The near-abolition of grammar schools appears to have led to a decline in the number of science specialists at school and university, according to a new study from Brunel University.
This effect of the change from selective to non-selective secondary schooling is pointed out by the authors, Alan Smithers and Pamela Robinson, who have traced the A-level and degree choices of some 750,000 students between 1975 and 1993.
The study also shows that the standard required for degree courses in physics and engineering has slipped by about half an A-level grade because too few bright sixth-formers are applying.
Although A-level results are closely associated with degree performance, intriguingly the proportion of first and upper second-class degrees has risen over the same period, Dr Robinson said.
The figures from the study, funded by the Leverhulme Trust, cover only the long-established universities, not the former polytechnics which became universities in 1993, so they may under-estimate the decline in entry standards for all universities.
Professor Smithers and Dr Robinson trace a striking change in the pattern of A-level study. In 1985, four-fifths of entrants to science-based degrees had studied only maths and science A-levels; by 1993, the share had fallen to about half.
The number of sixth-formers taking a mixture of science and arts subjects had meanwhile increased sharply, and so had the proportion of those going on to study science or engineering; in 1993, more than two in five entrants to science and engineering degrees had mixed A-levels.
But the growth in the number of entrants with mixed A-levels has not led to a rise in university entry standards because the high-flyers in the mixed group tend to opt for non-science subjects, says the report.
A small decline in the proportion of students from the poorest social classes has also harmed science and engineering, say the researchers, since such students are more inclined to study science than arts subjects.
And - possibly linked to this - the decline in the grammar schools from 700 to 160 since the early 1970s seems to have produced fewer science specialists. Whereas such schools had traditionally provided more than their share, students from independent schools are more likely to study the non-sciences (with the exception of medicine, dentistry and veterinary science).
Dr Robinson, deputy director of Brunel's centre for education and employment research, said this week: "The anecdotal evidence that there are not enough scientists and that they are of poorer quality is based on reality."
The need to persuade more sixth-formers to study both arts and science was urgent. The Government's plan to persuade sixth-formers to study five subjects in their first year through the introduction of a one-year AS-level was "a half-hearted approach to broadening", she said. "We need a broader course in five subjects over two years."