Nice summary, but could use more illustrations...
If we evolved from monkeys then why am I still having sex with them?
If I built a new house, why are my parents still living in another house?
What about my cousins? Or the guy across the street? Or Shareef Mu'izz Mustafa?
To be fair, though, the common ancestor of all vertebrates was a fish - it would have had fins and gills. It just wasn't any fish that is alive today. Likewise humans did evolve from monkeys; our ancestors were simians with tails. It seems to me there is a growing tendency to abstract ancestors completely out of the picture, like the featureless circles in your diagram, but we can say more about them than that.
Anyway, my answer to the question would be "why, how well do you think you would do living in the treetops?" Except in practice, I don't usually engage much with people who prefer gotcha questions to understanding something.
The smallest clade that contains both old-world and new-world monkeys also contains apes (including gorillas, chimps, and humans). So in a sense, we are all monkeys.
Another way to answer this question if (for example) you are addressing a light-skinned American: "You are descended from Europeans, but there are still people in Europe. Just not the ones you descended from."
Phil Plait answers creationist questions about evolution
erm because the monkeys were too busy jerking off and missed the bus?
Why are there still monkeys? Because someone has to run for congress.
Where's that from? I'd love to be able to link to it directly. I'm a genealogist who uses DNA as part of my research, and explaining the reality of how many ancestors are actually in someone's family tree is always one of the initial discussion points.
I don't recall... I saved it a while back because I thought that it was nice and succinct -- I think that it came out of an illustration contest.
Just did a google image search...
This looks like the best page:
Family Tree vs Phylogeny
Here's the person who made the illustration:
Apparently I’ve gone viral -or- Stick figures and evolution | The Evolving Paleontologist
Because monkeys are fucking hilarious. Who the hell wants to live in a world without monkeys doing monkey stuff?
Because you're still using OK Cupid.
Puritanism ... for monkeys?
Humans are evolved?
I'd always rather give credit to the creator if at all possible.
A simple way to put it (or a way to express the concept to people with simple minds) is: if American football evolved from British rugby, why is there still rugby?
A mutation that appears in one subset of a species does not automatically appear throughout it's range in all individuals.
It's inexact, but good enough for people who don't understand evolution; the more detailed you get with the explanation, the more likely you are to confuse them.
No because we're apes, not monkeys. Primates yes, not monkeys - missing the tail you know. As for the rest of the question.... Ugh, why? That isn't how evolution works. If we're humans why did we (we being the human population) successfully mate with Neanderthals and perhaps Denosivans too, does that make non-Africans less human? Now, that is a better question.
There are still monkeys so that when we all finally do ourselves in, someone can still play on this planet.
That's a much better explanation than that website's, which was frankly a mess. All that talk of conga lines just confused the issue by reinforcing the idea of a single, linear chain they were trying to dismantle.