Viruses that cause persistent productive infections (e.g., cytomegalovirus, HIV) are a particular problem because the infected person is a continual source of virus that can be spread to immunologically naïve people.

In genetic hitchhiking, a gene is propagated because it occurs in conjunction with a favourable mutation.

Christmas is a hard time of year. And what makes it harder is Kris Kringle. As if you didn’t have enough on, now you have to buy a gift under $10 for someone at work who you don't know very well. … In an office Kris Kringle, people often don't care, or don't care enough. And it shows. For example, in last year's Kris Kringle, I mistakenly bought some very nice beer for a young guy in the office who turned out not to drink. I had no idea. Sorry again.

And the road goes on forever / And I've got one more silver dollar / But I'm not gonna let 'em catch me, no