If there is NO SELECTIVE SURVIVAL based on shell thickness w

If there is NO SELECTIVE SURVIVAL based on shell thickness within a population of snails, what happens to shell thickness in response to crab predation?

(a) The average shell thickness increases within each generation, but there is no change in shell thickness from generation to generation.

(b) There is evolution by natural selection of shell thickness, and average shell thickness increases every generation.

(c) There may be evolution of shell thickness, but not through natural selection and not necessarily toward thicker shells.

(d) There is no change in shell thickness within the population.

I can\'t decide between c or d as the correct answer.

Solution

(c) There may be evolution of shell thickness, but not through natural selection and not necessarily toward thicker shells.

As there is no selective survival based on the shell thickness, the shell thickness need not necessarily increase. But the shell thickness may be changed in response to the other factors, but not through natural selection because natural selection always deals with the traits that increase survival fitness.