Killer whales that feast on seals and hunt in small packs are thriving while their widely beloved siblings are dying out.

Identical twins are not exactly genetically the same, new research shows.

Gorillas are highly sociable animals – up to a point. A crowded mountain can make silverbacks more violent, scientists say.

Gray wolves rebounded in parts of the American West with remarkable speed following their reintroduction 25 years ago.

Tasmanian devils, the carnivorous marsupials whose feisty, frenzied eating habits won the animals cartoon fame, have returned to mainland Australia for the first time in some 3,000 years.

This animation shows how the proton gradient across the mitochondrial membrane powers the ATP synthase enzyme to make ATP. It is the third of three animations about cellular respiration.

This animation shows how the enzyme complexes of the electron transport chain harvest energy from cofactor molecules to pump protons across the mitochondrial membrane and establish a chemical gradient. It is the second of three animations about cellular respiration.

This animation shows the reactions of the citric acid cycle, which splits off carbon atoms and generates energy-rich reduced forms of cofactor molecules. It is the first of three animations about cellular respiration.

Every year, as many as 400 million people are infected with life-threatening diseases by the Aedes aegypti mosquito. It wasn’t always so dangerous.

Trees now cover most of the exclusion zone, and climate change is making them more likely to burn.

Although scientists often worry most about the loss of the world’s predators, a comprehensive new study finds that plant-eating herbivores are the animals most at risk of extinction.

For centuries, scientists have obsessed over a primordial blob that can shape-shift, clone itself, and live indefinitely.