by Greg Mayer

In a soon to be published paper in the Royal Society’s Biology Letters (abstract only), Carles Lalueza-Fox of Universitat Pompeu Fabra ( website in Catalan!) in Barcelona and colleagues report that they have sequenced the gene TAS2R38 from a Neanderthal man (press coverage by the BBC and NY Times). The ability to sequence genes from fossil material is remarkable enough in itself, but this study has particular interest, and not just because it was done on one of our fossil relatives.  Variation in the gene they sequenced is responsible for the polymorphism in modern man for the ability to perceive bitter tastes (some people can tast bitter, some can’t). Determining the frequency of the two forms (or alleles) of the gene is a classic high school biology exercise, carried out by seeing who can taste the bitter chemical PTC.  People who have either one or two copies (humans are diploid, so most genes are present in each individual’s genome in two copies) of the taster allele can taste bitter; those with two copies of the non-taster allele cannot. Today, the two alleles are about equally frequent, so that about 25% of people have two taster alleles (i.e. they are homozygous for the taster allele), about 50% have one taster and one non-taster (they are heterozygotes), and 25% are homozygous for the non-taster allele.

The Neanderthal they sequenced was a heterozygote, and thus could taste bitter (and also [with sample of only 1, mind you] had the same allele frequencies as we do). The polymorphism thus goes back somewhere on the order of 40,000 years. But Neanderthals split from the lineage leading to modern humans on the order of 300,000 years ago, with little or no subsequent interbreeding. So the polymorphism probably goes back even further, predating the modern Homo sapiens/Neanderthal split. Although an exciting find, this is not a record for the antiquity of a modern polymorphism: some are known to predate the human/chimp split (abstract only), and that’s millions of years ago.