A carefully chosen date makes it easier to remember.
I really don't mean this as flamebait, but I see it as a very good example of evolution.
Honestly now. One needs to differensiate between the various forms of evolution. Micro-evolution, or variations within a species, is common and well documented. Please don't use this to prove macro-evolution, meaning the idea that one species can breed offspring of a different species - offspring capable of reproduction, mind you.