Tue Apr 9, 2013, 06:53 AM
RainDog (25,879 posts)
Rewriting an erroneous narrative: humans are more like bonobos than common chimps
One of the features of primatology that popular science articles and popular culture get so wrong is assumptions about our primate ancestors. Males are depicted as brutes and the history of human development assumes war-like aggression as the norm.
That this idea supports right-wing capitalist ideology isn't just secondary - it's co-mingled - it's derivative of the current culture, not necessarily an ancestral one.
Evidence suggests humans have more in common with bonobos - and that common chimps have been portrayed as more war-like and murderous than they are *as a rule*
...Anatomically, bonobos were also found to be strikingly human-like and many initially doubted Dart’s claim that Australopithecus africanus was a human ancestor precisely because the skull was so similar to that of the newly discovered bonobo. Subsequent research on bonobos has found regular bipedalism, face-to-face mating (requiring a more ventral orientation of the vagina), reduced limb and body proportions, reduced canines, greater breadth of diet, larger group sizes and reduced competition within groups; all traits shared more closely with humans than chimpanzees. Recent research has also found that bonobos are closer to humans in the genetic expression of hormones promoting sociability and in the brain regions that give rise to empathy. As early as 1933, Harold Coolidge, the anatomist who gave P. paniscus its eventual taxonomic status (and who did the post-mortem on Prince Chim), concluded that this ape “may approach more closely to the common ancestor of chimpanzees and man than does any living chimpanzee”.
Bonobos directly contradict the monstrous reflection of human nature reproduced over the subsequent 80 years. While they are far from passive, they reveal a species that succeeds more through mutual aid than through aggressive violence. “From the point of view of individual survival, they are the most successful species among the higher primates,” says Takayoshi Kano, a Japanese primatologist who has overseen the longest continuous field study of bonobos in the wild. “They prove that individuals can coexist without relying on competition and dominant-subordinate rank,” he writes in The Last Ape (1992).
...According to Kano, the differences between bonobos and chimpanzees are likely the result of the bonobo habitat remaining “a relatively stable forest environment”, whereas chimpanzees adapted to more variable conditions. These differences in habitat may be reflected in the recent PLoS Genetics analysis that suggests chimpanzees have undergone more alterations in their genetic code than the bonobos, an estimated divergence of 12.4 per cent from our Homo-Pan ancestors.
“They’ve found that chimpanzees have one extra substitution for every six between humans and bonobos, and that’s strange,” says John Hawks, biological anthropologist at the University of Wisconsin-Madison. Chimpanzee nucleotides – the A, C, T or G base pairs that make up the vocabulary of DNA – have been evolving faster, substituting one for another at a higher rate since the two species separated from their common ancestor.
This assumption that common chimps are more like our common ancestor is repeated in assumptions such as the claim that humans lost the coding that chimps now have that relates to brain development (and penis features.) But, unless we know if bonobos have these same sequences (or deletions), we are only making an assumption humans lost these, rather than assuming chimps acquired them. You can see that in this article:
It has long been believed that humans evolved smooth penises as a result of adopting a more monogamous reproductive strategy than their early human ancestors. Those ancestors may have used penile spines to remove the sperm of competitors when they mated with females. However, exactly how this change came about is not known.
The researchers did not set out to study penile spines. Rather, they were looking for chunks of DNA that had been lost from the human genome but not the chimp genome, so they could then try to pinpoint what those chunks did.
(One primatologist pointed out, after this study was published, btw, that few chimp spines have actually been seen and they're more like little bumps than spines, but that, too, detracts from the bloody teeth and claw view. http://zinjanthropus.wordpress.com/2011/03/11/penis-spines-pearly-papules-and-pope-benedicts-balls/)
The approach differs from that in most studies, explain Bejerano and Kingsley, in looking at what has been deleted from the human genome rather than what is present. "In the case of our study, had you started from the human genome, there would be nothing there to see," says Bejerano.
They first systematically identified 510 DNA sequences missing in humans and present in chimps, finding that those sequences were almost exclusively from the non-coding regions of the genome, between genes. They then homed in on two sequences whose absence in humans they thought might be interesting — one from near the androgen receptor (AR) gene and one from near a gene involved in tumour suppression (GADD45G)
Until the bonobo genome is compared, it's an assumption to say those DNA sequences were deleted from humans rather than added to common chimps.
What's also interesting about the study when it has been reported is the mingling of the two DNA sequences, as tho the expression or deletion of one was necessary for the other.
Someone did compare the three genomes.
Because the population split between bonobo and chimpanzee occurred relatively close in time to the split between the bonobo–chimpanzee ancestor (Pan ancestor) and humans, not all genomic regions are expected to show the pattern in which DNA sequences from bonobos and chimpanzees are more closely related to each other than to humans. Previous work using very low-coverage sequencing of ape genomes has suggested that less than 1% of the human genome may be more closely related to one of the two apes than the ape genomes are to one another12. To investigate the extent to which such so-called incomplete lineage sorting (ILS) exists between the three species, we used the bonobo genome and a coalescent hidden Markov model (HMM) approach13 to analyse non-repetitive parts of the bonobo, chimpanzee6, human14 and orang-utan15 genomes. This showed that 1.6% of the human genome is more closely related to the bonobo genome than to the chimpanzee genome, and that 1.7% of the human genome is more closely related to the chimpanzee than to the bonobo genome.
Even when the issue isn't divided into common v bonobo chimp activity and humans, when a conclusion reinforces right wing views of human behavior (i.e. sex as an commodity exchange.) this story gets told and the evidence that contradicts this view never seems to get the same amount of attention.
for instance - http://www.newscientist.com/article/dn18968-exchange-meat-for-sex-no-thank-you.html
"I kept finding references to 'meat for sex' all over the place, saying this is what chimpanzees do," says Ian Gilby, a primatologist at Duke University in Durham, North Carolina. "Knowing from observation and reading the evidence, they really don't."
Most reports of male chimps trading meat for sex are anecdotal, Gilby says. Only one study has found statistically meaningful, if indirect, support for such swaps, showing that male chimpanzees are more likely to hunt for monkeys when oestrous females are around.
Yet when Gilby's team examined observations from four chimpanzee communities in Uganda and Tanzania spanning 28 years, they found no evidence that female fertility affected whether males hunted or not.
The article goes on to note that begging - from both genders - results in sharing, and the likely reason is because, until the meat is shared, others will keep begging.
Another study indicated meat sharing with females resulted in more mating with them - but this could occur more than a year after the sharing - so there was no one-to-one trade off in one action related to the other. Instead..
Gomes (who did the study immediately above) also notes that Gilby's team examined only east African chimpanzees, and points out that the west African animals she studied in the Ivory Coast's Taï National Park behave differently. Compared to their eastern brethren, western chimps share meat more often but have less sex.
So...so much for that worn out idea too.
What do we know about bonobos? We know that females leave their group seek their mate - they don't wait for a male to find them. Female bonobos in estrus wander from community to community - their sexual readiness allows them to mate with male and female to avoid attacks from strangers.
They don't pair bond, but females may return to their original community when they're pregnant, or they may remain in a new community if the females there accept them - because bonobo societies are based upon female bonds.
When people write about bonobos, they call them the "free love" chimpanzees - but the reality is that their social structures are matrilineal - and that's what you don't usually hear about them. Males stay home. Females roam.
Proto human A. africanus populations that have been studied in southern Africa also suggest females left their childhood homes, while males stayed at home, based upon the analysis of metallic traces in teeth (these traces are related to geological areas.) The samples indicated most the males lived and died around the same river valley, but not the females. This is the same pattern found in chimpanzees and bonobos.
There is no evidence of female monogamy among our proto human ancestors - although our current sexual physiology places us as less promiscuous than either common or bonobo chimps but without the male dominance of gorillas. We fall in between these two reproductive strategies in terms of relative size of females and males (sexual dimorphism) and penis and testes size.
Have I just not been paying attention to media - or are these pertinent realities of human prehistory considered givens? It seems like the standard stereotype is the he-man cave man, not the wandering woman.
But it's the female who goes on the "hero's journey" in human prehistory.
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