top of page

What is Speciation?


Speciation is one of the most exciting topics in evolutionary biology: The formation of a whole new species!


There are several different ways to define a species in biology, but one of the most common ways is via reproductive isolation. Essentially, this idea states that two organisms are from different species if they cannot interbreed or can interbreed but can’t produce fertile offspring. For example, donkeys and horses interbreed, but the offspring they produce (mules) are infertile.


Speciation can occur for a variety of different reasons. Two of the most common types of speciation are allopatric and sympatric speciation.


Allopatric speciation occurs when there is some kind of physical barrier between the two populations involved. For example, let’s start with a single population of butterflies. Over geologic time a mountain splits their habitat in half, with half of the population on one side and half on the other.


For thousands of years these two populations evolve in isolation. Different mutations arise and spread throughout each population. Eventually the mountain is worn down and there is no longer a barrier, but by this point they are no longer capable of breeding with each other because they are too genetically different. At this point, the two butterfly populations are considered different species.


Sympatric speciation occurs when there is no physical barrier between two diverging populations. Let’s say we have a bird population that uses specific songs to choose their mates. Simply by genetic randomness, some birds in this population greatly prefer mates with high-pitched songs, while others prefer mates with lower pitched songs.



Since high-pitched singers are only mating with other high-pitched singers and low-pitched singers are only mating with other low-pitched singers, there two groups are just as reproductively isolated as if there was an actual physical barrier between them. Eventually this lack of genetic exchange between the two groups of birds will lead to them becoming separate species.


Scientists can actually observe speciation taking place in real life: There are groups of organisms alive right now that are beginning to diverge from one another on the way to becoming separate species. Unfortunately for the interested scientists, it will take many hundreds of years for the speciation event to be complete. 


Image Citation


Tan, Vinson (photographer). (2019). Flycatcher Golden-Bellied Fly [photography]. Retrieved from

bottom of page