Question: Because Humans have different immune systems is it therefore impossible for the human race to be wiped out by a virus?

Stephen Curry answered on 21 Jun 2010:

That’s a very interesting question – I think you are probably right.

It is certainly true that some infectious disease have been very deadly. I think about 95% of the native American population were wiped out by the smallpox virus that was introduced when Spanish explorers turned up in the wake of Christopher Columbus.

And in the 14th Century about one third of the population of Europe died of the ‘black plague’ (bubonic plague – caused by a bacterial parasite – Yersinium pestis).

But in both those cases, people did survive.

These days it has become apparent that some individuals are resistant to infection by HIV, the virus that causes AIDS.

In each case of course it is the people who happen to have resistance who survive and the resistance is then passed on to their offspring.

It is believed that many human disease have arisen from animal diseases which have switched their ‘preference’ for humans. This probably happened quite frequently when farming with animals started thousands of years ago. One reason why the Spanish killed off so many Americans with their germs is that they were already immune to viruses that the Americans had never been exposed to (the Americans did much less animal farming and had different animals anyway).

For this reason, people take the threat of bird flu very seriously – since this is a disease that might make the jump to humans who have no immunity to new types of flu virus.

If you want to read more about this, a great book on the topic (and much else) is “Guns, Germs and Steel” by Jared Diamond.