advantage: longer time to learn typically makes for a better end result.

      As another poster

    • by jandrese (485)
      This doesn't really follow. Animals that suddenly find themselves an abudance of food don't grow massive, rather they reproduce in greater numbers. If food were always highly available then we might select for large size and big brains over time, but any one person with too much food is not going to suddenly become superman.

      I'm not an expert in this, but my guess is that our energy hungry brains are one of the factors in the relatively long development period for our offspring, but it's not the only fa
    • Well, glucose in the blood is basically a toxin; by overfeeding carbohydrates you're really just taxing the bodies ability to cope with blood sugar (IE, insulin spikes and making you fatter).

      The brain has its own needs, and will take what it needs basically no matter what. Not enough dietary carbohydrates to provide glucose? No problem, some of your muscle (or protein from our diet) is broken down and converted by the liver. Bear in mind the amount of glucose the brain needs per hour, and the fact that

    • by asmkm22 (1902712)

      You assume the body can process as much glucose as you can feed it, which simply isn't true. There's a point where any glucose beyond this threshold is "wasted" for the purpose of positive development, but it does still get processed (into fat). Put another way, the a child's body is a machine that can process 100 units of glucose (arbitrary number) at any given time, 80 of which go to the brain. If you feed it 120 units of glucose during that time, it still only processes 100. Again, 80 goes to the bra

    • by LWATCDR (28044)

      "If that were the case, kids who are overfed carbohydrates would be smarter and taller, not fatter and dumber."
      Every look at an AP class? Fatter does not mean dumber.
      Of course the best combination might be a high carbohydrate and a high activity diet for young people.

    • by operagost (62405)

      If that were the case, kids who are overfed carbohydrates would be smarter and taller, not fatter and dumber.

      Now who's drawing premature conclusions!

      Here's the legendary Slashdot car analogy. Put an 850 CFM Holley on a straight six in a 1960s Pontiac Lemans. Will that turn it into a GTO? No! The human body can't process those calories any faster. They have to be changed into glucose.

      Your implication that being overweight makes kids dumber is so stupid, I wonder what your motivation is.

      • by arth1 (260657)

        The human body can't process those calories any faster. They have to be changed into glucose.

        They already have been changed to glucose before they become fat, which means that the body quite obviously could process them. That they became fat is because there weren't any takers for the glucose.

    • Wow! I can't believe such an ignorant comment was a +5 insightful.

      1. The correlation between obesity and intelligence doesn't seem to have a connection. There is a stronger correlation between obesity and poverty and poverty with low test scores. But that is chaining a bunch of consolations together to come up with a faulty premise. You will need to compare Intelligence of Fat vs Skinny people in similar economic environments.

      2. Obesity is a factor of over use of a nutrients, not a normal healthy usage.

      • by arth1 (260657)

        Wow, I can't believe that someone missed the point so completely!
        The point being that it is unlikely that the brain is stealing the glucose and thus stunting growth like the article supports, because when kids are fat, that means they have metabolized carbs->glucose->fat, and thus have had plenty of glucose. That fat kids' bones don't appear to shoot past normal kids in growth strongly suggest that there are other reasons why kids don't grow physically to adults in half the time.

        I suggest that being

    • Glucose is a strict subset of 'carbohydrates' ... many of which are more fructose (which tastes sweeter without triggering 'no longer hungry' warnings) or sucrose (which is some sort of glucose/fructose combination) than pure glucose (which basically everything in the body uses as fuel).

      Fructose/Sucrose at least seems to lead to "fatter and dumber"; not sure there are any records of what happens when you go with a primarily glucose-based diet.
  • There are other related factors that seem to fit.

    1. Humans also have a lot more to learn than other primates: e.g. language and culture. It makes sense that we evolved with extended childhoods to give us time to learn things.
    2. Neoteny: [wikipedia.org] It's well-known that humans have an innate attraction for the general proportions of children: small, with big eyes and a large head. The longer kids look like kids, the more likely parents and other humans are likely to nuture, protect, and teach them.
  • Gotta milk that free ride as long as possible.

  • by Anonymous Coward

    ... we have been feeding children tons of sugar in US and they don't seam to grow faster.

  • just another effect of climate change. 30 is the new 16, dude.
  • Critical Path (Score:5, Insightful)

    by Livius (318358) on Monday August 25, 2014 @11:41PM (#47753897)

    I would speculate that it's simply that, for humans in their eusocial foraging societies, brain development was the priority and there was no point in reaching sexual maturity and adulthood before the brain had developed and the individual had learned enough to be a full member of the community. The brain and the rest of the body are not competing for glucose, the brain is simply the critical path and the rest of the body has no need to develop faster.

    • by aberglas (991072)

      +1. And obviously so.

  • So that means that tall gangly kids are stupid?
    Disclaimer: I'm short and a genius :)

  • by Michael Woodhams (112247) on Tuesday August 26, 2014 @12:49AM (#47754129) Journal

    For most species, childhood is all risk, no benefit (where benefit = breeding), and so it is to be got through as fast as possible (or at least in time for next breeding season). If glucose shortage was the only reason for doubling the length of our childhood, there would be a huge evolutionary pressure towards kids who could metabolize much more food and reach adulthood in half the time.

    There is an obvious reason why humans have such a long childhood - it is because we have so very much to learn. Little bodies can learn as well as big bodies, and cost less to maintain.

    • For most species, childhood is all risk, no benefit (where benefit = breeding)

      Unless the benefit is that the older generation can live longer, and gain more wisdom, before the younger kids become......teenagers.

      That is, the race would benefit from the greater wisdom of older folks, not individuals.

  • If it is the brain stealing calories that slows development, how come when you feed a child a high-calorie diet he becomes a fat child rather than a young adult?

    How about this: if we took only three years (or less!) to reach adulthood like some animals, you'd have toddler with an adult body. I'm pretty sure it's actually an advantage that our young are easily restrained. It's actually rather common for more intelligent creatures to take longer to mature. Taking longer to prune the excess synaptic connections seems to allow for greater learning at the cost of slower development. In the case of humans, we're also born with an especially undeveloped brain and a squishy skull, for which your mother is probably grateful.

  • Leave it to the Armchair Slashdot Scientist crows dismiss a study and throw in their own contrary opinion.

  • I've always looked young for my age; now I know why. Yes, my brain does use more glucose than most people's, ladies.
  • by Lumpy (12016) on Tuesday August 26, 2014 @08:49AM (#47755673) Homepage

    WE have some wierd fetish with letting kids be kids for as long as possible. Sorry but at 13 you are biologically an adult so you need to have adult responsibilities and adult expectations. these teenagers need to get off their asses and work, build, etc.. Instead we extend this out to age 20 before we expect them to get a job and start being responsible.

    Less than 100 years ago it was not uncommon for marriage at age 16 and that young couple working hard to build their family Average age of a woman getting married was around 21 years of age. Today it is far higher at 26 years of age and insanely uncommon for a 16 year old marriage, Although outside the USA it is far lower. Mexico has a median for women at around 18 years old. Many states in the USA still have the age of consent at age 16. This means that 16 year olds can make decisions as an adult, yet for some reason we think they cant today and are still children.

    Note on marriage ages, some of this is economics, back 100 years ago it was a lot easier to make a living as you made about $35.00 a month working at a foundry or smelter and typically renting a house is $5.00 a month less that 20% of your income was your rent. today most of the young pay 60% of their income as rent and have to split that rent with room mates because they can not even hope to even meet rent with their meager income. So 100 years ago it was easier for young and uneducated to make it in the world with the sweat of their brow.

    • by geekoid (135745)

      "Sorry but at 13 you are biologically an adult s"
      false.

    • by prgrmr (568806)
      So many poor assumptions there. The average life expectancy was a lot less 100 years ago: http://demog.berkeley.edu/~and... [berkeley.edu] Consequently, people got married earlier because they died sooner; this goes back through the beginning of recorded history, and it was really only in post-WWI 20th century that marrying while a teenager became not just not the norm, but socially frowned upon. Also, look at the drops in life expectancy in 1918 and 1943; what you are seeing it the effects of both world wars and the sp
      • by Lumpy (12016)

        Where were the population centers? How many farmers lived in NYC?

        30% were farmers so 70% were not farmers. Thus the Bulk of workers were NOT farmers.

    • WE have some wierd fetish with letting kids be kids for as long as possible. Sorry but at 13 you are biologically an adult so you need to have adult responsibilities and adult expectations. these teenagers need to get off their asses and work, build, etc.. Instead we extend this out to age 20 before we expect them to get a job and start being responsible.

      More like not allow them to get jobs or otherwise have the legal authority to function as adults. There are very few, if any, jobs anyone under 16 is legally allowed (not counting allowance for doing family chores). And not many that 16 and 17 year olds are legally allowed. At age 10, my daughter wanted a real, paying job. And she was actually capable of doing meaningful office work. She also wanted to stay in school. She thought she could handle 2 hours per day of office work along with her studies. She mi

  • by Anonymous Coward

    I learned 2 things from the summary

    1. Humans grow up - really? Don't see much evidence for that these days.
    2. Brain development detracts from maturing - so why are there so many stupid adults?
  • This article is incorrect, as everyone else said. Eating more sugar doesn't make you grow faster so it's wrong. If children grew any faster, their bones and joints wouldn't take the stress. My evidence is kids who grow too fast and have bone and joint problems (duh). Also, if they grew any faster, they were be even less coordinated due to limb length alterations and prone to accidental injury or death.
    • by geekoid (135745)

      " Eating more sugar doesn't make you grow faster so it's wrong. "
      where does the paper say that?

  • by sootman (158191)

    DIFFERENT SPECIES ARE DIFFERENT. Film at 11.

    "Humans are late bloomers when compared with other primates -- they spend almost twice as long in childhood and adolescence as chimps, gibbons, or macaques do."

    And since chimps, gibbons, and macaques are the dominant life forces on the planet -- what with their iPhones and running water and skyscrapers and space programs and whatnot -- it is obvious that this difference in growth is a PROBLEM that must be FIXED.

    WE MUST LEANT THE SECRET OF THE MACAQUE'S POWER!

    Serio

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