Monday, November 3, 2008

Cleverest of them all



Monday, October 2, 2000
Science


With the completion of of the Human Genome Project
earlier this year, scientists can finally figure out
how many genes make up a human being. The result of
the count is not only surprising but also raises
questions about the further evolution of the human
race, writes MATT RIDLEY.

HUMAN self-esteem seems to depend on seeing our
species as exceptional. That is partly why the likes
of Galileo and Darwin went down so badly at first:
they made our planet and our species routine, not
special.

The geneticists are about to deliver another blow.

It concerns the number of different genes that a
species has. The number of genes is a good measure of
how complex a creature is because it reflects the
quantity of information needed to put the body
together. The flu virus has eight genes, syphilis has
1,000 and yeast 6,000. The fruit fly has nearly 15,000
and a microscopic worm has surprised everybody by
having 19,000.

On this scale, because of our complex and clever
brains, we expect to be top scorer by a mile. Until a
year ago or so, scientists were predicting that human
beings would have about 100,000 genes, comfortably
more than any other species. But now, for the first
time, they are in a position to count them and the
score is only 40,000.

Scientific humiliation looms: we are only twice as
complex as one of the simplest worms. Worse, we might
find that some other creature--a budgerigar, perhaps,
or an oak tree--has more.

In vain do we comfort ourselves with the fact that
40,000 genes is still a very large number. Even to
list them all, let alone describe what they do, would
fill a decent book. Yet all over the world, people
will be seeking counselling for their wounded
self-esteem: just 40,000 genes is all they have.

However, reassurance is at hand. A brilliant new book,
Mendel's Demon, by the Oxford evolutionary biologist
Mark Ridley (no relation), argues that we are,
nonetheless, about as complicated as life can get. It
is unlikely that we are going to be overtaken.

Ridley sees the evolution of complex life as a matter
of combating genetic decay. The more genes a creature
has, the greater the risk it runs of accumulating
disastrous mutations, so it was not until
sophisticated proof-reading mechanisms were invented
that complex life even became possible.

One of these mechanisms was sex, which efficiently
purges mutations from the species. So does selective
mate choice.

Once these mechanisms were working, complexity was
bound to increase, as it paid dividends in the
struggle for existence, first through size, then
through intelligence. Despite occasional setbacks
caused by asteroids, the largest brains on earth
(relative to bodies) grew progressively larger until
the appearance of people.

Can it go further? Ridley argues that it cannot,
partly because we have probably relaxed the pressure
imposed by natural selection to purge mutations (we
keep alive people who might have died young in the
Stone Age; colour blindness has probably doubled in
frequency since civilisation began).

So the "mutational meltdown'' of our species may
already have begun: our genes are fraying. This is not
yet happening to our brainiest competitor, the
bottle-nosed dolphin.

In any case, Ridley calculates that we may be near the
limit of complexity for the current
mutation-correcting machinery and that a more complex
creature, such as a man with wings, is probably
impossible (although he bases his calculations on
60,000 human genes).--


 Telegraph Group Ltd, London



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