Two Species, One Field

You'll learnthat speciation is the cutting of gene flow, not a change in looks or distance.

A species is not a look; it is a gene pool with the door shut. Ask the one question that counts — can they interbreed and produce fertile offspring? — and identical mosquitoes turn out to be two species, two very different dogs turn out to be one, and a mule turns out to be a dead end. Twelve short steps; press Next for each one.

AP BIOLOGY · 12 STEPS · 6 QUICK CHECKS · SPECIES = REPRODUCTIVE ISOLATION · GEOGRAPHY IS A ROUTE, NOT A RULE · v6

gene flow · cut · two species

Before you start

What you're looking at

Two populations of individuals with a two-headed arrow running between them, labeled gene flow.

The question

What makes two populations one species — a look, a place, or a flow of genes?

Step 1 / 12