Small teeth & sexual dimorphism?

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A Hunk’s Dental Downfall:

When males and females were about the same size, so were their teeth. But in species in which larger males evolved, tooth size increased relatively little. Thus, females ended up with larger chewing surfaces for their size than did males, the researchers report in the September issue of American Naturalist. The team concludes that teeth probably didn’t grow at the same rate as body size because males can successfully compete for females only in their prime. Once teeth wear down, they become ineffective, and the animal gets weaker and more susceptible to disease or injury. But that doesn’t matter to these males, as once they are too old to beat out rivals for mates, there’s no need to live a long life. When it comes to how many offspring a male can father, “it seems that compared to body mass, tooth size is relatively unimportant,” says Joanne Isaac, a mammalogist at James Cook University in Townsville, Australia, who was not part of the study team.

In highly polygynous species males in their prime are the fathers of a multitude. These species’ males enter into a winner-take-all lottery game when it comes to reproduction. It makes sense that these males wouldn’t live that long. It isn’t likely that they could greatly increase the fitness of their numerous offspring through parental investment simply because there might be so many of them. Male investment in humans makes some sense in the case where a typical man may have only a few children who survive to their reproductive years. Nevertheless, there is some reproductive skew within our own species, and the extent of that skew varies from population to population and across historical epochs. The reproductive outcome for the total population may remain the same no matter if it is characterized by a equilibrium of low risk & low yield male strategies, or high risk and high yield strategies, but the dynamics within the society are likely going to be very different. I am not convinced that our current low risk & low yield strategy (i.e., monogamous pair-bonding) isn’t just a metastable situation, highly susceptible to disruption.



  1. Why the two negatives in the last sentence? Do you mean “I am convinced that our current low risk & low yield strategy (i.e., monogamous pair-bonding) is just a metastable situation, highly susceptible to disruption.”

  2. Bryan: I think he meant “I suspect that [our current strategy] might be metastable and susceptible to disruption.” By which I suppose he meant invasion by a rival strategy. I’m not sure how that would work though. 
    Also I’m not sure how low-risk the current strategy is, especially considering the possibility of divorce and/or philandering. Competition for females is certainly present in modern human societies, and non-reproduction is not uncommon.

  3. In this connection readers might be interested in UCLA anthropologist Christopher Boehm’s hypothesis of “a reverse-dominance heirarchy” evolving in humans. 
    The idea is that polygamous alpha males dominated for so many thousands of generations in our hominid past, that even their less-than-alpha offspring were deeply embued with a lust to dominate and a horror of being dominated.  
    This fact, combined with our highly evolved rational brain, led to a kind of “egalitarian” strategy among all the runners-up in the band: “anybody around here try to lord it over us, and we’ll get together and beat the shit out of him.” Boehm uses this hypothesis to account for the ethnographic observation that all known primitive hunting-and-gathering societies (hundreds of them) practiced a rough egalitarianism except for temporary intervals of warfare, when one guy might be temporarily “the maximum leader.” 
    This same hypothesis might account for the stability of democracy (so far) in capitalist societies. All those alpha males running big corporations and such are not going to sit idly by if somebody like Bush, or anybody else, tries to crown themselves king. (Maybe this trait only evolved among monogamous northern European populations, as opposed to males in the Middle East?) 
    Reverse dominance heirarchy: my candidate for most interesting new political/biological idea of the 21st century.  
    His book, “Heirarchy in the Forest,” is available on Amazon:

  4. *One can cure oneself of the not un- formation by memorizing this sentence: A not unblack dog was chasing a not unsmall rabbit across a not ungreen field.

  5. How do you humans were ever the same size? It could be the case that primates were sexually dimorphic long before humanity speciated away from the main branch. Even among bonobos, known as matriarchal “hippy apes”, males are larger.

  6. TGGP asks how do we know humans were ever the same size? Correct me if I am wrong, but I do not think it necessarily matters, to the points being made, how far back the dimorphism goes.

  7. I certainly agree that under some cultural conditions the pair-bonding is only meta-stable. 
    But the reason it’s so entrenched in the west is that it’s simply WAY more successful … in reproducing productive citizens. 
    Other modes are possible — and in use in other cultures (or deviant subcultures). But they generally produce quanity, of low quality. If you want people that can actually do something, you end up with monogamy and high parental investment.  
    That’s why this state is stable.