11 April 2011
ByAppeared in BioNews 603
As another geneticist, sitting in the packed lecture theatre last Tuesday evening, my knee-jerk response at the start of the evening was to agree with celebrity genome scientist Craig Venter, who said that following the completion of the entire human genome sequence it was evident that 'race is a social concept, not a scientific one'. Quoted by Dr Prasad in her excellent overview of the topic at the start of the evening's proceedings, Venter 's comment reflects the finding that people, genetically speaking, are approximately 99.5 percent identical (if all types of DNA variation are considered). Furthermore, the vast majority of the 0.5 percent of genetic information that varies can be found between any two people chosen at random, with only a tiny amount accounted for by population-specific differences. This is because all human beings alive today are believed to be descendants of a small group of people that migrated out of Africa roughly 150,000 years ago.
But while the scientific evidence does not support the concept of different human 'races', it became clear during the evening's debate that important genetic differences do exist between different human populations. The discussion developed around two major themes: 1) the semantic issue of whether the term 'race' - which in addition to being biologically inaccurate, is sullied by its association with the evils of slavery, Nazi eugenics and racism - should be abandoned in favour of 'ethnicity', 'ancestry' or some other term; and 2) whether the accurate identification of genetically distinct populations was possible or desirable.
All the speakers agreed that the genetic differences between human populations do exist, but that they form a continuum, rather than discrete groups. They also all agreed that superficial similarities between people, such as skin colour, are a wholly unreliable way of identifying shared genetic ancestry. However, the relative frequencies of genetic variations in human populations can often be used to pinpoint an individual's ancestry with great accuracy, as Dr Wilson showed in his presentation.
Dr Wilson presented some of his group's data showing genetic 'signatures' of different human populations from around the world, which form clusters representing distinct geographical regions. For the most part these overlapped - with the startling exception of the Pacific Islanders, isolated both genetically and geographically. Dr Wilson pointed out that as people travel around more, the boundaries between these clusters will become increasingly blurred. However, for some rural areas it is currently possible to genetically distinguish between people from neighbouring villages just a few miles apart. He concluded by reminding the audience that it is possible for people to be 'different but still equal'.
The final presentation, by Dr Bradman, echoed the sentiment that while genetic diversity can be used to study differences between people, it does not mean that 'races' exist. However, giving the example of his group's work showing a common genetic origin for the Jewish priesthood, he qualified this by saying that self-identified human 'tribes' can serve as useful starting points for the scientific investigation of history. He also noted wryly that when such studies confirm historical events, they tend to be widely reported, but when they fail to do so, they are generally ignored. Later in the discussion, Dr Bradman highlighted the importance of asking the right question when trying to identify genetic differences between groups of people, by asking the audience if they thought a woman's choice of hairdresser was influenced by her genes. Most thought not, but were forced to reconsider their answer when Dr Bradman pointed out that most women would choose a hairdresser who best understood their hair type - which is of course a genetic trait!
The wide-ranging discussion, expertly chaired by PET chair Professor Marcus Pembrey, started with questions about the best word to use when describing different human populations. There was no consensus on this issue, with some people (including Dr Prasad) asking if the term 'race' could perhaps be reclaimed from its murky past.
Other audience members asked if genetic differences in behaviour could be identified in different populations; if genetics could be used to settle legal questions such as who should be given land promised to American Indians; and whether 'religion was the new race'. However, arguably the most important issue of the evening was raised by an obstetrician, who explained that he needs to make clinical judgements based on the self-described or perceived ancestry of his patients on a daily basis. Length of pregnancy and risk of genetic disorders such as cystic fibrosis and sickle cell anaemia vary in different human populations. If he could not make decisions about treatment and care using ethnic group or 'race', he asked, then how else was he to gather this vital information?
The panel agreed that 'personalised medicine' based on complete genetic information for every patient may eventually make identification of ethnic group irrelevant, but until that day, questions about ancestry will continue to play a vital role in clinical practice. The promise of future genomic medicine will be addressed in more detail at the second debate in the series: 'Will Pharmacogenetics Lead to Colour-Coded Medicine?', to be held at the University of Liverpool on 10 May.