Question

An interbreeding population of finches became separated geographically, forming two isolated groups. Each group then became subjected to different selective pressures. One group was then introduced to the habitat of the other. Which one of the following would determine whether they now formed two distinct species?
A. They had been separated for more than three million years.
B. They failed to produce fertile $F1$ hybrids
C. They showed marked differences in the shape of their beaks
D. Their plumage had become markedly different

Answer 1

In an environment the living organisms are constantly under the influence of evolutionary processes. The evolutionary processes are constantly changing and several changes are included in the organisms. These changes are reflected in the population of the organisms. The evolutionary process which allows and causes population to evolve to become distinct species is known as speciation.

Complete answer:
All the natural processes occurring in the environment take place over the course of evolution in due course of natural selection a population may lead to the formation of new and distinct species. Speciation is the formation of new species within a population with separate gene pools and physical characteristics. In due course of time species having a single evolutionary lineage are divided into two or more genetically independent lineages.

Speciation can be distinguished into two types which are allopatric speciation sympatric speciation. The allopatric speciation occurs due to geographical isolations. When the members of the population are separated into small groups by physical barriers or geographical barriers such as mountain, river or desert is known as allopatric speciation. The separate groups adapt to their particular environment and include special genetic characteristics. The changes accumulated prevents the members of one population to inter-breed with the individuals of the other population as they cannot interbreed or do not produce fertile offspring’s interbreeding is stopped. The two groups now evolve as two species that were once from the same ancestral species but are now distinct species.

The interbreeding population of the finches remain separated through geographical barriers for many millions of years and accumulate certain characteristics that are exclusive and are different from other groups. Due to different selective pressure, they are found to include genetic characters which are different from the other groups.

Due to certain genetic changes, the interbreeding between the isolated species fails to produce viable first-generation hybrids.

In addition to the reproductive changes, the species under evolutionary stress may include several changes in the physical characteristics due to changes in the habitats or environment. The species that cannot reproduce or produce offspring are said to be evolved as individual species.

Hence, the correct answer is option (B).

Note: In the process of geographical isolation of a population, the isolated species evolve as individual species under different types of evolutionary stress. If the individuals of the two isolated species are allowed to mate, the resultant offspring is not fertile in nature. Thus, the species isolated by geographical barriers have evolved as two distinct species. This process of formation of new species from a common ancestral species is known as speciation.