Misconceptions about mitochondria and mammalian fertilization: implications for theories on human evolution

Abstract

In vertebrates, inheritance of mitochondria is thought to be predominantly maternal, and mitochondrial DNA analysis has become a standard taxonomic tool. In accordance with the prevailing view of strict maternal inheritance, many sources assert that during fertilization, the sperm tail, with its mitochondria, gets excluded from the embryo. This is incorrect. In the majority of mammals-including humans-the midpiece mitochondria can be identified in the embryo even though their ultimate fate is unknown. The "missing mitochondria" story seems to have survived--and proliferated-unchallenged in a time of contention between hypotheses of human origins, because it supports the "African Eve" model of recent radiation of Homo sapiens out of Africa. We will discuss the infiltration of this mistake into concepts of mitochondrial inheritance and human evolution.

Figure 1

Human sperm within the egg. The partially decondensed sperm head is still attached to its midpiece circa 6 h after penetration (circa × 22,000). [Reproduced with permission from Sathananthan et al. (24) (Copyright 1986, Wiley, New York).]

Figure 2

One of the examples of the erroneous loss of the sperm tail depicted in a cartoon. [From Lewin (53) (Reproduced by permission of Blackwell Scientific, Oxford).]