Question

which event occurs prior to speciation?
a population is divided.
different species share the same space.
a major change on earth takes place.
organisms of different populations join together.

Explanation:

Speciation is the process by which new species form. One of the key initial steps in many cases of speciation (such as allopatric speciation) is the division of a population. When a population is divided (for example, by a geographical barrier like a mountain range or a river), the two sub - populations start to evolve independently. Over time, due to different selective pressures, genetic drift, and mutation, they can become so different that they can no longer interbreed, which is the criterion for being different species.

• Different species sharing the same space is a situation that can occur after speciation or in sympatric speciation (a less common form), but it is not a prior event in the general sense of speciation.
• A major change on earth is too broad. While major environmental changes can be a factor in speciation (by causing population division or new selective pressures), it is not as directly relevant as population division.
• Organisms of different populations joining together would be more related to gene flow between populations, which would act against speciation rather than being a prior event.

Answer:

A. A population is divided.