during this ebook, Belgian scientist Jos Verhulst offers the main thorough examine thus far elaborating an evolutionary idea first set forth by means of Dutch anatomist Louis Bolk within the early twentieth century. This thought is predicated at the proposition that dynamic ideas inherent within the improvement of person organisms also are at paintings in animal evolution as an entire. for instance: A chimpanzee fetus is strikingly just like its human counterpart: its skull is rounded, its face flat, and its hair is particular to its head. because it develops, even though, the chimp diverges from its unique, humanlike shape, assuming really expert apelike positive factors. In an in depth comparative examine of diverse organs, Verhulst indicates that, not like the opposite primates, people preserve their unique juvenile shape. status Darwin on his head, he concludes that people haven't descended from apes yet particularly that apes advanced via diverging from a humanlike prototype. He additionally exhibits that our human tendency to preserve our fetal shape (fetalization, or retardation) is complemented by way of extra improvement (hypermorphosis) of such organs because the legs, heels, forebrain, and larynx by which we reach our eminently human capacities of upright posture, considering, and speech.
In the final bankruptcy, Verhulst sketches a large view of ways retardation and hypermorphosis have labored jointly in animal evolution. He speculates, for instance, that vertebrates advanced from invertebrates whilst old sea squirts (a kind of tunicate, a marine invertebrate) retained their larval features and constructed them additional as they developed into fish. Sea squirt larvae are free-swimming and resemble tadpoles. Their mind features a light-sensitive eyespot, they usually have a rudimentary spinal wire. of their grownup degree, even if, they're sessile filter-feeders with neither nerve twine nor eyes. Verhulst postulates that primitive tunicates just like the sea squirt retained their larval features (through retardation) and developed (through hypermorphosis) into fish, the 1st vertebrates. Following in a practice as outdated as Darwinism, he proposes that, from the very starting of animal evolution, those dynamics have led steadily towards the emergence of the human shape. during this view, the steadily rising human prototype is visible because the motive force and principal trunk of the evolutionary tree, because the wellspring from which the animal global has sprung.