I wrote a few weeks ago about newly-discovered dynamics of DNA that make Lamarckian genetic inheritance more plausible than ever. I wrote that there was now just one step missing from a fully-documented Lamarckian mechanism. In a comment on that page, a reader pointed me to a paper that fills in that final step.
Almost everyone looking at the process of evolution that has created the vast biosphere is struck initially by how surprisingly efficient the whole process has been. But quantitative estimates that might tell us whether this intuition is valid are frustratingly elusive. No one has been able to model or to estimate or even to place a reasonable lower bound on the pace of evolutionary change in a biosphere with the stats of our own Gaia. The question we would like to be able to ask is whether blind mutation and natural selection constitute a sufficient mechanism to explain all that we see in biology, and the answer is, “no one knows”. I hasten to add that it is not just religious fundamentalists who are skeptical. My favorite example is an essay by Carl Woese, but I might have cited a dozen others.
One key to the question (how evolution manages to be as efficient as it is) is the realization that the process of evolution is subject to evolution. This is “evolution of evolvability” or, as I like to call it, Evolution Squared. The idea is that in the beginning, evolution may have depended on blind mutation and natural selection, but the process has become vastly more sophisticated and efficient since then, because as nature selects (directly) for increasing fitness, she also selects (indirectly) for those communities that are advancing in fitness more rapidly. I use the word “communities” advisedly, because evolution isn’t something that happens to an individual; the smallest unit that can evolve is a deme, meaning a local set of animals or plants, all of the same species, that interbreed with one another.
Evolution of evolution has led to many innovations that we see and document, the greatest of which is sexual sharing and mixing of genes. There is no doubt that the ability to adapt to the environment within an individual’s lifetime and transmmit that adaptation to offspring would be a tremendously useful innovation. This is Lamarckian inheritance, and if it were ever to arise, it would have been copiously rewarded by natural selection for ever increasing fitness. Is Lamarckian inheritance a reality?
Fifty years after Lamarck, Darwin believed that Lamarck’s mechanism played a role in evolution. But Darwin’s heirs in the 20th Century decided that Lamarckian inheritance was implausible. If, for example, a muscle is conditioned and strengthed by constant exercise, how could the information about that muscle ever be communicated to the germ cells, the sperm or egg cells in the gonads that would be the progenitors of the next generation? Then, in the 1920s, Lysenko’s wild claims about Lamarckian inheritance pulled all credibility out from under the idea, and the scientific community firmly rejected the possibility.
Then, toward the end of the twentieth century, a strange thing happened. A new kind of semi-permanent inheritance was discovered, and it was fully Lamarckian in its implementation. This is epigenetic inheritance, the inheritance not of different versions of genes, but of patterns of gene expression. The choice of which genes are turned on or off is erased from the DNA and reprogrammed with each new embryo. But through the reprogramming, a selective memory remains; an afterimage of what was found to be useful in the previous lifetime is transmitted to the next generation.
Epigenetic memory lasts a few generations, but it is not as permanent as changes in the DNA sequence (= genetic inheritance). Could it be that genetic changes are not completely random but, like epigenetic changes, they are subject to Lamarckian influence? The prevailing skepticism of this idea is rooted in theory, and our understanding of biochemistry. Remarkably, there has been no thorough experimental exploration, not even a well-designed single trial looking for evidence of Lamarckian inheritance.
But we now know that information about gene expression does get fed back to the germline in the form of epigenetic markers. From here, it does not seem so implausible that the epigenetic markers may be translated into more permanent changes in the genome. In this paper from Washington State biologists last year, the last link in the chain is closed. The authors expose rats to a toxic fungicide, and confirm the previously-observed epigenetic changes in the rats, changes that are transmitted to their offspring. They then go on to breed the rats for three more generations, and note that there are extra copies of hundreds of genes, some of which are useful in the detox of the fungicide. These genetic changes appeared in the third generation after exposure, but they were absent in the first generation. They can’t be written off as mutagenic effects in the fungicide, because they were three generations removed from exposure.
This report does not claim creation of new genes or even new alleles, but it does include permanent changes to the germline DNA. The emerging view is that gene expression is more important in determining an organism’s structure and function (and fitness) than the precise form of the alleles themselves. 98% of our DNA is not genes but introns, the segments of DNA between genes that collectively determine the timing and circumstance of gene expression. A curious finding stressed by the authors of this study is that there is zero overlap between the areas of the genome that were epigenetically modified in Generation One after exposure and the areas of the genome that later produced extra copies in Generation Three. This suggests that the mechanism for this first example of Lamarckian genetic inheritance remains a complete mystery.
I now believe that the remaining pieces of a fully Lamarckian evolutionary mechanism will fall into place. Books on evolution will have to be rewritten starting from Chapter 1. Everything that was learned about evolution in the 20th Century will be subject to reinterpretation, and much of it will be deemed irrelevant or naive. If Lamarckian inheritance pans out, it will turn the science of evolution on its head, and give it a good shake.
I was excited about a news story of last week,
_Personality changes in fish affect body shape, movement_.
“Zebrafish bred to be bolder also became sleeker and faster.”
“Complex behaviors, like the behaviors we call ‘personality’ or ‘temperament,’ can be associated — genetically correlated — with other traits that one might think are independent of such behaviors, like body shape and swimming abilities,” Brian Langerhans, an assistant professor of biological sciences at North Carolina State University
Epigenetic modification seems to ‘entourage’ off-site changes in gene expression in the direction of enhancing the trait being trained by experience in an organism (at least, in zebrafish).
In humans I’d jokingly submit that inheritance of larger fists may accompany parental training in boldness. Maybe sleekness and speediness for the occasionally required escape?
I’ve much to ponder about my paternal inheritance possibly resulting from extreme conditioning in Japanese, North Korean, and Chinese POW camps.
I have had to opportunity to prove my mettle. With boldness and speedy escapes!
Your reopening consideration of Lamarkian inheritance is welcome and timely, Josh.
Your comment is kind of funny, but more arrogant. The heart of science is essentially respect for fact. Josh has presented a reasonable hypothesis, that organisms evolving more flexible mechanisms of adaptation would have a competitive advantage.
Experimentation can determine if he is correct. Self-satisfied smartass comments will not.
I tender apologies with a bit of bewilderment. No intent for smart-assery. Sooo, the zebra fish material was experimental, no? The POW transgenerational effects, not so much?
I think there’s a lot we don’t know. The know-it-alls who tell you evolution works by mathematical precise mechanism based on natural selection (and especially at the level of individuals and not demes (which can be totally eliminated – so, group selection) don’t account for how much of change was pre-ordained by inherited developmental modules, how much influenced by environment, epigenetic mechanisms (which “they” consider a sort of glaze on the doughnut of evolutionary theory having nothing to do with the ‘meat’ of it.).
If we look throughout evolutionary time – from the pseudocoelomates to us the same modules control aging through the microRNAs – let-7 and lin-4 and their cognate transcription factors and inhibitors (and vice versa) control those changes. But what controls them? Stay tuned.
“A curious finding stressed by the authors of this study is that there is zero overlap between the areas of the genome that were epigenetically modified in Generation One after exposure and the areas of the genome that later produced extra copies in Generation Three. This suggests that the mechanism for this first example of Lamarckian genetic inheritance remains a complete mystery.”
It also suggests that this experiment needs to be replicated before anyone makes a big deal out of it.
Quote: I use the word “communities” advisedly, because evolution isn’t something that happens to an individual; the smallest unit that can evolve is a deme, meaning a local set of animals or plants, all of the same species, that interbreed with one another.
That is why I still have a problem with the monkey to human story. How could breeding have taken place between the rare chromosome pairs mutated individual and the norms?
Are you aware of any suggestion or study that implicates human expectation born of passive observation as a determinant of longevity?
Yes, the dynamism of “communities” provides the crucial vetting of individuals’ probabilistic generation of _variation_ as the latter encounter their particular slant of the (loaded) local environment. But that is only a superficial view, as is the “gene” view. (I tread softly here lest I arouse the “smartass” troll.)
The actual dynamics underlying these phenomena are of the same (set) by which life on all scales has functioned in organizing itself. It’s always been there, though in its locally accessible venues it is too sparse to provide the reassuringly distinct action sequences as imaginatively demanded by the current (gene) paradigm. However, our situation here is worse than one might expect, arguably because the wrong set of _dynamics_ (attending the gene paradigm) is the underlying problem.
Briefly, the modern synthesis demand control by DNA sequences more or less in a mechanistically direct fashion of singular events, like that operating an on-off light switch. But nature organizes and functions _strictly_ by dint of (diverse) populations (“communities”). There’s more at the (WordPress.com) blog: LifesSecretLife.com/5-lifes-march/
I have just today revisited LaMarck’s theory. I understood that the Weisman Barrier has never been proven and in fact it was completely trashed as a worthless deviation to the main argument. To me, it could never have been otherwise. How ridiculous to chop off mice tails and expect it to affect offspring. Intellectually it is ludicrous; equally, how can vital experience, essential to development of the specie NOT be transmitted. Anecdotal evidence, tells us. I had a friend who was encouraged to move his electronics factory from Nottingham (with a long history of industry) to Scotland, to an agrarian region with no history of manufacture. The employees lacked the abilities needed- mental and manual dexterity- and the business folded. It could not have been otherwise in hindsight.
I don’t think it is obvious. Lamarckian inheritance is a question that should be settled with experiments.