Scientifically Speaking | Moving continents and migrating monkeys
The story of how monkeys migrated from one continent to another is tied to moving continents. Here's how
Indians are aware of the mythological story of the crossing to Lanka by the army of monkeys narrated in the Ramayana. Most will not be aware of an even more arduous crossing made by prehistoric monkeys around 40 million years ago across a vast ocean to a new homeland.
But before I get to this remarkable voyage, I need to set the stage by recounting the most important idea in geology — plate tectonics. This theory, which proposes that the upper part of the Earth’s surface is made up of pieces that move around, is one of the most outstanding scientific concepts of the last 150 years. It is taught in schools today. But it was ridiculed by professional geologists for decades after it was proposed. And the story of how monkeys migrated from one continent to another is tied to moving continents.
Only a century ago, most geologists thought that movements of the Earth’s crust were primarily up and down in vertical motion. In 1912, Alfred Wegener noticed something striking that every kid notices on a map. The eastern shore of South America and the western shore of Africa line up perfectly like they’re two pieces of a jigsaw puzzle. Wegener’s big idea wasn’t that this connection was on a map. He took it to the next level by showing that the two continents had a connection that was much deeper in time. Rocks on both continents had many similar features. Similar fossils of extinct in similar layers of rock was strong evidence that they had been attached at one point. The same plants and animals had been found until the continents moved apart.
Scientists are people too, and people often stick with conventional wisdom even if it is wrong. Unfortunately, the field of geology overlooked Wegener’s concept until the 1950s. But then a mountain of evidence began to accumulate. Wegener’s idea of continental drift evolved into the theory of plate tectonics, and today it is a foundation of modern geology.
Now, we know that the Earth wasn’t always like it is today. Around 335 million years, there was one massive landmass on the planet — a supercontinent centred on the equator. Wegener named it “Pangea”. We know that Pangea started breaking up around 175 million years ago, ultimately giving rise to the continents that we have today.
Dinosaurs were still around at the end of the Cretaceous Period around 66 million years ago when a massive asteroid hit the Earth near the Yucatan Peninsula. At that time, the continents of North and South America had not joined, but Africa and South America had already drifted apart.
The mass extinction event caused by the asteroid strike paved the way for the rise of mammals such as us. As continents moved apart, geological isolation caused mammals to evolve in different ways.
And this is where the monkeys come into the picture. If you’ve been to Central or South America, you may have encountered different kinds of monkeys. In Panama and Costa Rica, I saw howler monkeys and capuchin monkeys living near cities and people when I visited a few years ago. They’re hard to miss. But the surprise is that ancestors of these monkeys didn’t originally evolve in the Americas, they migrated across the ocean.
All living monkeys in the Americas (and a few other rodents such as capybaras) are descendants of just a few animals that are thought to have crossed the Atlantic Ocean from Africa on tree-rafts starting 40 million years ago.
In his fantastic book on natural history, Otherlands: A Journey Through Earth's Extinct Worlds, Thomas Halliday describes the journey of monkeys from tree branches and raft islands of river deltas in Africa to the tropical forests of South America.
“Trees still standing, held up by the intertwining of roots that have knitted together the soil, an undergrowth filled with creatures oblivious to their imminent voyage. Around it, smaller, unattached patches swarm like tugboats around a ferry… Only a rough patch of rapids or collision with the bank at a bend in the flow will halt the procession, and if none are encountered, the island raft will eventually emerge from an estuary into the open ocean, and will be carried from shore with the momentum of the river current. The odds of anything good then happening to the inhabitants of these floating islands are minute, but they are good enough that several of these rafts, blown by lucky winds, and each carrying a small population or a pregnant female, arrived in South America.”
The trip across the Atlantic would’ve taken around six weeks, but even given the slim chance of survivors, successful ocean voyages happened multiple times.
A research paper published in Science in 2020 pointed to different trips in which Old World monkeys made the arduous voyage across the Atlantic to South America. In the new continent, survivors lived, bred, and evolved into all the myriad monkeys that we see today in the Americas. It is an incredible, accidental voyage that shaped the course of natural history.
Thinking of moving continents and migrating monkeys is a good reminder to modern humans. We have been around for a very short time in comparison to the age of the Earth. We like to think that the Earth and life on it are immutable. But as the recorded history of the planet in geology and biology remind us, movement and change are all around us.
Anirban Mahapatra is a scientist by training and the author of a book on COVID-19
The views expressed are personal