Commentary by James H. Schwartz

How seriously should we take Crick and Koch's idea of an unconscious homunculus?

The homunculus was defined by Paracelsus in a treatise published in 1572 entitled De natura rerum, which gives the recipe for synthesizing the creature (Pagel, 1982, p. 117). A homunculus is produced by incubating sperm in a hermetically sealed vessel for 60 days in horse manure at high temperatures. Then, if fed properly, the product is an artificial man generated without the assistance of a woman (Paracelsus, p. 124). Like other instances of artificial men (most notably, the Golem), the homunculus was regarded as we now regard extraterrestrials—with fear, disbelief, and satire. The concept of the little man, however, was taken quite seriously by late seventeenth-century biologists to explain the role of sperm in reproduction. Some early microscopists actually drew a little man in the sperm. Others, like Antoni van Leeuwenhoek, who saw only worms in his sperm samples, nevertheless concluded that man with all of his adult parts first exists as a little animal contained within the sperm. Still others placed the little man in the egg (Pinto-Correia, 1997).

At the beginning of the eighteenth century, knowledge about how animals develop was primitive. There were two warring schools. One believed that the material in the egg was preformed, being arranged precisely as in the mature animal. For the preformist school, the sperm simply acts as a trigger. The other school, the epigenetic, considered the material within the egg to be formless. A little man fully formed in miniature in the sperm would grow after entering the egg.

We now know that neither school was correct and that postulating a little man either in the sperm or in the egg does not provide an adequate explanation of development. Yet, there are aspects of the idea of a homunculus that are formally correct. Although a little man does not actually exist in either gamete fully formed, he is present in the form of information: the genome p