Weapons hypothesis for human bipedalism.

[sprite]

When it comes to the cause of the bipedalism of Ardi, Dr. Lovejoy freely speculates that the females were CHOOSING males that were collecting and bringing food to them. There are two big guesses here.
One, that females had the luxury of a free choice, and two, the collecting and carrying of food. I have no problem with this, but the evidence for it is every bit as thin as that which I have cited for weapons. Where are the howls of derision?

Lovejoy has been attacked on this over the last nearly thirty years since he made this argument. Many have been against his argument for female monogamy and male provisioning of females and many still are. Lovejoy has also argued against sexual dimorphism in australopithecus.

When I postulated that an activity, adopted by males only, could lead to bipedalism, everone was shouting me down. Many were boldly declaring that this would not produce bipedalism in females.
There seems to be no problem, when Lovejoy suggest it. So it seems to me that it's not the suggestion, but who is making it, that is the problem.
I have no problem with this suggestion, but I don't think it's any more supported by facts than my own.

The point about Lovejoy's argument is that the females do not travel much and the males bring food to them, so the fact that female transport of young would be compromised by bipedal locomotion would fit with Lovejoy's argument and not contradict it.
Your argument had all cost and no benefit to females/offspring survival and therefore is very different from Lovejoy's view.

I don't particularly agree with Lovejoy, that females would have benefited from such a dependence on male provisioning but I do think it is possible that some sort of pair-bonding came early. Even baboons have females with one or two male 'friends' so this type of thing within a patrilocal ape species could have meant some degree of male bonding with females together with (unlike baboons) the male bonding patrilocality enables.

But I think there may well have been some foraging benefit to females themselves that enabled bipedalism in females that countered the females' problems with infant transport.
Your argument was that the females had no pressure to be bipedal other than it had been selected for in males - and in increased male aggression (male brothers and other male relatives) at that.

I am still investigating how intralocus sexual conflict for bipedalism could play out.
See eg:
http://en.wikipedia.org/wiki/Sexual_conflict

Intralocus sexual conflict, where the same set of alleles in males and females have different optima. i.e. they are expressed differently in the sexes. A classic example is the human hip, where females need larger hips for childbirth. The genes that affect hip size must reach a compromise that is at neither the male optimum nor the female optimum. In some cases, this conflict may be resolved through the differential expression of such loci in males and females, but evidence indicates that intralocus conflict may be an important constraint in the evolution of many traits[citation needed].

And finally, the same arguments against weapon use can never go away - there is absolutely no evidence that weapons were used 5+ million years ago.
Re. canines:
http://209.85.229.132/search?q=cache:08 ... clnk&gl=uk

Ardipithecus’s canine teeth are significantly reduced compared to those of chimpanzees and gorillas. Reduction of canine size is a trend that was continued in later hominins. Two, not necessarily mutually exclusive explanations may account for this change. First, as foods that require grinding with the molars, such as seeds, became a larger part of the diet, large canines became an impediment to the necessary side-to-side motion.

The second possible factor in canine reduction may have to do with aggression within the social structure. Large canines are used by modern ape males in threat displays in order to gain social dominance. Males also tend to be significantly larger than females, also thought to be a product of social competition. The available evidence seems to indicate that there was little sexual dimorphism (i.e., difference between males and females) with respect to body size in Ardipithecus. The researchers suggest that the reduction in canine size may be related to a reduction in aggression between males and possibly marks the beginning of pair bonding between males and females. This proposal, by Owen Lovejoy of Kent State University, is one of the most controversial made in the series of articles in Science. It has been disputed by other researchers, notably David Pilbeam of Harvard, as being unsupported by the available data.

http://www.sciencemag.org/cgi/content/f ... 949/69/DC2

In basal dimensions, the canines of Ar. ramidus are roughly as large as those of female chimpanzees and male bonobos, but their crown heights are shorter (see figure). The Ar. ramidus sample is now large enough to assure us that males are represented. This means that male and female canines were not only similar in size, but that the male canine had been dramatically “feminized” in shape. The crown of the upper canine in Ar. ramidus was altered from the pointed shape seen in apes to a less-threatening diamond shape in both males and females. There is no evidence of honing. The lower canines of Ar. ramidus are less modified from the inferred female ape condition than the uppers. The hominid canines from about 6 Ma are similar in size to those of Ar. ramidus, but (especially) the older upper canines appear slightly more primitive. This suggests that male canine size and prominence were dramatically reduced by ~6 to 4.4 Ma from an ancestral ape with a honing C/P3 complex and a moderate degree of male and female canine size difference.

In modern monkeys and apes, the upper canine is important in male agonistic behavior, so its subdued shape in early hominids and Ar. ramidus suggests that sexual selection played a primary role in canine reduction. Thus, fundamental reproductive and social behavioral changes probably occurred in hominids long before they had enlarged brains and began to use stone tools.

[gib]

When it comes to the cause of the bipedalism of Ardi, Dr. Lovejoy freely speculates that the females were CHOOSING males that were collecting and bringing food to them. There are two big guesses here.
One, that females had the luxury of a free choice, and two, the collecting and carrying of food. I have no problem with this, but the evidence for it is every bit as thin as that which I have cited for weapons. Where are the howls of derision?

'Mack i'm broadly in agreement here. I've yet to hear exactly why provisioning is supposed to lead to smaller canines. In the 'round table discussion' it came across as a real non sequitur.

btw thanks for that last post sprite, fascinating stuff.

[sprite]

When it comes to the cause of the bipedalism of Ardi, Dr. Lovejoy freely speculates that the females were CHOOSING males that were collecting and bringing food to them. There are two big guesses here.
One, that females had the luxury of a free choice, and two, the collecting and carrying of food. I have no problem with this, but the evidence for it is every bit as thin as that which I have cited for weapons. Where are the howls of derision?

'Mack i'm broadly in agreement here. I've yet to hear exactly why provisioning is supposed to lead to smaller canines. In the 'round table discussion' it came across as a real non sequitur.

btw thanks for that last post sprite, fascinating stuff.

Lovejoy's argument is essentially one for early monogamous pair-bonding which would show in sexual monomorphism in body size and canine size. Males would not be competing for copulations with a number of females and would be investing in the offspring they share with a single female. Monogamy and monomorphism go together.

I think Lovejoy's argument has been one for increased reproduction rate in females - rather than a female producing one offspring every four years or so, if a male shared the provisioning of the offspring then one could be produced every two years or so.
Certainly this is possible. In orangs it is very difficult for females to raise each offspring and can take up to eight years while the males do nothing but, if they are the big mature ones, fight each other at intervals in their otherwise solitary lives, or if they are the smaller males, sexually harass the mothers with their young.

In tamarins and marmosets where the males share the infant care then twins can be produced. Gibbons and siamangs have paternal care too. Some lemurs too. And in all these pair-bonded the males and females are virtually the same in size and canine size.

So if females - or infant survival - selected for male parental care then we would see this in reduced sexual dimorphism and male canine size.

Lovejoy has been greatly criticized for this over the years from all sides, including women who considered he was presenting justification for the modern belief that males provide for their wife and offspring while the mother waits at home and just does the housework and childcare. Hunter gatherers show us that the women often in fact do most of the provisioning for the family.

But we do have widespread male parental investment too - crucial provisioning of food, especially when women are in the greatest need when lactating, for example.
Some argue that females could have helped each other, but females are going to be busy with their own offspring so would not have much in the way of surplus resources.
Males that are no longer putting their resources into being big and competing with other males become a potential resource for females to 'tap'. And certainly with Homo where preganancy, birth, lactation etc is such a burden on the female, male provisioning became crucial.

The question for me would be whether male provisioning would have been a factor at such an early point where the burden of reproduction for the female was not so great. Protection may have been a greater selection factor for females and young - monogamy is also seen as having the important role of protecting infants from infanticide and females from aggression and more important than male provisioning because in monogamous species males often do not provision but they do protect.

I think Lovejoy also argues that the males protected the females but if they were off gathering food they would be absent from the females and therefore unable to protect them - and what's more, female animals do not tend to be monogamous unless the males stay with them all the time and keep other males away. (This is not necessary in modern humans because the female relatives of the males watch the sexual beahviour of his wife or wives, and social constraints on females and punishments do the job of controlling females pretty well without the need for the actual constant presence of the husband).



The point about bipedalism and the negative effects on females in terms of mobility and infant transport could have been 'solved' by male provisioning but I'm not convinced.

I'm thinking more along Johnathan Kingdon's 'squatting ape' theory again - that this mode of feeding produced adaptations that led to changes that led to the inability to be quadrupedal. But I need to read him more thoroughly. He has, from what I remember, been supported by the Ardi evidence that the last common ancestor with chimpanzees was a woodland ape that did not climb vertical trees as extant apes do and did not have that top-heavy morphology.

With a squatting ape, feeding in the woodland leaf-litter and stretching up to branches, and continually standing and squatting, it could be that long-distance travel and therefore infant transport was not such a big issue. And if the hand grip was strong and the foot grip remained strong then infants perhaps had the ability to grip onto their mothers for more easily and for longer while she was upright.
Also there would be large groups which would be important for defense, and males and female would remain together as they moved around in these large groups.

Anyway, the point about provisioning for Lovejoy is that it would be due to monogamy and that would mean lack of sexual dimorphism in bodies and canines.

[mistermack]

Lovejoy has been attacked on this over the last nearly thirty years since he made this argument. Many have been against his argument for female monogamy and male provisioning of females and many still are. Lovejoy has also argued against sexual dimorphism in australopithecus.

Thanks Sprite, I didn't know that. In fact, I'm very surprised that he chose to colour the presentation of the Ardi findings with his 'pet hypothesis'. It would have been better if he had done that separately, in a presentation of his own. Maybe his fellow team members agreed with the hypothesis.

I can't help feeling though, that if he has argued the case for this for so many years, it leaves open the possibility of unconcious bias in the Ardi findings. The danger of finding what you want to find.
I thought the dimorphism evidence was rather weak for the conclusions they drew, maybe they were looking too hard for what they wanted to see.

Your argument had all cost and no benefit to females/offspring survival and therefore is very different from Lovejoy's view.

I'm afraid I strongly disagree on that one. The benefit of being protected by males with weapons is absolutely huge, and I would argue that it has been crucial to the ability of hominids to spread, ensuring safe crossing of less wooded areas, that would previously have been a barrier. The problem of carrying the young would be mitigated by the fact that a group of apes could 'own' the area they currently were foraging, moving slower in a group, and making rapid escape to trees less important, in the daylight hours at least.

Lovejoy doesn't explain how these monogamous males would stay safe, with their small canines and slow climbing. Presumably they would have to forage in large groups, and then split up and take what they collect to their individual mates. Who would guard the females with males away foraging? It calls for a very organised and human-like division of labour that seems unfeasible for apes.

And finally, the same arguments against weapon use can never go away - there is absolutely no evidence that weapons were used 5+ million years ago.

That's absolutely true, but is that actually 'an argument against weapon use'? There is no evidence for, and no evidence against weapons-use. Unless you can demonstrate that the evidence SHOULD be there, but isn't, then that is just neutral, and supports neither position.
Where was Darwin's evidence for natural selection? The argument made great sense, but wasn't supported by direct evidence till many years later.
Where is the evidence for monogamous pairs 5+ mya? None at all.


Re Canines, I can see the canines having opposing selection pressures on them. On one hand, they help to increase rank, there is no doubt about that, or they would not be there. On the other hand, females may find them scary, and avoid them if the choice arises. So a balance between the two pressures is maintained. If using weapons upsets that balance, removing the rank advantage, the other pressure takes over and a quick reduction occurs.
.

[sprite]

Another aspect of Lovejoy's provisioning by males argument is based on 'concealed ovulation'.
In most species either the female has very obvious physical signals that she is ovulating which attracts the males, or she has behavioural changes where she solicits matings when she is ovulating. (In many species females will also 'falsely' advertise ovulation either by extended sexual swellings or proactive sexual behaviour.)

Lovejoy argued (argues?) for an initial condition something like that of chimpanzees, with male philopatry and therefore lower competition between the related males, but a male dominance hierarchy where the alpha male excluded other males from mating when the female had the largest sexual swelling but the other males could mate outside this most fertile period.

If the most dominant male was focussed on mating with the different females in turn when the sexual swelling was at its largest and brightest, while the males with the smaller canines got to mate at other times, and they also exchanged food with the females at these other times to gain matings, then females with reduced sexual swellings who could choose to mate with these smaller-canined but provisioning males, would also be more often becoming pregnant by these males.

In other words, if the males with big canines lost their almost exclusive sexual access to ovulating females then males with smaller canines would be fathering more offspring, the latter also more willing to exchange food for sex which would also bias the female mate choice.

And for one attack on Lovejoy see Dean Falk's chapter here from 'Women in Human Evolution':
Brain Evolution in Human Females
An answer to Mr Lovejoy
http://books.google.co.uk/books?id=WTsu ... oy&f=false

[sprite]

Lovejoy has been attacked on this over the last nearly thirty years since he made this argument. Many have been against his argument for female monogamy and male provisioning of females and many still are. Lovejoy has also argued against sexual dimorphism in australopithecus.

Thanks Sprite, I didn't know that. In fact, I'm very surprised that he chose to colour the presentation of the Ardi findings with his 'pet hypothesis'. It would have been better if he had done that separately, in a presentation of his own. Maybe his fellow team members agreed with the hypothesis.

I can't help feeling though, that if he has argued the case for this for so many years, it leaves open the possibility of unconcious bias in the Ardi findings. The danger of finding what you want to find.
I thought the dimorphism evidence was rather weak for the conclusions they drew, maybe they were looking too hard for what they wanted to see.

As far as I can see there is nothing about body size dimorphism in Ardi.
But the number of canines found seems to definitely point to little sexual dimorphism in them. It would be odd for there to be no sexual dimorphism in the canines alongside large sexual dimorphism in body size.

And, though I don't go along with Lovejoy's views I do think the sexual dimorphism in Australopithecus is also being accepted when it should not be - at least to the extent of it being a large (gorilla-like) rather than a smaller (chimpanzee-like) dimorphism. I posted some papers etc concerning this before.

Your argument had all cost and no benefit to females/offspring survival and therefore is very different from Lovejoy's view.

I'm afraid I strongly disagree on that one. The benefit of being protected by males with weapons is absolutely huge, and I would argue that it has been crucial to the ability of hominids to spread, ensuring safe crossing of less wooded areas, that would previously have been a barrier. The problem of carrying the young would be mitigated by the fact that a group of apes could 'own' the area they currently were foraging, moving slower in a group, and making rapid escape to trees less important, in the daylight hours at least.

But the point about Ardi is that the bipedalism evolved in a heavily wooded environment, not grasslands. Crossing open areas does not seem to be a factor in bipedalism in this scenario from what I'm getting from this new info.

And your original argument was individual male-male competition, not group protection by multiple males.

Your argument was that as long as the male could defeat other males it did not matter that bipedalism might reduce female fecundity. The benefit of having a son - presuming a female could manage to raise one now that she can't move around very easily to feed etc - outweighs the fact that she cannot produce many offspring anymore.

Now you are saying that a group of males is jointly 'owning' the territory and that infant transport problems are mitigated by this. Your argument has changed from weapons in male-male sexual combat to males joining together and, presumably, also not competing over the females so much? A group of weapon-wielding males defending the group against predators rather than an individual one winning in sexual combat.

We went through this predator-defence weapons argument for bipedalism with Jayjay.

Lovejoy doesn't explain how these monogamous males would stay safe, with their small canines and slow climbing. Presumably they would have to forage in large groups, and then split up and take what they collect to their individual mates. Who would guard the females with males away foraging? It calls for a very organised and human-like division of labour that seems unfeasible for apes.

Quite.
But if the males and females are together in a large group in a familiar environment with familiar predators, and predators have always been dealt with by vigilance and avoidance etc rather than using canines against them, then a reduction in male-male competition may well make the large male canines redundant.
Bonobo males have smaller canines, don't they. One of the papers said about an Ardi male canine being the size of that of a female chimpanzee or a male bonobo.
I'm not sure about that though I've read about smaller male canines in bonobos.
I don't know enough about the bonobo canines yet so more info on this would be useful.
We do know that bonobo male-male competition is less than eg chimpanzees.

The thing is that male philopatry in itself is very unusual across species yet very real in our (and other great ape) evolution and perhaps we have not fully appreciated its effects yet. It certainly needs to be thought through in how it affects intragroup male-male competition. And social and mating systems. And morphology.

[gib]

But if the males and females are together in a large group in a familiar environment with familiar predators, and predators have always been dealt with by vigilance and avoidance etc rather than using canines against them, then a reduction in male-male competition may well make the large male canines redundant.

This makes a bit more sense now (i'm still thinking about the Lovejoy angle). Relaxing the selection pressure for keeping large canines, ok.

But i'm still not sure how Lovejoy then connects this to provisioning. Surely the reduced male-male competition is the only thing we'd need to invoke here?

[sprite]

But if the males and females are together in a large group in a familiar environment with familiar predators, and predators have always been dealt with by vigilance and avoidance etc rather than using canines against them, then a reduction in male-male competition may well make the large male canines redundant.

This makes a bit more sense now (i'm still thinking about the Lovejoy angle). Relaxing the selection pressure for keeping large canines, ok.

But i'm still not sure how Lovejoy then connects this to provisioning. Surely the reduced male-male competition is the only thing we'd need to invoke here?

I would agree.

For Lovejoy it is about increasing the reproductive rate.
See Lovejoy writing on the reproductive adaptations of hominds from page 15 here:
http://books.google.co.uk/books?id=jh8I ... q=&f=false

Reduced female mobiltiy leading to increased female survival, with the males carrying food (therefore we get selection for bipedalsim) to the females which increases production of offspring.


Basically he is arguing that when females mated with provisioning males they increased their offspring numbers and therefore out-reproduced those who carried on with the older strategy of males putting their effort into competition and females raising offspring purely from their own effort with no provisioning by males.
Small-canined males could only out-reproduce large-canined males by provisioning the females and gaining matings when the females were actually ovulating which had been enabled by the ovulation being concealed from the dominant males who otherwise monopolized females when ovulating.

[sprite]

And if anyone is interested they can read Lovejoy's 'The Origin of Man' from 1981:
http://www.anthro.utah.edu/PDFs/courses ... ovejoy.pdf

[gib]

But if the males and females are together in a large group in a familiar environment with familiar predators, and predators have always been dealt with by vigilance and avoidance etc rather than using canines against them, then a reduction in male-male competition may well make the large male canines redundant.

This makes a bit more sense now (i'm still thinking about the Lovejoy angle). Relaxing the selection pressure for keeping large canines, ok.

But i'm still not sure how Lovejoy then connects this to provisioning. Surely the reduced male-male competition is the only thing we'd need to invoke here?

I would agree.

For Lovejoy it is about increasing the reproductive rate.
See Lovejoy writing on the reproductive adaptations of hominds from page 15 here:
http://books.google.co.uk/books?id=jh8I ... q=&f=false

Reduced female mobiltiy leading to increased female survival, with the males carrying food (therefore we get selection for bipedalsim) to the females which increases production of offspring.


Basically he is arguing that when females mated with provisioning males they increased their offspring numbers and therefore out-reproduced those who carried on with the older strategy of males putting their effort into competition and females raising offspring purely from their own effort with no provisioning by males.
Small-canined males could only out-reproduce large-canined males by provisioning the females and gaining matings when the females were actually ovulating which had been enabled by the ovulation being concealed from the dominant males who otherwise monopolized females when ovulating.

Sprite i agree with your interpretation. I guess it comes down to the piece i have bolded. Lovejoy seems to be saying that this is the only way the small-canined males could possibly have thrived, yet i really don't see how that's any better than 'mack's story about stick-weapons.

So i still call non sequitur. Canine reduction was surely the result of a relaxation of selection pressure. And we know it happened - that is to say we know the smaller canined variety were the ones that led to ourselves. But to then say 'ah well the smaller canined guys must have had some other advantage' strikes me as odd - why do we even need to invoke further selection once the pressure is off? Even odder is how Lovejoy can say 'AND i know what advantage these small-canined guys had! They were better provisioners!'

[mistermack]

As far as I can see there is nothing about body size dimorphism in Ardi.
But the number of canines found seems to definitely point to little sexual dimorphism in them. It would be odd for there to be no sexual dimorphism in the canines alongside large sexual dimorphism in body size.

They do make the claim of little or no size dimorphism, but it's hard to track down what they base it on. All I can find is the large size of the main skeleton, which they determine is female because of canines at the small end of the scale. They inferred body size of other specimens, deduced from the size of ankle and wrist bones. That's why I remarked that their conclusion is weakly supported at the moment, I don't see where the confidence comes from.

It does definitely appear that the canines reduced very recently, though, going by the very large roots of the small canines. So if the canines reduced quickly, body size dimorphism could have reduced much more slowly. Females might still be attracted to bigger males, but put off by large canines. It seems to be a species in rapid transition, in evolutionary terms.

I was disappointed that they didn't make a more in-depth comparison with Australopithecus, feature by feature. After all, if they are claiming Ardi as an ancestor of Lucy, that is the most relevant comparison. They actually did more comparisons with modern humans and chimpanzees, than with Australopithecus.
I'll have to search out the evidence for dimorphism in Australopithecus. Everything I've read puts it as about 2:1 in body weight. I did read what you posted, It's the only thing I've seen that makes that conclusion. I'm surprised, given the amount of evidence, that it isn't settled.
One thing I haven't found yet in the pdfs is how the Ardi canines compared to Australopithecus canines. It must be in there, but its a lot to get through.

But the point about Ardi is that the bipedalism evolved in a heavily wooded environment, not grasslands. Crossing open areas does not seem to be a factor in bipedalism in this scenario from what I'm getting from this new info.

That's right. I was really making the point that later developments would have been nearly imposssible without weapons, making the case that weapons use is far more ancient than what we have evidence for.
After all, if no evidence means no weapons, we have to believe that humans achieved all the expansion they did, up to 385,000 years ago, without the help of a stick or spear.

And your original argument was individual male-male competition, not group protection by multiple males.

It was on this site. My original post was dashed off in about five minutes on a whim, without any planning at all. ( which I regret ).
I did go into far more detail in a little book that I got self published in a small batch, some time ago. Most went to people I know, but the rest went recently, after I started this thread, so it did do me some good.

We do know that humans began using weapons at some point, so it's perfectly right to try to imagine what the consequences were. I think they had to be enormous, and compicated, whenever it happened.
Once they began to be carried, they would be used. If I was carrying a stick for protection against rivals, I would also use it if attacked by predators, and vice versa. The same applies to protecting a group, or a female. If you carry it, you will use it for everything.
I did give the opinion earlier that IF the society was based around monomale groups when weapons-use began, it would quickly turn around to multimale groupings as a result. If there are multiple males with weapons, then guarding a group with those weapons is a natural scenario.
.

[sprite]

As far as I can see there is nothing about body size dimorphism in Ardi.
But the number of canines found seems to definitely point to little sexual dimorphism in them. It would be odd for there to be no sexual dimorphism in the canines alongside large sexual dimorphism in body size.

They do make the claim of little or no size dimorphism, but it's hard to track down what they base it on. All I can find is the large size of the main skeleton, which they determine is female because of canines at the small end of the scale. They inferred body size of other specimens, deduced from the size of ankle and wrist bones. That's why I remarked that their conclusion is weakly supported at the moment, I don't see where the confidence comes from.

It does definitely appear that the canines reduced very recently, though, going by the very large roots of the small canines. So if the canines reduced quickly, body size dimorphism could have reduced much more slowly. Females might still be attracted to bigger males, but put off by large canines. It seems to be a species in rapid transition, in evolutionary terms.

Have you read this paper?:
http://www.sciencemag.org/cgi/content/full/326/5949/69

The ARA-VP-6/500 skeleton and sexual dimorphism. Of the 21 individuals with canines, ARA-VP-6/500 has UC and LC that are strikingly small; its UC ranks either 12th or 13th (of 13), and its LC ranks seventh (of eight) in size (table S6). However, postcranially, ARA-VP-6/500 is a large individual with an estimated body weight of ~50 kg (23). Was ARA-VP-6/500 a small-canined male or a large-bodied female?

We began our evaluation of ARA-VP-6/500 (24) by estimating the degree of dimorphism in the Ar. ramidus canine (SOM text S3). Even in modern humans, the canine is metrically the most dimorphic tooth. Mean basal crown diameter of human male canines is about 4 to 9% larger than that in females (table S5). Our analysis indicates that Ar. ramidus was probably only marginally more dimorphic than modern humans (tables S6 to S9 and SOM text S3), with a probable range of 10 to 15% dimorphism (in canine mean crown diameter). This is substantially less dimorphic than modern great apes, whose male canines (mean crown diameter) are larger than those of females by 19 to 47%.

On the basis of the above dimorphism estimate, the probability of a male having canines as small as those of ARA-VP-6/500 can be evaluated by bootstrapping (2). Assuming 12% dimorphism in mean canine size (table S8), the probability that ARA-VP-6/500 is a male is <0.03 (if the UC is ranked 12th of 13) or <0.005 (if ranked 13th) (table S9 and SOM text S4). We conclude that ARA-VP-6/500 is a large-bodied female, a conclusion also corroborated by cranial anatomy (25). This shows that skeletal size dimorphism in Ar. ramidus must have been slight (11), as is the case in both species of Pan (26, 27).

The ARA-VP-6/500 skeleton and dimorphism estimates allow us to place the Ar. ramidus dentition within a broader comparative framework. Scaling analyses (2) show that the UC of Ar. ramidus was relatively small in both sexes (fig. S22 and SOM text S2). In particular, male UC height of Ar. ramidus is estimated to be close to that of female P. paniscus and Brachyteles and to be much lower than that of male P. paniscus (which has the least projecting male canine among extant catarrhines) (Fig. 2).

and:

Conversely, extant Pan and Gorilla, each with its distinctive dental morphology, are best considered derived in their dietary and dental adaptations. This is consistent with the Ar. ramidus postcranial evidence and its interpretations (11, 23) and strengthens the hypothesis that dental and locomotor specializations evolved independently in each extant great ape genus. This implies that considerable adaptive novelty was necessary to escape extinction in the Late Miocene forest and woodland environments.

These analyses also inform the social behavior of Ar. ramidus and its ancestors. The dental evidence leads to the hypothesis that the last common ancestors of African apes and hominids were characterized by relatively low levels of canine, postcanine, and body size dimorphism. These were probably the anatomical correlates of comparatively weak amounts of male-male competition, perhaps associated with male philopatry and a tendency for male-female codominance as seen in P. paniscus and ateline species (52, 53).

From this ancestral condition, we hypothesize that the P. troglodytes lineage secondarily enhanced its canine weaponry in both sexes, whereas a general size reduction of the dentition and cranium (25) occurred in the P. paniscus lineage. This suggests that the excessively aggressive intermale and intergroup behavior seen in modern P. troglodytes is unique to that lineage and that this derived condition compromises the living chimpanzee as a behavioral model for the ancestral hominid condition. The same may be the case with Gorilla, whose social system may be a part of an adaptation involving large body size, a specialized diet, and marked sexual dimorphism.

In the hominid precursors of Ar. ramidus, the predominant and cardinal evolutionary innovations of the dentition were reduction of male canine size and minimization of its visual prominence. The Ar. ramidus dental evidence suggests that this occurred as a consequence of selection for a less projecting and threatening male upper canine. The fossils now available suggest that male canine reduction was well underway by 6 million years ago and continued into the Pliocene. Further fossils will illuminate the tempo and mode of evolution before 6 million years ago.

One point about this being that "male canine reduction was well underway by 6 million years ago".

If nothing else this does present new thoughts about the LCA and whether there was a low male-male competition which then increased in the chimpanzee line and gorilla line too.
I seem to remember there is at least one extinct ape with small male canines.
Much to think about, anyway.
And to look more closely at other primates. I've done that before and it just got more and more complicated but perhaps I'll have another go.

I was disappointed that they didn't make a more in-depth comparison with Australopithecus, feature by feature. After all, if they are claiming Ardi as an ancestor of Lucy, that is the most relevant comparison. They actually did more comparisons with modern humans and chimpanzees, than with Australopithecus.
I'll have to search out the evidence for dimorphism in Australopithecus. Everything I've read puts it as about 2:1 in body weight. I did read what you posted, It's the only thing I've seen that makes that conclusion. I'm surprised, given the amount of evidence, that it isn't settled.
One thing I haven't found yet in the pdfs is how the Ardi canines compared to Australopithecus canines. It must be in there, but its a lot to get through.

There is some mention in the paper above and Fig 1

As for sexual dimorphism and A afarensis, wiki mentions it:
http://en.wikipedia.org/wiki/Australopi ... Morphology

In Australopithecus, however, males can be up to 50% larger than females. New research suggests that sexual dimorphism may be less pronounced than this, but there is still debate on the subject. [2]

So "up to 50% larger" is much less than the 100% you mention - I think that may be from the earlier mixing of different species that was rectified - I quoted something about it earlier from "Upright: The Evolutionary Key to Becoming Human" by Craig Stanford where he said how the sexual dimorphism was much less than had been thought when 'robust' and 'gracile' individuals were mixed together.

The best overview I can find on the debate that continues is from a blog here:
Sexual Dimorphism in Australopithecus afarensis
http://anthropology.net/2008/02/08/sexu ... afarensis/

i don't think anyone now argues more than 50%. The question is where they fit on the 15-50%.

But the point about Ardi is that the bipedalism evolved in a heavily wooded environment, not grasslands. Crossing open areas does not seem to be a factor in bipedalism in this scenario from what I'm getting from this new info.

That's right. I was really making the point that later developments would have been nearly imposssible without weapons, making the case that weapons use is far more ancient than what we have evidence for.
After all, if no evidence means no weapons, we have to believe that humans achieved all the expansion they did, up to 385,000 years ago, without the help of a stick or spear.

There's a big difference between arguing about when weapons might first have been used and arguing that their use would have been the cause of bipedalism perhaps as long ago as 6mya.

[mistermack]

Have you read this paper?:

Yes, I downloaded all the pdfs. There is a huge amount there, so it's a lot to go through in detail. As I said initially, the deductions are fairly made, but leave some room for newer finds to give a different picture. They give a 3% chance that the main skeleton could be male, or 1/2% using a different method. So it's highly probably female, but still possibly male.
It's a large body for a female, but we don't have a full adult male skeleton to compare it with, so the dimorphism is inferred, rather than catagorically proved.
I'm not rejecting their opinions, just pointing out that they are not conclusive.

One point about this being that "male canine reduction was well underway by 6 million years ago".

This is making an assumption about the speed of the change in the canines, if they are just basing this on Ardi.

There's a big difference between arguing about when weapons might first have been used and arguing that their use would have been the cause of bipedalism perhaps as long ago as 6mya.

That's true of course. But it doesn't mean that it's totally irrellevant. If they found a fossil spear five million years old, it still wouldn't prove a weapons hypothesis, but would improve the odds somewhat. So any indication that weapons were used earlier is relevant, but not conclusive.

On a different note, it's interesting that they make the confident assertion that knuckle walking is a derived trait, and not one of the LCA. If that is the case ( and it does seem likely ), then there are only two possibilities.
Either it evolved twice, independently, in Gorilla and Chimpanzee, or once, and the two species diverged afterwards.
If it evolved once only, then the split-date from Humans should be identical for both Chimpanzees and Gorillas. So those who give different dates for the two species are saying in effect that knuckle walking evolved twice. If you extend that argument to Bonobos, then it evolved three times, seperately.
.

[Steviepinhead]

You're right that the conventional dating -- which has an earlier split for gorilla-chimps+humans -- may require two independent derivations of knuckle-walking if the LCA of humans and chimps was not a knuckle-walker (as appears increasingly likely).

You're not right that tossing bonobos into the mix requires three derivations: we have no reason to suspect that knucle-walking evolved after the chimp-bonobo split. At this point, it's more parsimonious to suppose that the LCA of common chimps and bonobos had already evolved knuckle-walking...

[mistermack]

You're not right that tossing bonobos into the mix requires three derivations: we have no reason to suspect that knucle-walking evolved after the chimp-bonobo split. At this point, it's more parsimonious to suppose that the LCA of common chimps and bonobos had already evolved knuckle-walking...

Depends on the dates that genetics indicate for a split from humans. If they are the same for Chimps and Bonobos, then that's right. I suspect that they probably are.

[sprite]

You're not right that tossing bonobos into the mix requires three derivations: we have no reason to suspect that knucle-walking evolved after the chimp-bonobo split. At this point, it's more parsimonious to suppose that the LCA of common chimps and bonobos had already evolved knuckle-walking...

Depends on the dates that genetics indicate for a split from humans. If they are the same for Chimps and Bonobos, then that's right. I suspect that they probably are.

Aren't chimpanzees and bonobos accepted as having split from each other less than two million years ago?

[mistermack]

Aren't chimpanzees and bonobos accepted as having split from each other less than two million years ago?

Ok. But if that's the case, the spit dates for Bonobos and Chimps from humans should be identical.
But what we still have is Chimpanzees, Gorillas and Orangutans all with very different dates for the split from the human line, all with either knucle or fist walking. If humans never went through a knuckle or fist walking phase, then these must have all evolved it independently.
.

[eversbane]

Aren't chimpanzees and bonobos accepted as having split from each other less than two million years ago?

Ok. But if that's the case, the spit dates for Bonobos and Chimps from humans should be identical.
But what we still have is Chimpanzees, Gorillas and Orangutans all with very different dates for the split from the human line, all with either knucle or fist walking. If humans never went through a knuckle or fist walking phase, then these must have all evolved it independently.
.

That determination goes with the evidence, not with incredulity. Multiple analogous traits from homologous features is not the most parsimonious solution, but nature is not inherently parsimonious. Parsimony is a tool of logic where evidence is lacking. The newly accumulating evidence (the latest being the Ardi papers) is demonstrating that perhaps, on occasion, nature does what it wants. It doesn't care what we think. I have said previously that the Ardi papers have completely flipped me on the issue of early bipedalism (pre-6Ma). I remain open to the evidence on the issue of possible multiple knuckle/fist modes of locomotion. Lets wait for the evidence.

[eversbane]

One point about this being that "male canine reduction was well underway by 6 million years ago".

This is making an assumption about the speed of the change in the canines, if they are just basing this on Ardi.

Orrorin's canines are somewhat reduced. I assume that Orrorin's date of 6Ma provided the reference date for that statement. Contrast this trend (seen earliest in Orrorin) with Salehanthropus who's canines are more typical of Miocene apes, and more similar to Gorilla and Pan, than to Hominid canines.

[ericv00]

Aren't chimpanzees and bonobos accepted as having split from each other less than two million years ago?

Ok. But if that's the case, the spit dates for Bonobos and Chimps from humans should be identical.
But what we still have is Chimpanzees, Gorillas and Orangutans all with very different dates for the split from the human line, all with either knucle or fist walking. If humans never went through a knuckle or fist walking phase, then these must have all evolved it independently.
.

That determination goes with the evidence, not with incredulity. Multiple analogous traits from homologous features is not the most parsimonious solution, but nature is not inherently parsimonious. Parsimony is a tool of logic where evidence is lacking. The newly accumulating evidence (the latest being the Ardi papers) is demonstrating that perhaps, on occasion, nature does what it wants. It doesn't care what we think. I have said previously that the Ardi papers have completely flipped me on the issue of early bipedalism (pre-6Ma). I remain open to the evidence on the issue of possible multiple knuckle/fist modes of locomotion. Lets wait for the evidence.

And this particular line of evidence and its possible implications are a very interesting topic. Is there a thread on E&NS on this specifically? I would be interested to see additional thoughts on this. Mainly, WHY, if knuckle walking is an analogous trait and not homologous, gorillas and chimps both developed that method of locomotion.

My first thoughts are that there is some sort of anatomical predisposition for it, given a pressure for quadrupedal locomotion in apes, or that there was a basal form of locomotion that used both knuckle walking and partial bipedalism, but not enough for basal knuckle walking structures in the hand to form.

[Delvo]

Before walking either bipedally or quadripedally on the ground, these apes' ancestors were primarily adapted for living and moving in trees. Given the adaptions they already had in place for that (palms turned in toward each other rather than simply down/back, and wrist & finger joints much better at bending in than out so even the most relaxed & neutral position is slightly curled in), walking on the knuckles/fists instead of the palms is the form of quadripedalism for which they were best predisposed.

[gib]

Before walking either bipedally or quadripedally on the ground, these apes' ancestors were primarily adapted for living and moving in trees. Given the adaptions they already had in place for that (palms turned in toward each other rather than simply down/back, and wrist & finger joints much better at bending in than out so even the most relaxed & neutral position is slightly curled in), walking on the knuckles/fists instead of the palms is the form of quadripedalism for which they were best predisposed.

That does make sense.

[ericv00]

Before walking either bipedally or quadripedally on the ground, these apes' ancestors were primarily adapted for living and moving in trees. Given the adaptions they already had in place for that (palms turned in toward each other rather than simply down/back, and wrist & finger joints much better at bending in than out so even the most relaxed & neutral position is slightly curled in), walking on the knuckles/fists instead of the palms is the form of quadripedalism for which they were best predisposed.

That is along the lines of what I was thinking. And that makes knuckle-walking as a separately derived trait in gorillas and chimps much more understandable and even somewhat predictable/testable. Thanks.

[mistermack]

Before walking either bipedally or quadripedally on the ground, these apes' ancestors were primarily adapted for living and moving in trees. Given the adaptions they already had in place for that (palms turned in toward each other rather than simply down/back, and wrist & finger joints much better at bending in than out so even the most relaxed & neutral position is slightly curled in), walking on the knuckles/fists instead of the palms is the form of quadripedalism for which they were best predisposed.

it sounds perfectly logical, but the same principle applies to most of the monkeys and smaller apes and lemurs, but it didn't happen there. I think body size must come into it somewhere, or maybe the LCA was a knucle walker after all, and Ardi lost the signs of it when it started to walk bipedally.
After all, we are only inferring lack of knuckle walking in the LCA because of the Ardi evidence.
The time it took for Ardi to evolve bepedalism, was probably long enough to lose the signs of knuckle walking.
So the LCA could have been a knuckle walking ape, giving rise at various times to Orangutan, then Gorilla, then Chimpanzee, and finally becoming bipedal and losing the signs of knuckle walking, ending up as Ardi.
.

[sprite]

Before walking either bipedally or quadripedally on the ground, these apes' ancestors were primarily adapted for living and moving in trees. Given the adaptions they already had in place for that (palms turned in toward each other rather than simply down/back, and wrist & finger joints much better at bending in than out so even the most relaxed & neutral position is slightly curled in), walking on the knuckles/fists instead of the palms is the form of quadripedalism for which they were best predisposed.

it sounds perfectly logical, but the same principle applies to most of the monkeys and smaller apes and lemurs, but it didn't happen there. I think body size must come into it somewhere, or maybe the LCA was a knucle walker after all, and Ardi lost the signs of it when it started to walk bipedally.
After all, we are only inferring lack of knuckle walking in the LCA because of the Ardi evidence.
The time it took for Ardi to evolve bepedalism, was probably long enough to lose the signs of knuckle walking.
So the LCA could have been a knuckle walking ape, giving rise at various times to Orangutan, then Gorilla, then Chimpanzee, and finally becoming bipedal and losing the signs of knuckle walking, ending up as Ardi.
.

Apes - gibbons, orangs, gorillas, chimpanzees, bonobos and ourselves have different shoulder joints from monkeys which means apes can swing through branches in a way that monkeys cannot. Monkeys walk along branches whereas apes swing from them in an upright position.
So the hands of apes are different from those of monkeys as Delvo says.
Gibbons do not come to the ground.
Gorillas, chimpanzees and orangs have different ways of 'knuckle-walking', but each could be linked to the similar shoulder joints and the branch-swinging and hand morphology.
Why Ardi should be different I don't know. We would expect branch-swinging in the trees with similar shoulder joints and hands as the other apes.

One thing about the other apes is that when they knuckle-walk it puts the body in a more upright position than they would be without it - raising the front of the body. Great apes all have this more upright posture whether in the trees or on the ground than do monkeys. If Ardi was bipedal on the ground anyway then using knuckle-walking to raise the front of the body would not be needed.

Also, chimpanzees and gorillas are 'top-heavy' as their arms and shoulders are particularly strong for tree-climbing.

If we look at it from the the gibbon and orang split we have an ape that is almost always in the trees but mostly upright within the trees. From there we could have an Ardi-type ape that was mostly bipedal on the ground. Gorillas first and then chimpanzees became adapted to vertical tree-climbing evolving their top-heavy forms which meant that when they came to the ground the upper body had to be supported by their front limbs and in both cases knuckle-walking was the easiest way to move quadrupedally.