List of unsolved problems in biology

This article lists currently unsolved problems in biology.

• Arthropod head problem, a long-standing zoological dispute concerning the segmental composition of the heads of the various arthropod groups, and how they are evolutionarily related to each other.
• Biological aging: there are a number of hypotheses why senescence occurs including those that it is programmed by gene expression changes and that it is the accumulative damage of biological processes.
• Extraterrestrial life: might life which does not originate from planet Earth also have developed on other planets?
• Paradox of the plankton: the high diversity of phytoplankton seems to violate the competitive exclusion principle.
• Cambrian explosion: what is the cause of the apparent rapid diversification of multicellular animal life around the beginning of the Cambrian, resulting in the emergence of almost all modern animal phyla?
• In cell theory, what is the exact transport mechanism by which proteins travel through the Golgi apparatus?
• Evolution of sex: what selective advantages drove the development of sexual reproduction, and how did it develop? What causes some organisms to be homosexual?
• Butterfly migration: How do the descendants of Monarch butterfly all over Canada and the US eventually, after migrating for several generations, manage to return to a few relatively small overwintering spots?

See also

• List of unsolved problems in neuroscience