Question: if we r able to inject stem cells into the human body that r able to rebuild your heart, over time wont we just evolve to have in us if u introduce it into our body then it would just increase the population and it would stop people from dying and then too many people would live on the earth?

David Christensen answered on 20 Nov 2013:

Errrr wow that’s a long complicated question m6a2!

Evolution works naturally as we get mutations that can make us better able to survive in comparison with others that don’t have those mutations. This happens over a very very long time. Injecting stem cells or other cells into a person’s body will not cause them to evolve. Actually, by injecting stem cells into people we are less likely to evolve to have more stem cells in us! Evolution works by making those with a genetic advantage survive while others die. If there are some people who have a genetic advantage that means they have more stem cells they might be more likely to survive to pass on their genes. But, if we are injecting stem cells into the people who do not have this genetic advantage and are helping them survive, then actually everyone is surviving and we are stopping evolution from working. I hope this makes sense!

You’re right though that by making more treatments for disease and stopping people from dying, we will have a growing population. This is happening. The world’s population is growing faster than it ever has before! Soon we might start having problems with having too many people on Earth, which will be a difficult problem to solve.

The difficult question is whether we should let more people die to stop the population growing too much? Or maybe we should stop people from having more than 1 or 2 kids? What do you think? It’s a tricky question.