A blue morpho butterfly sits on a leaf. A new study finds that butterflies likely originated somewhere in western North America or Central America around 100 million years ago. Kristen Grace/Florida Museum hide caption
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evolutionary biology
Scalloped hammerhead sharks can dive to depths of more than 2,600 ft (800 m) to hunt for squid and other food. Gerard Soury/Getty Images hide caption
Hammerhead sharks 'hold their breath' in deeper, colder waters, research shows
About 6,500 mammal species live on Earth today. Credit from left to right: John Moore/Getty Images; Yoshikazu Tsuno/AFP via Getty Images; Koichi Kamoshida/Getty Images; Paula Bronstein/Getty Images Getty Images hide caption
Welcome to the mammalverse: Scientists sequence DNA from 240 species around the world
A female cockroach considers accepting a sugary offering from a male cockroach. Ayako Wada-Katsumata hide caption
These cockroaches tweaked their mating rituals after adapting to pest control
The Summers Place Dodo skeleton dates from around the 16th century. Leon Neal/Getty Images hide caption
Macaques use stones as hammers to smash open food items like shellfish and nuts. Lydia V. Luncz hide caption
Stone flakes made by modern monkeys trigger big questions about early humans
Colored transmission electron micrograph of a section through an Escherichia coli bacterium. This rod-shaped bacterium moves via its hair-like flagellae (yellow). Kwangshin Kim/Science Source hide caption
In 2003, Acanthamoeba polyphaga mimivirus, also known as mimivirus, was the first giant virus to be described. It's larger than many bacteria, and was found in a water sample from a hospital cooling tower in England. Didier Raoult/Science Source hide caption
An artist's impression of Saccorhytus coronarius, a sea creature that lived 540 million years ago. Jian Han, Northwest University, China hide caption
The killer whale J2, better known as "Granny," pokes her head out of the water in the Salish Sea near the San Juan Islands of Washington in July 2016. Granny, who was thought to be about 105 years old at the time, was presumed to have died later that year. Mark Malleson/Center for Whale Research/AP hide caption
Menopause Mystery: Why Do Female Killer Whales Experience The Change Of Life?
These mitochondria, in red, are from the heart muscle cell of a rat. Mitochondria have been described as "the powerhouses of the cell" because they generate most of a cell's supply of chemical energy. But at least one type of complex cell doesn't need 'em, it turns out. Science Source hide caption
Male treehoppers make their abdomens thrum like tuning forks to transmit very particular vibrating signals that travel down their legs and along leaf stems to other bugs — male and female. Courtesy of Robert Oelman hide caption
An illustration of Pappochelys, based on its 240-million-year-old fossilized remains. This ancestor to today's turtle was about 8 inches long. Rainer Schoch/Nature hide caption
The most recent common ancestor of all today's snakes likely lived 120 million years ago. Scientists believe it used needle-like hooked teeth to grab rodent-like creatures that it then swallowed whole. Julius Csotonyi/BMC Evolutionary Biology hide caption
The size of the brain of a chimpanzee (right) is considerably smaller than that of a human brain. Probably multiple stretches of DNA help determine that, geneticists say. Science Photo Library/Corbis hide caption
Recent research sequenced 48 bird species, including (from left) the budgerigar, the barn owl and the American flamingo. (Left and center)iStock; (Right) Chris Minerva/Ocean/Corbis hide caption
More than just hungry or wet? George Marks/Getty Images hide caption