Archaeologist Peter Bogucki has written that, "Archaeology is very much constrained by what the modern imagination allows in the range of human behavior." A glaring example of this constrained thinking was published in one of the world's leading scientific journals last week. A very prominent anthropologist with the unbeatable name of Owen Lovejoy published a paper called, "Reexamining human origins in light of Ardipithecus Ramidus" in which he argues that 4.4 million year-old bits of bone found in Africa demonstrate that our ancestors were joined by love-joy in pair-bonded couples even then. (The papers are available here, free. Lovejoy's is the last in the list.)
This isn't the place for a technical appraisal of Lovejoy's argument. (I've submitted a letter to Science, co-authored with Todd Shackelford for that. If it's published—or not, I'll say something here.) But even a cursive look at Lovejoy's paper illuminates—not how our ancestors lived 4.4 million years ago—but the constrained thinking reflected in his factually flawed, logically incoherent analysis that somehow made it through rigorous peer review, editing, and fact-checking at Science—one of the world's most prestigious journals.
In a nutshell, Lovejoy argues that the evidence he and his colleagues presented indicates an absence of sperm competition in the human line and shows male provisioning of females that eventually led to the modern nuclear family. Simple enough. But to make this all-too-familiar argument, Lovejoy misleads, misunderstands, and mis-states his own findings to the point where, if this were a graduate-school paper, his professor would demand a re-write.
Some examples:
- Lovejoy's argument is founded on the idea the minimal difference in the size of males and females indicates reduced competition between males for mating. This is true. But Lovejoy—like many other theorists—too easily assumes that reduced male-male competition can only indicate monogamy, whereas it's more likely that promiscuity explains the lack of conflict, given that our two closest relatives (chimps and bonobos) both have roughly the same m/f size differences and are both promiscuous.
- To dismiss the question of promiscuity among our ancestors, Lovejoy tries to show that our contemporary bodies are ill-equipped for sperm competition (a sure sign of promiscuity in mammals) (4, 5). He cites a few "facts" in support of this position.
- Lovejoy writes that human sperm production capacity is less than 0.06x106 in humans, whereas the paper he cites for this number has it at 6x106, a hundred-fold difference. Other sources confirm that he's dramatically under-stated human sperm production capacity, and that the latter figure is correct (1).
- Lovejoy writes that "Humans have the least complex penis morphology of any primate." Unfortunately, he never defines what he means by "complex;" nor does he discuss the fact that the human penis is, by most measures, the longest, thickest, most prominently displayed penis among primates. No mention of the unusual flared head or the external scrotum—both strong indications of sperm competition in our species.
- He argues from contemporary anatomy without mentioning significant evidence that our bodies, particularly spermatogenic tissue, is subject to extremely rapid evolution (6).
- Aside from his oversights and outright errors concerning sperm competition, Lovejoy gets basic facts about primates wrong. For example, much of his thesis hinges on the absence of pronounced canines teeth (fangs) in the fossils found. He writes that we can assume that both males and females lacked these canines (even if the teeth were from a female) because "The SCC [sectorial canine complex] is not male-limited; that is, it is always expressed in both sexes of all anthropoids…." But this is wrong. Male bonobos have long canines, while females don't (2, 3). Lovejoy also claims an association between reduced canines and pair-bonding, but as this photo of the skull of a monogamous gibbon demonstrates, even this claim is suspect.
You might ask, as I did, "How can such basic, glaring mistakes make it to publication in one of the world's premier journals?"
In Spanish, the word esperar, can mean to expect or to hope-depending on context. Perhaps editors, fact-checkers, and general readers are over-eager to accept even the weakest arguments, as long as these arguments support the notion that sexual monogamy is characteristic of our species' evolutionary past. This is what they expect and hope to be told.
References and Notes
1. E. J. Peirce, W. G. Breed, Reproduction 121, 239 (2001).
2. F. B. M. de Waal, F. Lanting, Bonobo: The Forgotten Ape (University of California Press, Berkeley, 1997).
3. A. F. Dixson, Primate Sexuality: Comparative Studies of the Prosimians, Monkeys, Apes, and Human Beings (Oxford University Press, New York, 1998), page 219.
4. T. K. Shackelford, N. Pound, A. T. Goetz, Review of General Psychology 9, 228 (2005).
5. R. L. Smith, in Sperm Competition and the Evolution of Animal Mating Systems (Academic Press, Orlando, FL, 1984), pp. 601-659.
6. G. J. Wyckoff, W. Wang, C. Wu, Nature 403, 304 (2000).
Correction (10/15/2009): Due to my own bone-headed miscalculation, my numbers on testicular tissue to body mass ratios were wrong. I've removed the offending paragraph.
