Neanderthals, Brain Size, and Maturation

There is a new paper coming out in PNAS called Neanderthal brain size at birth provides insights into the evolution of human life history (wouldn’t you know it is not open access, so if anybody out there has access can you mail me a copy) that argues Neanderthals grew quickly but reached maturity later. The high growth rates placed greater demands on Neanderthal women and ultimately increased interbirth intervals. Consequently, they were out competed by anatomically modern Homo sapiens who had a shorter birth intervals, etc.


National Geographic has a write up of the paper, which is interesting but seems to focus on the more, um, extravagant claims of the paper:

Young Neanderthals’ rapid growth required lots of energy, experts say.
“Neanderthals must have had a rich diet in protein and fat for children to fuel rapid growth in [their] brains,” said Holly Smith of the Museum of Anthropology at the University of Michigan, who was not involved in the research.
Mothers also likely had to consume vast quantities of calories to produce enough breast milk.
This energy-intensive child rearing may have caused “somewhat longer interbirth intervals, or somewhat older mothers,” study co-author Zollikofer said.

According to National Geographic the researchers reconstructed the skulls of two neanderthal infants (one from Mezmaiskaya Cave in Russia – a find new to me – and the other from Dederiyeh Cave in Syria) along with reconstructing a female Neanderthal pelvis found at Tabun.
Christopher Dean is skeptical:

“I think they might be trying to push their data too far,” he said.

H’mm, anybody remember Trinkaus and his claim that Neanderthal gestation length was a year…

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19 Responses

  1. I’m handicapped by not having access to the full article. However….
    (1) Neanderthal infants and modern Homo sapiens sapiens had roughly the same brain size at birth. Makes sense — Neanderthal and Hss females are about the same size, face similar difficulties giving birth, etc. etc. Really big brained infants would have killed an awful lot of Neanderthal monthers, so we might reasonably expect that natural selection would have eliminated such a trait.
    (2) The notion that follows is that Neanderthal brains being larger than those of Hss (roughly 1450 cc to 1300 cc, if memory serves) must have grown over a longer period than in Hss, and that this would have required more maternal nuturing on the part of Neanderthals, thus reducing the number of opportunities that Neanderthal women had for becoming pregnant.
    (3) Um well…. Neanderthal women (and Hss women of 40,000 years ago) didn’t live in a welfare state. Odds are most of them were dead — of old age — by 25 or so. Odds are, that with a limited diet and the very real stresses of raising children, the number of opportunities paleolithic women had for becoming pregnant was always pretty damned small. We’re talking about dozens of opportunities here — not the 200-400 opportunities open to healthy modern women.
    (4) Bearing this in mind, the single most important factor in restricting fertility in healthy mothers — as observed today — is the length at which children are nursed. A woman who does not nurse her child may return to full fertility within a year of giving birth; contrawise, a woman can postpone full fertility by nursing a child for up to four or five years, or even longer. (I lack at hand references, but accounts of the San Bushmen and perhaps some South American peoples ought to establish the point).
    (5) We don’t know how long Neanderthal women chose to nurse their children. We don’t know if Neanderthal women from Southern Spain to central Siberia, from 120 kya to 35 kya, spaced their children in the same fashion. We don’t know if Neanderthal and modern human women followed similar stategies for lactation.
    (6) My bet: the length of lactation is the greatest factor in determining female fertility, and high female fertility was probably of great importance to the Neanderthals. The length of lactation is under individual/cultural control; it is not a natural constant. The number of children a typical Neanderthal mother might have expected was small in almost all cases. This suggests Neanderthal females did NOT employ a fertility-reducing strategy of long lactation of infants; it suggests they probably did not nuture their large brained infants in any fashion that differered from the behavior of contemporary Homo apiense sapiens.
    (7) Interesting topic. I’d love to see the full article. But my initial take is negative, for the reasons I’ve given.

  2. Sent the article.
    Looks interesting!

  3. Thanks!

  4. If I might correct a few minor details in the otherwise excellent summary above, while Neanderthal and H. sapiens infants had roughly similar head sizes at birth, Neanderthal infants had wider shoulders. That is the widest point that has to come through the pelvis, actually. But, from the 1/2 pelvis discovered at Tabun, we know that the Neanderthal pelvis was also a bit wider, so that should not have posed any special difficulty.
    Studies of the teeth of Neanderthal infants and children have not suggested early weaning, such as at the extremely young age of one to two years. Nor do ethnographic studies of foraging populations, including the San (also pygmies, the Dani, and other modern humans). An average of 4 years is more like it which, interestingly enough, is about what the modern great apes average (bonobos, chimps, gorillas, and orangutans in that order).
    As an additional note, there is evidence from a different article that the distinction between the two types of humans may have been cultural rather than physical. That is, there is no evidence that female Neanderthals had any different social role than male Neanderthals. There is some evidence fairly early in the Paleolithic for a sexual division of labor (although indirect) among H. sapiens. If this separation occured then, into the stereotyped pattern of men hunting large animals and women gathering plant foods and firewood, perhaps also small animals and fish, while caring for little children, this may be what gave H. sapiens the edge. Reproductive success per se would not have to be invoked. Fewer women would be at risk from being gored or chewed by wild critters. Eventually, the same was true for men, too, as H. sapiens developed the spear thrower, something Neanderthals never did. See Bruce Bower, Dec. 2, 2006. “Stone Age Role Revolution: Modern humans may have divided labor to conquer” in Science News 170 (23):358.

  5. Weighing in here,it’s fairly obvious that Neandertals had a rather small, scattered population. This is almost always disadvantageous if environments fluctuate a lot, as they apparently did in the Pleistocene. OTOH, it was probably “advantageous” to live that way when resources were scarce and scattered; it didn’t affect the local environment, temporally, quite as much as a concentrated population might. Another possible factor to consider is, that organisms living in warmer ones, and Neandertals seem to have followed this pattern.
    So for Neandertals, it quit3e possibly “paid” to space their children(maybe by nursing them for a fairly extended period, though this doesn’t always work), but it also “paid” them, as a population, to be at least *reasonably* fertile, just to keep an adequate population size going. In this, they were most likely at a disadvantage to “modern” humans, who *started out* with higher populations(and could keep on coming when some local Neandertal population died out), but they were very well adapted in this way, to the kind of environments they mostly lived in. This does not mean they couldn’t adapt to change; they did, and the archaeological record for later Neandertals seems to suggest this. Nor does it mean that their abilities were unequal to those of “moderns”. It just means that they were a rather small population living in a crummy climate, which didn’t help them very much, though they did very well, for some 200 kyr, with the tools they had, in the environment they lived in.
    Anne G

  6. Diana Gainer –
    Nice point about infant shoulders and female pelvis width. I stand corrected and abashed … one shoulder hunched higher than the other!
    As for weaning dates for Neanderthals, 1-2 years strikes me as reasonable. Kids need SOME teeth before they can be weaned, I’d think. Though perhaps Neanderthals pre-chewed meat to break it into smaller, more easily digestible food for infants. My basic thought was that Neanderthals simply couldn’t afford to nurse children for four years or so, but possibly you can correct me again….
    As for the notion that male and female Neanderthals practiced the same foraging/feeding habits… let me reserve judgement again. It wasn’t that long ago that Lewis Binford was arguing that female Neanderthals kept close to the caves of Southern France with their kids while male Neanderthals spent 90 % of their lives hunting big game on the German plains, only rarely returning to the “home base” where they dealt with the females like “visiting firemen” and fixed and ate their meals in lonely masculine seclusion. Maybe the actual archaeological evidence for the rituals of Neanderthal home life is just a bit thin…. In particular, we need to find more female Neanderthal skeletons, and see if they’re as badly banged up by accidents as male Neanderthals tended to be.
    Anne Gilbert —
    Hello again. Like meeting an old friend to see one of your posts.
    My thought is, it’s not so much that Neanderthals happened to be fewer than anatomically modern Homo Sapiens — though this may well be true. But person for person, Neanderthals probably had higher metabolic requirements than AMHS. Bigger bodies despite their shorter stature, more active and riskier hunting practices, lack of sewn clothing, etc. They needed to eat more, they probably got a bit colder at night, etc. So maybe a ten mile by ten mile hunting/foraging range kept four Neanderthals alive, while Cro Magnons could have fitted in six.
    So what happens to a Cro Magnon family of six, if one of the two or three male hunters is disabled? Well, belt tightening (figuratively, of course). But the odds are most of the family survives the next few seasons, even through winter. What happens to a Neanderthal family of four, if the single male hunter is disabled? Disaster, and perhaps even the death of all.
    We don’t need to assume Neanderthals were less intelligent than modern humans, to explain their dying out, or that they had an inferior culture. Simple ecological constraints provide an adequate answer.
    Sad in a way. I’ve never really regretted that Homo erectus didn’t survive to the present day, or the Australopithicines, or Homo antecessor, or Heidelberg Man, or even the Flores Island hobbits. But it’s always struck me that our true cousins, the Neanderthals, got a raw deal from Mother Nature, and that we’re all the poorer for it.

  7. It seems to me that the commenters here are leaving out the issue of warfare. If Sapiens were able to breed even just a little faster than Neandertals, that would give them an advantage in war. If two tribes of equal technology fight, the more numerous one will win. If so, the extinction of the Neandertals would’ve been essentially a matter of attrition. They simply wouldn’t’ve been able to replenish their war losses as quickly as Sapiens, and therefore were gradually attrited into extinction. It would only take a minor difference in birth rates for that to work, given a timescale of several thousand years.

  8. There doesn’t seem to be any direct evidence, in terms of trauma or what not, for the kind of scenario you are presenting. IMHO, the debate goes back to Trinkaus and his suggestion that Neanderthal gestation was one year. I’ll have more to say on that tonight…

  9. Mike Shupp:
    I find myself agreeing with your analysis on most points, but I think 1-2 years is a lowball estimate of how long Neanderthals probably nursed. What (admittedly scant) evidence I’ve seen suggests that they probably nursed about the same or slightly longer than anatomically modern humans in natural fertility settings. Tooth wear from solid food, for instance, seems to first appear around age five rather than four.

  10. Erin:
    Well, phooey! I hate it when a Beautiful Hypothesis is ruined by Ugly Fact!
    I hates it! I hates it! I hates it to pieces!
    Thanks for the correction, I guess. I’ll have to do some rethinking now. Fortunately, not much Wonderful and Grand depends on my correct understanding of these issues …
    -ms

  11. Paper Hand:
    Lawrence Keeley, as discussed here by africanus, has pretty well made the case that War (or at least, large scale deadly violence) has shaped human prehistory, and I’m certainly not going to argue against him for the period covering the last 20,000 years or so.
    Earlier than that, however … we might assume that modern Homo sapiens and Neanderthals were in contact from roughly 40,000 BC to 30,000 BC (give or take the odd five millenia) across the face of pre-glacial Europe. Surely there was SOME contact, and some of it might have been violent. But at the same time, populations of both species were extremely low, and they were spread over a broad area (John Hawkes, at http://johnhawks.net/weblog/reviews/neandertals/neandertal_dna/how-many-samples-mtdna-2008.html cites an estimate of 5000 persons of either species in the region from southern Spain to the Urals for the Middle Paleolithic and Upper Paleolithic time periods). And these were Hunter-Gatherers with all that that entails — they didn’t have populations large enough to conduct continent-wide war, and they didn’t have a social structure advanced enough to coordinate any sort of war.
    I seriously doubt that either group had any sort of Racial Consciousness which would convince them that they ought to wipe out the other group. In fact, my sneaking suspicion is that most bands of AHMS and Neanderthals met and interacted without distinguishing which population group was which — that tiny little Neanderthal bands looked as “human” to tiny little AMHS bands as other AMHS bands and vice versa. [It’s taken LOTS of progress to make modern Homo sapiens so conscious of racial differences, and so aware of how differences MUST BE PUNISHED. These people were disgustingly primative.]
    So I’m sort of skeptical of the idea that modern humans wiped out other not-quite-human populations through any process that looked that “war.” Simply starving out other populations quite innocently by outhunting or out-surviving them would have had the same effect.
    If that fails to convince you … reflect that bows and arrows didn’t exist 30,000 years ago. Neither did devices for boosting throwing spears. Homo saps saps and Homo saps neanderthalis would have slugged it out with rocks and hand-carried spears in countless backyard-sized melees. Are you quite convinced modern humans — weaklings compared to Neanderthals — would have won most of those battles?
    Cheers.
    -ms

  12. Aferensis —
    Really sorry to chew up so much of your bandwidth, but … Well, it’s interesting.
    -ms

  13. You all aren’t leaving me much to write about 🙂

  14. Mike – not a problem, talk away…

  15. All the comments so far are, well, very interesting.  I sort of agree with Mike Shupp’s, simply because, among other things, organisms living in colder and more erratic climates tend to have fewer young than organisms living in warmer climates where there’s a more dependable food supply. And, like Neandertals, probably have somewhat higher metabolic requirements, just to stay alive.  This is a reasonable analysis of the situation.  I’m not sure that grand claims about one group wiping the other out through “war” are terribly valid; this idea is predicated on the notion that humans are “naturally violent” or something similar.  There is, in fact, a “human nature”, but it seems to be comprised of both violence and altruism, and everything in between.  So again, I suspect that Mike Shupp is right(whether or not there were ever any “wars” in the Pleistocene), and Neandertals and “moderns” recognized each other as “human” in essential ways, whatever they actually thought thought of each other — and that doubtless varied from time to time and place to place as well.  This may be one reason there is a Lapedo child, and it’s also the premise driving my Great Medieval Science Fiction Masterpiece With Neandertals.  But that’s another story. Anyway, the fact is, we don’t really know what caused their demise. Too bad we don’t have them around any more. They might have some very interesting stories to tell.
    Anne G

  16. Well, my thought wasn’t that there was any kind of co-ordinated genocide against Neanderthals, by any means. My thought was simply that there would’ve been conflict and warfare between AMH tribes, between Neanderthal tribes, and also between AMH tribes and Neanderthal tribes. In those cases, Neanderthal tribes might’ve taken longer to recover from deaths, which would’ve lead to a slow dying-out.
    Of course, that wouldn’t’ve been the SOLE cause, simply one of many factors.

  17. Let me back up a bit here and point out that nursing babies for only a year or two is relatively recent. It comes in with agriculture — about 10 thousand years ago. Before that, with foraging economies, women had no choice but to nurse for 4 to 5 years, as the studies of teeth demonstrate. So, H. sapiens was not outbreeding H. neanderthalensis at first. Another little point to recall here is that, at first, Neanderthals were BETTER adapted to northern climates because they were pale-skinned. H. sapiens came from Africa, if you will recall, and from there went to the Near East or southern Arabia, and from there to Central Asia. By the time they got to Europe, they may or may not have become pale. We don’t know. If not, they may have had some trouble health-wise as we know the early H. erectus did. I don’t have the reference at hand, but fossils of a young H. erectus jave been found in Anatolia with a type of tuberculosis found primarily among dark-skinned monderns who move to northern areas. It’s due to not enough vitamin D, you see, which compromises the immune system. If it happened to H. erectus and still happens today, presumably it happened in between.
    So I’m still inclined to think it was culture that made the difference for H. sapiens — whether clothing (as evidenced by bone needles) or shelter (perhaps Neanderthal “tents” didn’t have tops?) or fire use (Neanderthals apparently did not use it as much as H. sapiens) or sexual role division (Neanderthal females have bones that are every bit as massive as those of males; in fact little children only 8 years old have huge bones!). Or maybe it was as simple as language. Neanderthals may only have used speech that was comparable to the semantic relations stage of language acquisition (2-word stage in which children do not yet use language-specific syntax but express relationships such as Agent-Object, Modifier-Modified, Action-Object, etc.). There are many possibilities, but I really think culture was the distinction, not the physical differences.

  18. Pardon me for being so wordy, but I thought I ought to mention warfare also. At the band level of organization, which is what foragers have, not as complex as the tribe, mind you, there is no warfare per se. There is interpersonal violence, of course. But with the need to find marriage partners outside the band — in which each person is normally related by blood to everyone else, or else by marriage already — more often there is greater interest in peaceful relations at this economic level. It is at the tribal level and at the horticultural economic level or the pastoral economic level that endemic warfare is most commonly found for the first time. This is due to strong competition for resources, when it occurs. At the band level, it is more common for people to simply move, that is, to relocate when competition or conflict occurs. And this appears to be what was going on in the Paleolithic when H. sapiens appeared in territories where H. neanderthalensis had formerly been living without competition (and where H. erectus had been living without competition). The previous inhabitants of these areas simply moved outward to uninhabited or less densely populated areas.
    Also, I should point out that Trinkaus himself, while he originally proposed a gestation of 12 months for Neanderthals, later decided there was no evidence for this and it is now generally accepted that 9 months was standard for all Homo species. Again, I do not have the specific reference at hand, as this has been several years back.
    Another point is that while generally less is known about H. erectus in the Far East than about Neanderthals in Europe, the humans in the east had progressed to approximately the same level, although their technological specifics differed. Northern China eventually acquired Acheulian-style bifaces, for example, perhaps from Neanderthals in eastern Siberia interfacing with the northernmost of the Homo erectus folk (Michael Shunkov, 2005. “The Characteristics of the Altai [Russia] Middle Paleolithic in Regional Context” in Indo-Pacific Prehistory Association Bulletin 25, Taipei Papers, Vol. 3:69-77). Hand-axes have been found at Gongwangling in Shaanxi province dating to the Middle Pleistocene. They have also been found at about the same time period at Kehe in Shanxi (not the same province). A cleaver was discovered at Zhoukoudian 13 near Beijing also. So, although the Levallois technique was not used in China or elsewhere in the Far East, fairly advanced types of tool manufacture were utilized by late H. erectus there. In Indonesia, at Sambungmacan and Ngandong, skulls dating to perhaps as late as 40 thousand years ago were as large as some modern ones (1200 cc and more), although clearly H. erectus, also. So these archaic humans were also probably as intelligent as Neanderthals and moderns, though more isolated. They may well have been making most of their tools from bamboo, which has mostly not survived (see Tattersall and Schwartz 2001).

  19. One more tidbit, which, as a nurse, I’ve witnessed in watching babies being born. They don’t come out as the diagram shows in the article on the Neanderthal brain size at birth. The baby’s head doesn’t come straight down, facing to the side, although it might seem logical. Instead, the head deforms somewhat as it passes through the birth canal, with the crown of the head acting something like a battering ram, pushing downward through the process of labor, as the mouth of the cervix gradually widens (ouch!). The baby’s head gradually takes on a shape rather like a peanut, elongated, not rounded as shown in the pictures, otherwise it gets stuck (in which case the doctor either has to reach it with his hand (double ouch!) or forceps (triple ouch!) and unstick it with a strong yank (quadruple ouch!).
    If the baby is facing the wrong way, the poor little tyke’s face becomes the battering ram and if it survives this mistreatment and doesn’t get stuck, the face will probably be quite swollen and painful at birth (as was my number 2) and Mom has terrible “back labor” in the process. If the baby’s feet are downward, there is no proper battering ram at all and baby is likely to strangle on the way out. In the bad old days, this often happened. The baby’s bottom or feet coming first very often meant that Mom had a very hard time of it, indeed, and she or baby or both did not make it.
    So it’s not just a matter of baby turning its little head so that one shoulder and then the other comes (what “rotational” birth is partly about), or turning so that the big head will make it through the tight squeeze of those unmoving pelvis bones — the whole head deforms, the pelvic bones also do move a bit (there’s a piece in the middle that half-dissolves very late in pregnancy so as to form a semi-joint), and labor itself may take between 4 and 24 hours, depending on whether it’s the first or the 14th child. With each successive birth, it tends to go more quickly. But the pain is no easier with repetition and positioning problems are just as likely with each one. In fact, as the womb becomes more stretched out, with repeated child-bearing, the child can more easily get into very odd positions — like sideways. That would never occur with a primipera (first timer).
    But saying a modern woman has over 100 chances of getting pregnant is still a stretch. 20 is still an exaggeration. In my genealogical research, looking at records of women who had no access to birth control of any kind, in a day when it was considered bad form to nurse over 2 years for any reason (as Granny put it, if the baby could ask for it, baby was too old for it), two years between births was the average, and very few had more than 12. Even then, most did not see more than 10 grow up — and that was in the 19th century! It cannot have been anywhere near that good in the Paleolithic.

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