Author Topic: Homo sapiens and Their Cousins  (Read 7570 times)

Recusant

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Re: Homo sapiens and Their Cousins
« Reply #60 on: November 27, 2018, 07:39:12 PM »
I've personally never thought that the 'just the once' hypothesis (in which anatomically modern humans only interbred with Neanderthal on a single occasion) made any sense.

"Study suggests multiple instances of inter-breeding between Neanderthal and early humans" | PhysOrg

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A pair of researchers at Temple University has found evidence that suggests Neanderthals mated and produced offspring with anatomically modern humans multiple times—not just once, as has been suggested by prior research. In their paper published in the journal Nature Ecology and Evolution, Fernando Villanea and Joshua Schraiber describe their genetic analysis of East Asian and European people and how they compared to people from other places. Fabrizio Mafessoni with the Max Planck Institute for Evolutionary Anthropology offers a News and Views piece on the work done by the pair in the same journal issue.

In recent years, scientists have discovered that early humans moving out of Africa encountered Neanderthals living in parts of what is now Europe and Eastern Asia. In comparing Neanderthal DNA with modern humans, researchers have found that there was a least one pairing that led to offspring, which is reflected in the DNA of humans—approximately 2 percent of the DNA in non-African humans today is Neanderthal. In this new effort, the researchers have found evidence that suggests there was more than one such encounter.

[Continues . . .]

A full pre-print version of the paper is available: "Spectrum of Neandertal introgression across modern-day humans indicates multiple episodes of human-Neandertal interbreeding" | BioRxiv

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Abstract:

Neandertals and anatomically modern humans overlapped geographically for a period of over 30,000 years following human migration out of Africa. During this period, Neandertals and humans interbred, as evidenced by Neandertal portions of the genome carried by non-African individuals today. A key observation is that the proportion of Neandertal ancestry is ∼12-20% higher in East Asian individuals relative to European individuals.

Here, we explore various demographic models that could explain this observation. These include distinguishing between a single admixture event and multiple Neandertal contributions to either population, and the hypothesis that reduced Neandertal ancestry in modern Europeans resulted from more recent admixture with a ghost population that lacked a Neandertal ancestry component (the “dilution” hypothesis). In order to summarize the asymmetric pattern of Neandertal allele frequencies, we compile the joint fragment frequency spectrum (FFS) of European and East Asian Neandertal fragments and compare it to both analytical theory and data simulated under various models of admixture.

Using maximum likelihood and machine learning, we found that a simple model of a single admixture does not fit the empirical data, and instead favor a model of multiple episodes of gene flow into both European and East Asian populations. These findings indicate more long-term, complex interaction between humans and Neandertals than previously appreciated.
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Icarus

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Re: Homo sapiens and Their Cousins
« Reply #61 on: November 27, 2018, 11:10:26 PM »
That interbreeding may have occurred is not the least surprising. Not improbable either.  Sex drives are powerful enough to cause males to attempt interbreeding with sheep and whatever else is at hand. (Hand: no pun intended)

Ecurb Noselrub

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Re: Homo sapiens and Their Cousins
« Reply #62 on: November 29, 2018, 12:58:04 AM »
That interbreeding may have occurred is not the least surprising. Not improbable either.  Sex drives are powerful enough to cause males to attempt interbreeding with sheep and whatever else is at hand. (Hand: no pun intended)

I did NOT have sex with that sheep!

It seems more and more that they were not really all that different from us.  Maybe no more different than modern races, which aren't that different at all.  I suspect there was a whole lot of shakin' going on.   

Tank

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Re: Homo sapiens and Their Cousins
« Reply #63 on: November 29, 2018, 12:03:57 PM »

I did NOT have sex with that sheep!

Really? I was sure it was ewe!
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Ecurb Noselrub

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Re: Homo sapiens and Their Cousins
« Reply #64 on: November 30, 2018, 01:08:14 AM »

I did NOT have sex with that sheep!

Really? I was sure it was ewe!

Ewe just had to ram that one through, didn’t you?

Tank

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Re: Homo sapiens and Their Cousins
« Reply #65 on: November 30, 2018, 06:34:15 AM »

I did NOT have sex with that sheep!

Really? I was sure it was ewe!

Ewe just had to ram that one through, didn’t you?

I felt I should Shepard that train of thought.
If religions were TV channels atheism is turning the TV off.
“Religion is a culture of faith; science is a culture of doubt.” ― Richard P. Feynman
'It is said that your life flashes before your eyes just before you die. That is true, it's called Life.' - Terry Pratchett
Remember, your inability to grasp science is not a valid argument against it.

Recusant

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Re: Homo sapiens and Their Cousins
« Reply #66 on: January 17, 2019, 04:52:18 PM »
Interesting story about a study which appears to show that there was a fairly widespread hybrid of Neandethals and Denisovans that contributed to the modern human genome.

"Artificial intelligence applied to the genome identifies an unknown human ancestor" | ScienceDaily

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By combining deep learning algorithms and statistical methods, investigators from the Institute of Evolutionary Biology (IBE), the Centro Nacional de Análisis Genómico (CNAG-CRG) of the Centre for Genomic Regulation (CRG) and the Institute of Genomics at the University of Tartu have identified, in the genome of Asian individuals, the footprint of a new hominid who cross bred with its ancestors tens of thousands of years ago.

Modern human DNA computational analysis suggests that the extinct species was a hybrid of Neanderthals and Denisovans and cross bred with Out of Africa modern humans in Asia. This finding would explain that the hybrid found this summer in the caves of Denisova -- the offspring of a Neanderthal mother and a Denisovan father -- was not an isolated case, but rather was part of a more general introgression process.

The study, published in Nature Communications, uses deep learning for the first time ever to account for human evolution, paving the way for the application of this technology in other questions in biology, genomics and evolution.

[Continues . . .]

Full paper available: "Approximate Bayesian computation with deep learning supports a third archaic introgression in Asia and Oceania" | Nature Communications

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Abstract:

Since anatomically modern humans dispersed Out of Africa, the evolutionary history of Eurasian populations has been marked by introgressions from presently extinct hominins. Some of these introgressions have been identified using sequenced ancient genomes (Neanderthal and Denisova).

Other introgressions have been proposed for still unidentified groups using the genetic diversity present in current human populations. We built a demographic model based on deep learning in an Approximate Bayesian Computation framework to infer the evolutionary history of Eurasian populations including past introgression events in Out of Africa populations fitting the current genetic evidence.

In addition to the reported Neanderthal and Denisovan introgressions, our results support a third introgression in all Asian and Oceanian populations from an archaic population. This population is either related to the Neanderthal-Denisova clade or diverged early from the Denisova lineage. We propose the use of deep learning methods for clarifying situations with high complexity in evolutionary genomics.
"Religion is fundamentally opposed to everything I hold in veneration — courage, clear thinking, honesty, fairness, and above all, love of the truth."
— H. L. Mencken