Horses pranced around the western hemisphere until they went extinct in the late Holocene. They were reintroduced by European colonists — though where, when, and how has remained unclear.

Let's hope that squid don't evolve lungs and legs, or humanity might be in real trouble.

The zebras were originally part of a newspaper tycoon's private zoo. Now they roam the San Simeon grasslands, growing in numbers. 

Turning off a gene called “Myc” has a surprising effect in male fruit flies: They start courting other males.

Livestock now outweighs wild mammals and birds ten-fold.

Mammals have a history stretching back 325 million years. To study that ancient history is to know our own origins.

Flies are in no way smart, but they experience time in an almost Matrix-like fashion.

Scuba divers often appear to be swimming through a calm and muffled universe. This couldn't be farther from the truth.

There's a fatal prion infection killing deer and elk across North America.

Sorry, humans.

Back to the drawing board.

More than 90% of human faces are home to mites that live in our skin pores. These friendly guests might be merging with us.

Research sheds light on social behavior of these mysterious predators.

Here's what the weather phenomenon baking large parts of the country actually means.

Yorkicystis lived during the “Cambrian explosion,” 539 million to 485 million years ago – hundreds of million years before the dinosaurs.

All marbled crayfish descended from a single clone discovered in Heidelberg, Germany in 1995. 

It's not about leaves in tall trees.

For 40 years, scientists thought a specific gene was linked to aggression in hamsters. Removing it, however, had violent consequences.

Scientists have discovered enzymes from several plastic-eating bacteria. So, why are our oceans still full of plastic pollution?

We already know animals feel emotions, and that they can understand humans' emotions. But can they understand each other's emotions?

Some astrobiologists believe life is rare, while others believe it is common in the Universe. How can we find out which view is correct?

Cats know more than they let on.

Disgusting behavior is often crucial to survival.

The apes taught sign language didn't understand what they were doing. They were merely "aping" their caretakers.

Symmetrical objects are less complex than non-symmetrical ones. Perhaps evolution acts as an algorithm with a bias toward simplicity.

Fish are surprisingly good in numbers tests — a skill that sometimes makes the difference between life and death.

Two types of leaves for two different drastic weather conditions.

A dog's breed isn't as predictive of behavior as many think it is. Environment and upbringing play a much larger role.

Research shows that octopuses are sentient, emotional creatures.

There is strong evidence that invertebrates are sentient beings.