"Men are simply more intelligent than women."

I saw that was a headline in the Times of Oman and had a few outraged thoughts on my way to the link, then was surprised to find an article from London about some British research:

In a paper to be published in a leading research journal, one of Britain’s most outspoken academics will argue that men have larger brains and higher IQs than women, to such an extent that they are better suited to “tasks of high complexity”.

Richard Lynn, emeritus professor of psychology at Ulster University, who has caused outrage in the past with claims that white people are more intelligent than blacks and that criminal traits are genetic, will publish the work with Paul Irwing, senior lecturer in organisational psychology at Manchester University.

The study, due to be published in the British Journal of Psychology in November, concluded that men not only have larger brains but also higher IQs, on average by about 5 points, than women....

Dr Irwing said that he had initially been reluctant to take part in the study arguing that he would have personally preferred not to have discovered that men had a biological advantage.

“I came from a perspective that I would like to believe that all people, whether men or women, were equal in potential achievement,” he said.

Why does Irwing assume performance on an IQ test is the result of biology as opposed to, say, a stimulating intellectual environment?

UPDATE: Here's the BBC link for the article.