A scientist believes that crocodiles may be able to sleep with one eye open. What’s more, he thinks that humans may have had this same ability thousands of years ago.
Would it be useful to be able to sleep with one eye open? It could be helpful in the classroom, but having one eye open may look a bit strange and attract the attention of the teacher. There is not much point keeping one eye open when you are asleep in bed – unless you are worried about burglars. Research has indicated that many millions of years ago, man may have been able to do just that – but times were different then. We didn’t have burglar alarms.
Some reptiles, birds and mammals that live in the sea – like dolphins – are able to give the appearance of sleeping with one eye open. Scientists believe that only half of their brain goes into sleep mode whilst the other half remains awake. Whereas the reptiles and birds do this to make sure that no predators come along, the dolphins keep one eye open to make sure they keep within their family group.
Dr John Leshu of La Trobe University decided to investigate this a little further. He purchased a number of young saltwater crocodiles from a local farm, each about 50 centimetres long. They were kept in an aquarium lined with video and infrared cameras. This is what they found that:
- The crocodiles kept both their eyes closed for about 17 hours each day.
- They usually kept only one eye open for one hour per day.
- For six hours, they had both their eyes open.
The scientists observed that if a crocodile had both its eyes closed, but another crocodile moved into its area, it would open one eye and watch the other crocodile very carefully. Dr Leshu was not sure whether or not the crocodiles were actually asleep when they had just one eye open.
Dr Leshu believes that birds are more similar to crocodiles than to other reptiles like snakes and lizards. They may even have been related to each other at one time, 155 million years ago. He asked whether humans may have had the same ability to sleep with one eye open, but over time, humans have lost this ability. If this were the case, it would mean that a human’s sleeping activity is not normal; the crocodiles’ sleeping activity is.
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