Science Frontiers

ONLINE No. 104: Mar-Apr 1996 Issue Contents



Search-and-destroy sperm

Even book reviews can yield delightful anomalies. Take, for example, the January Scientific American review of Human Sperm Competition, by R.R. Baker and M.A. Bellis. Baker and Bellis have advanced the Kamikaze-Sperm Hypothesis. (SF#78) Central to this idea is the observation that the sperm of many animals, including humans, are polymorphic. They come in a variety of shapes and sizes, some of which are patently unsuited for penetrating an egg. Baker and Bellis draw upon their own studies and classifications of sperm types as well as research by R.A. Beatty and D. Ralt. They assert that sperm come in at least four varieties:

"Fertilizers," the egg-penetration specialists,

"Blockers," the ones that construct copulatory plugs to prevent further insemination,

"Search-and destroy sperm" that hunt down as kill "enemy" sperm from other sources,

"Family-planning sperm" that kill all sperm.

One can liken this array of sperm types to polymorphic ant colonies with their castes of workers, soldiers, and queen. Baker and Bellis go further and suggest that the numbers of each sperm type are under the control (certainly not conscious control) of the males. For example, where promiscuity is observed, as is common in chimpanzee troops, the numbers of seek-and-destroy sperm are very high.

All this out of a short review! Unfortunately, the book itself lists at $78.95, and we don't have a copy.

(Sozou, Peter D.; "Mating Games," Scientific American, 274:102, January 1996)

Comments. Exercising self control, we add only two comments. First, these specialized sperm cannot be as simple as those drawn in the biology books. The search-and-destroy type must have evolved biochemical "devices" that find, identify, and destroy other sperm and maybe even defend itself. Second, one should not ignore the eggs, which are much larger and likely more sophisticated. The receptivity of the eggs may be influenced (perhaps not unconsciously) by the female.

From Science Frontiers #104, MAR-APR 1996. © 1996-2000 William R. Corliss