The concept of "fixity of species" was a common belief based on a very limited understanding of: the biblical principle "after its kind" genetics taxonomy paleontology

The correct answer is the biblical principle after its kind.  

Fixity of species refers to a term, which signifies that all the species remained unaltered all through the history of the Earth. This theory is usually not accepted by the most in the contemporary times as of the supposed huge amount of proof encouraging evolution.  

It is a religious claim that all the species are created by a superpower or God and they do not vary with time. According to the hypothesis, it shows that evolution via natural selection is a hoax.  

The correct answer is the biblical principle "after its kind".

Explanation:

The concept of "fixity of species" is based on the basic idea that all the species on earth were created as it is by god and they do not change therefore evolution does not take place and they do not get extinct.

Fixity of species is based on the biblical principle "after its kind" which tells about the genesis of creatures by god. These principles are poorly understood because they can not be co-related with the present term of species.

Today we know that all the species evolved from its ancestor and natural selection drives the evolution of a species. Therefore the correct answer is the biblical principle "after its kind".