DrTdaxp

For most of hominid evolution, newer meant bigger. Newer species had bigger brains than older ones, and later members of a species had bigger brains than earlier members (Rightmire, 2001). And for generations researchers have puzzled over the Neanderthal’s quick demise (Hrdlicka, 1927), especially puzzling in light of apparently developed communicative abilities (Arsenburg, Tilier, Vandermeersch, Duday, Schepartz, & Rak, 1989) and the fact that some Neanderthals may be more closely related to humans than other members of their own species (Paablo, 2003). Yet fifteen thousand years ago the human brain began shrinking (Ridley, 2003). Though perhaps the decline is older than that – Neanderthals may have had larger brains than we do (Klein, 2003).

I do not know what this means. We know that “within primates the relative size of the neocortex is significantly correlated with group size” (Bjorklund & Pellegrini, 2002, 102). We like to think that our brains make us special, though apparently the seemingly-simpleminded purposes are large-brained as well (92). Additionally, considering that “brain size is correlated (negatively) with litter size” and that larger-brained “animals tend to have smaller litters and to give birth to infants at longer intervals” (97), this implies that modern humans are more expendable and less precious than our ancestors of fifteen thousand years ago, or even the ancient Neanderthals! Clearly humans are evolving, but how and why?

Bjorklund & Pellegrini give hints of an answer. They write that “brain growth continues into adolescence” (100) and (quoting Bjorklund & Green, 1992) “lessons learned as a young child will not interfere with the qualitatively different tasks required of an adult” (108). These facts must be synthesized with a view of evolution that leads to us, an agricultural species, to having smaller brains and the Neanderthals, another recent non-agricultural species, to have larger ones. The most likely explanation to me is that human agriculture allowed even young children to become productive workers, as there are a myriad of tasks on a farm requiring little muscluar or intellectual strength (such as feeding chickens, etc.), and that human society allowed the formation of an “anatomically distinct worker caste” (Wilson & Holldobler, 2005, 13368). In other words, children are something like worker bees, who learn lessons appropriate for worker bees, but upon adolescence are able to be reprogrammed to be functioning adults. Thus the claim that “childhood and adolescence, are not observed in any other species” (Bjorklund & Pellegrini, 2002, 99) misses the mark – asexual workers exist in many species, and adolescence is a form of functional cocooning. And this is why (quoting Mason, 1968) “Developmental stages are less sharply delineated in humans than in other primates. Sensitive periods in development are more difficult to establish…” (Bjorklund & Pellegrini, 2002, 106): humans develop twice, once into a worker, and then into an adult.

Clearly, a view of children as “worker humans” should not be taken to extremes. Deprived environments will hamper children through the rest of their lives (Bjorklund & Pellegrini, 2002, 105) and children are safer when cared for by biological parents (Buller, 2005). Yet many children are surprisingly resilient to early traumas (Caspi, et al., 2003) and the traits that predict criminality may be largely heritable (Pinker, 2002, 315) so most children may be all but assured a good life. Other policy implications of resilient cihldren – everything from social services to educational styles – are too many to list.

Yet this gets me away somewhat from my primary question, about brain size. Clearly it would be possible for humanity to develop children as a worker caste without limiting the skull size of adults. Even if skull size and less reproductively valuable children correlate, unless these effects are caused by the same alleles there still has to be a reason for our smaller brains. My guess is that this is also from socialization, and that there is less need for us to think now that we have evolved to live in agricultural communities. If a caveman is largely on his own, with only his band to protect him, he must be a jack-of-all-trades. Everything from possible ritual cannibalism (White, et al., 1991) to warfare (Zollikofer, Ponce de Leone, Vandermeersch, & Leveque, 2002) would have to be done with the same band, meaning a successful live with a cognitively flexible life. However, humans in a modern economy rely on others for most of their needs, and they only need to learn a few things well. Thus the human brain may be evolved to be a specialist – an extraordinary mind (Gardner, 1998) — in only one domain, and a naïve generalist in others. Anyway – that’s my guess.

Bibliography
Arensburg, B., Tillier, A. M. , Vandermeersch, B. , Duday, H., Schepartz, L. A. & Rak, Y. (1989). A Middle Palaeolithic human hyoid bone. Nature (338): 758-760.
Bjorklund, D.F. & Green, D.L. (1992). The adaptive nature of cognitive immaturity. American Psychologist 47: 46-54.
Bjorklund, D. F., & Pellegrini, A. D. (2002). The origins of human nature: Evolutionary developmental psychology. Washington, DC: American Psychological Association.
Buller, D.J. (2005). Adapting Minds. MIT Press: Cambridge, MA.
Capsi, A., et al. (2003). Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene. Science. Vol. 301 No. 5631 pp. 386-289.
Gardner, H. (1998). Extraordinary Minds. Basic Books: New York, NY.
Hrdlicka, A. (1927). The Neanderthal phase of man. The Journal of the Royal Anthropological Institute of Great Britain and Ireland 57: 249-274.
Klein, R.G. (2003). Whither the Neanderthals? Science 299(5612): 1525-1527.
Mason, W.W. (1968). Early social deprivation in the nonhuman primates: Implications for human behavior. In D.C. Glass (Ed.), Environmental influence (pp. 90-101). New York: Rockefeller University Press.
Paabo, S. (2003). The mosaic that is our genome. Nature 421: 409-412.
Pinker, S. (2002). The Blank Slate: The Modern Denial of Human Nature. Viking Adult: New York, NY.
Ridley, M. (2003). Nature via Nurture. Harper Collins: New York, NY.
Rightmire, G.P. (2001). Brain size and encephalization in early to Mid-Pleistocene Homo. American Journal of Physical Anthropology 124(2): 109-123.
White, T.D., et al. The question of ritual cannibalism at grotta guattari [and comments and replies]. Currently Anthropology 32(2): 118-138.
Wilson, E. O., & Holldobler, B. (2005). Eusociality: Origin and Consequences. PNAS 102(38)-13367-13371.
Zollifoker, C.P., Ponce De Leone, M.S., Vandermeersch, B., & Leveque, F. (2002). Evidence for interpersonal violence in the St. Cesaire Neanderthal. PNAS 99(9): 6444-6448.

Evolutionary Cognitivism, a tdaxp series
1. Selection and Cognition
2. Epigentics and Diversity
3. Children and Civilization
4. The Implicit and the Explicit
5. Man Among Men
6. More Than Genes
7. Bibliography

I am very enthusiastic about Bjorklund & Pellegrini’s 2002 text, Evolutionary Developmental Psychology. I am going to discuss four places I believe that the book’s discussion can be extended, on ADD, domain generality, geological time, and group selection. While I feel the authors’ work to be incomplete in these areas, I choose these areas because otherwise the book seems flawless.

On page 5, the authors mention mention that “natural selection has similarly shaped domain-general information processing mechanisms,” and that “working memory” and “speed of processing” are examples of such domain-general mechanisms. I agree that these things exist, are important, and were shaped through evolution, though I do not know if they are “domain general.”

For instance, I think it is clear that working memory effects how we memorize names, how we do long division, and how we solve complicated puzzles. But does working memory capacity load only cheater detection, or in the hundred subconscious ques we receive to tell us how the person we talk to is feeling? I believe the authors could have been more accurate had they spoken of these “conscious, domain-multiple” skills instead of domain-general ones.

Additionally, I think the author’s words on the nature of selection cover much of evolution. They write that “natural selection does not necessarily yield what is ‘best for the group’ but rather works on the level of the individual” (14). Sometimes this is true. However, eusocioal adaptations (those that benefit the group but harm an individuals’ inclusive fitness) have been observed in the wild (Wilson & Holldobler, 2005) and computer simulations (Hammond & Axelrod, 2006) and network analysis (Bloom, 2000) imply that something similar may exist among men . Selection pressure is not limited to the individual level, or the genetic level, or the group level, but exists on every level of organization (Alford & Hibbing, 2004).

Relatedly, the authors claim that “individuals who truly have ADHD would be at a disadvantage in any environments” (28). This may or may not be true, but the Goldstein & Barkley (1998) paper they say they agree with goes further, arguing that ADHD could not be “adaptive” (1) or “adapted” (2) (it is not clear that Goldstein & Barkley understand the difference in these concepts) because because it is not shown to be beneficial in some economic activity (hunting, wading, etc). Goldstein & Barkley then bizarrely state: “[Advocates for ADHD] can not on the one hand argue that ADHD needs to be taken seriously as a legitimate developmental disability. Then on the other hand simultaneously sing its praises as a once successful adaptation that leads to higher intelligence, greater creativity, and heightened sensory awareness, but that now results in suffering due to an overcontrolled, linear-focused, and intolerant culture” (4-5). Why this should be true is beyond me. It may well be that ADHD is adapted on a genetic level to increase reproduction. For instance, if ADHD leads to rape (Giotakos, Markianos, & Vaidakis, 2005) then it easily could be an adaptation that is beneficial to a selfish gene while being harmful to individuals and society. Alternatively, ADHD may well be a stable polymorphism, in other words humanity may be “a mixed population [that] is evolutionary stable” (Buller, 2005, 42) with regard to ADHD. This could arrive if at certain times a group’s survival hinged on having hyperactive members, and at other times hinged on having members capable of concentration.

Last, while I agree that the “human mind has been prepared by natural selection, operating over geological time, for life in a human group” (Bjorklund & Pellegrini, 4). However, human minsd have also been prepared by natural selection, operating over historical time, for life in human groups (Voight, et al., 2006). That is, human genomes of different populations have undergone selection within the past few thousand years. Evolution acted in the past, giving us stone-age brains for our modern lives. But it also acted more recently, adapting those stone-age brains for live in agricultural communities.

However, while these are nit-picks, Bjoklund & Pellegrini’s contribution to the field should not be underrated. Their text competently integrates evolutionary psychology and cognitive psychology, two fields who share many assumptions but whose practitioners are often unaware of each other’s advances. It is through books like this can scientists in both domains leverage each other’s unique contributions and advance the state of our unified, scientific view of the world.

Bibliography
Alford, J. & Hibbing, J. (2004) .The Origin of Politics: An Evolutionary Theory of Political Behavior. Perspectives on Politics, 2(4), 707-723
Bloom, Howard. (2000). Global Brain. Wiley & Sons: New York, NY.
Bjorklund, D. F., & Pellegrini, A. D. (2002). The origins of human nature: Evolutionary developmental psychology. Washington, DC: American Psychological Association.
Buller, D.J. (2005). Adapting Minds. MIT Press: Cambridge, MA.
Goldstein, S., & Barkley, R. (1998). ADHD, hunting, and evolution: “just so” stories. The ADHD Report 6(5): 1-4.
Giotakos, O., Markianos, M., & Vaidakis, N. (2005). Aggression, impulsivity, and plasma sex hormone levels in a group of rapists, in relation to their history of childhood attention-deficit/hyperactivity disorder symptoms. Journal fo Forensic Psychiatry and Psychology 16(2): 423-433.
Hammond, R., & Axelrod, R. (2006) The Evolution of Ethnocentricism. Journal of Conflict Resolution, 50(6).
Spielman, R.S., Bastone, L.A., Burdick, J.T., Morley, M., Ewens, W.J., & Cheung, V.G. (2007). Common genetic variants account for differences in gene expression among ethnic groups. Nature doi:10.1038/ng1955.
Voight BF, Kudaravalli S, Wen X, Pritchard JK (2006) A Map of Recent Positive Selection in the Human Genome. PLoS Biol 4(3): e72 DOI: 10.1371/journal.pbio.0040072
Wilson, E. O., & Holldobler, B. (2005). Eusociality: Origin and Consequences. PNAS 102(38)-13367-13371.

Evolutionary Cognitivism, a tdaxp series
1. Selection and Cognition
2. Epigentics and Diversity
3. Children and Civilization
4. The Implicit and the Explicit
5. Man Among Men
6. More Than Genes
7. Bibliography