We have evolved very long lifespans, probably because or our large brains, tool use, and social organization, which cause us to be less victimized by predation.
I'd modify that a bit.
The reason traits like "long lifespan" exist is through evolution: those without that trait die out, leaving a population of individuals with that trait. This is "selective pressure".
In the case of humans we need to identify a selective pressure on long lifespan. I think that it is indeed connected with our large brains, tool use and social organization (our "culture"), but the way that it's connected is not related to less predation. Rather, our culture is so complex that it takes a long time to learn all of it, and there is a need for a storehouse of knowledge.
The fact that it takes a long time to learn means that we need longer lived individuals around both to teach it and to protect the younger individuals until they've learned it. The fact that it's complex means that there will be elements of experience which relate to infrequent events, such as illnesses, animal attacks (17 year locusts, etc.) severe weather conditions or other natural disasters. The knowledge of how to deal with these infrequent events is held in the brains of older individuals, who must stay alive long enough to pass down this "wisdom" to the younger ones.
So in my view, the selective pressure which produced our long lifespans is that shorter-lived humans would be at a disadvantage because too much knowledge would be lost between each generation
The bible was mentioned in regards to the question of whether humans may have been much longer-lived in the past. If this were true, it would need to be able to be explained in evolutionary terms.
Remember that humans have been around for hundreds of thousands of years and writing is only a few thousand years old. With the advent of writing, it may have become less essential for humans to live quite as long as before, since some critical knowledge could be preserved in written form rather than in the brains of the elders. So (again, if the ages mentioned in the bible are at all correct) perhaps the selective pressure for VERY long lifespans was reduced, and we ended up with the lifespans we see today.
Similar claims have been made with regard to intelligence: in societies with a less developed technology, everyone has to be rather intelligent in order to survive. Each person has to have mastery of all the knowledge regarding each type of plant and animal, each technique for hunting, making plants edible, treating all kinds of problems, how to build traps and dwellings, etc. And each person has to be flexible enough to respond to changing environmental conditions. As technology became more advanced, with the advent of agriculture, division of labor allowed some people to learn only a few tasks while others did the other tasks. This allowed less intelligent people to survive and reproduce, thereby reducing the average intelligence of the species.
So perhaps long lifespans of two hundred years or more could be a trait we have lost. If so, the capacity may lie dormant in us, opening up the possibility that we could, through some combination of treatments and supplements, reawaken this existing trait and fairly easily double or triple our lifespans.
It's only a hypothesis, but it's one that implies that we shouldn't give up too quickly on the idea that we may see significant life extension from C60 or some other agents.
