The Fetalization Theory of Louis Bolk

The collapse of Haeckel's biogenetic law and the rise of Garstang's neoteny virtually guaranteed that a century of observations would be gathered to yield a paedomorphic theory of human origins. J. Kollmann (1905), inventor of the term "neoteny," paved the way with a curious theory that humans had originated from pygmies who had simply retained their juvenile features during phyletic size increase. The pygmy progenitors, Kollmann added, probably arose from juvenile apes that had lost the ancestral tendency to regress (zurücksinken) during ontogeny to lower levels of cephalization: "The juvenile orang-utan is doubtlessly better qualified for human ancestry than the ape of Trinil" (1905, p. 19).¹

Louis Bolk (1866–1930), professor of human anatomy at Amsterdam developed the inevitable idea in a long series of papers (1915, 1923, 1924, 1926a, 1926c, 1929, for example), culminating in his pamphlet of 1926, Das Problem der Menschwerdung. Bolk's theory of fetalization set the stage for all later discussion. The subsequent debate has been murky and confused because Bolk's arguments have been presented outside the context of his philosophical positions. His insight has been ridiculed in the light of modern doctrine and dismissed in toto because he linked valid and important data to evolutionary views now rejected. In presenting this detailed exposition of Bolk's views, I am trying to establish a ground for the acceptance of his basic notion by referring the old observations that lie at its core (and that date at least to Geoffroy) to a philosophical context of current orthodoxy. I shall try to support three statements: (1) It is irrelevant that Bolk's evolutionary theory seems outdated or even foolish today; his theory was reasonable in his time and he supported it cogently. (2) The data that he presented can survive the collapse of his explanatory structure. (3) We must try to identify the "philosophical baggage" that underlies all theories—both to understand why a man says what he does and to aid in rescue operations when new philosophies require a separation of baby from bath water.

I want to rescue Bolk's data—and his basic insight—from the evolutionary theory to which he tied it and from which it has not been adequately extracted.

Bolk's Data

To support the argument that we evolved by retaining juvenile features of our ancestors, Bolk provided lists of similarities between adult humans and juvenile apes: "Our essential somatic properties,