One hundred years after the death of Francis Galton, the "father of eugenics", geneticists are increasingly baffled by the nature versus nurture debate, writes Professor Steve Jones.

Type the phrase "scientists find the gene for" into Google and 68,000 results appear. Most of the hits are about human beings - which is a pretty impressive number, given that we have only 20,000 genes altogether.

The hits include genes for depression, religiosity, insomnia, marital failure and, perhaps surprisingly, premature ejaculation.

Does what we are born with make us what we will become, or is it the way we live? Newspapers tend to believe in nature - DNA, while sociologists go for nurture - the environment.

As they learn more, geneticists are finding that they have less and less of an idea about which is more important, or whether the question means anything in the first place.

Charles Darwin had an equally brilliant, but less well-known, cousin. He died 100 years ago in 1911.

Image caption Galton applied statistics to many things, including the efficacy of prayer

This year is Galton year - a celebration of Francis Galton, a genius - but a flawed genius. He did many surprising things. He was the first person to use fingerprints in detective work and the first to publish a weather map, in the Times newspaper in 1875.

Galton is best known for his interest in inheritance. His book Hereditary Genius is sometimes said to have founded human genetics, and Galton founded the science (if that is the right word) of eugenics.

Its main aim was "to check the birth rate of the Unfit and improve the race by furthering the productivity of the fit by early marriage of the best stock".

Beauty map

At his death, he left the then enormous sum of £45,000 to found the Laboratory of National Eugenics at University College London (UCL).

The term was soon abandoned by UCL, although we still have a Galton Professorship. Even so eugenical ideas of good genes, bad genes, and all the rest is still very much in the public mind.

In fact, the most important part of Galton's work had nothing to do with eugenics, for he was one of the first to realise that science - biology as much as physics - needs maths rather than words. He was one of the founders of the science of statistics, and he measured many things.

He made statistical inquiries into the efficacy of prayer - he got into trouble for that for he found that those people frequently prayed for, like monarchs, lived no longer than anyone else.

He even made a beauty map of Britain, based on a secret grading of the local women on a scale from attractive to repulsive (the low point was in Aberdeen).

In a letter to Nature in 1879 entitled The Average Flush of Excitement, Galton recounts a visit to the Derby. He noted that while he was there he was able to assess what he called "the average tint of the complexion of the British upper classes" by observing the distant crowd through his opera glass.

He observed that after the race started, the crowd became "suffused with a strong pink tint, just as though a sun-set glow had fallen upon it". Galton found that he could work out the mood of a mass of people even without being able to distinguish one person from the next.

Some of his work has a strong resonance in modern science. Everyone knows that tall parents tend to have tall children, but Galton was the first to do some measuring.

He noted that the children of two six-footers tended to be tall, but not quite as tall as their parents. He called that "regression to the mean" and we now know that it happens because lots of genes are involved, with some hidden by others.

Sex is a way of mixing those genes - of reshuffling the genetic cards - and the child tends to inherit a more average kind of hand than that received by either of their exceptionally tall parents.

Of course, the environment is involved too. Food, exercise, good health, all are important in deciding how tall one will become. For height, and for almost anything else, nature and nurture always work together. It makes no sense to try to separate them.

Image caption We know of more than 50 different genes associated with height

That has not percolated into the public mind, as the Google search for "scientists find the gene for" shows. The three letter word for - the gene FOR something - is the most dangerous word in genetics. As Galton did not realise and as headline writers still do not, it is almost entirely ambiguous.

'A gamble'

A few months ago, the press reported with impressive unanimity that "Attention Deficit Hyperactivity Disorder is genetic". To the rolling of publicists' drums (and geneticists' eyes) came the news that some children behave outrageously because they inherit damaged DNA.

The Daily Mail came out with a hand-wringing piece entitled "Are some children just born bad?", which claimed "previous thinking was flawed and that some children, through no fault of the parents, are simply bad seeds".

That's an outrageous statement. Geneticists need to remind the public how little the word "genetic" actually means. One gene can do very different things, and the same thing can be under the influence of many genes - and nurture nearly always gets a look-in.

With all the fantastic technology now available, within a year we should be able to read a whole human genome in 15 minutes. But the biggest problem faced by geneticists is that we are not finding the genes.

Take height. As Galton noticed, height is highly heritable. We can now reach the scene of crime - the DNA - with the greatest of ease. The mappers have used their molecular tape measures on about 30,000 people.

They have found more than 50 different genes associated with being tall or short but altogether they account for only one-twentieth of the total variation needed to explain the similarity of children to their parents.

Where are the missing genes? We do not know.

Take adult diabetes, now a major health problem, and one that certainly runs strongly in families. Genome scans reveal scores of different bits of chromosome as possible culprits but together they explain just one part in 20 of the overall inherited liability to the disease.

The chance of being born with a predisposition to a common illness such as diabetes or depression is a gamble with huge numbers of cards.

So many small cards can be shuffled that everyone who falls ill fails in their own fashion and no gene says very much about whether or not you will get the illness (although the number of cheeseburgers you eat certainly does).

Steve Jones is a professor of genetics at University College London