Madagascar broke away from Africa around 160 million years ago. Lemurs didn’t evolve in Africa until 100 million years later, by which time the Mozambique Channel was 560km (350 miles) wide, but the sea currents at that time flowed strongly towards Madagascar. Chance migrations of lemurs that fell into rivers and were swept out to sea, clinging to floating trees, would have been enough to colonise the island. The ancestral lemurs eventually died out in continental Africa because they were outcompeted by squirrels and monkeys, but by then, continental drift had moved Africa and Madagascar north and the ocean current now flowed away from Madagascar. So lemurs were free to spread across the island without any significant competitors for sustenance or living habitat.