Speciation: 1 Becomes 2

The process of speciation is how natural selection can sometimes split one species into two. The most important step in this occurring is the separation (physically or biologically) of the species into 2 or more groups. For reference here's the Amoeba Sister's example.

Sometimes speciation creates very similar forms in new places. Several times in the past birds have lost their ability to fly. PBS Eons shows us these species forming events.

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Terror Birds of South America