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Asked by jumentous to Ed, Katie, Sam, Steve, Vera on 15 Jun 2011.
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Katie Marriott answered on 14 Jun 2011:
That’s a really good question! Although I suppose we never know what turn evolution might take next. So it might be stronger bones but it might be something else nature thinks we need!
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Sam Tazzyman answered on 14 Jun 2011:
It is unlikely that evolution will lead to humans having stronger skeletons. Imagine you had two people, one who had a gene to make a really strong skeleton, and one who didn’t. Would the one with the stronger skeleton be more likely to survive and have children and so pass on the gene for making a strong skeleton? Well, maybe, but we should remember that people don’t usually die from broken legs or arms. But we also should remember that having a stronger skeleton will have to come at some cost. If the skeleton is stronger because the bones are thicker, then the person will also be heavier, and will find it harder to move as quickly. So maybe this might make the person less likely to survive.
These sort of things (having thicker, stronger bones, but at the expense of being slower) are called “trade-offs” in evolution, and they happen all the time. Organisms often can’t get something for nothing: a genetic mutation that causes a benefit in one place might cause a problem for some other reason. Whether the mutation stays in the population will depend on whether on average the trade-off is good or bad (in the example of the stronger, thicker skeleton, it would depend on whether it was better to have a stronger skeleton but be slower, or whether it was better to have a normal skeleton and speed).
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Steven Daly answered on 14 Jun 2011:
One time we would probably evolve stronger skeletons would be if we managed to colonize a planet larger than the Earth. On a large planet the gravity will be stronger, and this will mean that our bodies need more support. Although this is a long way off it is something not may people will think about when thinking of living on a new planet.
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Vera Weisbecker answered on 14 Jun 2011:
I agree with Sam and Steven, 100%. Not everything you think would be nice to happen is actually of an evolutionary advantage. Pity, I’d love to be able to fly!
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Ed Morrison answered on 15 Jun 2011:
No, I don’t think so. Modern technology and healthcare probably means that strong bones are less important than they used to be. In fact, we can see by looking at the bones of human ancestors that our skeletons have become less strong over time, probably because of the tradeoffs Sam talks about.
Having thinner, weaker bones helps animals move more easily. Birds are an example – their bones are hollow to make them light so they can fly, but they are vulnerable if they caught by a predator.
Comments
Anna commented on :
Sam’s answer is spot on. Basically, car crashes and accidents aren’t enough of a selection pressure to mean that people with weaker bones don’t survive long enough to pass on their genes. Also, the selection pressure has to be applied for a long period of time, and many many generations, for it to have a significant effect on the human skeleton.