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
The eruption of Mount Pinatubo in the Philippines in 1991 spewed almost 20 million tons of sulfur dioxide into the atmosphere, causing worldwide temperatures to drop half a degree on average.
Arlan Naeg/AFP/Getty Images
Stars over the Cerro Tololo Inter-American Observatory in Chile. Sheppard and Trujillo used the new Dark Energy Camera (DECam) on a telescope there to find the distant dwarf planet 2012 VP 113.
An example of a human precision grip — grasping a first metacarpal from the thumb of a specimen of Australopithecus africanus that's thought to be 2 to 3 million years old.
T.L. Kivell & M. Skinner
The newly described L. larvaepartus (male, left, and female) from Indonesia's island of Sulawesi. Odd, sure, but at least they don't use their stomachs as breeding chambers, as some other frogs do.
Jim McGuire/UC Berkeley
An inside view of this fossil Pseudodon shell shows that the hole made by Homo erectus is exactly at the spot where the muscle attached to the shell. Poking at that spot would force the shell open.
Henk Caspers/Naturalis Leiden/The Netherlands