Some factors could be:
weather
ressources
The parents both need to be heterozygous, meaning they have to have one dominant and one recessive allele.
The term "law" is a historical relic going back to Newtonian times, when after Newton's development of classical mechanics, it was thought that the workings of the universe were directly analagous to a perfectly constructed and perfectly predictable clockwork. That was turned on its head as a result of quantum mechanics, and modern scientists typically avoid use of the term "law" anymore because it is too dogmatic. Newton's "Laws" are still called that mainly for historical reasons now. What used to be called laws are now called theories.
