In modern times, most people survive and reproduce despite their addictive behaviors. Are these due to a basic flaw in how our motivational systems work?
Evolutionary psychologists often express doubts about how well we humans are suited to our current environment. Perhaps our bad habits do not have enough of an impact on survival and reproduction to be screened out by natural selection.
Despite doubts about human adaptation to the current environment evidence shows that biological evolution not only worked after the Agricultural Revolution but actually works quickly.
Examples include the emergence of adult lactose tolerance in societies that consume milk and the lightening of skin color among early European farmers in response to cereal farming that produced a vitamin D deficiency correctable by permitting more light to enter the skin (1).
Analogous changes among Asian rice farmers may have produced the alcohol intolerance that is common there.
Rice Wine and Alcohol Intolerance
Asian populations have a high frequency of alcohol intolerance and this is particularly true of regions where rice was grown as a staple food source (1). Those affected have a low tolerance for alcohol so that even small quantities produce a reaction that causes reddening of the skin and other signs of toxicity.
Surplus rice could be used to make rice wine and this was produced in large quantities. Abundant inexpensive alcohol proved a mixed blessing. Those who drank too much were vulnerable to alcoholism that leads to child neglect, and marital instability. They were evidently less reproductively successful (1).
Rice farmers who were made ill by alcohol consumption, and therefore drank less would have enjoyed a reproductive advantage so that alcohol intolerance was naturally selected. Over many generations, alcohol intolerance could have become both more common in the population and more intense.
If evolutionary mechanisms reduced excessive alcohol consumption for Asian rice farmers, we hear more about other drug addictions from which evolution seems to offer little protection. A commonly cited example of the vulnerability of modern populations to bad habits is provided by smoking and nicotine addiction.
Just as opiate drugs stimulate receptors in the brain, thereby generating feelings of intense pleasure, and resulting in strong addiction, nicotine also taps in to natural reward mechanisms in the brain. The pleasure may be much milder but people can become strongly addicted to tobacco after multiple exposures.
Pleasure mechanisms in the brain evolved to promote functional behaviors such as eating nutritious foods, being sexually attracted to fertile mates, and finding comfort in social bonding. Addictive drugs are therefore a biochemical trick through which our brains get pleasurable sensations in the absence of the activities that normally trigger them. Are we completely vulnerable to such chemical errors by the brain?
In practice, people continue to use drugs at the expense of survival, vigor, and reproductive success. Smokers develop health problems not because they choose to smoke but because they are nicotine addicts.
According to anthropologist Donald Symons (2) , the fact that people voluntarily engage in such damaging habits as smoking means that looking for adaptive explanations for human behavior in modern societies is a fool’s errand. Despite such views, we have colonized far reaches of the planet at a pace that is unprecedented for any mammal, much less a primate. We must be doing something right!
The smoking problem may not be so intractable to an adaptationist approach as Symons thinks. Instead of restricting the analysis to a single generation, one must consider a longer time frame.
People acquire contradictory information about smoking over time (3).
At first, tobacco is perceived as a pleasurable stimulant that is associated with relaxation, leisure, happiness, success, and the good life, as depicted in movies of the 1950’s featuring stars such as Humphrey Bogart and Marlon Brando.
During that period, tobacco companies conspired to bury scientific research establishing the strong link between smoking and lung cancer. Once the scientific evidence became widely known, there was a steep fall in smoking rates that continues to this day (4).
History may be repeating itself in the vaping controversy, however. This new method of administering nicotine is less harmful to pulmonary health but it is the same addiction in the end and could increase, rather than reduce, the use of tobacco if it induces a lifetime of nicotine addiction.
How Natural Selection Affects Addictions
While some drugs, such as modern opiates are extremely addictive and thus extremely dangerous, in reality most sensible people avoid them and do not become addicted unless exposed for medical reasons. It seems that we are not completely unprotected by evolution.
Contrary to Symon’s assertion that human behavior in modern societies is hopelessly maladaptive, a more nuanced conclusion is appropriate.
New users experience nicotine as a mildly pleasant stimulant that taps into the brain’s evolved neurochemistry. So the widespread adoption of tobacco by residents of under developed countries is understandable.
Residents of poor countries are not only less informed about the link between cigarette smoking and cancer. They also live their lives in the present and are less concerned about the distant future (5).
Once people become fully informed about the link between smoking and cancer, smoking rates do decline (3)
So the rapid adoption of smoking by Americans following widespread availability of cigarettes early in the 20th century encountered an abrupt reversal from the 1970’s on (4).
The decline occurred despite a distressing tendency for some young people to adopt smoking as a sign of adolescent rebellion..
Just as adoption of smoking was a multi-generational phenomenon, so too the the decline in tobacco use is a protracted process.
The decline in smoking helps people to lead longer, healthier, lives so that it is adaptive in Darwinian terms. The mere fact that it occurs by learning and experience rather than gene selection does not make it any the less adaptive.
1 Henrich, J. (2015). The secret of our success: How culture is driving human evolution domesticating our species and making us smarter. Princeton, NJ: Princeton university Press
4 Cummings, K. M., Brown, A., & O’Connor, R. (2007). The cigarette controversy. Cancer Epidemiology Biomarkers and Prevention, 16, 1070-1076.
5 Clark, G. (2007). A farewell to alms: A brief economic history of the world. Princeton, NJ: Princeton University Press.