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