Biters spawn via pollution. Dead biters is an accurate measure of who is causing the pollution and can be used to advance evolution.

That would be pretty hard to evaluate as you can also move around the map and biters would still spawn without any pollution, if you have any algorithm to propose i can look into it

It doesn't have to be perfect. Someone would have to go through a lot of trouble to lure biters into another player's defenses to inflate evolution. If they were doing that, they might as well just attack the base and lead the biters through the hole.