Ancient DNA and Neanderthals

Neanderthal Genes for Red Hair and More...

Red-Headed Neanderthals

Ancient DNA has been used to show aspects of Neanderthal appearance. A fragment of the gene for the melanocortin 1 receptor (MRC1) was sequenced using DNA from two Neanderthal specimens from Spain and Italy, El Sidrón 1252 and Monte Lessini (Lalueza-Fox et al. 2007). Neanderthals had a mutation in this receptor gene that has not been found in modern humans. The mutation changes an amino acid, making the resulting protein less efficient. Modern humans have other MCR1 variants that are also less active resulting in red hair and pale skin. The less active Neanderthal mutation probably also resulted in red hair and pale skin, as in modern humans.

The specific MCR1 mutation in Neanderthals has not found in modern humans (or occurs extremely rarely in modern humans). This indicates that the two mutations for red hair and pale skin occurred independently and does not support the idea of gene flow between Neanderthals and modern humans. Pale skin may have been advantageous to Neanderthals living in Europe because of the ability to synthesize vitamin D.  

A reconstruction of a male Neanderthal head by John Gurche

This reconstruction of a male Neanderthal by John Gurche features pale skin, but not red hair.

 

Neanderthals, Language and FOXP2

The FOXP2 gene is involved in speech and language (Lai et al. 2001). Changes in the FOXP2 gene sequence led to problems with speech, oral and facial muscle control in modern humans with a mutation in the gene. It impairs language function. Modern humans and Neanderthals share two changes in FOXP2 compared with the sequence in chimpanzees (Krause et al. 2007). Neanderthals may also have their own unique derived characteristics in the FOXP2 gene that were not tested for in this study.

The human FOXP2 gene is on a haplotype that was subject to a strong selective sweep. A haplotype is a set of alleles that are inherited together on the same chromosome. The researchers then tried to determine how the FOXP2 variant came to be found in both Neanderthals and modern humans. One scenario is that it could have been transferred between species via gene flow. The researchers do not think this is likely since there is no evidence indicating that gene flow has occurred. Another possibility is that the derived FOXP2 was present in the ancestor of both anatomically modern Homo sapiens and Neanderthals with the selective sweep that made it prevalent occurring after the divergence between the groups. A third scenario, which the authors think is most likely, is that the changes and selective sweep occurred before the divergence between the populations.  

 

ABO Blood Types and Neanderthals

The gene that produces the ABO blood system is polymorphic in humans. Various selection factors may favor different alleles, leading to the maintenance of distinct blood groups in modern human populations. Though chimpanzees also have different blood groups, they are not the same as human blood types. While the mutation that causes the human B blood group arose around 3.5 Ma, the O group mutation dates to around 1.15 Ma. Lalueza-Fox and colleagues (2008) tested whether Neanderthals had the O blood group. They found that two Neanderthal specimens from Spain probably had the O blood type, though there is the possibility that they were OA or OB. Though the O allele was likely to have already appeared before the split between humans and Neanderthals, it could also have arisen in the Neanderthal genome via gene from modern humans.

 

Bitter Taste Perception and Neanderthals

Like some modern humans, some Neanderthals were able to taste bitter substances. Some items that taste bitter may be toxic in large quantities so the ability to taste bitter substances may have protected hominins from accidental poisoning. Some of these bitter chemicals are found in vegetables. For instance, humans vary in their ability to perceive a bitter substance similar to that found in Brussels sprouts, broccoli and cabbage.

The ability to taste bitter substances is controlled by a gene, TAS2R38. Some individuals are able to taste bitter substances, while others have a different version of the gene that does not allow them to taste bitter items. Possession of two copies of alleles associated with tasting bitter substances gives the individual greater perception of bitter tastes than the heterozygous state, in which individuals have one tasting allele and one non-tasting allele. Two copies of a non-tasting allele leads to inability to taste bitter substances.

A Neanderthal from El Sidrón, Spain, was sequenced for the TAS23R38 gene. They found that this individual was heterozygous and thus was able to perceive bitter taste, although not as strongly as a homozygous individual with two copies of the tasting allele would be able to (Lalueza-Fox et al. 2009). Since the Neanderthal sequenced was heterozygous, the two alleles (tasting and non-tasting) were probably both present in the common ancestor of Neanderthals and modern humans. Though chimpanzees also vary in their ability to taste bitterness, their abilities are controlled by different alleles than those found in humans, indicating that non-tasting alleles evolved separately in the hominin lineage.

 

Microcephalin and Archaic Hominins

The microcephalin gene relates to brain size during development. A variant of this, haplogroup D, may have been positively selected for in modern humans – and may also have come from an interbreeding event with an archaic population (Evans et al. 2006). Mutations in microcephalin cause the brain to be 3 to 4 times smaller in size. All of the haplogroup D variants come from a single copy that appeared in modern humans around 37,000 years ago. However, haplogroup D itself came from a lineage that had diverged from the lineage that led to modern humans around 1.1 million years ago. Although there was speculation that the Neanderthals were the source of the microcephalin haplogroup D (Evans et al. 2006), the Neanderthal DNA recently sequenced does not contain the microcephalin haplogroup D (Green et al. 2010).