Did Neanderthals (Homo neanderthalis) really Interbreed with Humans (Homo sapiens)?

Warning: Do not read this blog entry, if you are younger than 18.  The nude images might cause blindness.

A new study published in the scientific journal, Nature, of a 40,000 year old skull suggests Neanderthals (Homo neanderthalis) interbred with humans (Homo sapiens).  This particular specimen, found in Romania, is thought to be 6%-9% Neanderthal, and the authors of this study think this individual had a great-great-great-great Neanderthal grandparent.  He left no living  descendants, but other studies of Neanderthal DNA determined Homo sapiens and Homo neandetheralis did hybridize, and some modern Europeans and Asians might be 1%-3% Neanderthal.  The media likes this story, and a study casting doubt on the assumptions used to identify past hybridization is being ignored.  I didn’t even see the study listed in the new journal article’s references, so the scientists involved in Neanderthal DNA studies are unaware of the article or are ignoring it as well.

The ignored study, referenced below, was written by A. Ericksson and A. Manica.  They write “tests for hybridization rely on the degree to which different modern populations share genetic polymorphisms with genomes of other hominins.”  A polymorphism is defined as 2 clearly different phenotypes existing in the same population of a species.  A phenotype is the composite of an organisms observable characteristics.  For example a population of humans could consist of big blondes and small brunettes–2 different phenotypes.  The authors of this study show that examples of shared polymorphism attributed to hybridization could actually have originated before H. neanderthalis and H. sapiens diverged over 200,000 years ago.  Both species of humans evolved from H. heidelbergensis.  The population of H. heidelbergensis that colonized Europe evolved into H. neanderthalis.  The population of H. heidelbergensis that stayed in Africa until ~45,000 years ago evolved into H. sapiens.  An Asian colonization evolved into the poorly known Denisovans.

The authors of this study believe their findings don’t rule out the possibility of hybridization in Europe, but they urge “caution” when making the assumption that hybridization occurred.  To determine whether or not the degree of shared polymorphism was the result of hybridization or was part of an earlier genetic pattern from the founding population structure would require DNA from a specimen pre-dating the divergence of these 2 species.  Viable DNA can’t be extracted from specimens that old.

Representation of a female Neanderthal based on DNA studies.  Note the red hair.  Neanderthals had red hair.

Nude female Homo sapiens.  Human women are much cuter than Homo neanderthalis.  Moreover, female Neanderthals were probably considerably stronger than male Homo sapiens.  I doubt the 2 species interbred.  Genetic studies can’t discern certain hybridization without studying the DNA of the ancestral common ancestor of both species.  This is impossible because those fossils are too old to harbor DNA.

I doubt H. sapiens bred with H. neanderthalis.  The 2 populations of humans had been isolated from each other for over 200,000 years.  Behavior patterns likely dramatically differed. Facial features were significantly different, and I think they didn’t recognize each other as mating material.  Neanderthals were intelligent ambush predators that used thrusting weapons, and they were physically more powerful than humans.  But humans were smarter and had developed projectile weapons.  Humans ate a wider variety of foodstuffs, contributing to greater fertility.  I think humans wiped out Neanderthals within a few thousand years.  Assimilation was unlikely.

Reference:

Ericksson, A.; and A. Manica

“Effect of Ancient Population Structure on the Degree of Polymorphism Shared between Modern Human Populations and Ancient Hominins”

PNAS 2012

http://www.pnas.org/content/109/35/13956.full

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Tags: Homo heidelbergensis, Homo neanderthalis, Homo sapiens, phenotype, shared polymorphism