100 reasons to change the way we think about genetics
May 18, 2009For years, genes have been considered the one and only way biological traits could be passed down through generations of organisms. Not anymore.
Increasingly, biologists are finding that non-genetic variation acquired during the life of an organism can sometimes be passed on to offspring -- a phenomenon known as epigenetic inheritance. An article forthcoming in the July issue of The Quarterly Review of Biology lists over 100 well-documented cases of epigenetic inheritance between generations of organisms, and suggests that non-DNA inheritance happens much more often than scientists previously thought.
Biologists have suspected for years that some kind of epigenetic inheritance occurs at the cellular level. The different kinds of cells in our bodies provide an example. Skin cells and brain cells have different forms and functions, despite having exactly the same DNA. There must be mechanisms—other than DNA—that make sure skin cells stay skin cells when they divide.
Only recently, however, have researchers begun to find molecular evidence of non-DNA inheritance between organisms as well as between cells. The main question now is: How often does it happen?
"The analysis of these data shows that epigenetic inheritance is ubiquitous …," write Eva Jablonka and Gal Raz, both of Tel-Aviv University in Israel. Their article outlines inherited epigenetic variation in bacteria, protists, fungi, plants, and animals.
These findings "represent the tip of a very large iceberg," the authors say.
For example, Jablonka and Raz cite a study finding that when fruit flies are exposed to certain chemicals, at least 13 generations of their descendants are born with bristly outgrowths on their eyes. Another study found that exposing a pregnant rat to a chemical that alters reproductive hormones leads to generations of sick offspring. Yet another study shows higher rates of heart disease and diabetes in the children and grandchildren of people who were malnourished in adolescence.
In these cases, as well as the rest of the cases Jablonka and Raz cite, the source of the variation in subsequent generations was not DNA. Rather, the new traits were carried on through epigenetic means.
There are four known mechanisms for epigenetic inheritance. According to Jablonka and Raz, the best understood of these is "DNA methylation." Methyls, small chemical groups within cells, latch on to certain areas along the DNA strand. The methyls serve as a kind of switch that renders genes active or inactive.
By turning genes on and off, methyls can have a profound impact on the form and function of cells and organisms, without changing the underlying DNA. If the normal pattern of methyls is altered—by a chemical agent, for example—that new pattern can be passed to future generations.
The result, as in the case of the pregnant rats, can be dramatic and stick around for generations, despite the fact that underlying DNA remains unchanged.
LAMARCK REVISITED
New evidence for epigenetic inheritance has profound implications for the study of evolution, Jablonka and Raz say.
"Incorporating epigenetic inheritance into evolutionary theory extends the scope of evolutionary thinking and leads to notions of heredity and evolution that incorporate development," they write.
This is a vindication of sorts for 18th century naturalist Jean Baptiste Lamarck. Lamarck, whose writings on evolution predated Charles Darwin's, believed that evolution was driven in part by the inheritance of acquired traits. His classic example was the giraffe. Giraffe ancestors, Lamarck surmised, reached with their necks to munch leaves high in trees. The reaching caused their necks to become slightly longer—a trait that was passed on to descendants. Generation after generation inherited slightly longer necks, and the result is what we see in giraffes today.
With the advent of Mendelian genetics and the later discovery of DNA, Lamarck's ideas fell out of favor entirely. Research on epigenetics, while yet to uncover anything as dramatic as Lamarck's giraffes, does suggest that acquired traits can be heritable, and that Lamarck was not so wrong after all.
More information: Eva Jablonka and Gal Raz, "Transgenerational Epigenetic Inheritance: Prevalence, Mechanisms, and Implications for the Study of Heredity and Evolution," The Quarterly Review of Biology, June 2009. http://www.journals.uchicago.edu/toc/qrb/current .
Source: University of Chicago (news : web)
Jan 18, 2009 |
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I wonder if this means that the generation just being born now will have lower than expected rates of diabetes and heart disease, due to better nourishment over the past few generations?
How do you define 'better nourishment'? Access to lots of sugar and fat and other junk food? Lack of sunshine to skin to generate needed D-vitamin? Mineral poor agricultural land that results into mineral deficiencies? Ingestion and inhaling of multitude of technological materials like plastic, pollution and poisons such as hormone distrupting phalates and birth control pill chemicals that aren't filtered out of drinking water?
Yeah, surely we eat differently than before, but is it an improvement? How about obesity at adolescents? It was very seldom, almost unheard like 100 years ago, but it is now rising at alarming rate.
Regardless, 100 years ago people were so under-nourished that they weren't receiving anywhere near the required levels of vitamins and minerals. (Vitamin-D deficiency? Do you people not drink milk?)
Yeah, sure they didn't have plastic or PCEBs, but they had so much lead and arsenic around that they were *all* suffering from heavy metal poisoning. That's a great world they were living in:P. (plus they had 12 kids per family, and 10 of them died of childhood diseases because they didn't have vaccines or antibiotics. You can't have either of those without chemical plants, power plants, mines, and other infrastructure. So yeah, great world those people had, living all the way up into their mid-30's, just like humans should!)
This is not a new idea; this article merely describes further confirmation of the idea using a new (and interesting) testing method.
As someone else mentioned, identical twins are clones of each other. The E.coli bacteria in a colony are all clones of each other. If DNA was the only mechanism for trait transfer, then identical twins *would* be truly identical (they're not), and all those E.coli bacteria would all behave in exactly the same way (they don't).
So this has been strongly suspected for a long time, it just hadn't been confirmed in an controlled experiment.
Lamarckian evolution is something completely different. It suggests that the evolution of a creature is largely controlled by the actions that creature chooses to take.
The penultimate example of this line of thought is a giraffe stretching its neck, and the neck getting longer **during the lifetime of the creature** in response to the stretching. That longer neck would then be passed on to its children, and they in turn would stretch their newly long necks even further. This is not true, and it will never be true.
Lamarckianism essentially holds that environmental pressures can effect a change in the offspring of a creature subjected to those pressures. Epigenetics holds the same, that the environment can effect changes in a creatures offspring.
This is not at all congruent with evolution theory. But evolutionary scientists can include such opposite theories into evolution.
No other theory in the history of mankind is as malleable as evolution theory.
Uh, no, that isn't what Lamarckian evolution says. What you're describing is part of Darwinian evolution. Look it up to make sure. I did.
Lamarckian evolution says that environmental pressures cause *the creature itself* to adapt to those pressures within its own lifetime. Those adaptations are then passed on to the offspring. Like, if I become a bodybuilder and build up giant muscles, my kids would all automatically have big muscles as well.
And that idea is just wrong. And it won't be revived, ever.
Believe as you will. We already have a TOE (Theory of Everything). That theory is evolution, because it can add and discard other hypotheses and theories at will.
Nothing anyone says about evolution can be wrong because we will just change the theory to match the current argument.
What alternative system would you propose? A system in which knowledge is set down in stone and proclaimed to be correct, regardless of the evidence that is eventually brought against it? Well, you're in luck, cause we already have such a system! We call it "religion".
Theories are models and models should be changed as knowledge changes.
People elevate evolution theory above that, however, stridently asserting that evolution is true, real, etc.
If it is true today, something can't change it tomorrow and it still be true.
It is a theory. Keep it that way and you will do well.
I must say, I'm really disappointed with this article. Epigenetics is NOT a new field. Our understanding of it is barely scratching the surface, but it does NOT conflict with modern evolutionary theory. If anything, it complements it, as epigenetic mechanisms allow for more genetic diversity without lowering the organism's fitness.
Quite frankly, I'm terrified of how ignorant people are over so many issues they don't even begin to understand. It doesn't seem right that they should determine what is taboo and what isn't, when they don't even understand what is going on. (Go on, ASK the preacher to explain the mechanisms of evolution. I bet he'll be hard pressed to even bring up random DNA sequence variation, let alone explain what that is or how it could come about.)
Sorry, I got a little angry about halfway through this post. :) People still confused about Lamarckism should investigate neo-lamarckism to find out how it has successfully been shown to be a part of evolution.