STEVE INSKEEP, host:
Residents of New York City have a reputation, not really deserved, for being rude. The classic example is the New York City waiter who ignores you or insults you or doesn't wanna serve you lunch. It turns out this is an old habit in New York according to science correspondent Robert Krulwich, it's been going on for ten million years.
ROBERT KRULWICH: So here I am right in front of Saks Fifth Avenue in New York City with my friend, the biologist Guy Robinson. We are not shopping. We are looking at trees.
Mr. GUY ROBINSON (Biologist): If you look up, now, if you look into the branches up here, you'll see some sprouting out of the branches.
KRULWICH: He is talking about thorns, big spiky, sharp-looking thorns, high up on the trees in front of Rockefeller Center right on Fifth Avenue. Local shoppers can just look up?
Mr. ROBINSON: They're right there.
Unidentified Woman #1: Yes, I do. I see them there.
KRULWICH: And if you touch one?
Mr. ROBINSON: Ow, oh, it's really? it's very nasty. You wouldn't want to walk into one of these.
KRULWICH: But if you were Professor Robinson, you would ask?
Mr. ROBINSON: Why are there all these spikes here?
KRULWICH: Trees typically produce thorns to repel something, but what could possibly be bothering this tree?
Mr. ROBINSON: It's protecting itself against what?
Unidentified Man #1: Cab drivers.
(Soundbite of laughter)
KRULWICH: Cab drivers? But, no, but it is a puzzle really.
Mr. ROBINSON: Because there's nothing around here that it's affectively defending itself against.
KRULWICH: So what scientists do in a situation like this is they can ask is there any other tree, anywhere in the world that produces a thorn that looks just like this. And it turns out there is.
Mr. ROBINSON: Acacias, which you find in Africa?
KRULWICH: Acacia trees have the same size and the same shaped thorns and why?
Mr. ROBINSON: Well in Africa, they seem to be protecting themselves against elephants.
KRULWICH: In Africa, elephants like to lunch on acacia fruit and then for desert they often peel and eat the bark.
Mr. ROBINSON: The bark's very nutritious.
KRULWICH: But it's not, of course, good for the tree, 'cause without bark, an acacia tree will die. So over millions of years, they have evolved thorns to poke at elephant tongues.
Unidentified Woman #2: You wouldn't want to lick that tree.
Mr. ROBINSON: Oh, no, no, no, no.
KRULWICH: No, so what are you saying here? If acacia trees developed thorns to fight elephants, then the New York trees did the same thing in Manhattan, 'cause I'm standing here across from St. Patrick's Cathedral, I just don't feel elephant in this vicinity.
Mr. ROBINSON: Not now?
KRULWICH: But 11,000 years ago, there were elephants in Manhattan. We call them?
Mr. CARL BUELL (Artist): Mastodons.
KRULWICH: And says Carl Buell who draws ancient animals, mastodons were kind of hairy and very big.
Mr. BUELL: Eight foot at the shoulder, maybe for a female, ten for a male. That's a big animal.
KRULWICH: Wow, and they lived in New York?
Mr. ROBINSON: Oh, yes we found Mastodon remains and bones literally all over New York State.
KRULWICH: But when I said to shoppers outside Sak's Fifth Avenue, here's a picture of what these thorns are fighting against?
(Soundbite of laughter)
Unidentified Man #2: Against a mammoth.
KRULWICH: Yeah, you don't believe me?
Unidentified Woman #3: No.
KRULWICH: But they should. Mastodons and this species of honey locust have been neighbors for millions of years.
Mr. Robinson: Oh yes.
KRULWICH: So it is totally possible the trees were once attacked by local mastodons. And even though there hasn't been a mastodon in Manhattan for 11,000 years, the thorns stayed.
Mr. ROBINSON: It took millions of years for it to happen and it will probably take a couple hundred thousand at least to get to the point where a honey locust said, well I don't need these thorns anymore.
KRULWICH: To be fair, there is no direct evidence that mastodons actually eat these trees.
Mr. ROBINSON: Well, we need to look at mastodon dung to know that.
KRULWICH: 'Cause if there's honey locust root in mastodon dung, then you know they ate these trees, and guess what? Professor Robinson happens to have a fossilized sample.
Mr. ROBINSON: Yeah, there's this great big bolus which to us could only have been?
KRULWICH: You can say it.
Mr. ROBINSON: ?poop.
KRULWICH: But he hasn't checked his sample, not yet. So for the moment, this is still a hypothesis, it's not proven, but what a notion.
So for 11,000 years these trees have been getting ready for the mastodon that never comes?
Mr. ROBINSON: Absolutely, yeah. I mean the?
KRULWICH: They're like "Waiting for Godot" and it's sort of sad.
Mr. ROBINSON: It - it kind of is. They seem a little lonely.
KRULWICH: Standing there on 49th street, on 50th Street, thorns ready, but no mastodon.
Robert Krulwich, NPR News in New York.
INSKEEP: If you can't get enough of Robert Krulwich, we can solve that problem for you. You can download his Podcast, Krulwich on Science at npr.org/podcasts.
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