Science Correspondent Scientists, sociologists and educationists who have taken sides in the controversy about whether dif- ferences in intelligence quotients (IQs) are mainly hereditary or caused by soclal conditions, can consider themselves firmly rebuked.

This is one of the important conclusions to emerge from a paper by Dr John Dobbing, of the Depart- ment of Child Health, Manchester University, given- yesterday to a conference entitled “The Biology of Brains” and organized by the Institute of Biology.

He described research into what he called “the beginning of a bet- ter understanding of some of the factors wbich are now preventing so many children from achieving their full potential “.

His subject was the latest work in the study of the most vulnerable periods for the development of the brain before and after birth. This has disclosed many unexpected findings about possible connexions between the social and biochemical conditions that may influence the development of intelligence.

He said that apart from the com- paratively uncommon diseases before birth and immediately after, there were several common situa- tions in which good bodily growth, and hence good brain development, were threatened. In world terms the most important was maternal and infant malnutrition. Another common one was heavy smoking during pregnancy. But there were other less well understood causes of failure to thrive.

He described work at Manchester into some conditions which might affect brain development other than the more easily recognized malformation. There was evidence that if bodily growth was’retarded when the brain was developing with a rapid spurt. then there was irre- trievable failure of the brain to grow to its proper size.

It would have too few cells in some regions, and this loss of struc- ture was associated with a change in the normal biochemical constituents. Evidence was emerging that these irremediable losses might be reflected in poor mental capacity.

Further understanding of this important point was hamstrung by tota] ignorance of -the physical basis within the brain for higher mental development. It was neces- sary to determine the times of most rapid growth before suggesting the periods which might bring, height- ened vulnerability for mental development.

Hitherto the most vulnerable period was thought to end at about five months after birth, leaving little postnatal opportunity to catch up with any retardation which might hiave occurred. As a result of work at Manchester. the human brain was now considered’ t6 continue growing fast for at least 18 months after birth. thus providing a much longer period for potential damage.

An unexpected finding had been the identification of a period of growth before birth when nearly all nerve cells were produced. This time of cell multiplication begarn at about 15 weeks of gestation. and by 27 to 30 weeks everyone had as many nerve cells as they were likely’ to possess.