What is the only evolutionary mechanism that consistently leads to adaptive evolution?

natural selection

Explanation:

Natural selection refers to the never ending battle for survival that happen to all organisms with their own varied genetic structure.

When certain type of organisms live in one specific environment for a long period of time, there is a huge chance that the organisms who have the most adaptable characteristics will survive and produce more children. Over time, the number of organisms that have that adaptable characteristic will keep increasing and dominate the environment.

natural selection

Explanation:

Adaptation is the ability to reproduce and produce viable offspring in a particular environment. Natural selection is the evolutionary mechanism that produces adaptation.