Why did the human body evolve to crave nicotine?
June 17, 2012 11:38 AM   Subscribe

Why did the human body evolve to crave nicotine?

People addicted to nicotine have my sympathy. Using an emulsified
stick of chemicals just to get their fix from their last use of the product.

I can understand why the body becomes addicted to high-fat and sugary foods, because in the past, calories meant survival for our species. I can understand peoples addiction to sex. Again, an evolutionary reason.

But, I cannot understand the evolutionary reason why or how people become physiologically addicted to nicotine. How did the physiology of the human body ever evolve to crave this wretched substance?
posted by jacobean to Health & Fitness (16 answers total) 10 users marked this as a favorite
Humans didn't evolve to crave nicotine specifically. Nicotine coincidentally causes a reaction among the pleasure receptors in our brains (I think) that we grow to crave. If tobasco sauce caused the same physiologic reaction, then we would find ourselves easily addicted to tobasco sauce.
posted by Think_Long at 11:45 AM on June 17, 2012 [12 favorites]

It's not exactly that we evolved to crave nicotine -- (Really simplified neurochemistry story time!): We have receptors in our brains for our neurotransmitters, where they each fit into their own receptor (imagine a game of perfection in the brain), and one is called Acetylcholine. Nicotine happens to fit really nicely into one type of the receptors for Acetylcholine (so much so that they're named nicotinic acetylcholine receptor -- so well that the nicotine attaches to all these receptors, and then gets stuck and keeps Acetylcholine out for a while. And then people get used to having their Acetylcholine receptors ON all the time because of the nicotine, so going back to "normal" -- without the nicotine acting on these acetylcholine receptors, is really uncomfortable.
posted by brainmouse at 11:45 AM on June 17, 2012 [21 favorites]

Was coming in to say something similar to Think_Long. From wikipedia: "By binding to nicotinic acetylcholine receptors, nicotine increases the levels of several neurotransmitters – acting as a sort of 'volume control'. It is thought that increased levels of dopamine in the reward circuits of the brain are responsible for the apparent euphoria and relaxation, and addiction caused by nicotine consumption."

If, instead of phrasing the question "how did humans evolve to crave nicotine," you asked, "how is it that humans have not yet evolved to distinguish this foreign chemical from actual neurotransmitters," the answer is much more intuitive. Obviously the human body cannot prevent other plans, animals, etc., from producing chemicals similar to its own neuro-regulators. And it should also not be surprising, if such a chemical were to interfere with human functioning in a significant way, that evolution to alleviate the problem would not be immediate.

In the long run, if nicotine addiction is bad enough for the human species, we will evolve to get over it. (Or it will kill us all, take your pick.)
posted by Joey Buttafoucault at 11:49 AM on June 17, 2012 [1 favorite]

I can understand why the body becomes addicted to high-fat and sugary foods, because in the past, calories meant survival for our species. I can understand peoples addiction to sex.

What all of these things have in common, including nicotine, is that it makes us feel good. What we get addicted to is feeling good. That's because we have to be evolutionarily bribed into doing what's good for us. Then it becomes too much of a good thing and we can't stop.
posted by bleep at 11:52 AM on June 17, 2012 [3 favorites]

I expect you have it backwards: plants evolved nicotine because it fucks up the nervous systems of animals that eat them, or just kills them.

The flipside is that animals frequently like having their nervous systems messed with a little bit, even if more thorough messing would be fatal.
posted by ROU_Xenophobe at 11:59 AM on June 17, 2012 [11 favorites]

Tobacco has done very well for itself by evolving the capacity to provide a chemical that mimics a pleasurable brain chemical found in the brains of Creation's dominant species.
posted by notyou at 12:22 PM on June 17, 2012 [1 favorite]

It's a mistake to expect every trait that survives to have some identifiable positive reason for it to exist... mutations start out as accidents, and they can persist just fine if there isn't enough selective pressure against them, i.e., if the trait isn't actively preventing its bearer from surviving until reproductive age or reproducing.

So we inherit any number of iffy propensities just because they weren't lethal enough to our ancestors.
posted by Zed at 12:22 PM on June 17, 2012 [7 favorites]

"Addictions" generally short-circuit the brain's reward mechanisms. Cigarettes affect significantly neurotransmitters, including (as mentioned) acetylcholine, insulin, and dopamine.

The first increases attention and focus. Often writers and musicians are able to better sustain creative thought processes with amplified amounts of acetylcholine present. That ability to focus can be 'addictive', for one may well be more creatively-productive on nicotine than off it.

This has been posited although not proven to be associated with the comorbidity between nicotine and depression, although the link is not very well understood. If depression is often marked by overly generalised attention and an inability to accurately discriminate between thoughts and reality, increased acetylcholine may well help the user focus their attention on stimuli rather than mental chatter.

The second – insulin – changes blood sugar levels, thus tricking the body into thinking it's not hungry. That basically boosts metabolism in a way, for the body changes it set-point for where 'hungry' kicks in. Individuals can become 'addicted' to enacting conscious control over their diet. More than one smoker has gone back to smoking due to weight gain.

The third – dopamine – is the brain's reward system. Dopamine is a 'rewarding' chemical, inducing euphoria after completing an activity beneficial to one's organism. It's responsible for the post-coital bliss, the feeling of satiety after a big meal, the high after running. The dopamine kick is designed to encourage whatever behaviour led to the dopamine kick. And the brain learns complex patterns of being rewarded.

The greater one's income, the greater volume of high-quality food one can afford. When someone goes to work all day, and then eats a great meal, they are essentially pairing the work (input) with the food (reward) for the dopamine kick. The same with sex. The more physically fit a person is, the more sexual attention they receive from other people. Thus, exercise and fitness (input) leads to greater opportunity for sex. After the moment of orgasm, when the sperm has been deposited, the male receives a tremendous dopamine kick, for he has done that for which he was inherently designed, propagating his genes.

And it is possible to short-circuit the dopamine system with substances including but not limited to nicotine. I have often noticed that smokers are 'less clean' than non-smokers. They are more disheveled and inhabit less pristine abodes. Part of the reason may well be that the rewards for being clean are complicated reward chains. Dressing up may well one get ahead in life, however it's not immediate. It's only through sustained and continual effort. When a person has a cigarette, they get a small dopamine bump from it.

What this essentially does is puts the person in control of how they feel (also implicated in the comorbidity between smoking and depression). If a person is a smoker, they don't need to go to work, eat, have sex, exercise of receive external validation to receive a dopamine kick, they can have one whenever you like – simply light up a cigarette.

That's part of the reason nicotine use is so present in stressed populations – developing nations, soldiers, lower economic classes. In those situations, the external environment is stressful. Dopamine kicks may be hard to come by as the individual has little control over the external environment. Yet light a cigarette, and relax. The person are no longer at the control of the external environment, you are now in control of yourself. It's also a big reason for teen smoking, as teenagers often have little control over their environment (their parents do).

And it's one reason why smoking is so hard to quit. If one has control over their dopamine releases, they can build a life around them that is more stressful than is healthy for them. They don't notice the stress because the feedback loop has been broken. Depression can well mean that whatever a person is doing is not healthy for them; a job, a relationship, friends, etc. For whatever reason, the body is actively attempting to inhibit them from doing things. With a cigarette, that chain is broken. The message of the body lost in the cigarette's dopamine release. For a while. Until the dopamine shot fades... and then they need another cigarette. It's very easy to tell how stressed a smoker is by how much they smoke. They are a monkey pushing the button for relief from their stress – bite-sized pieces of control.

A simple way to think about it is that nicotine changes the stress point at which stress goes from "routine" to "a problem". It raises that level way up. Thus people can put themselves into situations that normally would set off warnings. When one quits nicotine, that level comes back down... but they well may have built a life that requires that much stress to generate all the other dopamine kicks – income, social standing, reputation, etc. Thus, removing nicotine essentially exposes an individual to the true stress of the world they have created for themselves. They cannot handle that level of stress without nicotine, thus something has to change. Change is difficult, and it's easier to keep the stress set-point high. That is why it's addictive; because it allows one to build a life around themselves that normally would be quite difficult.
posted by nickrussell at 12:34 PM on June 17, 2012 [32 favorites]

I don't have any data to back this up, but isn't nicotine consumption a relatively recent phenomenon? A few thousand years is not much on an evolutionary timescale - give it a few hundred thousand more and we might very well evolve to be resistant to nicotine, though I understand modern medicine and travel has seriously messed up the normal processes of evolution for humans.
posted by Dr Dracator at 1:02 PM on June 17, 2012

"...give it a few hundred thousand more and we might very well evolve to be resistant to nicotine"

I certainly won't say that smoking generates good health, but the health problems it can cause generally won't kill you until you are past breeding age. In the meantime, for reasons stated above, it's in heavy use all over the world. Despite our current culture's turn against tobacco, I don't think we're ever going to evolve a resistance to nicotine.
posted by The Light Fantastic at 1:12 PM on June 17, 2012 [2 favorites]

a relatively recent phenomenon? A few thousand years

I recall there were nicotine residues found in Egyptian mummies and Maya wares. Wikipedia put it at 5000 BC which gives us approximately 7000 years of tobacco, before the bronze age.

What's probably changed tobacco is industrialisation. Previously, it was quite an honoured gift. One can imagine that ancient peoples would have used it more symbolically and in much lower quantities. Now that we can produce billions of cigarettes on assembly lines, the price of tobacco production has probably never been lower.

In terms of evolution, it's so highly available now that it's turned into a significant toxin. It's actually a poison in high quantities and has been used in agriculture as a natural pest control substance. What was a relatively exclusive commodity for the last 6950 years has in the last 50 become too available.

I doubt we'll 'adapt' out of it, any more than we would adapt out of a craving for sugars or fats. What seems to be going on is that we're pricing it to the health effects now, which is a sort of artificial evolution I suppose.
posted by nickrussell at 1:13 PM on June 17, 2012

There's millions of plants that do nothing to people when smoked, ingested or rubbed on our skin. We've gone out of our way to find ones that do, and we grow them to sell to each other. We improve on the wild stocks we find by breeding and genetic engineering to provide competition and diversification in what is basically a commodity market.

Most of the plants that society thinks (or thought) could be put to bad use (Nightshade, poppies, cannabis, belladonna, etc... )have been made illegal to cultivate or harvest in various ways - mainly as an attempt to promote the general welfare of the public.

Evolutionary pressures work on a much longer timescale than human activity - AFAICT, Tobacco was a sacrament among most of the cultures that partook (Assumedly in non-damaging quantities) up until the last six hundred years or so.

(Side note - the framing of your question implies a thought process that kind of pulled out 'creator' and stuck 'evolution' in it's place. - Creators have a vision and a purpose, evolution is a process like going through a sieve: Everything bigger than X gets stuck - Evolution's rule is, anything that stops you from breeding gets left out of the next generation. Smoking tobacco, in 99% of the use cases, won't stop you from breeding.

You might be better off asking why tobacco cultivation is still allowed, when so many other human-affecting plants are prohibited from being harvested.
posted by Orb2069 at 1:13 PM on June 17, 2012 [1 favorite]

This is a rough interpretation...but I seem to remember a talk by Nora Volkow from the National Institute on Drug Abuse say that nicotine is the only drug of abuse that causes a sort of up regulation in the brain instead of down regulation.

Down regulation is when receptors prune themselves or shut down to accommodate for the huge surges in dopamine and other neurotransmitters. Down regulation is one aspect of why cocaine, amphetamine and heroin addicts usually experience depressive phases once they stop using. How hard, how much, how long they used coupled with their overall mental/emotional health before they started influence the severity and length of post-acute depression - among other things.

Nicotinic Acetylcholine Receptors apparently grow themselves with more exposure to nicotine - they up regulate. This is one theory why the relapse rate for smokers is so high and why there is such a high ratio of folks who try nicotine to folks who become dependent on it. It's as if nicotine acts like kudzu vine in the brain...the more nicotine it has, the more it vines it grows to suck up the nicotine.

When folks talk about how addicting a drug is they are usually talking about the percentage of people who go from trying a drug to becoming dependent on it along with drugs that have high recidivism rates. Heroin and nicotine are usually lumped in this "very addictive" category whereas alcohol and marijuana are not.
posted by space_cookie at 1:38 PM on June 17, 2012

I had coffee when I got up this morning. Now I'm having a cigarette; I might have just smoked some weed; in a little while, I will make myself a rye lime rickey.

As others have pointed out, nothing in me evolved to enjoy/get addicted specifically to any of the above substances. I did evolve to repeat actions that make me feel good. (Yes yes long-term vs short-term etc. Still, lots of people who really get pleasure from, say, running, will continue to run even when injured, even if nothing is chasing them.)
posted by rtha at 1:49 PM on June 17, 2012 [1 favorite]

I recall there were nicotine residues found in Egyptian mummies and Maya wares. Wikipedia put it at 5000 BC which gives us approximately 7000 years of tobacco, before the bronze age.

Nicotine was found only in the Americas until the time of Columbus. Prior to that, smoking in the Old World generally means cannabis.
posted by goethean at 4:01 PM on June 17, 2012

@Goethean: I may well agree with you. The rest of the read is fascinating as well, in terms of how tobacco moved from ritualistic use, to a darling of European society, to the mixed blessing it's become today.
The Long Tobacco Road: A History of Smoking from Ritual to Cigarette [from RandomHistory.com]

Humans first came into contact with tobacco plants about 18,000 years ago when migrant Asiatic people first crossed the Bering Strait and spread across the continents known today as the Americas, where tobacco is native....
posted by nickrussell at 4:40 PM on June 17, 2012

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