Katagenesis

Katagenesis is a term used in evolutionary biology and paleontology to describe a process where a lineage or group of organisms becomes progressively simpler or less complex over time. This contrasts with anagenesis, which typically involves increasing complexity. Katagenesis is often associated with a reduction in the number of specialized features or a loss of complex structures. It can occur when organisms adapt to stable or simplified environments, or as a consequence of specialization where certain functions are no longer necessary for survival.

Examples of katagenesis are sometimes debated and can be difficult to definitively identify. Some proposed instances include the reduction of limbs in certain snake species, or the loss of eyes in cave-dwelling animals. The concept suggests that evolution is not always a unidirectional march towards greater complexity. Instead, simplification can be a viable evolutionary strategy under specific ecological pressures. It is important to note that the term is not universally adopted, and some scientists prefer to describe these changes using more specific terms related to reduction or loss of traits rather than a broader concept of katagenesis. The interpretation of whether a lineage has undergone katagenesis often depends on the chosen criteria for measuring complexity.