Are Addictions a Byproduct of Evolution?

iStock/Charles Wollertz
iStock/Charles Wollertz

Franklin Veaux:

Addictions are a byproduct of chemical warfare.

Plants evolved chemicals like caffeine, opioids, nicotine, cocaine, and theobromine because they are chemical poisons that protect the plant from being eaten by pests. They work by disrupting signaling in the brain, usually by binding to receptors for neurotransmitters in the brain.

They’re extremely potent neurotoxins that kill insects. A plant can’t run away from predators, so it uses chemical warfare instead: It secretes these chemicals that disrupt brain signaling, insects try to eat the plant, insects die.

Animals like humans are much bigger than insects. Doses of these chemicals that
disrupt an insect’s brain signaling to the point where insects die disrupt our brain signaling in ways that feel pleasant to us.

Many of these chemical poisons are effective at killing insects because they mimic natural neurotransmitters, but they are more effective than normal neurotransmitters. They grab hold of receptors and don't let go, or they persist longer than natural neurotransmitters—or both.

Your brain tries to maintain a normal baseline. If you take a chemical that disrupts brain signaling, it tries to work around the disruption to get things back to normal.

Let’s say you take a chemical that activates opioid receptors, like morphine. Your opioid signaling system starts sending out a flood of signals. You perceive this as pleasure.

Your brain says “hang on, the opioid signaling system is going crazy. I’m going to turn it down to get back to normal.” So it changes the number of opioid receptors.

You take the morphine again, and you don’t feel that incredible pleasure, because you have more opioid receptors in your brain for the morphine to activate. This is how tolerance works.

So you take more. Now you feel that rush of pleasure again.

But your brain says “Hang on, something still isn’t right. The opioid signaling system is still going bonkers. I better dial it down some more.” So it changes the number of receptors even further.

Now you stop taking the drug. Your brain has turned the opioid signaling system way way down, since you were blasting it with a chemical that sends it into hyperspace. Now you’ve stopped taking that chemical that was sending it into orbit, which means now it’s underactivated. You perceive that under-activation as intense pain. This is what withdrawal is.

This post originally appeared on Quora. Click here to view.

Why Are Sloths So Slow?

Sloths have little problem holding still for nature photographers.
Sloths have little problem holding still for nature photographers.
Geoview/iStock via Getty Images

When it comes to physical activity, few animals have as maligned a reputation as the sloth. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so sedate? And what horrible, poop-related price must they pay in order to maintain life in the slow lane?

According to HowStuffWorks, the sloth’s limited movements are primarily the result of their diet. Residing mainly in the canopy vines of Central and South American forests, sloths dine out on leaves, fruits, and buds. With virtually no fat or protein, sloths conserve energy by taking a leisurely approach to life. On average, a sloth will climb or travel roughly 125 feet per day. On land, it takes them roughly one minute to move just one foot.

A sloth’s digestive system matches their locomotion. After munching leaves using their lips—they have no incisors—it can take up to a month for their meals to be fully digested. And a sloth's metabolic rate is 40 to 45 percent slower than most mammals' to help compensate for their low caloric intake. With so little fuel to burn, a sloth makes the most of it.

Deliberate movement shouldn’t be confused for weakness, however. Sloths can hang from branches for hours, showing off some impressive stamina. And because they spend most of their time high up in trees, they have no need for rapid movement to evade predators.

There is, however, one major downside to the sloth's leisurely lifestyle. Owing to their meager diet, they typically only have to poop once per week. Like going in a public bathroom, this can be a stressful event, as it means going to the ground and risking detection by predators—which puts their lives on the line. Worse, that slow bowel motility means they’re trying to push out nearly one-third of their body weight in feces at a time. It's something to consider the next time you feel envious of their chill lifestyle.

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Are Any of the Scientific Instruments Left on the Moon By the Apollo Astronauts Still Functional?

Apollo 11 astronaut Neil Armstrong left the first footprint on the Moon on July 20, 1969.
Apollo 11 astronaut Neil Armstrong left the first footprint on the Moon on July 20, 1969.
Heritage Space/Heritage Images/Getty Images

C Stuart Hardwick:

The retroreflectors left as part of the Apollo Lunar Ranging Experiment are still fully functional, though their reflective efficiency has diminished over the years.

This deterioration is actually now delivering valuable data. The deterioration has multiple causes including micrometeorite impacts and dust deposition on the reflector surface, and chemical degradation of the mirror surface on the underside—among other things.

As technology has advanced, ground station sensitivity has been repeatedly upgraded faster than the reflectors have deteriorated. As a result, measurements have gotten better, not worse, and measurements of the degradation itself have, among other things, lent support to the idea that static electric charge gives the moon an ephemeral periodic near-surface pseudo-atmosphere of electrically levitating dust.

No other Apollo experiments on the moon remain functional. All the missions except the first included experiment packages powered by radiothermoelectric generators (RTGs), which operated until they were ordered to shut down on September 30, 1977. This was done to save money, but also because by then the RTGs could no longer power the transmitters or any instruments, and the control room used to maintain contact was needed for other purposes.

Because of fears that some problem might force Apollo 11 to abort back to orbit soon after landing, Apollo 11 deployed a simplified experiment package including a solar-powered seismometer which failed after 21 days.

This post originally appeared on Quora. Click here to view.

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