Neanderthals & humans may have interbred

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Soficaru, A. et al. (2006). Early modern humans from the Petera Muierii, Baia de Fier, Romania. Proc Nat Acad Sci, USA 103:1 7196-17201.

The early modern human remains from the Petera Muierii, Romania have been directly dated to ~30,000 radiocarbon years before present (~30 ka 14C BP) (~35 ka cal BP) (“calendrical” age; based on CalPal 2005) and augment a small sample of securely dated, European, pre-28 ka 14C BP (~32.5 ka cal BP) modern human remains. The Muierii fossils exhibit a suite of derived modern human features, including reduced maxillae with pronounced canine fossae, a narrow nasal aperture, small superciliary arches, an arched parietal curve, zygomatic arch above the auditory porous, laterally bulbous mastoid processes, narrow mandibular corpus, reduced anterior dentition, ventral-to-bisulcate scapular axillary border, and planoconcave tibial and fibular diaphyseal surfaces. However, these traits co-occur with contextually archaic and/or Neandertal features, including a moderately low frontal arc, a large occipital bun, a high coronoid process and asymmetrical mandibular notch, a more medial mandibular notch crest to condylar position, and a narrow scapular glenoid fossa. As with other European early modern humans, the mosaic of modern human and archaic/Neandertal features, relative to their potential Middle Paleolithic ancestral populations, indicates considerable Neandertal/modern human admixture. Moreover, the narrow scapular glenoid fossa suggests habitual movements at variance with the associated projectile technology. The reproductive and scapulohumeral functional inferences emphasize the subtle natures of behavioral contrasts between Neandertals and these early modern Europeans.

Apparently, this means that the bones have features of both Neanderthals and modern humans. I’m no anthropologist, so as far as I’m concerned, the abstract may as well have been written in a foreign language. But John Hawks knows what he’s talking about.

There’s more evidence of Neanderthal-human interbreeding in this paper from Bruce Lahn‘s lab at the University of Chicago. This time, the evidence is genetic rather than palaeontological, and comes from the investigation of the origins of a version of the microcephalin gene called the haplotype D allele.

microcephalin is one of the genes that is known to have been subjected to strong positive selection in the human lineage. Although the exact function of microcephalin is unclear, it is known to be involved in regulating brain size during development, and may promote the proliferation of neural progenitor cells during development of the nervous system. Mutations in the gene give rise to microcephaly, a condition in which growth of the brain is retarded.

Previous work by Lahn’s team has shown that there are two distinct groups of microcephalin alleles (versions of the gene), called the D alleles and the non-D alleles. The genes in the D alleles group have very similar DNA sequences, and arose from the amplification of a single ancestral gene approximately 37,000 years ago.These versions of the microcephalin genes are now found in some 70% of the human population.

The paper published this week describes a detailed comparison of  the DNA sequence of haplotype D from 89 people from around the world. This sequence comparison suggests an early evolutionary origin for the allele that is prevalent in humans today, even  though the allele appeared in humans only 37,000 years ago.

Lahn and his colleagues therefore conclude that the haplotype D allele must have originated in another species of Homo before  being transferred to humans. They estimate that the two groups of microcephalin alleles diverged approximately 1.1 million years ago, with the non-D alleles evolving in the Homo sapiens lineage and the D alleles evolving in another Homo species which is now extinct. However, approximately 37,000 years ago, a copy of a microcephalin gene from the D allele group crossed from the archaic Homo species to Homo sapiens, in a process called introgression, which involves the flow of genes between partially isolated populations.  

“By no means do these findings constitute definitive proof that a Neanderthal was the source of the original copy of the D allele,” says Lahn. “However, our evidence shows that it is one of the best candidates. The timeline – including the introgression of the allele into humans 37,000 years ago and its origin in a lineage that separated with the human line 1.1 million years ago – agrees with the contact between, and the evolutionary history of, Neanderthals and humans. And a third line of evidence, albeit weaker, is that the D alleles are much more prevalent in Eurasia and lower in sub-Saharan Africa.”

Thus, we may owe our distinctive large brains to the transfer of a gene from Neanderthals. This transfer would have occurred through an interbreeding event between Neanderthals and modern humans. Interbreeding between the two lineages species may have been rare, but was sufficient to transfer a copy of the microcephalin gene to Homo sapiens, which then became widespread throughout the human population and continued to evolve. 

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5 thoughts on “Neanderthals & humans may have interbred

  1. John Hawks post is quite good. This distinction between Neanderthals and modern forms in Europe has been blurred for quite awhile; it’s definitely not a new argument.

    One large arguement comes down to the shape of the back of the head. Neanderthals often had a flat piece of bone called a colotte where the neck muscles attach to the back of the skull.

    Early Europeans had a greater frequency of this feature (and others) than later populations. Some people still have this shape to the back of the skull today!

    You can count my universities best bioarchaeologist prof. in the camp of thinking that some Europeans are descended in part from Neanderthals.

  2. Primitivism might be classified as the human indulgence to combine his rudimentary physical characteristics and processes and his capacity for superior brain development to perform as if he/she is more animal than human.

    Rarely done without conscious effort, however, except in severely autistic or retarded persons, the tendency to do so generally evolves from expected anticipated benefits to be gained circumstantially by the pretense that he is bound intellectually, or emotionally, or psychologically within that sphere of primitive weakness.

    Hence, for adults, excuses of inability to control one’s appetites, or desires, is consistent with the syndrome as if adults are unable to act with self discipline more characteristic of adult intelligence rather than childlike cognizance.

    Unless coerced, mankind lifts his perception beyond the rudimentary aspects of his once animal like existence, aided by the educational opportunities afforded him.

  3. Could neanderthals be to a certain extent the ancestors of Middle Eastern Anatoonlians or Semitic peoples,?? I find a lot of Neandertal traits in modern Near Easterners, such as the thick eyebrows, big noses, heavy body, pilosity (hairiness), and the expression of the reconstructed face, even the temperamental psyche and the harshness of the Middle Eastern languages (they have sounds which don’t exist anywhere else and which are very hard)…could this be a Neandertal strong survival in modern Near Easterners??

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