The idea of a link between nationality and intelligence has a long pedigree – certainly as ancient as slavery and colonialism. And in its faux-scientific form, well, Darwin dabbled, Churchill embraced and Hitler implemented.

The latest burst comes from Randy Thornhill of the University of New Mexico, who once proposed the idea that men evolved with a genetic predisposition to rape (raising the question of why these genes are so much more prevalent in, say, Serbia or South Africa, than Tanzania or Sweden).

He and his team are back with their latest idea: a direct link between levels of infectious disease and average national IQ.

Their underlying case is perfectly valid – when children devote energy to fighting infection, brain development is sometimes sacrificed. But their evidence at a national level is more dubious, based on comparing World Health Organisation data with average IQ scores. The obvious point is that correlation is not the same thing as causation. In other words, there might be a range of other reasons why people in disease-ridden countries don't excel in IQ tests.

And it is also worth pointing out that it has been warmer countries (some in malaria zones – a key disease highlighted by Thornhill) that have been the catalyst for civilisation: Mesopotamia, China, Egypt, Greece.

But a more profound objection relates to Thornhill's obdurate belief that IQ is a true measure of "crystallised general intelligence" rather than just a measure of ability to perform in IQ tests.

The killer blow was delivered more than 20 years ago by the New Zealand academic Jim Flynn, who proved that average IQ test scores increased progressively in most countries (now known as the "Flynn effect"). If American children of a century ago took IQ tests of today their average score would be well below 70. In Britain, the average IQ has risen by 27 points since the war.

The reason has nothing to do with evolution. In fact, there is an emerging scientific consensus that human intelligence is unlikely to have evolved over the last 45,000 years, and perhaps more (for example, an engraved ochre plaque found near Cape Town, containing intricate symbolic designs, was carbon-dated at more than 70,000 years).

According to Flynn, generational rises are prompted by increased exposure to abstract logic. Other reasons might include nutrition levels, time spent in school, environmental stimuli and familiarity with aptitude testing. It makes no sense to compare average IQ scores of different populations because they are unlikely to have identical exposure to all of these factors.

So while it might be true that, on average, Ashkenazi Jews or Chinese people have higher average IQs than Ethiopians or Caucasian Britons, this does not mean that one group is innately more intelligent than another.

Yet this is precisely what Richard Lynn (quoted in the article) and other evolutionary psychologists such as Steven Pinker have argued – a perspective based on combining a discredited view of IQ with a faulty grasp of evolutionary theory.

Thornhill's disease-based hypothesis is less objectionable, but he is indulging in just-so story logic when he extends this to speculating that whole nations have adapted their immune systems at the expense of their brains: a modern version of a horribly ancient conclusion.