Neanderthals, Brain Size, and Maturation: Does Breastfeeding or Fish Eating Have an Impact?

As I mentioned here there is a new article out concerning Neanderthal brain size and life history. In some ways, this is the continuance of a debate started by Trinkaus a number of years ago.


Trinkaus had noticed that the Neanderthal pubic rami seemed to be longer than those found in anatomically modern Homo sapiens and, hence, had a wider birth canal. This led him to suggest that Neanderthal gestation length was a year long (this search gets you most of the relevant papers). This created a bit of controversy and two main theories were proposed to explan the pelvic differences. The first, by Stringer, argued that Neanderthals had their growth and life history accelerated compared to modern humans. The second, put forth by Karen Rosenberg, suggested that the pelvic differences were simply a matter of Neanderthal body size. The debate ended when the analysis of the male Kebara pelvis was published. This analysis indicated that the size of the pelvic inlet in Neanderthals is not different from that of humans. So, the year gestation hypothesis was dead, but the idea that Neanderthals had an accelerated growth schedule which, may or may not have had something to do with size remained.
Which is where the new paper comes in. Neanderthals do have larger brains than anatomically modern humans and there are a number of explanations for it. First, this could be due to rapid growth in utero resulting in larger neonates. Second, there could be a higher growth rate during infancy. Third, there could be a longer period of growth. Each of these possibilities is accompanied by certain costs and benefits, which I will get to below. The point of the de Leon paper was to test some of them.
The authors virtually reconstructed the skull of a Neanderthal neonate found at Mezmaiskaya and estimated the endocranial volume. The estimate puts it in the range of similarly aged recent modern human neonates (so it is not explanation one). The authors also virtually reconstructed the fragmentary Tabun 1 female Neanderthal pelvis and were able to dertermine that, like humans, Neanderthals had rotational birth. They also included some cool stereoscopic pictures in the paper and supplemental material:
View image
Then they reconstructed the skulls of two Neanderthal infants (Dederiyeh 1 and 2) and conclude that the two were at the upper end of the range for modern humans. This suggests that:

Comparison of endocranial growth trajectories from birth to adulthood further indicates that on average, Neanderthal brains expanded at a higher rate and attained larger adult volumes than those of rAMHS … However, Neanderthal and rAMHS trajectories coincide when related to taxon-specific adult mean ECVs …, indicating that both taxa reached adult sizes within the same time period, and along equivalent trajectories. Together, these graphs show that compared with rAMHS, Neanderthals attained their larger adult brains via higher growth rates rather than via an extended growth period. The graphs [not show – afarensis] also show that higher growth rates do not imply faster completion of brain growth.

This is where things get interesting. Back in 2004 Steve Leigh published a paper that examined brain growth and maturation in primates. Building on earlier work by RD Martin, he came to a couple of interesting conclusions. First, brain size and reproductive maturation are not directly associated in primates. Second, there seems to be two alternate life history strategies that are followed by primates. In the first strategy, females mature late, are larger, and produce larger brained infants. As Leigh explains:

Late maternal maturation may confer the ability to the meet metabolic costs of very early (fetal or infantile) brain growth through larger size and other sequelae of later maturation, such as better social skills, higher rank, and greater foraging proficiency. The advantages of larger maternal size in terms of metabolism may contribute to large brain size. In addition, an early maternal investment in brain growth may result in offspring that are precocious in terms of cognition, locomotion, foraging, and social behavior.

In the second strategy, females mature early and infant’s brains grow for a longer period postnatally. The advantages of this are:

Early maturation confers major demographic advantages to these species by enabling significantly increased intrinsic rates of increase (mediated by early reproductive maturation) … Thus, these species may realize the benefits of early maturation by ”distributing” the costs of offspring brain growth to the offspring itself or to other group members. Furthermore, shifting costs to offspring may enable shorter interbirth intervals in these species.

This makes me think that de Leon et al were a little confused in their claims to National Geographic (claims which do not appear in the PNAS paper). To refresh your memory:

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.

As Mike Shupp pointed out in comments to the previous post, breastfeeding can restrict fertility – something we also know from studies of hunter-gatherers so at least that portion of the above quote is accurate. My point here is that there seems to be to conflicting processes at work between high rate of growth, birth spacing and breastfeeding. From reading both Leigh and de Leon et al at least part of the problem is that Neanderthal growth does not seem to fit Leigh’s model. In Neanderthals there is a high rate of growth for the same amount of time as in anatomically modern humans. At any rate, breastfeeding confers additional benefits. According to this recent Science Daily article research indicates that breastfeeding is linked to better physical and cognitive development. Something that would apply to both Neanderthals and moderns. An interesting side note in the Science Daily article is that eating fish provides the same type of benefits as breastfeeding. I mention this because of the recent news about giant clams indicates that the amount of marine exploitation by both neanderthals and early modern humans may have been underestimated.
There is some other interesting stuff in the de Leon paper, but that is for a future post…
Literature Cited
de Leon et al 2008 Neanderthal brain size at birth provides insights into the evolution of human life history, PNAS 105(37):13764-13768
doi:10.1073/pnas.0803917105
Leigh (2004) Brain Growth, Life History, and Cognition in Primate and
Human Evolution, American Journal of Primatology 62:139-164

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8 Responses

  1. An interesting side note in the Science Daily article is that eating fish provides the same type of benefits as breastfeeding.
    A few years ago I read a pop-sci book about Neanderthals which asserted that in Middle Palaeolithic French cave deposits the remains of salmon were commonly associated with bears but never with Neanderthals. The author raised the question of whether they were so specialised for hunting large mammals that they couldn’t conceptualise eating the fish, and whether this might have contributed to their being out-competed eventually by us.
    But if other Neanderthal populations were happily eating clams, that seems a bit unlikely; so was the French evidence misinterpreted in the 1990s, or was there some other reason they would ignore a perfectly good source of food like that? If fish was developmentally important to them, I assume the former must be the case, but it seems an odd thing to overlook.

  2. Thank you for another interesting article about Neanderthals. Probably like many people, I find Neanderthals particularly interesting because they came so close to still being around today, like us and yet visibly different.
    As for the fish-eating, I can’t imagine an intelligent creature ignoring an easily obtained food source unless more desireable food was always abundant and as easy to get. Of course, shellfish are easier to catch than most fish, so if they lacked hooks or nets, clams (giant or otherwise), mussels etc. would be the seafood of choice.
    I live in an area where it is common for anyone who wants them to go out on the sand or mud flats at low tide and gather clams and mussels. They are abundant. Though we don’t usually eat them, there are a lot of other molluscs available in the same places; razor clams, surf clams, whelks, periwinkles and so on, plus crabs are easily collected by hand (if you’re careful). I can’t see any hungry human ignoring these critters.

  3. To answer the questions of both commenters, it seems that maybe Neandertals caught and ate fish.  In one cave, Grotte XVI in SW France workers several years ago found fish bones.  They also found what they interpreted to be evidence of them drying meat(maybe Neandertal jerky or the like).  There are a lot of little streams running through the Vezere valley and a lot of little valleys where fish swim in the streams. And it probably wouldn’t have been all that “high tech” or impossible for Neandertals to build simple fish weirs or traps to catch them. The association isn’t certain, however, but to me it’s quite suggestive. There have also been papers written on it, and if I can ever get the Family Computer Guru over here, I can get them traqnsferred to my new computer and then I can send them to anyone who is interested.
    Anne G

  4. To be clear, the extended gestation hypothesis is dead in the eyes of the field as a whole as well as the originator of the hypothesis (Trinkaus). In any case, it is historically relevant.

  5. In Trinkaus’s defense … the possibility of extended gestation of Neanderthal neonates was certainly one that merited consideration. If, as some folks claim, Neanderthals were a whole ‘nother species than REAL Homo sapiens, then the notion that it took 9 months of pregnancy to create a Neanderthal child, just as with REAL PEOPLE, was open to question. Establishing that the Neanderthal gestation period was longer (or shorter) than with Homo sapiens would have opened up any number of inquiries about how Neanderthal lives differed from modern humans. And the tools and techniques that had to be developed for establishing different gestation periods would have been put to use in many other areas of anthropology and archaeology.
    A mistaken idea, very likely. But a really clever one Respect Must Be Paid.
    -ms

  6. With that out of the way….
    There’s this thing called the Hydrological Cycle. The sun shines on the waters. Sea waters mostly, since oceans hold 3/4 or so of all the earth’s water. Water evaporates, and joins clouds in the sky, which eventually precipitate in the form of rain or snow or hail upon the earth. Including the solid, dirt- and rock-covered earth on which you and I and many other animals exist. Some falls into rivers and lakes and marshes and eventually flows back into the seas; some falls on soil and gets swallowed up by grass and other plants. Etc. Ultimately, the point is, this snow and rain water is ingested by animals and plants.
    And finally, in the ultimate ultimate, even the water in human and animal and plant bodies returns to the seas.
    The interesting thing is that all molecules of water are not the same. Some include deuterium atoms rather than hydrogen, but we can ignore this — deuterium is fairly rare. Oxygen comes in a variety of isotopes. 99.762% of the oxygen atoms encountered on the earth are of the O-16 variety, with 8 neutrons and 8 protons in the core. 0.037% are O-17, with 9 neutrons. 0.204% are O-18, with 10 neutrons and 8 protons. (There are other isotopes, but according to Wikopedia, the longest lived is O-15, which has a 2 minute half life. Essentially, these three are the only isotopes which matter over long periods.)
    It takes energy to boost a molecule of H2O (18 proton masses, roughly, for O-16) from sea water to atmosphere. It takes more energy to boost a molecule of water with a heavier isotope of oxygen into the air. So at all times we expect to find higher ratios of O-17 and O-18 than those I cited in sea water, and lower ratios in say rain water or snow. (An interesting complication is that in really warm periods, such as the present, more of these heavy oxygen isotopes will enter the atmosphere than during really cold periods — ice ages. So we can measure the ratios of 0-18 to 0-16 over the eras, by analysing core samples drawn from glaciers on Greenland or from the Antarctic, and establish dates for ice ages and other climatic changes.)
    Ignoring the interesting complications… the idea is that animals living in the sea ought to have more O-17 and O-18 in their flesh (proportionally speaking) than animals living on dry land. And ANIMALS ON DRY LAND THAT CONSUME MARITIME ANIMALS AND PLANTS SHOULD HAVE HIGHER O-18/O-16 RATIOS IN THEIR FLESH AND BONES THAN ANIMALS THAT CONSUME ONLY TERRESTRIAL FOOD. In principle, at least, we ought to be able to compare these oxygen isotope ratios as measured in Neanderthal bones with say cave bears or anatomically modern Homo sapiens or prehistoric porpoises, and make some judgement about whether or not Neanderthals ate sushi.
    The difficulty is that these measurements are not especially easy to make (they generally involve destruction of several milligrams of skeletal material, which rouses all sorts of … energetic obstruction … from most museum curators). The data plots have large error bars (since we’re vaporizing miligrams of bone and cartilage, rather than the POUNDS of material it would take to get nice precise figures.)
    And also, there aren’t a whole lot of seaside-living dead Neanderthals to question. Maybe there never were, but beond that, sea levels during the period in which Neanderthals flourished (say 120 to 30 KYA) were 10-50 meters below where they are today. The habitats of most coastal Neanderthals (if there were any) are now under water, and likely unrecognizable.
    OTOH, Neanderthal remains have been found at Gibralter. More might be found, and Gibralter has probably been an island or prometary for 100,000 years or more. So Neanderthal bones from there might be compared with human bones from inland locations elsewhere to see if marine resources were a significant portion of Neandetal diet.
    In principle. Let’s admit, I’m waving my hands so wildly here that I’m about to take flight myself…

  7. Well, fish has been called “brain food.” LOL

  8. Begone troll.

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