Elite universities are failing to recruit working-class students because IQ is, on average, determined by social class, according to an academic.

Bruce Charlton, a reader in evolutionary psychiatry at Newcastle University, claims that the greater proportion of students from higher social classes at highly selective universities is not a sign of admissions prejudice but rather the result of simple meritocracy.

Student union leaders responded angrily to his claim, which was also dismissed by a minister.

Charlton's paper, reported today in Times Higher Education, says: "The UK government has spent a great deal of time and effort in asserting that universities, especially Oxford and Cambridge, are unfairly excluding people from low social-class backgrounds and privileging those from higher social classes.

"Evidence to support the allegation of systematic unfairness has never been presented. Nevertheless, the accusation has been used to fuel a populist 'class war' agenda. Yet in all this debate a simple and vital fact has been missed: higher social classes have a significantly higher average IQ than lower social classes."

He argues: "The highly unequal class distributions seen in elite universities compared with the general population are unlikely to be due to prejudice or corruption in the admissions process. On the contrary, the observed pattern is a natural outcome of meritocracy. Indeed, anything other than very unequal outcomes would need to be a consequence of non-merit-based selection methods."

The National Union of Students described the paper as "wrong-headed, irresponsible and insulting".

Gemma Tumelty, NUS president, said: "Of course, social inequality shapes people's lives long before they leave school, but the higher education sector cannot be absolved of its responsibility to ensure that students from all social backgrounds are given the opportunity to fulfil their potential ... many talented individuals from poor backgrounds are currently not given the same opportunities as those from more privileged backgrounds. This problem will not be addressed as long as academics such as Bruce Charlton are content to accept the status quo and do nothing to challenge the inherent class bias in education."

Sally Hunt, of the University and College Union for acedemic staff, said: "It should come as little surprise that people who enjoy a more privileged upbringing have a better start in life. However, research has shown that students from state schools outperform their independent contemporaries when they reach university."

Bill Rammell, the higher education minister, told the Times Higher Education that Charlton's arguments had a definite tone of "people should know their place".