07.+What+is+Intelligence+(February+2006) - Get a Free Blog

What is Intelligence? 129
unlike one another that they surely cannot have the same purpose.
But they are somehow intertwined. In natural sleep, non-REM is
always followed by a bout of REM, so their functions are probably
linked in some way.
Amid the confusion, one thing is clear - sleep is for the brain. One
reason we know this is that animals sleep but plants do not. And
other organs, such as muscles and liver, do not sleep. This might
seem trivially obvious, but it was only this year that a large region of
the brain called the cerebellum was shown to participate in sleep.
Armed with the knowledge that sleep is a whole-brain phenomenon,
researchers are starting to unite behind the idea that non-REM sleep,
at least, is when the brain makes good the damage done by free
radicals, the toxic chemical by-products of metabolism. Other organs
repair this damage by sacrificing and replacing injured cells, but this
is not an option for the brain. So it switches itself off and, like a
highway-repair team working at night, gets on with the job when
things are quiet.
Several pieces of evidence have emerged to back this up. One is that
animals with a high metabolic rate, and hence a faster rate of free
radical damage, sleep more than those with a slow metabolism.
Another is that the brains of sleep-deprived rats suffer unusually high
levels of oxidative damage. And earlier this year gene-expression
studies confirmed that the brain actively switches on genes involved
in protein synthesis and membrane repair during sleep.
But what of REM? Some researchers have proposed that this is the
brain booting up to test out the repairs it made during non-REM.
Others suggest it has something to do with early brain development.
But we don't really know. Looks like we'll have to sleep on it some
more.
Graham Lawton
5 Is intelligence inevitable?
IT IS comforting to think of human intelligence as the pinnacle of
evolution. But cast that anthropocentric snobbery to one side and
consider this: intelligence is just another adaptation. It evolved
because it is the best way to survive in a particular ecological niche.
Intelligence is evolution's answer to unpredictability. If an organism
lives in an environment that is predictable then it can get by on
instinct and hard-wired responses. But animals that live in shifting
environments need to be flexible, they need to be able to weigh up
new situations and act accordingly. That is where intelligence can
come in handy.
But hang on, does that mean that once life appears, the evolution of
intelligence is inevitable? It's not as simple as that. Natural selection
only favours a trait if the benefits outweigh the costs. And there are
some serious costs associated with intelligence. For a start, the brain
is a gas guzzler. In humans it accounts for 20 per cent of our energy
requirement, while making up just 2 per cent of our body mass. There
is also the cost of being naive. A newborn animal with hard-wired
survival responses will be at an advantage in some situations
compared with one that must work out the best way to react. And
intelligence seems to carry other as yet unidentified handicaps, as
suggested by a study published last year showing that fruit flies bred