How quickly can speciation occur?

First, let's define speciation as the inability to generate viable progeny.

When discussing speciation, it's important to consider a number of factors, including the rate and method of a species' reproduction.

First, there's the crucial distinction between self-fertilization and fertilization by another organism. Self-fertilization means that an organism can only become a new species by undergoing a mutation (plants and bacteria are examples). This could result in faster speciation because almost any organism could be classified as a new species. Other organisms need two to reproduce, which takes longer because natural selection takes time to spread favorable traits through meisis and adds genetic diversity to a population.

Second, the duration of reproduction matters. For example, if an organism only needs to divide into two cells, a major mutation leading to the emergence of a new species would obviously occur much faster than in the case of elephants, whose gestation period is more than a year.

The time period being discussed must also be taken into account. For instance, the earth's biodiversity increased following catastrophic events, necessitating the emergence of new organisms to adapt to the altered conditions. Consequently, speciation increased during these periods, as natural selection was no longer stabilizing.

In some cases, speciation happens very quickly—for example, allopatric speciation resulting from geographic isolation can take thousands to millions of years. In other cases, however, speciation happens more quickly—possibly in hundreds to thousands of generations—when new species emerge within the same geographic area. The precise timeframe varies based on factors like genetic variation, selective pressures, and reproductive isolation mechanisms.