There were once these two kangaroos. They were really similar in many ways. One was darker, while the other was lighter.
One day, terrible weather came to their area and that soon changed the animals forever.
The terrible weather was a hurricane. It destroyed many features and ended up creating huge water pools.
One of the big water pools created, filled a raven, and it ended up being a river that splits the two land areas in half.
Unfortunately, The two kangaroos separated and over time much changed. This lead to geographic isolation.
Over time, these two became completely different species to fit in with their environment. One of them stayed the same and the other changed but still has some features, and traits that original kangaroos had.