Currents aren't the only thing flowing across the oceans - recent research shows that genetic cargoes move far faster than previously thought.
The rise of new species on land is largely due to allopatric speciation, where things find themselves cut off from their parent populations and gradually adapt on their own.
The isolation is essential to allow evolution, otherwise constant mixing with unaltered examples of the species would water down any changes which occur.
The most dramatic example of this is Australia, which evolved an entirely independent ecology - until settlers enable invasive species to cross the previously impenetrable barrier.
The rise of new species on land is largely due to allopatric speciation, where things find themselves cut off from their parent populations and gradually adapt on their own.
The isolation is essential to allow evolution, otherwise constant mixing with unaltered examples of the species would water down any changes which occur.
The most dramatic example of this is Australia, which evolved an entirely independent ecology - until settlers enable invasive species to cross the previously impenetrable barrier.