Charles Darwin developed the theory of how living things develop from simpler organisms over long periods of time.

VOA: special.2009.02.25

The next time you think about going without sleep, consider this: Laboratory animals that are kept awake for long periods of time ...die.

VOA: special.2009.08.26

Often the mother had to be treated in a hospital for long periods of time.

VOA: special.2009.12.06

Over long periods of time, these small changes result in the creation of new species.

VOA: special.2009.12.01

He thought that this was evidence that the bottom of the ocean had been lifted up by powerful geological forces over long periods of time.

VOA: special.2009.02.25

And to prepare himself, he went without sleep for long periods of time.

VOA: special.2009.03.18

He says even if people have a healthy body weight, sitting for long periods of time still has an unhealthy influence on blood sugar and blood fats.

VOA: special.2010.01.13