z53\doc\web\2001\10\birthead.txt
(I don't endorse it, but it's interesting...)
Philippe Rushton [rushton@uwo.ca] 10/2001 writes


I hope the following is useful for David Cohen's question about small
head sized babies and later IQ scores:


The overall correlation between head circumference at birth and IQ at
age 4 (and again at age 7) is 0.20. There is a lot of individual
variance in the strength of that relationship. In my own last
analysis of these kind of data (in the 1997 issue of Intelligence,

copies sent on request) there were two children (both boys) who were
born with birth weights and head circumferences more than 3 standard
deviations below the mean and were transferred to wards for the
premature. The two outliers provide a useful illustration of the
phenomenon of "catch-up growth."  At birth, the two boys averaged
1.816 kilograms in body weight with a head circumference of 29.25 cm
-- both measures 3 standard deviations below the mean.  However,
these disadvantages (for example, in cranial size) were reduced to
-0.77 SD by 4 months, to -0.60 SD by 1 year, and to only -0.10 SD by
7 years.  At age 7, one boy had an IQ of 115 and the other of 111.


    The phenomenon of "catch-up growth" following deficits caused by
malnutrition or illness demonstrates that development is guided by
constant self-corrections until some targeted end-state is reached.
Deprived children, if moved to a satisfactory environment,
subsequently develop very rapidly.  They regain the growth trajectory
they would have been on if the diversion had not occurred, following
which growth slows down and development proceeds at the normal pace.
Developmental processes are constantly involved in a match-to-model
process with an inherent growth equation.


From the Discussion section of that article.....


The data on catch-up growth, when applied to the Asian--White--Black
mean differences in both brain size and IQ, supports the genetic
hypothesis of the race differences.argues in favor of the existence
of genetic factors.  The reason for this is that by age 7, Asians are
above average in brain size but below average in body size whereas
the opposite pattern is found for Blacks and an intermediate pattern
is found for Whites.  If major environmental insult or nutritional
deprivation was the cause of the differences, as has often been
posited for low birth-weight infants, one would not expect the
particular pattern of catch-up growth that is demonstrated by these
data. Moreover, malnutrition does not usually influence brain weight,
suggesting that evolution has selected brains to be especially well
conserved.  Additional recent evidence for a genetic contribution to
racial differences in mean IQ can be found in Jensen (1998; in
press), Levin (1997), Lynn (1997), Rowe and Cleveland (1996), and
Rushton (1997).


    One of the major findings of the Collaborative Project has been
that low birth-weight babies are not as much at risk as has often
been supposed.  Broman (1989) reviewed the overall findings pointing
out that although mean raw scores at 8 months of age on the Bayley
Scales increased linearly with birthweight as predicted, with the
lightest group (<2,000 grams) scoring about two standard deviations
below the heaviest group (>3,501 grams), birthweight explained only
5% to 6% of the variance in test scores in this population of 31,000
infants.  By age 4, in a regression analysis with six covariates
(gestational age, birthweight, head circumference, sex of child,
ethnicity, and maternal education), birthweight explained less than
1% of the variance in IQ scores.  Ethnicity and maternal education
were the best predictors, accounting for 16% and 6% of the variance,
respectively.  In contrast to birthweight, head circumference at
birth was frequently retained in multivariate analyses, indicating a
greater independent contribution to cognitive outcome at both ages
(Broman, 1989). These results show that birthweight has less of an
effect on measures of cognitive development at age 4 years than at 8
months.  The most important predictors of cognitive performance were
characteristics of the family.