Human ancestor was less-chimp-like than thought: study

Dec 03, 2013 by Mariette Le Roux
Orrorin tugenensis femur. Credit: David Alba

The last common ancestor of Man and Ape was not a knuckle-walking, tree-swinging hominid resembling today's chimpanzee, said a study Tuesday challenging some long-held theories of human evolution.

Rather than a prototype chimp as commonly believed, our common forefather was an ape unlike any that exists today.

From it, humans and modern-day evolved into two completely different directions, according to research published in the journal Nature Communications.

"The majority of palaeoanthropologists tend to assume that the last common ancestor of and humans looked like a chimpanzee," said anatomical scientist Sergio Almecija of the Stony Brook University Medical Center in New York.

"However, there is growing evidence suggesting that the... great apes are not 'living time machines' reflecting our past, but that they have also evolved since their lineage split from that of humans millions of years ago."

Almecija and a team from the United States and Spain base their conclusions on the study of a femur from an ape dubbed "Millennium Man" that lived in Kenya some six million years ago.

Theirs was the first study to compare Millennium Man's physiology not only to humans and living apes, but also that lived in the Miocene period some 23 to 5.3 million years ago.

Their analysis placed the tree-climbing, upright-walking specimen, scientific name Orrorin tugenensis, into an evolutionary bracket between the unidentified common human-ape ancestor and the line that led to modern homo sapiens.

This, in turn, filled in some evolutionary knowledge gaps, and showed the common ancestor was likely very similar to Orrorin and very different to modern chimps—which diverged with humans about 7-6 million years ago.

"Our... reconstruction reveals that some Miocene apes represent a more appropriate model for the ancestral morphology from which hominins (humans and their ancestors) evolved than do (living) great apes," said the study.

The last , whose identity remains uncertain, most likely walked around on all fours like today's apes, but leaning on its palms instead of front knuckles, said Almecija.

Like the Miocene apes, it would have had smaller hands and shorter, straighter fingers than modern chimps, and probably did not swing through the trees hanging from branches—instead shuffling about the canopy on all fours, sometimes upright, grabbing onto branches for support.

The Miocene had a far greater diversity of apes than the world today, said Almecija.

But since they did not look or move like today's chimp, Man's closest living genetic relative, they were largely overlooked in the study of human evolution.

"Living apes (chimpanzees, gorillas and orangutans) have long and independent evolutionary histories of their own, and their modern anatomies should not be assumed to represent the ancestral condition for our human lineage," said Almecija.

"To understand the origins of human bipedalism, scientists should stop assuming a 'chimpanzee starting point'," he told AFP.

Such assumptions may lead to "strongly misguided hypotheses on the actual pathway of ," according to the study.

Explore further: Mexico archaeologists explore Teotihuacan tunnel (Update)

More information: Paper: dx.doi.org/10.1038/ncomms3888

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User comments : 16

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QuixoteJ
2.6 / 5 (5) Dec 03, 2013
ATTN Mariette Le Roux, writer of this article: Homo Sapiens invented something called a "paragraph". And you have no idea what one is.
AdamCC
3 / 5 (2) Dec 03, 2013
ATTN Mariette Le Roux, writer of this article: Homo Sapiens invented something called a "paragraph". And you have no idea what one is.


Wow ... I knew something was off, but didn't realize until reading this comment that each and every sentence is its own paragraph. Impressive.
foolspoo
3 / 5 (2) Dec 03, 2013
i've recognized this when i was in my early twenties... amazing how finite so many intelligent folks thought is
Torbjorn_Larsson_OM
5 / 5 (1) Dec 03, 2013
"a study Tuesday challenging some long-held theories of human evolution." More precisely, challenging again, there has been a lot of papers challenging this lately. In fact, I don't think it has been the consensus lately (but I'm no paleoanthropologist). The sometimes upright shuffling to be sure, but especially the ancestral generic hand vs the chimp/bonobo and gorilla different knuckle walk mechanisms in their hands.

@foolspo: Paragraphs or more generic ancestor? The latter has an old heritage [too =D] so it isn't lack of ideas but preconceptions that have ruled the area.
Torbjorn_Larsson_OM
5 / 5 (1) Dec 03, 2013
On paragraphs, I didn't notice it either (perhaps because the text was so interesting). There is also the reverse behavior. As an anecdote, my father has a business letter where the author built up subclauses like crazy resulting in three (3!) sentences as paragraphs.

The letter was readable because it captured the logic of the product order et cetera. It just took you a lot longer than usual, and you had to check the finishing clauses against the matching opening ones. But I had to laugh when I read a scifi where the story binds together Reality As Created By An Author with a similar story of substories, using a clause device. The recursive story ends in catastrophe as the clause structure "comes crashing down" when a sub-sub-sub-...-sub story happens to end ...
Maggnus
5 / 5 (4) Dec 03, 2013
It seems sort of like a "duh" comment to suggest that the great apes have been evolving alongside hominids. That seems so obvious as to invoke laughter that it wouldn't be considered by those studying hominid and/or great ape evolution.
TimChase
3 / 5 (2) Dec 03, 2013
Magnus wrote:
It seems sort of like a "duh" comment to suggest that the great apes have been evolving alongside hominids. That seems so obvious as to invoke laughter that it wouldn't be considered by those studying hominid and/or great ape evolution.
I almost get the impression you believe that evolution is like some sort of tree rather than a ladder... Of course, among bacteria and the phages that infect them, the tree of descent gives way to a web in which horizontal gene transfer plays a major role. Please see for example:

Hendrix, Roger W., et al. "Evolutionary relationships among diverse bacteriophages and prophages: all the world'sa phage." Proceedings of the National Academy of Sciences 96.5 (1999): 2192-2197.
http://www.pnas.o...192.full

But even among mammals...

Oliveira, Sarah G., et al. "Horizontal transfers of Mariner transposons between mammals and insects." Mobile DNA 3.1 (2012): 14.
http://www.mobile...ent/3/1/
Shakescene21
3 / 5 (2) Dec 03, 2013

"To understand the origins of human bipedalism, scientists should stop assuming a 'chimpanzee starting point'," he told AFP.

Forty years ago my zoology professor pointed out that hominids and chimps evolved from a common ancestor. I don't think many scientists think that the chimpanzee was the starting point.
Ens
Dec 04, 2013
This comment has been removed by a moderator.
Maggnus
4 / 5 (1) Dec 04, 2013
almost get the impression you believe that evolution is like some sort of tree rather than a ladder...


Certainly more a tree than a ladder, and frankly more like a bush than a tree. Describing it as a web is a good analogy for lesser species (such as bacteria) and there is evidence for horizontal gene transfer between species.

I fail to see your point?

Maggnus
4 / 5 (1) Dec 04, 2013
I don't think many scientists think that the chimpanzee was the starting point.


True, I would think the article was more aimed towards a layperson or a religious fundamentalist than scientists per se.

foolspoo
1 / 5 (1) Dec 04, 2013
Makes me wonder how long it will be until we begin to realize that we are not evolved from the species....
TimChase
5 / 5 (1) Dec 05, 2013
Maggnus wrote:
Certainly more a tree than a ladder, and frankly more like a bush than a tree. Describing it as a web is a good analogy for lesser species (such as bacteria) and there is evidence for horizontal gene transfer between species.

I fail to see your point?


I was agreeing with you, but trying to do so in a humorous fashion. Obviously it is more like a tree than a ladder. This much is something that has been with us since Darwin's "Origin." However, I didn't want to simply leave it at "tree" as this might have left me open to easy criticism to the effect of "how quaint..." So I brought in the lateral gene transfer, which plays a major role in the evolution of bacteria, but significant even at the level of mammals, e.g., the role of retroviruses in the origin of the placenta.

Please see:

Malik, H. S. (2012). Retroviruses push the envelope for mammalian placentation. Proceedings of the National Academy of Sciences, 109(7), 2184-2185.
http://www.pnas.o...tent/109
TimChase
5 / 5 (1) Dec 05, 2013
Maggnus, for the most part, bringing in the examples of lateral gene transfer was simply intended as a lagniappe. Something a little extra, because it might be of interest. By now a lot of people know about the role of endogenous retroviruses in the origin of the placenta, but that is essentially viral infection of the germline, which at one level at least isn't that strange. Nevertheless, worth including for those who aren't aware of it. The discovery of lateral gene transfer between multicellular species... that is more recent. And that is what I included the first time around. Anyway, just sharing with someone who I think had an important point, I guess out of a sense of shared values. Along the same lines as a thank you, I suppose. Take care.
Maggnus
5 / 5 (1) Dec 06, 2013
I was agreeing with you, but trying to do so in a humorous fashion.
Ah, I thought it must be so, but I wasn't sure, thus my question. And ya, I agreed with you on the lateral gene transfer, it's an interesting (to say the least!) aspect of evolutionary science that's showing up in some surprising places. I recall a study from my college days (sorry I can't find it to link to it) where a bacterium was introduced to a medium of cells, then a poison was added to the medium to cause the death of the cells. Later, a small colony was found, who seemed to have taken the bacterium's DNA into itself, and was thriving in the poison meant to kill it. When they removed the poison, the colony died off, suggesting that the introduction of the bacterium DNA actually altered the cells that survived, to allow them to resist the poison. The creation of a new species, perhaps.
simply intended as a lagniappe.
Lol I had to look that up! Thanks back at you :)
Moebius
not rated yet Dec 08, 2013
"Human ancestor was less-chimp-like than thought"

They say that like WE aren't chimp like, lol.
Returners
1 / 5 (1) Dec 27, 2013
One wonders when "science" will simply take a step back and look at the differences in morphology that exist within modern humans.

All one need do is stand in a grocery line and look around at the enormous variety in the height and the bone structure of any number of people, from dwarf to "giant," from rail thin, to "big boned," and not as an excuse to be fat either. Not everyone walks the same either. Some are knock-kneed and pigeon toed and others are bow-legged.

If presented with bones dug up from the local grave yard, but labelled in anonymity, one begins to wonder whether these "scientists" would classify each and every specimen as a different species. You could especially make them look fools if you use only one or two bones per specimen, and no skull. I think 10 specimens would likely yield nine "new species" announcements.

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