Why, you ask, is Kirstie writing about the
differences in brain development after birth between Neanderthals and modern humans? Well, it follows on from
this report on NPR which makes the case for slower (when compared to Neanderthals) development being beneficial to humans. I though instead of just reading NPR and taking their word for it I'd actually read the paper itself.
And let me tell you, there are a bunch of words I didn't know!! Now I know how everyone else feels when I use all the MRI and psychology jargon!
Did you know that "in phylogenetics, a trait is
derived if it is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors,
i.e. traits that have undergone secondary loss. Here the
lack of a structure is a derived trait." (stolen from
Wikipedia).
That definition allowed me to understand the conclusion that "the modern human pattern of brain development is derived compared to Neanderthals." Basically the authors found that human brain development goes through a globularization phase (becoming more globe-like aka spherical - another word I had to look up!) that is not seen in Neanderthal development.
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Neanderthal and modern human brains grow differently.
(A) For the virtual reconstruction of the Neanderthal neonate Le Moustier 2, CT scans of individual fragments were assembled on the computer. Fragments that were mirror-imaged to the other side are plotted in a darker shade. The gray surface represents estimated missing data. At birth, Neanderthals and modern humans have very similar endocranial volumes and shapes (red: Le Moustier 2; blue: modern human). (B) A principal component analysis of endocranial shape changes from birth (age group 1) to adulthood (age group 6). The convex hulls for modern humans (blue) are based on dental age groups. The fossil convex hull (red) is based on the Neanderthal adults only. The average developmental trajectory is plotted as a solid line. Endocranial mean shapes visualize the shape change during the modern human globularization phase between age groups 1 and 2. All fossils were reconstructed multiple times; each distribution of reconstructions falls within the respective semitransparent disks |
This figure is pretty cool because it shows how a neonatal human brain looks very similar to a neonatal Neanderthal brain (top part) and then shows how the developmental trajectories differ. The method's a little hard to explain but the authors do a good job in their
supplementary materials if you want to check it out!! I also think that the figure below (from a
different paper) is a littler clearer on what's going on with the globularization: in this paper they compare humans to chimpanzees and see that the chimpanzees look very different to humans and like Neanderthals, don't show the dramatic postnatal globularization phase.
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| Endocranial shape space. (a) PC 1 versus PC 2, (b) PC 1 versus PC 3. Humans are shown in blue and chimpanzees in green. Age groups are coded by numbers 1–6. Semi-transparent convex hulls indicate the variation of age groups. Mean shapes of each age group are connected with a solid line to the subsequent age group. Thin lines are shown between bootstrapped age group means to demonstrate the low uncertainty of the mean trajectory caused by the cross-sectional samples. One fetal chimpanzee specimen (“f”) indicates that prenatal shape change in chimpanzees does not correspond to perinatal human shape change (from age group 1 to age group 2). Shape change along the PCs is visualized as mean shapes plus/minus 2 standard deviations (±2 SDVs) from the sample mean. |
So, to get back to why on earth I'd care about this, I'll quote part of the NPR interview with the prinicipal investigator on this project: "We take a long time to grow up and become adults, and this has a lot of implications in terms of social organization, time for education, maturation of the brain, even psychology somehow."
I've suggested a conclusion from my data on white matter development that the slower a brain takes to mature the more cognitively able the child. Which is pretty crazy: you'd probably think that a brain which matures really quickly would get to being as smart as an adult faster. But that isn't what my results are showing and the longitudinal data will help to explain it further: is it that all smart people have less coherent white matter (which goes against some adult studies) or is it just that these clever children are taking longer to reach maturity (from a brain point of view)? Maybe they're "ripening on the vine" like those delicious tomatoes at the farmers market ;)
Gunz P, Neubauer S, Maureille B, Hublin JJ.
Curr Biol. 2010 Nov 9;20(21):R921-2
PMID: 21056830
