What defines a species?

A species is a group of organisms that can naturally interbreed to produce fertile offspring and are reproductively isolated from other such groups.

Biological Species Concept

Proposed by Ernst Mayr, it focuses on reproductive compatibility. Members share a common gene pool and traits, ensuring continuity of that lineage.

• Morphological: Species is defined by shared physical traits; useful for fossils.
• Ecological: Species occupy a distinct ecological niche.
• Phylogenetic: Species is the smallest group on an evolutionary tree with unique DNA markers.

Why defining species matters

Clear species boundaries guide conservation laws, agriculture (crop breeding), medicine (pathogen identification), and biodiversity counts. Misidentification can harm these efforts.

Reproductive isolation mechanisms

Barriers can be pre-zygotic (different mating calls, seasons, habitats) or post-zygotic (hybrid sterility like mules). These barriers keep gene pools distinct.

Modern tools

DNA barcoding and whole-genome sequencing help taxonomists decide if two populations are separate species or just subspecies. For example, African elephants were re-classified into forest and savanna species after genetic work.