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Asked by eye56 to Austin, Kirsty, Nicola, Nike, Sarah on 15 Jun 2012.
Keywords: diurnal, nocturnal, sleep
The short answer is that we’ve evolved not to; we don’t see well in the dark, unlike bush babies, our hearing isn’t very sensitive unlike owls, and we can’t do echo-location, unlike bats.
We’ve evolved good daytime sight, and are therefore best-suited to going about our business during the day, when we can see what we’re doing! Light is recieved by the eyes, and stimulates teh release of hormones, which regulate the brain to encourage us to feel awake in the day and sleepy at night, so that we best take advantage of the light.
Yes, fancy colour vision is definitely a day-time adaptation. Animals that are nocturnal (like rabbits) usually see well in the dark but have poor or even no colour vision. This is because they have lots of rod cells in their retina (good for low light levels, monochrome) but little/no cone cells (need more/stronger light to work but do colours). So rabbits see in black & white, but at night that doesn’t matter so much since they see well in monochrome (a bit like the night-vision goggles you see in movles).
Your body’s 24 hr clock (we say ‘circadian timer’) is mostly locked to light and dark, but there definitely seem to be people who are a bit ahead, or a bit behind. So some people are more ‘larks’ (best in the morning!) and some are more ‘owls’ (more likely to get up and go to bed late). But no-one is really well adapted to being awake all night and asleep all day, which is a real problem for people who work shifts. You also meed some sunlight so that your body can make Vitamin D.
My dad has worked three different shift patterns for years, which really does play havoc with his sleep patterns. Babies also respond to circadian rhythms. When a baby is breast fed, the mother makes milk with different hormones and proteins in it at different times of the day. Morning milk will therefore have a different constitution to bedtime milk. This has implications if you feed the baby expressed milk. If you give a baby expressed milk at night that was expressed in the day, you may find it keeps the baby awake rather than settling them down for the night!
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