To ensure that the enhanced LTP seen in the offspring was due to the mother’s exposure to EE as a juvenile, the authors carried out several clever controls. To eliminate the possibility that enhanced LTP may be paternally mediated, female wild-type and knock-out EE mice were mated with conventionally raised males. The researchers found that offspring of the wild-type mice had greater LTP capacity and that LTP was restored to baseline levels in the knock-outs’ offspring. To demonstrate that effects occur in utero, offspring of EE mice were raised in standard laboratory housing by conventionally raised mothers. As expected, LTP was enhanced in offspring of wild-type mice, and restored to baseline levels in knock-out mice.
Next, the authors compared the memory functioning of wild-type and LTP knock-out mice, to gauge how EE affects mice at the behavioral level. They assessed contextual memory using what is called the contextual fear-conditioning paradigm. Mice placed in a wire cage are given a mild shock; typically, mice respond to threats by freezing. To assess whether the mouse learns to associate the cage where shocks are administered with the shock, researchers measure the overall freezing time of the mouse during initial conditioning (training). Later, they test memory for this association by observing freezing upon re-exposure to the cage, either hours or days later, in the absence of shock. The researchers found that, while both wild-type and knock-out mice expressed similar levels of freezing during conditioning, memory for the context where the shock occurred was impaired in the knock-outs. Here’s where it gets interesting: offspring of knock-out mice exposed to EE as juveniles spent just as much time frozen as their normal counterparts. This finding provides a crucial link between EE exposure, LTP and the novel EE-induced molecular pathway supporting LTP and behavior.
The Importance of Context
Studies such as this one, investigating how the environment influences the epigenetic propagation of heritable traits, are a hot area of research. The topic’s appeal lies in the scientific credence it lends to the notion that we and our offspring are not simply at the mercy of a random evolutionary process and inherited genetic script but are, if not masters of our own fate, at least capable of influencing its course. On a practical level, such findings suggest that novel therapies based on simple interventions such as EE could mitigate the effects of genetically inherited diseases.
Although these implications are seductive, these specific results usually aren’t easily generalized, or broadly applied, to human populations, however. EE seemed to rescue the memory impaired phenotype of the non-enriched knock-outs, but it bears reiterating that under this manipulation, the wild-type mice that demonstrated improved contextual memory following fear-conditioning did not demonstrate enhanced LTP.
What is true for highly derived lines of conventionally housed (read: sensory deprived) laboratory mice may not generalize to non-deprived humans. We should not assume that children born to mothers who were chronically bored during their adolescence will have memory deficits. Second, in order to generate conclusions, scientists must control the number of variables in the experiment. In these experiments, scientists only analyzed one type of learning under a very specific set of parameters. It is entirely possible that these same knock-out mice raised in the enriched environment would be unable to learn if the stimulus—the context association tested—was for an emotionally positive, rather than a negative, event. On a related note, there are many ways to induce LTP. Thus, it’s at least possible that the molecular pathways explored by Arai, Li and colleagues might mediate LTP specific to contextual memory formation following fear conditioning.
Despite these caveats, this study provides some posthumous vindication of Lamarck’s theories of change and inheritance. Although Darwin’s theory of evolution and natural selection is still dogma, modern science is hinting that there is nevertheless a place for some of Lamarck’s intuitions in a complete account of the mechanisms of inheritance.
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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.
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