Homo Mysterious: Evolutionary Puzzles of Human Nature (49 page)

This chapter reviews the last of the human evolutionary mysteries that we’ll cover, but it certainly doesn’t exhaust the possibilities, even if we restrict ourselves to “mental mysteries.”
For example, in addition to considering why we became so darned smart, we might ask: Given the fact of cross-species organic continuity (which, after all, is the greatest single take-home message of evolutionary biology), why is there such a gap in mental capacities between people and other animals? One possible answer is that the gap isn’t really all that large. In fact, there is a burgeoning field known as “cognitive ethology,” which has demonstrated remarkable learning capacities on the part of other species, including African gray parrots, Caledonian crows, and dogs, as well as the ever-reliably surprising chimpanzees.

Another way of framing the question is, “How great is the divide between human mental functioning and that of other animals?” Are the intellectual worlds of
Homo sapiens
and other species continuous or discontinuous? Clearly there is a difference, but is it qualitative (a difference in kind) or merely quantitative (in extent)? And what are the implications of possible answers … for our self-perception, for the way we interact with other living creatures, and for the fraught question of which species—if any—has a soul?

1
. Attwell, D., & Laughlin, S. B. (2001). An energy budget for signaling in the grey matter of the brain.
Journal of Cerebral Blood Flow and Metabolism, 21,
1133–1145.

2
. Hamilton, J. A. (1935).
The association between brain size and maze ability in the white rat.
Ph.D. dissertation, University of California at Berkeley.

3
. Premack, D. (2004). Is language the key to human intelligence?
Science, 303,
318–320.

4
. Calvin, W. H. (1994). The emergence of intelligence.
Scientific American, 271
(4), 100–107.

5
. Alexander, R. D. (1971). The search for an evolutionary philosophy of man.
Proceedings of the Royal Society of Victoria, Melbourne, 84,
99–120.

6
. Bailey, D. H., & Geary, D. C. (2009). Hominid brain evolution: Testing climatic, ecological, and social competition models.
Human Nature, 20
, 67–79.

7
. Calvin, W. H. (2002).
A brain for all seasons
. Chicago: University of Chicago Press.

8
. Rozsa, L. (2008). The rise of non-adaptive intelligence in humans under pathogen pressure.
Medical Hypotheses, 70,
685–690.

9
. Hamilton, W. D., & Zuk, M. (1982). Heritable true fitness and bright birds: A role for parasites?
Science, 218,
384–387.

10
. Hopcroft, R. L. (2006). Sex, status, and reproductive success in the contemporary United States.
Evolution and Human Behavior, 27
, 104–120.

11
. Charlton, B. G. (2009). Why are women so intelligent?
Medical Hypotheses, 74,
401–402.

12
. Sandiford, P., Cassell, J., Sanchez, G., & Coldham, C. (1997). Does intelligence account for the link between maternal literacy and child survival?
Social Science and Medicine, 45,
1231–1239;
Č
vorovi
ć
, J., Rushton, J. P., & Tenjevic, L. (2008). Maternal IQ and child mortality in 222 Serbian Roma (Gypsy) women.
Personality and Individual Differences, 44,
1604–1609.

13
. Nettle, D., & Pollet, T. V. (2008). Natural selection on male wealth in humans.
American Naturalist, 172,
658–666.

14
. JoVe, T. H. (1997). Social pressures have selected for an extended juvenile period in primates.
Journal of Human Evolution, 32,
593–605.

15
. Jolly, A. (1966). Lemur social behavior and primate intelligence.
Science, 153,
501–506; Humphrey, N. K. (1976). The social function of intellect. In P. Bateson & R. Hinde (Eds.),
Growing points in ethology
. Cambridge, UK: Cambridge University Press.

16
. Byrneand, R. W., & Whiten, A. (1988).
Machiavellian intelligence: Social expertise and the evolution of intellect in monkeys, apes and humans
. New York: Oxford University Press.

17
. Alexander, R. D. (1990). How did humans evolve? Reflections on the uniquely unique species.
University of Michigan Museum of Zoology Special Publication, 1
, 1–38.

18
. Cheney, D. L., & Seyfarth, R. M. (2007).
Baboon metaphysics
. Chicago: University of Chicago Press.

19
. Silk, J., Alberts, S. C., & Altmann, J. (2003). Social bonds of female baboons enhance infant survival.
Science, 302,
1231–1234.

20
. Mercier, H., & Sperber, D. (2011). Argumentation: Its adaptiveness and efficacy.
Behavioral and Brain Sciences, 34
(2), 94–111.

21
. Dunbar, R. (1997).
Grooming, gossip and the evolution of language
. Cambridge, MA: Harvard University Press.

22
. Cosmides, L., Clark Barretta, H., & Tooby, J. (2010). Adaptive specializations, social exchange, and the evolution of human intelligence.
Proceedings of the National Academy of Sciences, 107
, 9007–9014.

23
. Cosmides, L. (1989). The logic of social exchange.
Cognition, 31,
187–276.

24
. Wrangham, R. (2009).
Catching fire: How cooking made us human
. New York: Basic.

25
. Kaplan, H., Hill, K., Lancaster, J., & Hurtado, A. M. (2000). A theory of human life history evolution: Diet, intelligence, and longevity.
Evolutionary Anthropology, 9
(4), 156–185.

26
. Gottfredson, L. S. (2007). Innovation, fatal accidents, and the evolution of general intelligence. In M. J. Roberts (Ed.),
Integrating the mind.
Hove, UK: Psychology Press.

27
. Aarssen, L. W. (2010). Darwinism and meaning.
Biological Theory, 5
(4), 296–311.

C
HAPTER
T
EN
Digging for Treasure

S
OCRATES WAS TOLD BY
the Delphic oracle that he was the wisest of men—not because of how much he knew, but because one of the few things he knew was how much he did
not
know. By the same token, the more you have read
Homo Mysterious
, the wiser you have become, as you learned more and more about what we do not know!

College students undergo a similar Socratic transition. Beginning their studies as freshmen, they are convinced that they know a great deal. As their education proceeds—especially if it is a really good education—they become increasingly aware of the gaps in their knowledge and wisdom, until, when ideally they have been helped to see that they know hardly anything at all, they graduate.

The current tour of what we do not know has been limited to but a small subset of our ignorance, its goal being to illuminate just some of the dark places on the human evolutionary map. Paradoxically, by shining a light on darkness, we have not abolished that darkness, but rather, rendered it more identifiable, even as it remains essentially obscure: not unknowable, mind you, just currently unknown. Isaac Newton famously wrote that if he had seen far, it is because he stood on the shoulders of giants, which was both an exercise in undue modesty (Newton was himself one
of the greatest such giants) and nothing less than the truth. In
Homo Mysterious
, instead of looking far, we have looked nearby—at ourselves—using a giant’s microscope: the principles of evolution by natural selection, as elaborated by that greatest of biological giants, Charles Darwin.

We haven’t come close to exploring all of our own evolutionary mysteries. In at least one such case—the question of the so-called missing link—this is because on closer examination the presumed mystery self-destructs. The phrase “missing link” has in the past been interpreted as a serious challenge to the evolutionary narrative of human phylogeny, implying that the key connector between modern human beings and our ancestral “apes” has not been found, ostensibly because it doesn’t exist. In fact, the concept of a missing link is altogether misleading: There are lots of links, some as yet missing, many found. And the more we find, the more there are: Picture two points and draw a line between them. One point is the ancestor we share in common with modern apes; the other is
Homo sapiens
. Next, let’s posit that along this line there exists a “missing link.” Imagine, now, that you have found such a point, perhaps roughly intermediate between the initial two. As a result, you now have two missing links, one on either side! Find another of these “links” and—voila!—three are now missing. Paleontologists have discovered a large litany of “found links,” each of which creates the opportunity, by definition, to find yet more. As this happens, the gaps between the various links grow ever smaller. We are all linked, no mystery here.

On the other hand, there are numerous small-scale peripheral mysteries, such as why we laugh, cry, and yawn. And what about Mark Twain’s observation that we are the only species that blushes … or needs to? Psychologists and biologists have come up with numerous explanations for these largely autonomic responses, most of them involving variations on a social theme: Only rarely do people laugh, cry, yawn, or blush when they are alone, so presumably these unconscious actions serve to communicate … but what? And what about other hidden and unintended communicative signals, such as pheromones that indicate ovulation status and other hormone conditions, unconscious sensitivity to gene combinations (especially the major histocompatability complex) that are unconsciously used to assess mate suitability, and pupillary
dilation and the concomitants of galvanic skin response (monitored in lie detector tests)? Why do our bodies give us away when we are—consciously, at least—trying to convey a different message? Along the same lines and, if anything, more perplexing is the question, “Why do we have an unconscious?” Or emotions?

And what about morality? Some theologians—and a significant number of laypersons—argue that people are not naturally good, so that without God, human beings would live according to Thomas Hobbes’s grim prediction that in the absence of an over-bearing (albeit secular) “Leviathan” to keep us in line,
Homo sapiens
would experience lives that are “nasty, poor, brutish, and short.” Others maintain that in view of the fundamental selfishness of natural selection, the very fact that most human beings remain decent, ethical, and moral is itself an argument for the existence of a deity. Yet others follow the lead of evolutionary biologists in pointing to a variety of altogether natural, selective pressures that seem likely to induce people to behave in ways that appear altruistic—but which, at the level of individual genes, are actually selfish nonetheless.

Selfish genes do not necessarily create selfish people. In fact, quite the opposite: One of the primary ways that genes see to their own selfish propagation appears to be via inducing their bodies to behave “altruistically” toward other bodies, especially those harboring identical copies of precisely those “selfish” genes. Moreover, there can be a huge self-serving payoff in being perceived as generous and altruistic.

Then there is suicide. According to French existentialist Albert Camus, it is the only serious philosophical question. Perhaps so. But in any event, suicide is also a serious evolutionary question: As with homosexuality, any genetically influenced inclination in this particular direction should be selected against and quickly disappear, especially if it manifests early in life. (Suicide among postreproductive individuals would experience much less negative selection.) There are many animals that engage in extreme forms of altruism that are tantamount to suicide—for example, honeybees whose sting in defense of their hive causes them to die—but no cases in which individuals take their own life without a clear benefit to others, such as their offspring or other close relatives. The question of inclusive fitness theory arises here once again, and
it would be gratifying (at least, scientifically) if human suicide correlated with payoffs to surviving relatives. But it doesn’t, so it isn’t.

An evolutionary consideration of suicide would also require a close look at the possible adaptive significance of depression, itself strongly correlated with suicide. Here is an especially rich trove of theory and data, compiled by psychologists and psychiatrists, providing alluring and sometimes even compelling explanations, but as yet, no “closure.” Ditto for schizophrenia and other psychiatric diseases that have a distinct genetic component and that also tend to reduce reproductive success.