Re: Sharon Begley's "Science Journal"
Posted: Tue Oct 29, 2019 2:23 am
Water-Flea Case Shows That Ability to Adapt Is What's Really Innate
by Sharon Begley
April 22, 2005
HELLS ANGELS have nothing on some water fleas. While these tiny crustaceans are best known for their uncanny ability to skim atop the water's surface, some also boast a "helmet" that makes them tough for a predator to swallow. But other fleas with the same DNA -- clones of the helmeted ones -- have no such armor. And the reason is shaking up the world of genetics.
The helmeted fleas live in a lab aquarium to which scientists added the chemical scent of fish, fleas' main predator. The fleas without helmets come from an aquarium with no fish in sight (or smell). The difference between genetic duplicates reflects the power of environment: It can elicit markedly different traits from the same DNA.
I have written in the past about how environment -- ranging from experiences to diet -- can alter DNA, putting the molecular version of a "not in service" sign on our genes so they remain silent and, as geneticists say, unexpressed. The water flea and other examples of "developmental plasticity" show that a given genotype can develop in any of several ways depending on what environment it's in. And that makes the notion of "innate" look more and more inane.
"If you have a gene with some purported effect, that effect depends on the environment in which it's expressed," says Eric Turkheimer of the University of Virginia. "Anything that looks genetic, because people with that gene always turn out a certain way, might not really be a genetic effect but an artifact of how few environments people with that gene have been exposed to. Once a new environment comes along it can change everything, so what you thought was a fixed effect of a gene isn't."
OAK-TREE caterpillars that hatch in the spring, for instance, eat oak blossoms and grow up to look a bit like flowers. Caterpillars with the same genome, but which hatch in the summer, eat leaves and grow up to look like twigs. The different composition of blossoms and leaves affects what traits the caterpillars' genes produce. If you had never seen spring caterpillars, you would think their genome produces only twiggy caterpillars. But the twiggy look is, as Prof. Turkheimer says, only an artifact of how few environments those caterpillars have been exposed to, not genetic determinism.
In the past few years, scientists have found the first examples of such an effect in people, discovering how life experiences can alter gene-based traits once thought to be innate.
A certain form of a gene called MAOA, for instance, was so closely linked to aggression and criminality that it became known as a "violence gene." In a 2002 study, however, an international team of researchers followed 442 male New Zealanders who carried either of two versions of the MAOA gene. One version produces small amounts of MAOA, an enzyme active in the brain; a dearth of MAOA had been linked to criminality. The other produces high amounts of MAOA, as in a normal brain.
But the study found that men with the low-activity ("violent") form of the gene were no more likely to grow up to be antisocial or violent -- unless they had also been neglected or abused as children. In that case, they were about twice as likely to engage in persistent fighting, bullying, theft and vandalism. If they had the "violence gene" but were raised in a loving and nonabusive family, they turned out fine. A 2004 study by different scientists confirmed this.
IN A 2003 study, geneticists examined claims that one form of a gene called 5-HTT is associated with depression and suicide. Instead, they found that people who carry this form are no more likely to suffer from depression than people with the "healthy" variant -- unless they also experience deeply stressful events. Two papers in 2004 confirmed this.
"These genes were not connected with aggression or depression, respectively, in the absence of exposure to environmental risk," says behavioral geneticist Terrie Moffitt of the University of Wisconsin, Madison, and King's College London. "That different environments can produce different [traits] from the same genotype is now emerging in many fields of health research."
For example, she says, studies show that "the effect of a gene on cholesterol levels depends on environmental risk -- high or low dietary fat. The effect of a gene on gum disease depends on whether you smoke or not."
Exactly how life experiences affect DNA has been most precisely worked out in lab animals. Last summer, Michael Meaney of McGill University, Montreal, and colleagues reported that a gene that shapes how fearful, jumpy and neurotic a rat is can be altered by how regularly its mother licks and grooms it. Maternal care changes the chemistry of a "neuroticism gene," and the rat grows up to be mellow and curious. The genetic trait of neuroticism -- deemed innate because scientists had found a gene "for" it -- is reversible by environment.
"The whole subject of what counts as innate has just exploded," says science historian and physicist Evelyn Fox Keller of the Massachusetts Institute of Technology. "Historically, nature/nurture divided what was fixed from what could be changed. But what our biology really gives us is our plasticity, our ability to respond to our experiences. That's what's innate."
by Sharon Begley
April 22, 2005
HELLS ANGELS have nothing on some water fleas. While these tiny crustaceans are best known for their uncanny ability to skim atop the water's surface, some also boast a "helmet" that makes them tough for a predator to swallow. But other fleas with the same DNA -- clones of the helmeted ones -- have no such armor. And the reason is shaking up the world of genetics.
The helmeted fleas live in a lab aquarium to which scientists added the chemical scent of fish, fleas' main predator. The fleas without helmets come from an aquarium with no fish in sight (or smell). The difference between genetic duplicates reflects the power of environment: It can elicit markedly different traits from the same DNA.
I have written in the past about how environment -- ranging from experiences to diet -- can alter DNA, putting the molecular version of a "not in service" sign on our genes so they remain silent and, as geneticists say, unexpressed. The water flea and other examples of "developmental plasticity" show that a given genotype can develop in any of several ways depending on what environment it's in. And that makes the notion of "innate" look more and more inane.
"If you have a gene with some purported effect, that effect depends on the environment in which it's expressed," says Eric Turkheimer of the University of Virginia. "Anything that looks genetic, because people with that gene always turn out a certain way, might not really be a genetic effect but an artifact of how few environments people with that gene have been exposed to. Once a new environment comes along it can change everything, so what you thought was a fixed effect of a gene isn't."
OAK-TREE caterpillars that hatch in the spring, for instance, eat oak blossoms and grow up to look a bit like flowers. Caterpillars with the same genome, but which hatch in the summer, eat leaves and grow up to look like twigs. The different composition of blossoms and leaves affects what traits the caterpillars' genes produce. If you had never seen spring caterpillars, you would think their genome produces only twiggy caterpillars. But the twiggy look is, as Prof. Turkheimer says, only an artifact of how few environments those caterpillars have been exposed to, not genetic determinism.
In the past few years, scientists have found the first examples of such an effect in people, discovering how life experiences can alter gene-based traits once thought to be innate.
A certain form of a gene called MAOA, for instance, was so closely linked to aggression and criminality that it became known as a "violence gene." In a 2002 study, however, an international team of researchers followed 442 male New Zealanders who carried either of two versions of the MAOA gene. One version produces small amounts of MAOA, an enzyme active in the brain; a dearth of MAOA had been linked to criminality. The other produces high amounts of MAOA, as in a normal brain.
But the study found that men with the low-activity ("violent") form of the gene were no more likely to grow up to be antisocial or violent -- unless they had also been neglected or abused as children. In that case, they were about twice as likely to engage in persistent fighting, bullying, theft and vandalism. If they had the "violence gene" but were raised in a loving and nonabusive family, they turned out fine. A 2004 study by different scientists confirmed this.
IN A 2003 study, geneticists examined claims that one form of a gene called 5-HTT is associated with depression and suicide. Instead, they found that people who carry this form are no more likely to suffer from depression than people with the "healthy" variant -- unless they also experience deeply stressful events. Two papers in 2004 confirmed this.
"These genes were not connected with aggression or depression, respectively, in the absence of exposure to environmental risk," says behavioral geneticist Terrie Moffitt of the University of Wisconsin, Madison, and King's College London. "That different environments can produce different [traits] from the same genotype is now emerging in many fields of health research."
For example, she says, studies show that "the effect of a gene on cholesterol levels depends on environmental risk -- high or low dietary fat. The effect of a gene on gum disease depends on whether you smoke or not."
Exactly how life experiences affect DNA has been most precisely worked out in lab animals. Last summer, Michael Meaney of McGill University, Montreal, and colleagues reported that a gene that shapes how fearful, jumpy and neurotic a rat is can be altered by how regularly its mother licks and grooms it. Maternal care changes the chemistry of a "neuroticism gene," and the rat grows up to be mellow and curious. The genetic trait of neuroticism -- deemed innate because scientists had found a gene "for" it -- is reversible by environment.
"The whole subject of what counts as innate has just exploded," says science historian and physicist Evelyn Fox Keller of the Massachusetts Institute of Technology. "Historically, nature/nurture divided what was fixed from what could be changed. But what our biology really gives us is our plasticity, our ability to respond to our experiences. That's what's innate."