Written by Olivia O’Sullivan
A study has shown that it may be DNA we have lost which sets humans apart from our nearest primate relatives.
The majority of mutations in DNA are harmful, and a loss of genetic information might be assumed to be catastrophic. In a paper published last week in Nature, a team of researchers from Stanford University in California have challenged this by identifying the loss of particular regions of non-coding DNA to be a key factor in shaping our unique minds and bodies, thus setting us apart from chimpanzees and the rest of the animal kingdom.
By conducting a genetic comparison of the human genome with that of a chimp and a macaque the team found 510 DNA sequences missing in humans that were present in chimps, almost all of these sequences were from the non-coding region of DNA, i.e. chunks of DNA responsible for turning genes on or off . Two regions of particular interest were the androgen receptor (AR) gene and ‘GADD45G’ – a tumour suppressor gene involved in brain development.
The AR gene is implicated in the production of hard, keratinized penile spines which are found in many mammals and play different roles in different species. It is thought that penile spines may have been used as a way of competing with other males for mating partners by removing the sperm of competitors. It is believed that the molecular changes resulting in a loss of human penile spines has allowed us as a species to form more complex social structures by adopting monogamous reproductive relationships.
Another ‘lost section of DNA’ in humans was found to code for a tumour suppressor gene that normally acts to suppress brain growth, putting an evolutionary brake on the growth of specific brain structures zones in our primate relatives. This ultimately paved the way for the evolution of a larger human brain, giving us an intellectual edge over our fellow animals.
The results of this study certainly underlines the fact that genetic information is both gained and lost during evolution and that despite sharing approximately 96% of our DNA with chimpanzees, it is thought that this genetic divergence may have occurred more than 800,000 years ago when our ancestors split from the Neanderthal lineage. This is an exciting finding, opening up new areas for discovery through the analysis of the remaining 508 DNA sequences which promise to reveal further secrets about the molecular basis of human individuality.
References:
McLean, C. Y. et al. Nature 471, 216-219 (2011)