Barrow and Tipler  review the consensus among such biologists that the evolutionary path from primitive Cambrian chordates, e.g. Pikaia, to Homo sapiens was a highly improbable event
. For example, the large brains of humans have marked adaptive disadvantages, requiring as they do an expensive metabolism, a long gestation period, and a childhood lasting more than 25% of the average total life span. Other improbable features of humans include:
Being the only extant bipedal land (non-avian) vertebrate. Combined with an unusual eye–hand coordination, this permits dextrous manipulations of the physical environment with the hands;
A vocal apparatus far more expressive than that of any other mammal, enabling speech. Speech makes it possible for humans to interact cooperatively, to share knowledge, and to acquire a culture;
The capability of formulating abstractions to a degree permitting the invention of mathematics, and the discovery of science and technology.
Barrow, John D.; Tipler, Frank J. (19 May 1988). The Anthropic Cosmological Principle. foreword by John A. Wheeler. Oxford: Oxford University Press. LC 87-28148. ISBN 9780192821478. The anthropic cosmological principle - Google Books
. Retrieved 31 December 2009. Section 3.2