Evolutionary background (Nesse & Berridge)

• drugs play upon chemical reactions in the brain that stimulate positive emotions and reduce negative ones

• characteristic of mammalian brain systems, evolved 500 million+ years ago

• drugs in pure form and direct routes of administration too recent for human adaptations to have evolved in response

• e.g., alcohol manufacture only in last 10,000 years

• positive emotions due to chemical reactions in brain serve adaptive function (e.g., pleasure during behaviors or experiences that increase inclusive fitness birth of child, sex, rise in status)

• drugs hijack these chemical reactions in brain

• drug use can initiate chemical cycle that impels the person to seek & use more drugs, even if no pleasure - addiction/dependence

Proximate risk factors

• people with these characteristics are more likely to use drugs

• research w/ longitudinal designs

• biochemical and genetic predispositions

• lower socioeconomic status
• child abuse and neglect, poor family management, permissive parenting
• family violence
• family history of substance abuse
• single parent family

• unhealthy communities (high levels of crime/violence/drug use, physical deterioration, low attachment to neighborhood)

• permissive laws and easy availability (low taxes, few restrictions in outlets, few regulations of who can buy, no prohibition)

• most people w/ these characteristics don't turn to drugs, but many addicts do have several of these characteristics

• not set at birth:

• impulsiveness
• hyperactivity
• risk-taking and sensation/excitement seeking
• early and persistent antisocial behavior/substance use
• academic failure
• lack of commitment to school
• alienation and rebelliousness
• association with drug-using others

Experiment with monkeys demonstrates importance of parenting (Higley et al.)

• rhesus monkeys randomly assigned to:

• live w/ similar age peers (w/o mothers) or

• be raised by mothers in the first 6 months of life

• all other conditions the same for both groups

• after 6 months of age, all monkeys put together

• peer-reared monkeys more anxious and stress-prone than mother-reared monkeys

• at age 4, monkeys given free access to alcoholic and nonalcoholic sweet drink

• results: mother-raised monkeys drank about 40% of the amount of alcohol as the peer-raised monkeys did

• drug use too recent for adaptations to have evolved

• drug use may be maladaptive - drug users have worse health, shorter lives, & fewer resources than nonusers

• failure in social competition -----> fewer positive emotions, more negative emotions ----> increased chance for drug use

• gazelles' stotting - risky & costly, but indicates mate value

• signals to predators and other gazelles

• males' substance use as signalling toughness/daring

• relapse rates high after treatment

• few factors predict treatment success

• drug abuse here to stay: universal vulnerability, widespread knowledge re drug manufacture, profits from drug selling