Human evolution News

Humans split from apes later than thought?

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6.6 MYA? See, for comparison, “Human and Chimp Genes May Have Split 13 Million Years Ago (LiveScience, 2014) Other estimates are on offer.

Trying to resolve discrepancies between the molecular clock and human/hominid evolution, from ScienceDaily:

Researchers at Columbia University introduce a model that considers how life history traits (e.g., age of puberty and reproduction) in parents affect the number of mutations inherited by their children. They find that because life history traits evolve, so should the mutation rate. In other words, the molecular clock is expected to wobble.

Based on this model, and using what we know about life history traits in apes, they revisit the question of when humans and other apes split. Accounting for changes to life history on the ape phylogeny suggests that mutation rates have declined toward the present, supporting the notion of a mutational slowdown. The resulting split time estimates reconcile the genetic and paleontological data, and in particular, they suggest that the human-chimp split may have occurred as recently as 6.6 MYA. More.

Note: It’s not often that we get to use “later than thought” in a sentence. See the history of “earlier than thought” for background.

See also: Dreadful row breaks out re cladistics A good deal surely depends on how evolution actually occurs. Talk to the fossils: Let’s see what they say back.

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Here’s the significance/abstract:

Significance: Recent estimates of mutation rates obtained by sequencing human pedigrees have challenged conceptions about split times between humans and our closest living relatives. In particular, estimates of human split times from chimpanzees and gorillas based on the new mutation rate estimates are more than twofold shorter than previously believed, seemingly at odds with the fossil record. Here we show that accounting for the effects of sex-specific life histories on mutation rates along the hominid phylogeny largely bridges this apparent gap and leads to more accurate split time estimates. Doing so can also explain other intriguing phylogenetic patterns in hominid and mammalian evolution.

Abstract: One of the foundational results in molecular evolution is that the rate at which neutral substitutions accumulate on a lineage equals the rate at which mutations arise. Traits that affect rates of mutation therefore also affect the phylogenetic “molecular clock.” We consider the effects of sex-specific generation times and mutation rates in species with two sexes. In particular, we focus on the effects that the age of onset of male puberty and rates of spermatogenesis have likely had in hominids (great apes), considering a model that approximates features of the mutational process in mammals, birds, and some other vertebrates. As we show, this model can account for a number of seemingly disparate observations: notably, the puzzlingly low X-to-autosome ratios of substitution rates in humans and chimpanzees and differences in rates of autosomal substitutions among hominine lineages (i.e., humans, chimpanzees, and gorillas). The model further suggests how to translate pedigree-based estimates of human mutation rates into split times among extant hominoids (apes), given sex-specific life histories. In so doing, it largely bridges the gap reported between estimates of split times based on fossil and molecular evidence, in particular suggesting that the human–chimpanzee split may have occurred as recently as 6.6 Mya. The model also implies that the “generation time effect” should be stronger in short-lived species, explaining why the generation time has a major influence on yearly substitution rates in mammals but only a subtle one in human pedigrees. Open access – Guy Amster, Guy Sella. Life history effects on the molecular clock of autosomes and sex chromosomes. Proceedings of the National Academy of Sciences, 2016; 201515798 DOI: 10.1073/pnas.1515798113

2 Replies to “Humans split from apes later than thought?

  1. 1
    DonaldM says:

    It would be interesting to research exactly how many papers have been published with varying estimates on when the supposed split between the chimp/human lineages took place. I suspect there are dozens if not hundreds of such peer reviewed papers in the various science journals.

    What never occurs to any of the researchers is that perhaps the problem of identifying when such a split took place is because it never actually did. Maybe the problem is there because they overlook (for purely ‘methodological’ reasons mind you) what may be staring them in face: DESIGN!

  2. 2
    GaryGaulin says:

    The large number of estimates help show how abundant the evidence for common descent actually is. There is so much of it the problem is more like where to begin, and how to accurately measure the elapsed time.

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