Monday, February 27, 2012

You (and your children) are what you do:

The Soft Influence of Lamarck
Increasing evidence suggests that your environment and behavior in life may affect the lives of your children and even your grandchildren.  The meme that suggests that all genetic information is passed through genes may be wrong, or at least incomplete.  But even when heredity was first being described there were at least two schools of thought on the issue.  The first school is the one in which we all know and love; Darwinian evolution, in which information is passed from one generation to the next via some genetic material, which it turns out was DNA.  The other less well examined idea of heritable evolution was proposed by Jean-Baptiste Lamarck, a French biologist, who suggested that traits were passed from one generation to the next, not by packets at the genetic level, but through use or disuse; a term often called soft inheritance.  I.e. giraffes have long necks because their predecessors stretched their necks more to reach leaves on tall branches.
 It also describes the passage of information from individual to individual to some degree.  Many scientists have heard of this theory, but it is less well discussed, except as an anecdote in high school biology, for everyone else.  Lamarckian evolution, was a major alternative to Darwinian evolution that had its day in the sun before the theory was discarded with yesterday’s paper.  However, the ghost of Lamarck is returning.  Not to say that Darwin was wrong; indeed Darwin never fully discounted Lamarck’s claims, he called it Pangenesis, and even suggested it might augment his natural selection theory.  One concept in biology, epigenetics, suggests that Lamarckian evolution may have a place in your life as well.  I will discuss some pieces of evidence that suggest that environmental impact and personal behavior may have an influence on not just you but your offspring. 
The examples have begun to mount in the literature.  Diseases such as autism and schizophrenia have been linked to prenatal stress for instance.  One example, published by Oberlander et. al. in 2008, suggests that prenatal exposure to depression or anxiety in the mother leads to increased methylation of glucocorticoids, which in turn leads to increased cortisol in response to stress in humans; i.e. anxious youths. They looked at depressed and non-depressed women and compared methylation patterns in their infants for a gene  involved in the stress response.  At three months the infants were examined for increased salivary cortisol, a steroid hormone; glucocorticoid, increased in response to stress, and found it to be higher in the infants of depressed mothers.  This correlated with the increased methylation patterns of the glucocorticoid receptor gene; NR3C1.
Father’s may be able to pass traits as well, see the 2011 report in the Journal of Neuroscience by Morgan and Bale, which discusses programs of dysmasculinization of second generation offspring via the paternal lineage of rats. 
The evidence above may seem dire.  In that it suggests that negative environmental or behavior impacts can push our offspring down the same path.  But is it possible for positive effects to be passed on as well?  One example of this was published this year by Nabeel Affara at the University of Cambridge suggests that micronutrients given before pregnancy can lead to gene modifications in offspring that may have such as positive effect.  While the details of these finding are still to be worked out Affara suggests that the resultant changes may influence how the immune system fights off disease.  Her population of Gambian women, while relatively small, suggested methylation changes in genes associated with immune defense.
As eluded to in the previous discussion, methylation of genes seems to be the key concept in the passage of information from the environment to the offspring in these examples.  This concept of gene regulation is known as epigenetics.  Epigenetics is most precisely defined as changes to the DNA or chromatin; the compacted form of DNA found in the nucleus, that leads to genomic alterations, which in turn control protein levels in the cells.  An interesting analogy to the soft inheritance described in Lamarckian evolution can be seen at any time when following a linage of cells.  All cells within the body of an organism are imbued with the same genetic code, yet the phenotype of these cells is diverse.  Human stem cells give rise to liver, heart, bone and brain, all from the same genetic stock.  This is accomplished via alterations in the pattern of ornamentation on the DNA and chromatin; a prime example of which is methylation, which in turn leads to selective changes in protein translation and therefore function and morphology of the cell (these linage specifications may be to topic of a future post).  So in this way, epigenetic changes from the cells local environment lead to functional alteration at the cellular level all of the time.  The evidence discussed here and elsewhere ( see review by Handel and article by Singer) now suggests that such changes can influence not only the cells in one organism but can be inherited from one organism to another as well.  Ere go, what you do; not just your genes, have an influence on what your offspring become. 
Many of these studies however, only assess epigenetic changes in children or infants and long term changes are not often reported, perhaps due to feasibility issues (human lifespans are hard to study in a human lifespan).  So, the human experiment that I propose to test this hypothesis is to take women who have never had any extensive athletic training but have had one child and rigorously train them in rock climbing, and then suggest they get pregnant again (selection based on this desire might work out better).  We choose a sport such as rock climbing because it is not easily accessible to most people and therefore unlikely that subjects would have extensive training in it prior to the study.  Then within 10 to 15 years we can test athletic ability in their offspring to see if differences can be noted in the first and second child.  For statistical purposes we would probably need between 200 to 300 women.  You can see the difficulty already (not to mention the irritated graduate student waiting for those kids to grow up so she can graduate).  Furthermore, no evidence thus far suggests athletic ability is affected by these methylation events, to my knowledge, and if it were, then the interesting question would be which genes would we be looking for in regards to methylation, or other ornamentation of the genes (several targets can be found from a cursory search of the scientific literature, I suspect).  For now, however, such a study is unlikely to occur.  
That being said; the data suggesting that epigenetics may play a decided Lamarckian role in your evolution is mounting and perhaps one day the evidence will be sound enough that we can make executive decisions that can prevent bad methylations from occuring, or reverse them once they do, but until then, just be warned.   

1 comment:

  1. Wonderful! I'd never heard of Lamarckian evolution, but I think it makes some sense--it sounds like a way of describing how our environments can shape how our children develop. Fascinating...looking forward to reading more!


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