The idea of evolutionary advantage can be a double-edged sword. You can explain away some bits of the mystery of existence with it and you can make some other aspects infinitely murkier. On Quora, someone asked why we have not evolved to be giants. Below is my answer.
Modern human beings are probably smaller, weaker, and more prone to physical damage than their ancestors were. We used to be more muscular (against animals), and hairy (against cold) than we are now. But we have still gotten to the stage we are in today — that of being the dominant species on the planet. We fear no predator and the climate does not pose as much of a threat to us as it does other members of the animal kingdom.
We got to this stage, not because we grew large and strong, but because we didn’t. While growing large would definitely have made us more ‘fit’ for survival, not evolving into giants worked out better.
once wrote that cranial capacity is no guarantee of a species growing smarter. Dolphins and whales are pretty smart, but they do not ‘rule the world’ like we do because they never had any reason to get clever.
We didn’t have that kind of bulk. What we had were hands with opposable thumbs. In order to survive, we had to make use of what we had. So we built weapons to help protect against predators, started hunting for food, invented agriculture to ensure availability of food through tough seasons, started wearing clothes to protect us against harsh climates as we travelled the planet. We survived, and better yet, we thrived.
So sure, we could have become giants and survived. But we didn’t. We got smarter and survived. And truth be told, I rather prefer it this way. I have a feeling that having the odds against you help you grow. If we had been giants today, we perhaps wouldn’t be talking about our place in the order of things (like we are right now). In all likelihood, we would have been preoccupied with the upcoming mating season, like a whale.