Nothing Much to Talk About

Nothing Much to Talk About

Neanderthal Speech Gene May be Due to Contamination

Nobody really likes a potty mouth, including anthropologists. But it looks like these scientists will have to put up with “contaminated” language from Neanderthals, at least if the results of new work are valid. It appears as if the recovery of the so-called language gene from the remains of Neanderthals is not authentic, but instead may be due to contamination from human DNA.

The question of whether or not Neanderthals possessed language capacity has precipitated much controversy. Anatomical studies are ambiguous towards this end. (See Who Was Adam? for a detailed discussion.) To help resolve this issue a team from the Max Planck Institute turned to ancient DNA analysis to probe for the language gene in the Neanderthal genome.

In 2001, a research team from the United Kingdom reported that mutations in the FOXP2 gene cause severe language disorders. Presumably the FOXP2 protein plays a key role in controlling the development of brain and facial structures that support aspects of human language capacity.

An initial evolutionary analysis of the FOXP2 gene, conducted in 2002, indicated that the human variant arose about 200,000 years ago. Subsequent work, published later that year, placed the origin of the human FOXP2 gene at about 100,000 years ago. From an evolutionary standpoint, this is well after the time that humans and Neanderthals allegedly split from a common ancestor. Accordingly, Neanderthals should not possess a human-like FOXP2 gene and, therefore, language ability.

However, to everyone’s surprise, the team from the Max Planck Institute did isolate the human variant of the FOXP2 gene from a recently recovered Neanderthal specimen. This result was interpreted by some as evidence that Neanderthals had language. If so, it creates problems for the RTB human origins model, which predicts that Neanderthals and other hominids should behave in nonhuman ways, and, therefore, should not have the capacity for language.

Did Neanderthals possess language ability? At the time that the recovery of the Neanderthal language gene was announced I wrote:

The very real possibility exists that this result stems from contamination by human DNA. Clearly, the research team went to painstaking efforts to avoid contamination. Anthropologists suited up in clean room gowns and face masks to excavate the Neanderthal remains using sterilized tools. They designed the extraction protocol to avoid isolating any human DNA and ran the appropriate controls to ensure the Neanderthal DNA samples had no human contamination. In spite of these heroic efforts, the possibility of contamination cannot be ruled out. The team from the Max Planck Institute introduced contamination into the Neanderthal genome sample they were previously working with and wrongly interpreted this as evidence for human-Neanderthal interbreeding.

It looks like my initial assessment was right. A research team for the University of Chicago re-assessed the likelihood that Neanderthals possessed the human variant of FOXP2 by looking at the genetic variation associated with this gene among modern human populations. They concluded that the scenario proposed by the Max Planck workers—namely the human variant arose prior to the time that Neanderthal and human lineages diverged from a common ancestor—is inconsistent with the genetic patterns observed among modern humans. They also estimated that the human variant of FOXP2 arose about 42,000 years ago. This result falls in line with earlier estimates, which places the origin of the human variant between 100,000 and 200,000 years ago.

The Chicago scientists suggest two possible scenarios to explain the recovery of the human variant of the FOXP2 gene from Neanderthal remains. First, humans introduced the language gene into the Neanderthal gene pool through interbreeding. They assert that if low levels of interbreeding took place between humans and Neanderthals, this could account for the appearance of the human language gene in the Neanderthal genome. This conclusion is not well supported by other studies, which have failed to find any direct evidence for interbreeding.

The other possibility is that the DNA extracted from Neanderthals was contaminated with modern human DNA. Even though the Max Planck Institute scientists took every precaution to avoid contamination and even ran controls to ensure that their samples were free from contaminants, human DNA, which is ubiquitous, could have easily made its way into the sample. The team from the University of Chicago raises questions about the effectiveness of the control samples. They assert that the controls selected by the Max Planck team do not necessarily ensure contaminant-free Neanderthal DNA samples.

It is really beginning to look like Neanderthals didn’t have language capacity after all—just contaminated language. Now I’d like to know who’s going to volunteer to wash their mouths out with soap.