Transcription
Every single monkey in South America is a descendant of African monkeys. We know that because we’ve looked at their DNA. But – and this is going to sound pretty obvious – South America and Africa are not close to each other – and even back in the day when those monkeys first arrived in South America, those continents were still very far apart. So how did monkeys get from Africa to South America? Strangely, most scientists think they took a raft.
Hi, I’m David, and this is MinuteEarth. When I say the monkeys took a raft, I don’t mean that they actually built some sort of sea-faring vessel. I mean they rode on a collection of driftwood, debris and vines, or on a piece of a boggy marsh that broke off the mainland and floated away.
But even still, the rafting hypothesis is, on its face, ridiculous. Think of all the things that need to go right for a monkey rafting trip to actually happen. First, a mat of vegetation – one that for some reason had a bunch of monkeys on it – would have had to break off and float out to sea perhaps as a result of a once-in-a-millennium storm. Second, that mat would have had to stay afloat for weeks on the waves without breaking apart. Third, the monkeys would need to have enough food and water on that raft to survive the journey. Fourth, the mat would have had to land in a place that monkeys could actually live. And fifth, enough monkeys of the right age and sex would have to have survived in order to successfully make new monkeys. The probability of any of these things actually happening are incredibly small, and the probability of all of them happening are astronomically tiny.
But there just aren’t any other potential explanations that could work. We know from studying plate tectonics that even 30 million years ago, when monkeys likely arrived, there were no land bridges connecting the continents of Africa and South America, so the monkeys did not simply walk into South America. We know from studying fossils that those ancestral primates were not great swimmers, so they couldn’t have monkey-paddled over there. If they didn’t walk and they didn’t swim, and they didn’t fly – because this isn’t the Wizard of Oz – then the only remaining way for them to get there would be to float.
And we've learned a few things that make a successful ancient rafting trip slightly more likely than it first appears. First, back then, the powerful east to west equatorial currents were even stronger than they are now. So once a raft was adrift from Africa, it would head basically straight West – and perhaps arrive in South America within just a few weeks, which means the monkeys wouldn’t need to be as lucky with their route. Secondly, we know that back then – just like now – there were times of the year when the Atlantic had very few waves, which means the monkeys wouldn’t need to be as lucky with their raft’s survival. And third, we know that back then, it rained basically every day along tropical latitudes, which means the monkeys wouldn’t need to be as lucky with their food and water supplies.
But perhaps most importantly, given enough attempts, extremely unlikely events can happen. Let’s say that a storm strong enough to send a monkey-laden mat of vegetation into the sea only happens once every two thousand years. Even still, over a few million years, there would be thousands of chances for voyages to start, and only one of them would actually need to succeed in order for old world monkeys to become, well, new world monkeys.
In fact, scientists are pretty sure that this kind of rafting also brought the ancestors of lemurs 400 miles from mainland Africa to Madagascar. And brought reptiles and rats about 600 miles from the South American coast to the Galapagos islands. And in 1995, scientists actually documented the voyage of a natural raft; this one brought 15 green iguanas more than 100 miles across the Caribbean to the island of Anguilla for the first time. It turns out that the world is big enough and time is long enough that things that we think are so improbable as to be impossible have actually happened many times ove