SURVIVAL OF THE DRUGGIES

Taking Narcotics May Be Part Of Our Evolutionary Inheritance

IF DRUGS are so bad for us, why do so many people use them? Because they
helped our ancestors survive, argue two anthropologists.

Our predilection for psychotropic substances is usually seen as a
biological accident. The conventional view is that drugs fool the brain
into thinking it is getting a reward when in fact it isn't.

But anthropologists Roger Sullivan of the University of Auckland and Edward
Hagen of the University of California at Santa Barbara point out that our
ancestors were exposed to plants containing narcotic substances for
millions of years. In the April issue of Addiction, they argue that we are
predisposed to drug-taking because we evolved to seek out plants rich in
alkaloids.

Consuming such plants could have been a basic survival strategy. "Stimulant
alkaloids like nicotine and cocaine could have been exploited by our human
ancestors to help them endure harsh environmental conditions " Sullivan
says. For example, until recently Australian Aborigines used the
nicotine-rich plant pituri to help them endure desert travel without food.
And Andeans still chew coca leaves to help them work at high altitudes.

Archaeological evidence shows that drug use was widespread in ancient
cultures. Betel nut, for example, was chewed at least 13,000 years ago in
Timor, to the north of Australia. Artefacts date the use of coca in Ecuador
to at least 5000 years ago.

Many of these substances were potent: pituri contains up to 5 per cent
nicotine, whereas tobacco today contains about 1.5 per cent. What's more,
these drug pioneers sometimes "freebased" drugs by chewing them together
with an alkali such as lime or wood ash. This releases the free form of the
drug and allows it to be directly absorbed into the bloodstream.

But in Pacific cultures where chewing betel nut is still widespread, it is
seen more as a source of food and energy than as a drug, Sullivan says. And
some drugs do have real nutritional value. For example, 100 grams of coca
leaf contains more than the US recommended daily intake of calcium,
phosphorus, iron and vitamins A, B2 and E.

And in some marginal environments, people's diets may have been so poor
that they struggled to produce enough neurotransmitters of their own.
Consuming plants containing substances that mimic neurotransmitters could
have helped make up for the shortfall, Sullivan and Hagen speculate. They
say this part of their theory could be tested by depriving animals of
certain neurotransmitters and seeing if they then choose to eat food rich
in substitutes.

Sullivan's adaptive model of drug use is definitely plausible, says Wayne
Hall of the University of Queensland, who until recently was head of the
National Drug and Alcohol Research Centre in Sydney. "There is certainly
evidence that plants evolved to mimic the neurotransmitters of mammals," he
says. "But the problem today is that we have much larger doses of much more
purified drugs."