Evolution and Increased Diversity

Preamble:
Life, through the evolutionary process "explores" all accessable niches in the biosphere. Thus the degree of diversity is shaped by what the environment allows, what is reachable and what is selected for.Here is my statement of the law:
Biodiversity increases to the maximum that the current environment allows and that the evolutionary processes working with the results of historic contingencies make possible.Thus if an environment is very restrictive (e.g., Mars today) the resulting maximum biodiversity will be very low.Since all living things themselves are part of the environment we ave a corollary:
After a contingent mass extinction the rate of increase in biodiversity will be high.

I don't know what you mean when you say "genes can be attributed to modifying habitats ...". Yes, I think so. That is what others mean by "ad-hoc" I think. It is contingent on the environmental conditions. Obviously some environments will allow for a wider diversity to develop and others will not. I don't see that it is any big deal at all.BTW, I think those using 'ad-hoc' should be using the word contingent. I must not understand this. It is so obvious that it seems odd to say it. Diversity obviously stems from genetic variation. Mutation (and other) generates diversity at the genetic level. Whether such diversity makes it into surviving phenotypes is dependent on the environment.