Interbreeding

Interbreeding is mating and reproduction between individuals from genetically distinct populations, breeds, or species, resulting in offspring and, in many cases, the exchange of genetic material. The term covers both intraspecific interbreeding (between populations within a single species) and interspecific hybridization (between different species). Interbreeding can occur naturally in the wild or as a consequence of human activities such as domestication, habitat alteration, or captive breeding.

Genetic exchange is shaped by reproductive barriers. Prezygotic barriers reduce mating or fertilization (differences in timing, habitat, or mating signals), while postzygotic barriers reduce the viability or fertility of hybrids. When hybrids occur and backcross with parental populations, they can introduce introgressed alleles and create a persistent pattern of gene flow known as introgression.

The consequences of interbreeding vary. It can increase genetic diversity and provide adaptive advantages, but it can also spread deleterious alleles or disrupt local adaptation. In agriculture and animal breeding, deliberate interbreeding is used to combine desirable traits. In conservation, outbreeding with distant relatives can threaten native gene pools or, conversely, rescue endangered lineages lacking variation.

Well-documented examples include interbreeding between modern humans and archaic hominins such as Neanderthals and Denisovans, evidenced by measurable archaic ancestry in contemporary genomes. Plants frequently form hybrids and may undergo allopolyploidization, leading to new crop or ornamental varieties. Hybridization also occurs among wildlife, producing a range of outcomes from fertile hybrids to sterile offspring.

Genomic research continues to quantify interbreeding across taxa, revealing its role in evolution, adaptation, and species boundaries. Understanding interbreeding informs fields from evolutionary biology to conservation and breeding programs.