So, did you read the groups' description and you are still not sure?

http://fold.it/portal/groups

None of the descriptions are attractive enough.
It seems that only the top 10 groups are really playing the game.

... you could be right.
There are many users, which are registered, but don't play anymore (see their scores), similar to BOINC.
Maybe they got frustrated or had an issue with their wife or girlfriend because of the game ;)

But if you want to evolve, you have to be in a group.

I am joining Team China for now. Can you only join one group?

When i looked at the details of the group, only a few members are actually playing lol maybe i should just join another one.

Yes, a group with only some active players is not that much fun.
It's waiting, waiting, waiting.

The top groups are request only. And I don't really want to join Richard Dawkins Foundation

...why?

You mean why I don't want to Richard Dawkins Foundation? I just don't feel attached to its group description. lol

So, if you want to participate in a group where you have to request, you'll have to ask the group manager, as far as I know.