Lespeciació

Lespeciació is the evolutionary process by which populations diverge genetically to form distinct species. It explains how biodiversity arises from ancestral lineages and is driven by genetic variation, natural selection, genetic drift, and reproductive isolation.

A central idea is that gene flow between populations must be reduced or eliminated for speciation to occur. Reproductive isolation can be prezygotic, barriers that reduce mating or fertilization such as divergent mating signals, timing, habitat use, or mechanical incompatibility, or postzygotic, where hybrids are inviable or sterile.

Modes of speciation include allopatric speciation, in which geographic barriers prevent gene exchange and divergence accumulates; sympatric speciation, within a continuous population, often via disruptive selection or polyploidy that leads to reproductive isolation; peripatric speciation, a small peripheral population diverges; and parapatric speciation, adjacent populations experience limited gene flow and divergent selection.

Evidence comes from comparative genomics, population genetic studies, experimental evolution, and the fossil record. Different species concepts, notably the biological species concept, emphasize reproductive isolation, but multiple definitions are used in practice.

Impact: speciation explains the distribution of species across landscapes and through time, from island radiations to rapid plant diversification after polyploidy or ecological shifts. The process operates over timescales from thousands to millions of years, and remains a central, dynamic component of evolutionary biology.