which is not a reason of maximum diversity topics

1. highest pest pressure
2. evolutionery older zone
3. high rate out of crossing
4. greater environmental variations

Correct option is 4.
Biological diversity is the variety of species of living beings of an ecosystem. In ecosystems which are more biodiverse, like tropical forests, a great variety of plants, microorganisms and animals live; in ecosystems less biodiverse, like deserts, there are less variety of living beings.