Ape-Human Split Moved Back By Millions Of Years

E++99 writes in to let us know about a development in paleo-anthropology. It seems that up until now, scientific consensus has placed the divergence of man from the ape line five to six million years ago (based on "genetic distances"). But newly discovered fossils in Ethiopia place the divergence at least twice as far back, and perhaps as long ago as 20 million years. They also largely put to rest any doubts that man and modern apes both emerged from Africa. From the article: "The trail in the hunt for physical evidence of our human ancestors goes cold some six or seven million years ago... Beyond that... fossils of early humans from the Miocene period, 23 to five million years ago, disappear. Fossils of early apes especially during the critical period of 14 to eight million years ago were virtually non-existent — until now... [T]he new fossils, dubbed 'Chororapithecus abyssinicus' by the team of Japanese and Ethiopian paleo-anthropologists who found them, place the early ancestors of the modern day gorilla 10 to 10.5 million years in the past, suggesting that the human-ape split occurred before that."

Comments

Re:Misleading to talk about a "human-ape split"

[j01123]

Apes are monophyletic, because apes include humans. You are correct though, that the non-human apes are paraphyletic, because the closest living relative of the chimps are humans.

My impression of the Nature article (subscription required) is that the authors are claiming that their paleontologic find pushes the gorilla split (from the human-chimp lineage) back to ~12 million years. Based on this, they essentially recalibrate the molecular clock as it relates to several of the ape divergences. This information is in section 5 of the paper's online supplementary materials (subscription not required), not the body of the article. Keep in mind that supplementary materials generally aren't peer-reviewed as rigorously as the rest of the article.

Easy... it's pretty butchered and you're wrong.

[Tatarize]

Dinosaurs died out 65 million years ago at the KT boundary.

Prior to that time the mammal line had already split much more than we previously gave it credit for, a lot of the main groups were developed. This article is a fairly worthless crock. Basically some teeth were found that looked vaguely gorilla like and dated back 10 million years. So we know that there was some ape-like creature with a gorilla-like diet 10 million years ago. However, saying that this is the Ape-Human split is as stupid as saying it's the Human-Mammal split. Humans are apes. We are clearly within the same grouping of gorillas, orangutans, and chimps. There's no real grouping of animals which includes those yet excludes humans. This find perhaps sets back the date of chimp-gorilla split but not "human-ape". That's just stupid. Chimp-human is a split which dates back about 4-6 million years. Gorilla-chimp goes back 8 million years, though perhaps 10 if this isn't just some offshoot.

Finally, 10 million years is about 2/17th of 85 million years. Basically your math is off, and you're using old information, and to top it off this article is totally stupid. It's 10 million year old gorilla-like teeth. It actually has almost nothing to do with human evolution, though if you studied gorilla evolution you might care. Though, it's even weak evidence that it's actually a gorilla just that it had a diet like that of a gorilla.

The rate of phenotypic change isn't constant.

[Grendel Drago]

As someone else pointed out, the KT boundary was 65 Mya, not 85. Also, early mammals of that era are usually described as "shrew-like" (also nocturnal, which is why we all have different color vision systems than reptiles), so probably even smaller than that.

The line that would eventually give rise to the mammals split from the reptile lineage before the emergency of the dinosaurs (the number cited is 324 Mya); look up "synapsid" for more information. It was actually the dominant type of land fauna until the greatest mass extinction in history at the end of the Permian (250 Mya), which was followed by the emergence of the dinosaurs. There were large synapsids in the early years of the Mesozoic, but the branch that would give rise to the mammals--the cynodonts--emerged about 220 Mya. There's a rather exhaustive description over at Wikipedia; also see talkorigins.

On a more relevant note, consider the whales. It appears now that whales are more closely related to hippos than hippos are to cows. (Again, see Wikipedia for a good summary.) This was mightily confusing, because we generally take phenotypic change as an indicator of distance between species. The important thing to remember here is that species change due to pressures put on them. Rapid pressures brought on by migration into a new environment (like the sea, for example) will cause a greater rate of phenotype change than would exist if the environment remained constant--consider the shark for this latter case.

Also, as another commenter has pointed out, the mammalian lineages had already split at that point; divergence points for some groups of mammals are after the KT boundary, but many are before it. However, it appears that even though the groups were separate, they all looked pretty much alike until they migrated into the niches vacated by the dinosaurs and diverged widely.

And lastly, your math isn't quite right. 7 million years (the divergence point for the chimp and human lineages, notwithstanding a very poorly written article) is more like a tenth of the time it took to get from (many kinds of!) shrew-like mammals to a similar level of mammalian diversity to what we see today.