A co-worker of mine made the assertion that genes can be altered over time by the cultural habits of our ancestors. She stated that this happens not by means of selection, but because of their activities. The example she gave was of English women wearing corsets which, over time, caused their offspring to have a different body shape. I have a decent grasp of genetics, and was pretty sure this was impossible, however, I figured I should check to make sure I was right. I’ve tried to Google the example she gave, but I cannot find anything about this. Can this actually be true?
Completely untrue. Your friend is a loony toon.
That would be an example of Lamarckian Evolution, which doesn’t happen in the real world. The example your friend used is amusing, though – usually the classic examples involve giraffes stretching their necks to reach the tall trees or blacksmiths giving their well defined muscles to the next generation.
Perhaps if there had been a high number corset-caused deaths it might work. Then the genes coding for stockier body types would have experienced corset-induced selection pressure, increasing the frequency of genes coding for more svelte body types… ok maybe not. But even then that would be because of selection, not because of the inheritence of acquired traits.
Yes. I knew it sounded familiar. When I Google Lackmarkian Evolution, I get cites saying it happens. It is possible that this actually happens?
This Wiki article mentions some instances in which Lamarkian evolution is alleged to occur. However, these examples are generally controversial or disputed, or in the case of epigenetic effects a matter of definition. While it is possible that Lamarkian evolution may occur in some limited circumstances, it is certain at this point that Darwinian evolution, that is, evolution by natural selection, is by far the dominant mode among most organisms.
You might mention to your co-worker that her understanding of the evolutionary process has been debunked for more than 70 years, since the rediscovery of Mendelian genetics and the forging of the Neo-Darwinian evolutionary synthesis in the 1930s.
So is she completely wrong, or right in some extremely limited circumstances?
Sounds like someone read too many Just So Stories.
For all practical purposes, and for all purposes involving humans, she is completely wrong. The example she gives has not a shred of supporting evidence and would be deemed wrong even by the scientists who argue for lamarckist effects in those limited circumstances (which are not generally accepted even there, remember). She should be challenged by you to produce some evidence, but she will find some excuse to beg off because she cannot do so.
Wrong, at least insofar as how the premise has been stated. There is no mechanism by which an acquired characteristic–be it a corset-narrowed waist or a blacksmith’s forearms–are converted into modifications of the genome and thereby transmitted to offspring. There is considerable evidence that “charcteristics” can be acquired from viruses inserting information into a chromosome, and that some exchange of genetic information is done via this mechanism–almost certainly in plants and bacteria, and likely animals as well–as a sort of natural genetic engineering, but this has nothing to do with Lamarck’s theory of acquired characteristics, which is often misstated anyway. Ever since the introduction of August Weismann’s germ plasm theory (which gave Mendel’s observations on inheretance and von Nägeli’s discovery of the chromosome a sound mechanism for communicating genetic information) Darwin’s theory of natural selection has had an undeniably premier position as the fundamental law of evolutionary processes. There’s just no method bywhich an outside influence acting upon the organism as a whole (rather than directly modifying the genome of a gamete) can effect a change in the genetic code that is transmitted to the offspring. It only affects gross changes in a population via the reproductive fitness of said organism in response to external influence.
Your co-worker may not be a “loony toon”, but she’s definitely outside the park as far as modern evolutionary biology goes. Perhaps you need to present her with Matt Ridley’s Genome or Richard Dawkins The Selfish Gene and Climbing Mount Improbable. Or, perhaps given her level of ignorance on the topic, start with Gould’s The Book of Life: An Illustrated History of the Evolution of Life on Earth and Mayr’s This Is Biology: The Science of the Living World, and build from there.
Or she can continue to live in blithe ignorance like the vast majority of humanity. Intelligence is vastly overrated and mostly unused, and has yet to demonstrate viability as a lont-term evolutionary strategy.
The normal thinking is only DNA is transferred between generations, so nothing you do outside of shooting your gametes with radiation will change your children. But there is evidence now that certain sections of chromosomes can be methylated or acetylated (something that has to be overcome during cloning) which leads to an increase or decrease of gene activation in that region, and this can be passed on to your offspring. So while you aren’t changing your DNA or proteins, you’re changing the levels at which they are expressed.
I presented a paper on this at a journal club about 5 years ago, and the gene in question was IGF2. I believe the terminology used was imprinting. Here is a very long Wikipedia article on the subject. There was also evidence that non-coding mRNAs also had more of a role in cells than we ever thought.
So no, it probably isn’t as drastic as changing body shape, but I do believe that there are some non-standard ways for information to be transferred to the next generation.
If you really want to pick nits, there is a phenomenon in bacteria and some eukaryotic cells by which a selection pressure causes them to become more prone to mutagenesis, and therefore more prone to evolve new traits based on situation. Since this happens in the stationary phase of growth, and is not thought to be replication-based (at least in bacteria), in some sense this is an alteration of genes based on environment.
The most defined example of this is stationary phase mutation in E. Coli. lac[sup]-[/sup] (lactose intolerant) bacteria carrying a plasmid encoding the enzyme necessary for lactose utilization with a +1 frameshift are replica plated onto media containing lactose as the only carbon source. Since these bacteria cannot grow (as they would need to utilize lactose), then they enter stationary phase. After a few days, what you notice is that a few colonies pop up. These have reverted their +1 lac frameshift, and they do so at a pretty high rate. Turns out they are actually downregulating mutation-repair genes as to let more sporadic DNA mutations slip through. The few with the advantageous -1 frameshift correction on the plasmid end up getting lactose tolerance and living. This can then be passed on.
Another example may be amplification of genes necessary for partial drug tolerance. This happens all the time in cancer. Let’s say gene A imparts 1% resistance to a drug. Then, you find a some cells ending up getting 100x copies of gene A. This again may happen due to a downregulation of mutation-repair genes.
A third example is slightly different. There is pretty good experiments on some populations of fruit flies that shows that shows that there is a system in their protein-folding machinery to supress or help refold slightly misfolded proteins (that presumably would be due to mutations). This system is easily overwhelmed in certain stress conditions, namely heat shocks (the class of proteins is actually termed heat-shock proteins or HSPs). In essence, in a population of fruit flies living at their optimal temperature, HSPs actually suppress variability as they are refolding their proteins. Now let’s say a segment of the population moves into a hotter area. HSPs get overwhelmed and all of a sudden there is more population variability. Some of this variability may lend fitness at higher temperatures. Lo and behold, these win out and the new population rapidly adapts to a higher temperature.
That said, none of these are true Lamarckian evolution. The only way that corsets could possibly affect gene variability are by sexual selection and perhaps (perhaps) negative disadvantage if stockier women are dying from corset use before breeding age. And these would take more than a few generations to notably alter allele frequencies.
Ask your coworker why Jewish boys still need to be circumcised.
Now that’s funny.
Does anything similar happen in humans? Also, do you have any cites for this? This is very interesting. Thanks in advance.
Review article about stationary phase mutation:
Review article about adaptive gene amplification:
Actually, if you pubmed “stationary phase mutation AND review[pt]” you pull up a lot of reviews. The authors of the second article (Phil Hastings and Susan Rosenberg) were professors of mine.
I’m having trouble finding the original paper for the HSP response in Drosophila – the literature is pretty big and since leaving grad school I’ve deleted all of my PDFs from this computer. Here is a typical review that brushes on the subject:
and another, from the same journal:
There is not much in the lay literature about these things as they are pretty narrow genetic concepts. I wouldn’t say that there is much evidence of any of these phenomena occuring at an organismal level in any larger animals, although I don’t know that anyone has carefully looked.