1. This condition, called neoteny, means it keeps its tadpole-like dorsal fin, which runs almost the length of its body, and its feathery external gills, which protrude from the back of its wide head.

2. In animals, neoteny comes about because of delays in development, points out molecular biologist Philipp Khaitovich of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

3. The juvenile stages and neoteny observed by him may also be explained in this way.

4. The incidence of neoteny is increasing in some cities. It doubts that neoteny is related to hormone fruit.

5. Gould's idea about neoteny remains controversial, to say the least.

6. Gould theorized that over the course of evolution, a tendency toward neoteny might have helped give rise to human beings.

7. They are now probing other parts of the brain in humans, chimps and macaques to see where neoteny might play a role.

8. But Alexander Harcourt, professor emeritus of anthropology at UC Davis, regards neoteny as "still a viable concept."

9. In 1977, Stephen Jay Gould weighed in with his neoteny hypothesis: nakedness was part of an evolutionary strategy for acquiring larger brains.