Psychology2016

Consciousness 143

Although people can do without sleep for a while, they cannot do without it alto-
gether. In one experiment, rats were placed on moving treadmills over water. They
couldn’t sleep normally because they would then fall into the water and be awakened,
but they did drift repeatedly into microsleeps, or brief sidesteps into sleep lasting only
seconds (Goleman, 1982; Konowal et al., 1999). People can have microsleeps, too, and if
this happens while they are driving a car or a truck, it’s obviously bad news (Åkerstedt et
al., 2013; Dinges, 1995; Lyznicki et al., 1998; Thomas et al., 1998). Microsleep periods are
no doubt responsible for a lot of car accidents that occur when drivers have had very little
sleep.

Okay, so we obviously need to sleep. But what does it do for us?

Why do we have to sleep at all?

THEORIES OF SLEEP While it’s clear that sleep is essential to life, theories about
why—the purpose of sleep—differ.

THE ADAPTIVE THEORY OF SLEEP Sleep is a product of evolution (Webb, 1992) accord-
ing to the adaptive theory of sleep. It proposes that animals and humans evolved differ-
ent sleep patterns to avoid being present during their predators’ normal hunting times,
which typically would be at night. For example, if a human or a prey animal (one a pred-
ator will eat) is out and about at night, they are more at risk of being eaten. However, if
during active hunting hours the prey is in a safe place sleeping and conserving energy, it
is more likely to remain unharmed. If this theory is true, then one would expect prey ani-
mals to sleep mostly at night and for shorter periods of time than predator animals; you
would also expect that predators could sleep in the daytime—virtually as much as they
want. This seems to be the case for predators like lions that have very few natural preda-
tors themselves. Lions will sleep nearly 15 hours a day, whereas animals such as gazelles
that are lions’ prey sleep a mere 4 hours a day, usually in short naps. Nocturnal animals

microsleeps

brief sidesteps into sleep lasting only a

few seconds.

adaptive theory

theory of sleep proposing that animals

and humans evolved sleep patterns

to avoid predators by sleeping when

predators are most active.

Figure 4.1 Sleep Patterns of Infants and Adults
Infants need far more sleep than older children and adults. Both REM sleep and NREM sleep decrease dra-
matically in the first 10 years of life, with the greatest decrease in REM sleep. Nearly 50 percent of an infant’s
sleep is REM, compared to only about 20 percent for a normal, healthy adult (Roffwarg, 1966).

REM Sleep

NREM Sleep

Waking

24

20

16

12

8

4

0

Hours

2461020

Age in years

30 40 50 60 70 80 90

Total

daily

sleep

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