John P. Holdren, the top science adviser to President Barack Obama, wrote in a book he co-authored with population control advocates Paul and Anne Ehrlich that children from larger families have lower IQs.
The book—"Human Ecology: Problems and Solutions"—argued that the United States government had a “responsibility to halt the growth of the American population.”
“It surely is no accident that so many of the most successful individuals are first or only children,” wrote Holdren and the Ehrlichs, “nor that children of large families (particularly with more than four children), whatever their economic status, on the average perform less well in school and show lower I.Q. scores than their peers from small families.”
However, from the same article:
“The columnist Dr. Joyce Brothers answered a question sent into Good Housekeeping (February, 1981) by a mother of four asking if she should consider having another baby as follows: ‘Studies have shown that children reared in small families are brighter, more creative, and more vigorous than those from large families,’” the authors noted.
“However,” they said, “the belief that, for a particular set of parents in a modem country like the United States, a larger family will lead to children with lower IQs appears to be, simply, wrong. The belief that birth order effects on intelligence act directly to decrease the intelligence of children born later in a given family also appears to be, simply, wrong.”
“Do large U.S. families make low-IQ children? No,” said the authors. “Are birth order and intelligence related to one another within U.S. families? No.”