I think it is compound, that is a I think so I might be wrong
I am not 100% sure but I thinking it responds when pathogens enter the body because the immune system is meant to protect your body from illness.
They differ in single trait
Natural selection would cause speciation because the new advantageous traits introduced in the population would help species survive and adapt to the new environment they are in because of isolation. The ability to make best from available leads to speciation in isolation.
Explanation:
Natural selection is a an important element of evolution. The change in traits which are beneficial and heritable are transferred from one generation to other. These traits come from random mutations.
Speciation is a process in which an existing population diverge in to two distinct population or species due to geographic barrier or without it also. The speciation occurs when species from one group become reproductive isolated.
When a group of species become isolated on an island or some other geographic boundary.
The increase or introduction of new beneficial genes in a population is caused by natural selection process. The populations manage to survive and adapt the new environment and become a new species if left isolated.