zoogenesis

Zoogenesis, from the Greek zoon meaning "animal" and genesis meaning "origin," is a historical term used to describe the origination of animal life. It is primarily encountered in older scientific and philosophical writings rather than in modern biology.

Historically, zoogenesis was employed to discuss how animal life first appeared on Earth and to frame debates about the origins of life, including topics such as spontaneous generation and abiogenesis. In this context, it referred to questions about the emergence of metazoan life and the early steps leading to the animal kingdom.

In contemporary biology, the term is largely obsolete. The origin of life is now usually addressed through abiogenesis—the study of how simple chemical systems give rise to self-replicating molecules and eventually to living organisms—and through evolutionary biology, which explains how animal lineages diverged and diversified over time. Because of this shift in emphasis, zoogenesis is rarely used in current scientific discourse.

Notes on usage vary, and some older sources applied zoogenesis in broader ways to refer to the development of animal life without a precise or consistent definition. Today, the term is largely of historical interest, helping to trace how early scientists framed the question of how animal life began.