Emus and their relatives may have lost the ability to fly because of changes in DNA that regulates genes. Here, an emu walks with its chick.

Being stressed or afraid may alter a person’s usual scent. That can throw dogs off the person’s track. People with a particular version of a gene may have a bigger change in odor when stressed, data show.

We inherit genes from our parents. Genes are like a recipe that’s passed along from one generation to the next. But the number of genes doesn’t explain why we are more complex than simple animals or bacteria.

Scientists engineered a plant called thale cress (above) to be nearly always on alert to leaf-eating predators. In the lab, these plants grew smaller and made fewer viable seeds than normal.