Why nature vs. nurture is ‘zombie idea’ we need to kill

Why do some people still believe that behavior is caused solely by genes or environment? A new paper offers some answers.

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  • Despite the fact that scientists have long known that behavior is caused by complex interactions between genes and environment, the debate still persists in the culture today.
  • A new paper outlines three reasons why this debate persists, and why behavior isn't special — it abides by the same evolutionary processes as other traits.
  • The authors say rejecting the false nature-nurture dichotomy can help kill this "zombie idea."

Which determines traits like sexual orientation, intelligence and behavior: genes or environment?

Many modern debates center on this question, from the #MeToo movement to transgender rights, to academic performance, to crime. But is the nature-nurture conversation even worth having? After all, it was more than three decades ago that the American biochemist Daniel Koshland wrote in an editorial published in Science, "The debate on nature and nurture in regard to behavior is basically over. Both are involved."

Now, a paper recently published in BioScience argues it's finally time to kill the "zombie" that is the nature-nurture debate. The authors—Marlene Zuk and Hamish G. Spencer of the University of Otago's Department of Zoology—note that behaviors aren't determined solely by genes or environment.

Zuk and Spencer divide their argument into three parts.

​Behavior is not special in its evolution

Behavior, the authors write, evolves in the same manner as other traits. People often mistakenly think that behavior — particularly human behavior — exists apart from the principles of evolution, in a separate realm from other characteristics, such as height.

The authors note the Venus flytrap as an example.

"The motor cells that close the trap need exactly two signals within 20 seconds to activate. Then, at least three—not one, not four—flicks of a trigger hair are needed to signal the production of digestive enzymes. Only then can successful consumption of the prey commence."

Does this precise predatory process count as behavior? It's a tricky question, sure. But the authors raise it because:

"If we can't draw a hard and fast line separating behavior from other traits, then the same rules apply to both, and behavior evolves the same way that leg length or other physical characteristics do. That is an important conclusion, because it means that we can't invoke culture as a get-out-of-evolution-free card."

Behavior is not explained solely by genes or environment

That might be obvious enough. But the authors also argue that behaviors aren't even the result of an additive combination of the two. In other words, you can't look at a world-class sprinter and say that their skill comes from 68 percent genetics, 32 percent environment.

Rather, behaviors stem from the complex and fluid interaction between the two.

"The effect of an organism's genes depends on the organism's environment and does so just as much as the effect of an organism's environment depends on its genes," the authors write. "Genes and environment interact. The philosopher of science Evelyn Fox Keller calls this the entanglement of genotype and environment, which also conveys the inextricable nature of the relationship between the two."

Genes do not code for behavior

Zuk and Spencer suggest that the way people talk about genes tends to confuse the public about the role genetics play in influencing behavior. For example, you might read a study saying that scientists have "found the gene for" intelligence, criminality, or whatever trait.

"What scientists mean when they talk about a gene for a trait is that variation at that gene (e.g., differences in the DNA sequence of that gene) leads, in a certain range of environments, to variation in that trait, and the concept involved is one called heritability," the authors write.

But a gene for a trait does not act as an off-on switch that produces behavior.

"The crucial point is that, regardless of the heritability of a trait, a change in the range of environments (or, for that matter, the genetic variation affecting the trait) can change the heritability. Everything is context dependent."

Killing the zombie

So, why do we need to kill the nature-nurture zombie? Zuk and Spencer suggest that these misguided beliefs can cause us to think certain behaviors are inevitable. For example, if people with anorexia read articles saying the condition is caused solely by genetics, they might feel like there's nothing they can do to improve their health. In this way, people may feel like they have an "out" to continue these behaviors, when, in reality, environmental interventions could benefit them.

Similarly, the belief that genes determine traits like intelligence or social mobility may influence public officials not to spend as much money on certain public programs. In this way, the nature-nurture dichotomy causes people to do nothing at all.

The authors say it's time to break our conceptual link between genetics and fate.

"A rejection of that equivalence, along with a view of the nature of the entanglement of genes and the environment, would be real progress, and just might kill the zombie."


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The surprise reason sleep-deprivation kills lies in the gut

New research establishes an unexpected connection.

Reactive oxygen species (ROS) accumulate in the gut of sleep-deprived fruit flies, one (left), seven (center) and ten (right) days without sleep.

Image source: Vaccaro et al, 2020/Harvard Medical School
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  • Surprisingly, the direct cause seems to be a buildup of Reactive Oxygen Species in the gut produced by sleeplessness.
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We don't have to tell you what it feels like when you don't get enough sleep. A night or two of that can be miserable; long-term sleeplessness is out-and-out debilitating. Though we know from personal experience that we need sleep — our cognitive, metabolic, cardiovascular, and immune functioning depend on it — a lack of it does more than just make you feel like you want to die. It can actually kill you, according to study of rats published in 1989. But why?

A new study answers that question, and in an unexpected way. It appears that the sleeplessness/death connection has nothing to do with the brain or nervous system as many have assumed — it happens in your gut. Equally amazing, the study's authors were able to reverse the ill effects with antioxidants.

The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

An unexpected culprit

The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

fly with thought bubble that says "What? I'm awake!"

Image source: Tomasz Klejdysz/Shutterstock/Big Think

The experiments

The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

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