Toys and exercise helped memory.
Image: iStockphoto/Emilia Stasiak
-
The Wisdom of Psychopaths
In this engrossing journey into the lives of psychopaths and their infamously crafty behaviors, the renowned psychologist Kevin Dutton reveals that there is a...
Read More »
Giraffes’ long necks are perfectly suited to harvesting tender leaves beyond the reach of other herbivores. Pondering the genesis of this phenomenon, two giants of modern biology, Jean-Baptiste Lamarck and Charles Darwin, arrived at remarkably different hypotheses. Lamarck believed that constant stretching of the neck somehow stimulated its growth. The giraffe would then pass along this new trait to its offspring. In effect, this newer, longer neck was a direct result of a giraffe’s interaction with its environment. By contrast, Darwin’s theory posited that traits evolve as part of a random, gradual process. The giraffes that happened to have been born with longer necks thanks to a random genetic mutation were better fed and thus healthier than their shorter-necked counterparts, making them more likely to live long enough to breed and pass on this trait. Because this mutation conferred a specific advantage to long-necked giraffes that aided their survival, the trait was preserved in future generations.
Lamarckian theories about the influence of the environment were largely abandoned after scientists discovered that heritable traits are carried on the genes encoded by our DNA. A recent study, however, published by neuroscientists Junko A. Arai, Shaomin Li and colleagues at Tufts University, shows that not only does the environment an animal is reared in have marked effects on its ability to learn and remember, but also that these effects are inherited. The study suggests that we are not the mere sum of our genes: what we do can make a difference.
The neurobiological investigation of environmental effects on learning and memory began in the late Sixties and early Seventies, when Mark Rosenzweig and colleagues examined how manipulating levels of sensory stimulation, exercise and social interaction affected rats’ behavior. Laboratory rats typically live in a cage with bedding, food and water but little else. In the enriched environments (EE) that Rosenzweig’s group created, animals got access to a changing roster of toys, and increased opportunities for socialization and exercise. The brains of EE rats were larger and they outperformed controls (which were housed in typical cages) in learning and memory tasks. Subsequent work by researchers looking at the cellular level has shown that EE triggers changes in neural morphology (shape), resistance to neurodegenerative disease and learning-related neural activity.
Rescuing Memory
Recently, Arai, Li and colleagues extended this line of inquiry, examining the role that EE plays in long-term potentiation (LTP), a form of synaptic strengthening that supports learning and memory. The physiological signature of LTP is an increase in the baseline level of a neuron’s electrical activity. Arai and Li showed that LTP in the hippocampus, a key brain structure involved in learning and memory processes, is greater in mice reared in EE.
What’s more surprising, however, is that EE is also sufficient to “rescue” a memory defect present in genetically altered mice. Parent mice born with the defect that were then exposed to EE as juveniles did not pass the same memory defects to their offspring. Their enriched surroundings corrected their genetic deficit.
How does this correction occur? Specific molecular pathways are required to generate LTP. When scientists silence the parts of the DNA code involved in the function of one of these pathways using what geneticists call “knock out” technology, as was the case in the mutant mice with a memory defect, both LTP and memory functioning are impaired. Arai and Li showed that EE increased LTP volume in wild-type (non-mutant) mice. Interestingly, mice that have had a standard molecular pathway required to induce LTP knocked out can still induce LTP. The researchers found that this EE-related LTP is induced via a novel molecular pathway that arises as a direct result of EE exposure. Moreover, they found that the enhanced LTP capacity of wild-type mice, and the rescued capacity for LTP in knock-out mice, can be transmitted epigenetically (that is, without any changes in their genetic code) from mother to offspring. Surprisingly, this transmission was true even when their offspring were raised in a conventional environment.
Is It Really the Environment?
See what we're tweeting about
9 Comments
Add CommentWomen who were bored as teen agers may not give birth to challenged offspring, but it might be due as much to the timing of the pregnancy, if they were not bored in later life when they become pregnant. In the mouse model, the stimulation of the EE on knock-out mothers who were pregnant in an EE, may have had a big effect on the offspring in utero. It would be interesting to see what happens to the offspring if the knock-out mothers were raised in an EE, but transferred to a conventional environment upon becoming pregnant.
Reply | Report Abuse | Link to thisNatural selection alone is too slow. We are changing as we interact with our environment as new cells are formed and are influenced by external stimuli. Lamarckian theories are right...
Reply | Report Abuse | Link to thisI would be interested in seeing the results of an assay where fertilized eggs are transplanted between the groups. This would shed some light on the mechanism of transfer between generations...does the secret lie simply in the gonads, in the uteran environment or in a combination of the two?
Reply | Report Abuse | Link to thisI wouldn't say Lamarckian theories are right, per se...I don't think that this mechanism would work in too many instances. It seems to me that it's a matter of activating existing but dormant genes, which occurs constantly in nature. Passing the "activated" gene to a new generation could simply be a matter of the offspring being conceived and/or nurtured in an environment where the activating stimulus is present... A.K.A. the mothers womb. But, then again, I could be on the completely wrong track.
Reply | Report Abuse | Link to thisIf Einstein's genius was due to but one genetic cause, there is a 50-50 chance that during reproduction it be discarded to the dustbin of evolution. If his children were intelligent, it was probably due to that genetic trait being inherited from Einstein's forbears. So intelligence is not inherited from Einstein's lifetime of intelligence, but from his and his wife's forebears disposition to have clever brains, if in the right environmental conditions.
Reply | Report Abuse | Link to this*Striving* was a crucial component of Lamarckism. It wasn't just about environmental effects; more about organisms' responses to their environments. Were the rodents in these experiments tested for striving?
Reply | Report Abuse | Link to thisNo. Their mental capacities, and those of their offspring, may have increased, but the former at least were not tested to have done so in a Lamarckian fashion, and so the characterisation of the results is somewhat misleading historically. I'll admit Lamarck is a slippery character when it comes to pinning down his ideas with precision, but I do think this article might have done a better job with its historiography.
This research invites serious debate. I hope Scientific American will invite major figures in evolutionary biology to weigh in on this hypothesis.
Reply | Report Abuse | Link to thisGreat article (despite the sensationalist headline, unfortunately an increasing SA trend). Genes can do nothing without environmental help - they can't even replicate in utero without external proteins. It's exciting how our understanding of gene-environment interactions is changing.
Reply | Report Abuse | Link to thisYeah man, even though I'm genetically predisposed to lottery tickets and supermarket tabloids, I still try to go to the art museum and the the ensemble society.
Reply | Report Abuse | Link to this