How do new species arise through evolution?

Speciation is the evolutionary process by which populations diverge until they can no longer interbreed and exchange genes, producing distinct species. Genetic variation introduced by mutation and recombination provides raw material, while forces such as natural selection, genetic drift, and restricted gene flow shape which variants increase or disappear. Theodosius Dobzhansky at Columbia University emphasized that genetic variation and its interaction with selection underlie evolutionary change, making divergence possible when populations experience different selective pressures.

Mechanisms that generate divergence

Geographic separation often initiates divergence by preventing gene flow between populations. Ernst Mayr at Harvard University argued that allopatric speciation, in which physical barriers like mountains or rivers isolate groups, is a primary pathway for new species to arise. In isolated populations, random genetic drift and local adaptation to different environments can fix different alleles, producing genetic incompatibilities over time. In contrast, sympatric speciation occurs without geographic separation when disruptive selection and assortative mating favor distinct ecological or behavioral types within the same area. Research summarized by Jerry Coyne at the University of Chicago and H. Allen Orr at the University of Rochester in their book Speciation documents empirical examples of both geographic and nongeographic modes, showing that the relative importance of each depends on ecology, life history, and genetic architecture.

Reproductive isolation and outcomes

Speciation is complete when reproductive isolating mechanisms prevent or reduce successful interbreeding. Prezygotic barriers include differences in mating timing, habitat preferences, or courtship signals, while postzygotic barriers involve hybrid inviability or sterility. Over generations, genetic incompatibilities accumulate so that hybrids, if produced, have lower fitness. The consequences of these barriers extend beyond taxonomy: they reshape community composition, alter ecosystem interactions, and influence the distribution of genetic diversity across landscapes.

Human and environmental context

Human activity alters the conditions under which speciation occurs. Habitat fragmentation can increase isolation and potentially accelerate divergence for some organisms, but it also reduces population sizes and genetic diversity, raising extinction risk before speciation can complete. Climate change forces range shifts that can both bring previously isolated populations into contact, promoting hybridization, or separate populations further, promoting divergence. Cultural and territorial dimensions appear in how societies recognize and manage biodiversity; indigenous naming systems and local conservation practices influence which populations are monitored and protected, affecting long-term evolutionary trajectories.

Relevance and consequences for conservation

Understanding how new species arise informs conservation strategies aimed at preserving evolutionary potential. Protecting habitat connectivity maintains gene flow where needed to prevent inbreeding, while protecting distinct habitats preserves the ecological contexts that drive divergence. As Coyne and Orr demonstrate through empirical synthesis, recognizing the processes and timescales of speciation helps predict how biodiversity will respond to ongoing environmental change and guides policies to sustain the continuation of evolutionary processes that generate Earth's biological diversity.