Human evolution News

Humans, primates split 2 mya earlier than thought?

Spread the love
Chororapithecus teeth, 8 mya/Gen suwa

From ScienceDaily:

Fossil analysis pushes back human split from other primates by two million years

A paper in the latest issue of the journal Nature suggests a common ancestor of apes and humans, Chororapithecus abyssinicus, evolved in Africa, not Eurasia, two million years earlier than previously thought.

“Our new research supports early divergence: 10 million years ago for the human-gorilla split and 8 million years ago for our split from chimpanzees,” said Los Alamos National Laboratory geologist and senior team member Giday WoldeGabriel. “That’s at least 2 million years earlier than previous estimates, which were based on genetic science that lacked fossil evidence.”

“Our analysis of C. abyssinicus fossils reveals the ape to be only 8 million years old, younger than previously thought. This is the time period when human and African ape lines were thought to have split, but no fossils from this period had been found until now,” WoldeGabriel said.

According to the paper, C. abyssinicus revealed answers about gorilla lineage but also provided fossil evidence that our common ancestor migrated from Africa, not Eurasia, where fossils were more prolific prior to this discovery of multiple skeletons. While some skeptics say that more fossil evidence is needed before they accept this team’s conclusions, many agree that the discovery of a fossil ape from this time period is important since only one other had been found. More.

Wouldn’t bet the rent on this but it raises a question: If it were really true that the human genome shows 98%-99% similarity with the chimpanzee after all these years, that is quite a lot of stasis. No?

See also: Stasis: Life goes on but evolution does not happen

Follow UD News at Twitter!

Here’s the abstract:

The palaeobiological record of 12 million to 7 million years ago (Ma) is crucial to the elucidation of African ape and human origins, but few fossil assemblages of this period have been reported from sub-Saharan Africa. Since the 1970s, the Chorora Formation, Ethiopia, has been widely considered to contain ~10.5 million year (Myr) old mammalian fossils1, 2, 3, 4, 5, 6, 7. More recently, Chororapithecus abyssinicus, a probable primitive member of the gorilla clade6, was discovered from the formation. Here we report new field observations and geochemical, magnetostratigraphic and radioisotopic results that securely place the Chorora Formation sediments to between ~9 and ~7?Ma. The C. abyssinicus fossils are ~8.0?Myr old, forming a revised age constraint of the human–gorilla split. Other Chorora fossils range in age from ~8.5 to 7?Ma and comprise the first sub-Saharan mammalian assemblage that spans this period. These fossils suggest indigenous African evolution of multiple mammalian lineages/groups between 10 and 7?Ma, including a possible ancestral-descendent relationship between the ~9.8?Myr old Nakalipithecus nakayamai8 and C. abyssinicus. The new chronology and fossils suggest that faunal provinciality between eastern Africa and Eurasia had intensified by ~9?Ma, with decreased faunal interchange thereafter9, 10, 11, 12. The Chorora evidence supports the hypothesis of in situ African evolution of the Gorilla–Pan–human clade, and is concordant with the deeper divergence estimates of humans and great apes based on lower mutation rates of ~0.5?×?10-9 per site per year (refs 13, 14, 15). (paywall) – Shigehiro Katoh, Yonas Beyene, Tetsumaru Itaya, Hironobu Hyodo, Masayuki Hyodo, Koshi Yagi, Chitaro Gouzu, Giday WoldeGabriel, William K. Hart, Stanley H. Ambrose, Hideo Nakaya, Raymond L. Bernor, Jean-Renaud Boisserie, Faysal Bibi, Haruo Saegusa, Tomohiko Sasaki, Katsuhiro Sano, Berhane Asfaw, Gen Suwa. New geological and palaeontological age constraint for the gorilla–human lineage split. Nature, 2016; 530 (7589): 215 DOI: 10.1038/nature16510

2 Replies to “Humans, primates split 2 mya earlier than thought?

  1. 1
    Larry Moran says:

    Denyse O’Leary says,

    Wouldn’t bet the rent on this but it raises a question: If it were really true that the human genome shows 98%-99% similarity with the chimpanzee after all these years, that is quite a lot of stasis. No?

    No! It gets really tiresome having to explain basic scientific facts to you guys every few months. We’ve been over this point dozens and dozens of times in the past twenty years or so.

    If you don’t want to learn about the science that you so irrationally oppose then just admit that you want to remain ignorant and stop asking stupid questions that have been answered over and over again.

    The human and chimp genomes are 98.6% identical at the sequence level. This is the value we use to calculate evolutionary divergence since deletions and insertion are single mutations that don’t contribute much to the calculation.

    That value (98.6%) works out to 44.8 million bp differences between the human and chimpanzee (haploid) genomes. If they diverged from a common ancestor then this means 22.4 million substitutions in each lineage.

    Those substitutions are almost all neutral with respect to natural selection since the vast majority occur in junk DNA (~90% of the genome). That means they will be fixed at a rate equal to the mutation rate according to modern evolutionary theory.

    You may or may not believe that chimps and humans evolved from a common ancestor and you may or may not believe that most of our genome is junk. That’s not the point. You can argue those issues separately. But if you ask the question Denyse asked then here’s the correct scientific explanation.

    We don’t know the exact mutation rate. Estimates vary from a low of about 75 new mutations per generation to a high of about 130 mutations per generation [see Human mutation rates].

    We don’t know the exact time of divergence of the human and chimpanzee lineages but the current consensus is about five million years. That’s 182,000 generations since the average generation time of modern humans and chimps is 27.5 years.

    If the mutation rate is 100 per generation then there should be 18.2 million fixed mutations in each lineage and that’s pretty close to the observed number of 22.4 million. Obviously, the values would match exactly if the mutation rate were 123 mutations per generation and this is well within the range that being discussed in the scientific literature [see Why are the human and chimpanzee/bonobo genomes so similar?].

    If the time of divergence was seven million years—as suggested in the article—then this corresponds to 255,000 generations. In order for that to explain the differences, we would need a mutation rate of 88 mutations per generation and that’s also well within the range (75 – 130) that’s been calculated. (These are rough estimates of the rate of mutation/fixation. There are more sophisticated ways of doing the calculation but it doesn’t change the bottom line very much and this calculation is simple enough, and accurate enough, for the average person.)

    We don’t know the exact mutation rate, although I think it’s likely to be about 100 per generation and we don’t know the exact time of divergence, although the date is likely to be closer to five million than seven million.

    But in spite of these uncertainties, there’s no problem for evolution. Everything we know is consistent with humans and chimps sharing a common ancestor millions of years ago and it’s consistent with our current understanding of mutation rates, population genetics, and evolutionary theory.

    Move along folks, there’s noting to see here. Ask the Intelligent Design Creationists if they have a different, and better, explanation that accounts for the data. (Hint: they don’t.)

  2. 2
    Virgil Cain says:

    Moran:

    It gets really tiresome having to explain basic scientific facts to you guys every few months.

    The basic scientific fact is that your position isn’t science, Moran. It isn’t science because its claims cannot be scientifically tested.

    The human and chimp genomes are 98.6% identical at the sequence level.

    That is incorrect and demonstrates ignorance on your part.

    If the mutation rate is 100 per generation then there should be 18.2 million fixed mutations in each lineage

    That doesn’t follow. Also are you saying that any ole mutations will do? How can we test the claim that changes to the genomes can produce the morphological and physiological changes required?

    But in spite of these uncertainties, there’s no problem for evolution

    Cuz Moran sez so! Science by proclamation at its finest!

    And Common Design is a better explanation for the data. At least we have real-time experience with that.

Leave a Reply