If a species produces an excessive number of males, then it becomes advantageous to produce more females to mate with them, so evolution is always nudging them

If a species produces an excessive number of males, then it becomes advantageous to produce more females to mate with them, so evolution is always nudging them back to a 50:50 ratio: https://www.blackwellpublishing.com/ridley/tutorials/Adaptations_in_sexual_reproduction26.asp https://www.blackwellpublishing.com/ridley/tutorials/Adaptat... So I guess the idea behind genetic engineering is to destabilize the ratio and wipe out the species faster than natural evolution can respond. I would suggest reading "The Selfish Gene", which covers a lot of topics like this.