The Primate Diaries

This post was chosen as an Editor's Selection for ResearchBlogging.orgGrand evolutionary dramas about human origins capture our imagination and the stories provide context as to how we view ourselves. They are the scientific version of creation myths. However, unlike Adam and Eve being fashioned in the garden or humanity being vomited up by the giant Mbombo (as the Bakuba people of Congo believed), scientific origin stories are rigorously critiqued based on the best available evidence.

Friedrich Engels, a sociologist and future collaborator with Karl Marx, wrote one of the earliest scientific human origin tales in 1876. In his essay “The Part Played by Labour in the Transition from Ape to Man” he argued that anthropoid apes, by using their hands differently, began to walk upright.

This was the decisive step in the transition from ape to man. . . Thus the hand is not only the organ of labour, it is also the product of labour.

Engels’ clear interest in promoting his political goals, rather than accuracy in science, resulted in the early death of his idea. In the years to follow there were a number of popular interpretations of human origins, each one seeking that fundamental difference which separated us from other apes. “Man the Hunter” lasted until chimpanzees were found to organize cooperative hunts of colobus monkeys. “Man the Toolmaker” was popular for a time, but then chimpanzees and bonobos were found to fashion implements themselves. Perhaps culture is what made us unique? Nope, wrong again. Each time that scientists tried to wedge an argument between human uniqueness and other great apes the result was the same: back to the drawing board. Given this background, it is wise to approach new origin stories with caution.

With the discovery of Ardipithecus ramidus, Owen Lovejoy has stepped forward to present a new vision for the evolution of humanity. Unfortunately, while the scope of his argument is impressive (incorporating bipedalism, increased brain size, concealed ovulation and monogamy all in one story) the pieces don’t all fit together very comfortably.

Like those before him, he starts his journey on the same wrong foot and announces that:

An essential goal of human evolutionary studies is to account for human uniqueness. [And, earlier, stating] We can no longer rely on homologies with African apes for accounts of our origins and must turn instead to general evolutionary theory.

Ardipithecus demonstrates this, Lovejoy says, because males and females were roughly the same size (low sexual dimorphism), they were quadrupeds that walked on all fours rather than being knuckle-walkers like chimps, bonobos or gorillas, and they had reduced canines suggesting an omnivorous diet unlike Pan or Gorilla. Based on this Lovejoy again insists that “Ar. ramidus now confirms that extant African ape-based models are no longer appropriate.”

Lovejoy’s origin story is as follows: The similar size between males and females suggests that Ardipithecus was monogamous. Bipedalism evolved when males would carry food back in order to entice her to have sex (as has been observed in chimpanzees and bonobos). Concealed ovulation then evolved when females wanted the males to stick around, so it was useful to disguise fertility to keep the male guessing. In a nutshell, Lovejoy has introduced “Man the Provider.” Now just imagine a manicured lawn with a white picket fence and you have all the trappings of 1950s Mayberry.

However, rather than a grand unveiling it would be more appropriate to call this theory a rebranding. Lovejoy made the identical argument in 1981 for Australopithecus afarensis. Ironically, a major portion of his argument then relied heavily on homology with chimpanzees. All of the same arguments for Austalopithecus were present and have been repackaged for Ardipithecus: male provisioning, concealed ovulation, and pair bonds. However, in his 1981 paper he took his argument even further:

Can the nuclear family not be viewed as a prodigious adaptation central to the success of early hominids? If the model is correct . . . it implies that the nuclear family and human sexual behavior may have their ultimate origin long before in the dawn of the Pleistocene.

As they say, if at first you don’t succeed… As noted above, the only evidence Lovejoy has that Ardi was monogamous is the reduced canines and low sexual dimorphism. However, bonobos also have reduced canines and paleoanthropologist John Hawks speculates (see comments on this post) that canine size dimorphism is just as great in these apes as in Ardipithecus (he also points out that canine size is highly variable in hominids).

Primatologist Frans de Waal has also criticized Lovejoy’s argument that Ardi was monogamous [also see his comments below]:

Whereas the chief anthropologist on the Ardi team goes by the bonobo-like name of Owen Lovejoy, he focuses all of this attention on the chimpanzee, as is tradition in his field. Since chimps are violent and Ardi probably wasn’t, he argues that we have a totally unique creature on our hands. His pet theory is that this must mean that Ardi and her contemporaries were monogamous, but unless the diggers come up with a male and female fossil holding hands and having wedding rings, the idea that these ancestors avoided conflict through pair-bonding remains pure speculation. There is no evidence for it, and the only pair-bonded primate we have in our direct lineage (the gibbon) has in fact huge canine teeth.

Furthermore, Richard Lawler in his recent paper in the Journal of Human Evolution shows that high sexual dimorphism in primates does suggest polygyny (single male – multifemale) but that the absence of sexual dimorphism is not an indicator of anything:

inferring polygyny from strong levels of sexual dimorphism is justifiable, however “. . . the converse–the absence of dimorphism–does not necessarily indicate monogamy, polyandry, or an absence of intense male mate competition” (Plavcan, 2000: 340).

Because Lovejoy didn’t have enough evidence to demonstrate that Ardi was monogamous, he sought to buttress his argument with examples from modern humans. This time around, rather than saying outright that he’s seeking to prove the naturalness of the nuclear family, he simply implies it with a myriad of selected details. He first suggests that humans have no sperm competition. This is wrong, as is clear from a quick perusal of Steven Platek and Todd Shackleford’s book Female Infidelity and Paternal Uncertainty.

His other approach is to argue from comparative neurophysiology. Here he is on even weaker ground because the neurological evidence for monogamy is from voles and has never been studied in humans. After discussing the role of the neuropeptides oxytocin, arginine vasopressin, and prolactin and their different distributions in monogamous versus polygynous voles, he states that the receptors are located in “the central corridor that is activated in human cocaine addiction.” He then reports a study in which women were shown pictures of men whom they were in love with and cites that they “looked remarkably similar to those observed after cocaine or u-opiod infusions”. This is very specious reasoning.

While it’s clear where Lovejoy wants to go with his argument, the reality is that humans just don’t fit nicely into the nuclear family household he’s been advocating for thirty years. The majority of human societies are not monogamous. Murdock’s Ethnographic Atlas shows that, out of 1157 human societies studied, 982 practiced polygyny. Only 14.5% were monogamous. Our own society is far from monogamous as well, with about 1/4 of all children born to unmarried mothers who were not cohabiting with the father and estimates that 1 in 25 dads are not actually the father of their children.

Across societies estimates of marital infidelity range from 26 to 70 percent for women and from 33 to 75 percent for men (Shackleford and Buss 1997). With the rate of divorce based on infidelity being what it is (about 25 – 50 percent of all marriages depending on the country), and the rate of extra-pair copulations being so high, it seems that monogamy would hardly be the word to describe our own society, let alone the human species as a whole.

However, it’s unlikely that humans would be classified as polygynous either. Human sexual dimorphism isn’t large enough to justify the often extreme differences in size that accompany such a mating strategy. The most parsimonious answer is that humans lie closest to the multimale-multifemale strategy that the majority of primates have (and our two closest relatives). Human cultural factors have then influenced various societies into one of the two primary marriage systems. However, as I demonstrated in my earlier post, many indigenous societies have had flexible marriage systems which frequently was to a woman’s advantage.

What does this mean for human societies today? Rather than trying to force a rigid mating structure onto our species we should embrace who we are. I for one am quite happily living in a stable monogamous relationship and don’t have any plans to change that. But that’s simply what I prefer, others are different. Human beings have the most varied sexuality of any primate other than bonobos. Our species has been attempting to deny their connection to the great apes for hundreds if not thousands of years. It’s clear that we share some aspects with chimpanzees, but I think further research with our other evolutionary cousin could show great promise.

What remains unfortunate is that, by merely repackaging information and attempting to make it work for a new species, Lovejoy has shown that he already had his mind made up and was simply adjusting the facts to fit a preexisting argument. What was left out of his story is nearly as telling as what was included. As for where we go from here, I wouldn’t be too discouraged. Anthropology enthusiasts are used to having fantastic claims made, only to find that the story was a little too good to be true. The grand evolutionary drama will continue. The good ideas will rise, the bad ones will fall, and in the end we’ll discover our place in the natural world.

Reference:

Lovejoy, C. (2009). Reexamining Human Origins in Light of Ardipithecus ramidus Science, 326 (5949), 74-74 DOI: 10.1126/science.1175834

Comments

  1. #1 Naraoia
    October 19, 2009

    Lovejoy’s origin story is as follows: The similar size between males and females suggests that Ardipithecus was monogamous. Bipedalism evolved when males would carry food back in order to entice her to have sex (as has been observed in chimpanzees and bonobos). Concealed ovulation then evolved when females wanted the males to stick around, so it was useful to disguise fertility to keep the male guessing.

    Isn’t concealed ovulation plesiomorphic for this phylogenetic neighbourhood, and hasn’t it been known to be so for quite some time?

  2. #2 jay
    October 19, 2009

    There are lots of attempts to recast traditional restraints as ‘the way it was supposed to be’. Of course evolution does not work this way. It rewards that what is successful regardless of whether it is ‘beautiful’ or not. When it comes to items of reproductive success (evolutions ultimate test) the actual test is what helps a particular species in a particular environment.

    Longterm mating (not lifetime mating) in humans is a speciies specific reproductive strategy helped solve some problems, so it persisted. It enabled a particular set of developments and lifestyles.

    With most mammals (raccoons are to me a good example of non-social but intelligent mammals) the female becomes sexually unresponsive as soon as she is fertilised. For those species, that is desirable: having a male around merely compounds the need for resources and food. Additionally, the young are vulnerable for a short period of time, so she can store enough body fat to feed them until they are ready to move out. The last thing she needs is a male hanging around.

    At some point in our history, as the development time for young lengthened and the ability to cooperate increased, it would seem likely that females whose responsiveness did not turn off (whether through mutation or variation) would start to have a reproductive advantage. The male would stick around, and as part of this would be providing more resources than she would get while trying to care for the long term young. Quite possibly all these traits extended together, the more useful the male, the longer the childhood, the more complex development was possible.

    Viewed that way it simply boils down to: in humans, at least, ‘non-reproductive’ sex is primarily about resources. Specifically ‘trading’ sex. Nature does not particularly care about monogamy or ‘morality’ or ‘love’. What works is what counts. Sex-for-resources also makes sense of the near universality of not only marriage arrangements, but prostitution and ‘gold digging’. This is NOT to say that evolution selected for prostitution but that the same underlying behavior patterns got adapted into a different behavioral parallel.

    From nature’s perspective is nothing inherently good or bad about monogamy. It is simply one of many reproductive strategies that different species have adopted for their own purposes.

  3. #3 EMJ
    October 19, 2009

    @Naraoia: Yes. Dixon, in Primate Sexuality (p. 353), makes that point and states:

    it is more fruitful to ask why conspicuous advertisements of ovulation have developed in some primates, rather than arguing that their absence must reflect an evolutionary strategy of concealed ovulation.

  4. #4 Frans de Waal
    October 19, 2009

    Great blog, Eric.

    I don’t know why we keep getting all this old wine in new bottles. What few people realize is that the monogamy-bipedality theory of Lovejoy came originally from Desmond Morris, who formulated it in “The Naked Ape.” His book was written tongue-in-cheek, but now the same theory is given us as gospel. It needs to be challenged at every turn.

    Like the “killer ape” theory, which has been around equally long, the monogamy-bipedality theory focuses entirely on the male (pair-bonding serves to avoid male conflict, which then leads to offspring care, which requires walking on two legs for males to provide food to the family) as if not females, such as Ardi, became bipedal at the same time. What good did it do for them to walk upright? I would very much prefer theories that explain the behavior of *both* sexes!

  5. #5 Vicki
    October 19, 2009

    I think the essential problem is that Lovejoy et al. are starting by trying to explain or define “human uniqueness,” to an extent that nobody would for any other species. Yes, humans are unique, but in the sense that every species is unique.

    You can’t define humans by any one characteristic, be it bipedalism, opposable thumbs, tool use, the kind of canine teeth, or social structures. Language, maybe, but that doesn’t fossilize. Trying may tell us a lot about the person making the attempt, but not about Homo sapiens.

    There are no good answers to the wrong questions, and “what one thing makes humans different from all other animals?” is a misleading question.

  6. #6 Michele Braa-Heidner
    October 19, 2009

    I agree with Frans de Waal. Why do these theories only include the male and his behaviors? Do they think females had absolutely nothing to do with evolution therefore they shouldn’t be counted? We have to include both sexes to get a complete understanding of the subject. I also agree with Eric, the author of this blog when he suggests we need to look more closely at the bonobo. If you dig deep enough you can find theories about the bonobo apes in that our species may be closer related to them versus the chimpanzee. This theory however has been dismissed because the bonobo’s behaviors seem to be more closely related to the female of our species and the chimpanzee’s behaviors on the other hand seem to be more closely related to what male anthropologist’s believed to be the male of our species (which unfortunately is all they were concerned with).

    If we take a look at the female of our species and her behaviors we could come up with another hypothesis about bipedalism that we have overlooked due to gender bias in anthropology. Perhaps it was the female of our species who promoted bipedalism when, having to carry her young in one arm and foraging and gathering food in the other, made it absolutely necessary for survival, for her to have both hands free while walking upright. Isn’t this just as feasible as the theory about the male needing both hands to hunt?

  7. #7 michellespidermonkey
    October 19, 2009

    While I think there’s a lot of problems with Lovejoy’s re-hashed just-so story, I also felt de Waal’s argument largely boiled down to re-hashing his ideas about using bonobos, or more accurately, both chimps and bonobos as models. And while I think incorporating both chimp and bonobo behavior into models is important, there are some important differences between Pan and Homo that need to be considered (particularly concealed ovulation, among other things). And I don’t think there is very strong support that humans have a multi-male/multi-female strategy similar to what chimps and bonobos have. Helen Fisher’s book, Anatomy of Love, is kind of outdated, but I think it has some pretty strong cross-cultural evidence for human pair-bonds, irrespective of the social organization of the society, and that these bonds often have a life of about 4 years (which she argues corresponds to the amount of time necessary to raise a human child to weaning age). I think our ancestral social organization (and current social organization, to some extent, depending on cultural pressure) is somewhere between baboons (multi-male/multi-female, but with preferred male-female “friendship” bonds that essentially are strong, but non-exclusive pair bonds) and the callitrichids (flexibly ranging form monogamy to polyandry, depending on environmental context, dominance relationships, and availability of helpers). I definitely think that we have the pull to pair-bonding, but have interest in other partners, depending on both situational needs/opportunities and cultural norms, and occupy flexible social organizations ranging largely from monogamy to polygamy (and occasionally polyandry) depending on the needs of child-rearing (sensu Sarah Hrdy’s argument in Mothers and Others), and secondarily, property and inheritance concerns. I do think that our overly-helpless and dependent offspring are the big factor in our pair bonds, and flexible social arrangements, but that these social tendencies did not arise until 1) hominid infants lost that grasping opposable toe (thus lost clinging ability), and 2) developed enlarge brains that required altricial births and even further extended periods of development.

    I really would like some research looking at human brain chemistry in comparison to both prairie and montane voles…. I think that research has identified somewhat of a neural signature for monogamous vs. polygamous tendencies (I believe–I don’t know enough about the social organization of montane voles) that really needs to be properly investigated in humans…

    Also, I think one of the big avenues of research we need to be researching is the costs/benefits of concealed vs. advertised ovulation (and for that matter, advertised ovulation might not be all that honest). Especially considering recent research on subtle differences in attraction around ovulation, I wonder if “concealed” ovulation and continuous sexual behavior might be a means of confusing paternity (as a strategy of infanticide avoidance) vs. unconsciously manipulating the chances of paternity…. Then again, I also think pair-bonds might be another strategy for infanticide reduction…

  8. #8 Naraoia
    October 19, 2009

    @EMJ: Thanks!

    @Frans de Waal

    Like the “killer ape” theory, which has been around equally long, the monogamy-bipedality theory focuses entirely on the male (pair-bonding serves to avoid male conflict, which then leads to offspring care, which requires walking on two legs for males to provide food to the family) as if not females, such as Ardi, became bipedal at the same time. What good did it do for them to walk upright? I would very much prefer theories that explain the behavior of *both* sexes!

    Weeeelll, in theory, female bipedalism could be a by-product of males becoming bipedal. Like male nipples.

    Now, that would put an interesting twist on human evolution…

  9. #9 Jim Thomerson
    October 20, 2009

    Until we catch a chimp or bonobo building a fire, a case can be made that we are unique. I’ve seen pictures of captive chimps smoking cigarettes. If they light their own smokes, so much for uniqueness.

  10. #10 mollyrogers
    October 20, 2009

    You write that Ardipithicus was not a knuckle-walker, “unlike … bonobos”.

    Wikipedia says:

    “The Bonobo walks upright approximately 25% of the time during ground locomotion. Its quadrupedal ground locomotion generally is characterized by forelimb ‘palm walking’, similar to orangutans and in contrast to the predominant use of knuckles as characteristic of gorillas and the Common Chimpanzees.”

    Does Wikipedia need correcting, or is this a similarity between Ardi and bonobos?

  11. #11 Tor Bertin
    October 21, 2009

    Given these conceptions, does anyone else think it’s hilarious that his last name is Lovejoy?

  12. #12 PalMD
    October 21, 2009

    Thanks for this…i love the science hype, but I like the considered reason better.

  13. #13 Anton Mates
    October 21, 2009

    I really don’t get Lovejoy’s exclusive focus on male provisioning. AFAIK, in most human hunter-gatherer societies, women contribute about as much food to the group as men do–everybody’s provisioning! (There seems to be some debate about the exact proportion of each contribution, but certainly men are getting a significant chunk of their calories from items gathered by women.)

    And we’ve known for decades that bonobo females share food, largely with other females but also with males.

    Lovejoy keeps making the point that we can’t assume our ancestors had chimpanzee-like characteristics. So why does he assume that about the particularly chimpish habit of male-dominated provisioning?

  14. #14 wulfmankarl
    October 22, 2009

    Monogamy/Polygamy is a red herring argument when talking about evolution of bipedality. The issue is how bipedality is rewarded by sex. Male provisioning dominance makes sense AFTER the woman is pregnant, when she is less mobile, but a better explanation of bipedality reward is that as both males and females became more able to carry more things, survival was enhanced. This is the simpler explanation.

    Funny video: Darwin serenades Ardi “My Funny Hominid”…he bags on creationists too
    http://02e56fa.netsolhost.com/blog1/index.php/2009/10/22/darwin-serenades-ardi-my-funny-hominid-a

  15. #15 Naraoia
    October 23, 2009

    Given these conceptions, does anyone else think it’s hilarious that his last name is Lovejoy?

    Haha, now that you mention it…

  16. #16 onix
    November 4, 2009

    i think for australopitheci it is known they were mostly sedentary. It probably means they minimised walks with the food. butchering marks appear to suggest, they might crowd a feeding place. I don’t seem to get the point, i have allways had the idea that in the somewhat limited number of evolutionairy tracks, developemnt of hands, in particular, was just a natural, (rats eg. have hands somewhat similar to humans, even frogs do), next somewhat similar like ostriches lost flight, we gained dedicated bipedality somewhere along the line, like ostriches (and chimps) we apparently allways lived in groups. doesn’t that a woman ovulates conceiled actually make her more available (in the eyes of also a some ‘set’ partner) for sex in the group? I assume it gave woman (mayb actually the baby’s) a food advantage (like with eg. bonobo) but you may also hypothesize she had a better option to still choose whom to become pregnant with. Perhaps defence with tools (sticks i think) was the defining factor for our upright posture, ardipithecus appears unable to defend itself without any, and develops the bipedality. to defend yourself more efficiently with a tool (sticks apparently work for even big predators when used with some skill) walking upright appears a pre. as soon as they used the sticks, or thornbranches perhaps, development of feet would become a natural. I don’t believe running away was ever much of a reason (altho succes at it would have a great effect on survival;) even modern people run so badly it would have been a rather meagre evolutionairy succes.

  17. #17 KSUgrad
    December 16, 2009

    EMJ: “As noted above, the only evidence Lovejoy has that Ardi was monogamous is the reduced canines and …bonobos also have reduced canines and paleoanthropologist John Hawks speculates that canine size dimorphism is just as great in these apes as in Ardipithecus (he also points out that canine size is highly variable in hominids).”
    >>>You seem to be missing the point & the reason for distinguishing length from the Sectorial Canine Complex (SCC). Within a SCC the larger, projecting upper canine is constantly honed by occlusion against the lower third premolar of anthropoid primates. This honing sharpens the canine making it a knife-like weapon used in territory defense & mate competition. Ardi, as well as all hominids, have completely lost this feature. Why would any hominoid give this up unless it provided a huge advantage to reproductive fitness?

    JHawks: “We have also known for thirty years that some australopithecines had substantial dimorphism of the SCC. LH 6 is no small canine, nor are the canines of STW 252.”
    >>>The problem with the examples you have given is that they are not contemporaneous. As you have pointed out you can find just as much (or more) variation in extant species of bonobos (when scaled). Should anyone be surprised to see widely varying dental measurements from specimens separated by as many as thousands of years/miles? The only assemblage we have that is not greatly separated temporally &/or spatially is AL-333. If you look within this single assemblage however, dimorphism is greatly reduced.
    That being said, even if there is some level of canine size dimorphism in hominids, what does that indicate? In the examples you give, you say that they are not small canines. I assume you mean that they are not small by hominid standards because, compared to any other hominoid they are quite tiny. This fact alone should tell you that canines are no longer used for display or defense purposes (as they are in nearly every other primate). So, in the end, any small level of canine dimorphism that may or may not be present is inconsequential compared to the fact that the canines are non-sectorial & reduced in length.

    Hawks: “But it seems to me that the gibbons are a pretty clear example showing that pair-bonded mating systems don’t cause canine size reduction.”
    >>>You’re absolutely right: a pair-bonded mating system alone does not equal canine size reduction. However, you’re ignoring the fact that, although pair-bonded, gibbons are highly territorial. Females have increased the size of their canines to help the male defend a territory. This is a completely different situation from the cooperative male-foraging troops proposed by Lovejoy.

    Plavcan: “…the absence of dimorphism–does not necessarily indicate monogamy…”
    >>>Of course not, just look at chimpanzees. They exhibit virtually no skeletal dimorphism & are highly promiscuous. Instead, they exhibit high levels of sperm competition, something which humans do not do.
    Besides, Lovejoy’s point wasn’t “reduced dimorphism = monogamy”. It simply shows that pair-bonding is a very reasonable possibility; whereas if we observed very high levels of sexual dimorphism, it would indicate that pair-bonding was not very likely. We should look at all of the evidence collectively to make conclusions (which is precisely what Lovejoy has done).

    EMJ: “[Lovejoy] first suggests that humans have no sperm competition.”
    >>>This is a misinterpretation. What Lovejoy actually said was that humans have very little sperm competition when compared to other, highly promiscuous primates; instead, we fall much closer to gibbons. In fact, the level of sperm competition present in humans is so low compared with “true sperm competitors” (e.g., Ateles, Brachyteles, Macaca, Pan, etc) that it may as well be looked at as 0 from a comparative standpoint.
    However, this does not mean that some level of sperm competition is non-existent in humans. Although pair bonded, cuckoldry would exist & thus some level of sperm competition would have been maintained. This is precisely the reason Lovejoy suggests that males would select for epigamic features in females that would reduce the likelihood of promiscuity (e.g., hidden ovulation, permanently enlarged breasts). I’ll say again, one must look at all of the evidence collectively.

    EMJ: “His other approach is to argue from comparative neurophysiology. Here he is on even weaker ground because the neurological evidence for monogamy is from voles and has never been studied in humans.”
    >>>This is a very specious argument. While the experiments carried out on voles have necessarily never been performed on humans (last I checked it was rather difficult to get approval to cut into a human’s brain) this doesn’t mean that it hasn’t been extensively studied in humans & supported by experimental & anecdotal evidence. See the following (& many others) for examples:
    Bartels A & Zeki S (2004) The neural correlates of maternal and romantic love. NeuroImage 21: 1155–1166.
    Esch T & Stefano GB (2005) The Neurobiology of Love. Neuroendocrinol Lett 26(3):175–192.

    EMJ: “The majority of human societies are not monogamous.”
    >>>This argument has absolutely no bearing on what Lovejoy has proposed. You seem to be suggesting that he is talking about extant human social systems. Lovejoy’s hypothesis pertains to hominid origins. Clearly, we’ve deviated substantially in many other ways (e.g., we no longer have grasping feet, our brains have increased dramatically, etc) so I think it’s to be expected that we’d deviate from our pair-bonding origins, too (especially with the development of human culture).

    EMJ: “Like those before him, [Lovejoy] starts his journey on the same wrong foot and announces that: ‘An essential goal of human evolutionary studies is to account for human uniqueness.’”
    >>>What else is there? Pan are our closest living relatives & understanding them is absolutely vital to understanding what it means to be human. But the primary goal is to understand how & why we are different. Why have apes been on an evolutionary path towards extinction since the end of the Miocene, while hominids became a “weed-species”? Why do humans have all of these crazy adaptations you don’t see in any other hominoid (e.g., small, non-sectorial canines, huge brains, bipedality, hidden ovulation, low/no sperm competition, decreased dimorphism, etc)? Why are we able to sit here & even discuss this? Knowing how/why we are the same as Pan tells us nothing directly about what makes us unique animals.

    In the end the only real “criticism” is that this is more or less the same model that Lovejoy proposed 30 years ago, updated to fit with Ardi. Such is the nature of scientific progress. As new data is put forth old ideas need to be reevaluated. If they still can be made to fit: great! If not, then old ideas (e.g., the assumption that the LCA was chimpanzee-like in morphology, behavior, locomotion, etc) must be tossed aside in favor of what is now known. I think it very befitting that you ended your column by saying “the good ideas will rise, the bad ones will fall.” We’ve seen many(!) ideas fall short over the years. However, after nearly 30 years—despite often being misunderstood, misinterpreted & misrepresented—Lovejoy’s provisioning model is still around & is even stronger than ever.

  18. #18 anadiomene
    July 13, 2010

    I cannot get how the argument of low sexual dimorphism meaning monogamy is serious. It does not mean monogamy, simple. Bonobos are not monogamous, neither are chimps. Lovejoy does not hold.

  19. #19 anadiomene
    July 13, 2010

    sarah Blaffer Hrdy writes about concealed ovulation as adaptation in polygamous (many males / many females) primate societies. In connection with promiscuity it is a part of strategy which protects the young from being killed by males – a reproductive strategy pretty common among our closest relatives.
    So, concealed ovulation needs not mean monogamy at all, either. May mean just the opposite.

  20. #20 Anonymous
    July 21, 2010

    anadiomene: “I cannot get how the argument of low sexual dimorphism meaning monogamy is serious. It does not mean monogamy, simple. Bonobos are not monogamous, neither are chimps. Lovejoy does not hold.”
    >>>As I have said before, Lovejoy’s point wasn’t “reduced dimorphism = monogamy”. It simply shows that pair-bonding is a very reasonable possibility; whereas if we observed very high levels of sexual dimorphism, it would indicate that pair-bonding was not very likely. We should look at all of the evidence collectively to make conclusions (which is precisely what Lovejoy has done).

    anadiomene: “sarah Blaffer Hrdy writes about concealed ovulation as adaptation in polygamous (many males / many females) primate societies. In connection with promiscuity it is a part of strategy which protects the young from being killed by males – a reproductive strategy pretty common among our closest relatives.
    So, concealed ovulation needs not mean monogamy at all, either. May mean just the opposite.”
    >>>This issue is two-fold. First, when we consider the fact that hominids are relatively monomorphic with greatly reduced canines & have completely lost the SSC (Sectorial Canine Complex) it is very unlikely that early hominids regularly engaged in infanticide (which is already unlikely due to philopatry). Thus, right from the start your example doesn’t apply to hominids.
    Secondly, if we assume minimal ovulatory signaling in the earliest hominids was primitive (all other hominoids exhibit some degree of ovulatory swelling, even if minimal), why did hominid females not prolong and intensify such signs so as to encourage sex-for-food exchanges (as Pan appears to have done)? The most logical answer is to prevent cuckoldry. Male provisioning within the context of a multimale group therefore requires selection of females with reproductive crypsis. That is, males could only succeed by provisioning mates with self-crypsis; they would otherwise be unprotected from female copulation with more dominant/aggressive males while ovulating.