You have been granted the magic fingers of extinction, one time use only. Snap them and name one species out loud and it will disappear forever from the face of the earth. Will you use this power? Upon what?
And note: we’re talking about a species - you might get away with several closely-related/allied species if you say ‘camels’ or ‘cows’, but if you say "bugs’ or ‘bacteria’, it just isn’t going to work, and by ‘isn’t going to work’, I actually mean the whole universe will explode, so be careful.
This was my vote, after reading the malaria article in the latest National Geo. They said that some scientists estimate that 50% of all the humans in history have died of malaria, and that it’s by no means controlled in most of the world even now.
HIV is a pretty freakin’ solid choice. I can’t think of anything else that would come close. If, however, researchers find out that cancer has a viral instigator, I’d choose that instead.
HIV
HPV
The Anopheles 'Skeeter (the malaria fiend)
The little amoeba that causes dysentery, unless it serves some useful purpose I don’t know about.
ants
I was curious about malaria, and I found out that resistance of Plasmodium falciparum to chloroquine has spread recently from Asia to Africa, making drugs ineffective against the most dangerous Plasmodium strain in many affected regions of the world.