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‘We are all virtually identical twins’
In this excerpt from the Gairdner Prize lecture he delivered in
Toronto this week, pioneering biologist J. Craig Venter discusses
how genetic sequencing shatters some stubborn cultural myths
It was just one year ago, in February, 2001, when [my team] published our
analysis of the human genome in the journal of Science and the publicly funded
researchers published their analysis in the journal Nature.
This information is impacting nearly everything in our daily lives, from
understanding the genetic code of anthrax and other key pathogens, to studying human
variation and human evolution as a means to understand human disease and design better
treatments.
One of the most exciting things we have shown is that our genetic code is our
living history. Written in the three billion letters of the genetic code contained in each of
our one hundred trillion cells is the recorded history of our humanity. We can trace some
duplications in our chromosomes back more than a billion years.
One of the biggest surprises is the lower-than-expected number of human genes.
Many scientists had predicted that there had to be hundreds of thousands of genes.
Indeed, if you hold a genetic deterministic view in which there is one gene for every
human trait, every disease, every human condition and function, then of course there
would have to be a very large number of genes. Others in the biotech community, who
viewed genes as commodities, also wanted there to be a huge number of genes.
Unfortunately for these groups, we found that there are only approximately
30,000 genes.
Fewer genes in fact means that our biology is even more complex than we
imagined. Probably 99 per cent of the discoveries in biology remain to be made. This is
very different from what I was told in the 1970s, when I was working on my doctorate at
the University of California, San Diego, which was that basically it was going to be very
difficult to come up with any new discoveries in biology because everything was already
known.
Another important finding is that we are all virtually identical twins. If we
compared each of our genetic codes, we would find only one out of roughly each 1,200
“letters” that differ between us. Even more dramatic, less than 1 per cent of the
differences actually occur in genes and affect our biology.
But clearly we aren’t all identical, so those small changes can be significant. For
example, a minor change in a few genes can affect whether someone will be resistant to
HIV infection or will die more rapidly from the infection.
One of these genes, which leads to resistance to AIDS, appears in about 9 per cent
of the Caucasian population but only in about one-10th of 1 per cent of the black
population.
Scientists at the National Cancer Institute have traced this event back to only
about 700 years ago. It turns out that the same variation in those genes leads to resistance
to the plague. Obviously, millions of people in Europe without this variation were killed.
The plague clearly did not have the same impact on Africa. But this illustrates that even
a recent event can change the overall impact to certain populations.
We sequenced five individuals’ genomes for our work – three women and two
men of self-described ethnicity as African American, Hispanic, Chinese and two
Caucasians. This is because race is not a scientific concept and it is not a genetic
concept. Many people find this hard to believe because they see differences in skin
colour and think that means we are different genetically. But we are all part of a
continuum. We can all trace our ancestors back to approximately four groups in Africa,
all black. There is more variation in the genetic code of the black population than there is
between the African American, Caucasian, Hispanic or Chinese populations.
This is not to say there aren’t medically important ethno-geographic differences –
groups that live in certain areas that are highly inbred do have much in common, and we
can trace those individuals to those areas. But we cannot determine anyone’s actual
ethnicity on the basis of the genetic code alone, as ethnicity is not a scientific concept. It
is a social one.