Question: Why don't homo-sapiens have natural defences? Brains count as tools, not actual defences.

Kevin Motherway answered on 11 Nov 2014:

Throughout nature there are different mechanisms/defences to cope with preadators. Some have armour plating (Armadillos), Spines and Spikes (Porcupines). Some have excellent camouflage and hide out from predators, some even play dead (the possum).

Homo Sapiens are not physically strong but we have the highest brain mass to body ratio of any creature, so its brain versus brawn and brain has clearly won out in the evolutionary trials that have given rise to our species. With our higher intellect we have engineered defences and behaviours that effectively make up for our apparent lack of physical defences otherwise our species would have become extinct.

The real risk we face are from microbes and the creatures we can’t even see and of course ourselves in terms of pollution and climate change. But as with any animal population there will always be some individuals who have immunity and human beings can adapt and live literally anywhere on the planet from Antarctica to the jungles so while our numbers may eventually crash due to some disaster (virus, asteroid, nuclear war….) it’s highly probable there will always be survivors and we will populate the Earth for quite some time to come. We may even get to other planets in a few millennia!