Ever wondered what you might have in common with a cuttlefish? Or, for that matter, an octopus? Apart from the eight-armed cephalopod's impressive dexterity at opening a jar, something far more fundamental appears to connect us. We each, it seems, dream.
Scientists have discovered that both cuttlefish and octopus show signs of displaying rapid eye movement (REM) while they sleep – a characteristic that indicates heightened brain activity and vivid dreams.
The whole business of how – and for how long – animals sleep is explored in a new documentary presented by zoologist Liz Bonnin, who admits to needing nine hours a night. "Categorically. I get very grumpy without it."
She had to cope with much less shuteye when making this film, spending an entire night inside Bristol Zoo observing the nocturnal habits of a range of different animals. Fifteen enclosures were rigged with night-vision cameras to see who got up to what. Sleepiest proved to be the gorillas and lions, each averaging about eight hours. Much more active were the penguins, who slept for just over three. Nobody, though, beats the giraffe for insomnia. It appears to get by on just two hours’ sleep in every 24.
“When you compare animals to humans it’s easy to think that we’re the most highly evolved and therefore we sleep the best. But if the giraffe gets the same quality of sleep as us in just two hours, does that mean that the giraffe’s brain is more effective than ours?” ponders Bonnin.
"Historically you think that the most highly evolved animals will need the most sleep, to recover and consolidate memory. But what's becoming clear is that it's got nothing to do with brain size or metabolic activity or where in the evolutionary tree the animal sits. It's really all about what it has to do in its environment to survive."
That means, in the case of dolphins, that they can sleep and swim at the same time, keeping one half of their brain awake (the eye that remains open is on the opposite side to the half-brain that’s sleeping). In the case of animals that are vulnerable to attack, they snatch their sleep in short bursts rather than in one long snoozing session. And when it comes to family groups and colonies, such as meerkats and ants, there are those who sleep deeply and those who only slumber lightly.
“When the meerkats are asleep, the matriarch will be in the middle and she will have the deepest sleep,” says Bonnin. “The sentries are on the outside of the huddle and, while they do go to sleep, they are the first to be roused by any noise. And the interesting thing we found out is that they do have the neurological ability to discern between benign sounds and alarm calls. We played recordings of the wind and that didn’t disturb them, but when we played the alarm call of another meerkat, they woke up immediately and went out to investigate.”
So why does it all matter? It helps us, says Bonnin, to better understand our own need for sleep. “The scientist who gets to the bottom of the function of sleep will win the Nobel Prize. It is still the holy grail.”
And if cuttlefish can dream, what, then, goes through Bonnin’s mind when she’s fast asleep?
“When I was stressed doing exams, I did dream about a person running after me, and me getting to a door but not being able to close it because the door was too small for the frame. Happily I haven’t had that dream for ages!"
Animals through the Night: Sleepover at the Zoo is on tonight at 9:00pm on BBC4.