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| [00:00.00] | Pythons, bats and giant armadillos are |
| [00:02.88] | among the longest sleepers at over 18 hours a day. |
| [00:05.78] | Human babies need 16 hours, |
| [00:08.13] | and most of us probably feel |
| [00:10.16] | we need around eight hours sleep to function well. |
| [00:11.99] | Professor Jerry Seigel from the University of California, |
| [00:15.04] | Los Angeles, conducted a study of the sleep times |
| [00:17.79] | of a broad range of animals |
| [00:19.12] | and found that they vary widely. |
| [00:20.95] | Some, like migrating birds, |
| [00:22.98] | can survive long periods without sleeping at all. |
| [00:25.63] | He believes that shows sleep evolved to conserve energy: |
| [00:30.00] | "It's animals that are needlessly active that will not survive, |
| [00:34.54] | but animals that are most efficient |
| [00:36.67] | and use their waking time to do vital functions, |
| [00:40.90] | and are otherwise asleep that will survive." |
| [00:43.85] | Sleep helps make best use of limited resources. |
| [00:46.95] | In humans, when we're awake, |
| [00:49.14] | our brain accounts for 20% of the energy |
| [00:51.59] | we use when just sitting around. |
| [00:53.05] | Sleeping also makes us less likely to get injured |
| [00:55.86] | and less likely to be detected by predators. |
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