Originally Posted by Blood Red Lucario
Early hominids also had a lot of adaptations we don't have now(fur, size, etc.). While yes they evolved into us as we got more intelligent we lost a lot of the natural defenses that would have kept us alive without us using our intelligence and tools. Perhaps we would survive in the tropics but hunting and gathering would be difficult because we can't kill things as easily as we normally would have with a spear or some other weapon. There would be little to no farming unless we tilled land by hand.
Our predecessors survived and evolved into beings that are good at making tools so we no longer needed biological advances to survive. If we lose our tools we are probably the most vulnerable species on the planet.
There are plenty of isolated tribes in South America, Africa, and the Pacific where people still hunt and gather in the same way they have thousands of years ago. Those guys would be perfectly fine of course.
@Ender: I have no doubt humanity as a whole would survive, but a lot of people would die nonetheless.