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

itoggle caption 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 hide caption

itoggle caption 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. Reidar Hahn/Fermilab hide caption

itoggle caption Reidar Hahn/Fermilab

Ultrasound is often used for prenatal screening. It's just one of several prenatal screenings available to pregnant women. iStockphoto hide caption

itoggle caption iStockphoto

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 hide caption

itoggle caption T.L. Kivell & M. Skinner

Bar-headed geese tend to follow the sharp ups and downs of the Himalayas as they migrate, research finds. John Downer/Nature Picture Library/Corbis hide caption

itoggle caption John Downer/Nature Picture Library/Corbis

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 hide caption

itoggle caption Jim McGuire/UC Berkeley

Farming helped fuel the rise of civilizations, but it may also have given us less robust bones. Leemage/UIG via Getty Images hide caption

itoggle caption Leemage/UIG via Getty Images

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 hide caption

itoggle caption Henk Caspers/Naturalis Leiden/The Netherlands