Birth Order and Intelligence: An Immunological Interpretation

Abstract

The literature indicates that the IQs and school performance of children tend to decline with increasing order of birth. A hypothesis is here presented that the effect of birth order upon intellectual performance may result from an increasing probability of maternal immune attack upon the fetal brain in utero with order of parity. In support of this hypothesis, evidence is adduced from the literature that the fetal brain is antigenic, that fetal antigens may reach the immune system of the mother, that the incidence of maternal sensitization to fetal antigens increases with parity, that antibodies may readily cross the placenta and reach the fetal brain, that antibodies can be highly teratogenic, and that certain antibodies may damage, in a lasting way, the structure, function, and learning capacity of brains in experimental animals and human infants.

The Flynn effect is partly caused by changing fertility patterns

“…The confluence theory (Zajonc & Mullally, 1997), constructed to explain the alleged birth order effect implies sibship size effects as well. Physiological factors, like increasing probability of maternal immune attacks upon fetal brains in utero by increasing birth order (Foster & Archer, 1979), and decreasing supply of fatty acids (important for brain development) to later-born children during pregnancy (Al, v Houwelingen & Hornstra, 1997) also entail possible sibship size effects on intelligence. Recent contributions indicate that considering pregnancy and birth from an evolutionary perspective may be informative (e.g.…”

Effects of gestational length, gender, postnatal age, and birth order on visual contrast sensitivity in infants

“…The first is based on a proposed change in the prenatal environment . Specifically, with increasing parity comes an increase in the probability of maternal immune attack upon the fetal brain, a hypothesis referred to as the “maternal immune hypothesis” (see Blanchard, 2001, 2004; Blanchard & Bogaert, 1996; Blanchard & Klassen, 1997; Foster & Archer, 1979). The second factor that could contribute to BO effects is presence of siblings , i.e., higher birth order children have more siblings.…”

Fødselsrekkefølge og utdanningsoppnåelse:Har foreldrenes landbakgrunn betydning?

“…Effektene kan imidlertid tenkes å vaere knyttet til biologiske prosesser som finner sted i fosterlivet, dersom disse varierer mellom første-fødte, andrefødte og videre nedover fødselsrekken (Conley 2004:36;. Immunoreaktiv teori tilbyr en slik forklaring (Foster & Archer 1979). Ifølge denne teorien øker nemlig sannsynligheten for immunologisk angrep på fosteret med hver fødsel, fordi mors immunforsvar utvikler antistoff mot fosteret.…”