Selfish centromeres and the wastefulness of human reproduction.

Many human embryos die in utero owing to an excess or deficit of chromosomes, a phenomenon known as aneuploidy; this is largely a consequence of nondisjunction during maternal meiosis I. Asymmetries of this division render it vulnerable to selfish centromeres that promote their own transmission, these being thought to somehow underpin aneuploidy. In this essay, I suggest that these vulnerabilities provide only half the solution to the enigma. In mammals, as in utero and postnatal provisioning is continuous, the costs of early death are mitigated. With such reproductive compensation, selection can favour a centromere because it induces lethal aneuploidy: if, when taken towards the polar body, it instead kills the embryo via aneuploidy, it gains. The model is consistent with the observation that reduced dosage of a murine drive suppressor induces aneuploidy and with the fact that high aneuploidy rates in vertebrates are seen exclusively in mammals. I propose further tests of this idea. The wastefulness of human reproduction may be a price we pay for nurturing our offspring.