Evolutionary biologists are uncovering genomic mechanisms that allow populations to adapt quickly to different, hyperlocal habitats without splitting into new species.

The green ecotype of Cristina’s timema, a species of stick insect, blends in with broad leaves. Other ecotypes of the same species are colored to blend in with narrower leaves. With genomics, scientists are answering century-old questions about how a single species can manifest such distinct traits.

Aaron Comeault

Introduction

When she was a graduate student in the 1970s, the evolutionary biologist Kerstin Johannesson regularly walked the shores of a Swedish archipelago, scanning the ground for pebbles that moved: marine snails. Her adviser, a taxonomist, had tasked her with describing the species present there by documenting their traits.…