Confirmation bias is one of the major logical fallacies. When philosopher Chris DiCarlo and I were teaching a course on critical thinking we used to spend quite a bit of time on it because it's a very common trap. We are all guilty, from time to time, of focusing on just the evidence that confirms our belief and ignoring all the evidence that refutes it.
Some examples of confirmation bias are a bit more complicated than others and people typically mix together several different fallacious forms of argument. Here's an example from Denis Alexander's book Creation or Evolution (p. 213) that combines begging the question and confirmation bias.
We know quite a lot about the origin of new genes (Carvunis et al., 2012; Kaessman, 2010; Long et al., 2003; Long et al., 2013; Näsvall et al., 2012); Neme and Tautz, 2013; Schlötterer, 2015; Tautz and Domazet-Lošo (2011); Wu et al., 2011). Most of them are derived from gene duplication events and subsequent divergence. A smaller number are formed de novo from sequences that were not part of a gene in the ancestral species.
In spite of what you might have read in the popular literature, there are not a large number of newly formed genes in most species. Genes that appear to be unique to a single species are called "orphan" genes. When a genome is first sequenced there will always be a large number of potential orphan genes because the gene prediction software tilts toward false positives in order to minimize false negatives. Further investigation and annotation reduces the number of potential genes.
Thanks for reading the commentary on my university’s communication page, hastily written for brevity and digestibility by me and our science communication officer, Lawrence Goodman. I was originally hoping the piece could focus on my latest research, but it turned into this sort of general Q&A chat. The commentary was written rather quickly and meant for a general audience perusing Brandeis research, so it is obviously not a peer-reviewed scientific publication.
I am well aware of both your reputations as fiery critics and experts of evolutionary biology, and you have somewhat of a following on the internet. Some of your earlier blog posts have been entertaining and even on point regarding how big projects like ENCODE have over-hyped the functional proportions of our genomes. So, it does NOT surprise me one bit that I would become your latest vitriolic target in your posts here, and here.
Could I learn more from you two about evolutionary biology theory? Indeed, I could. Can we revise our Q&A commentary to be more scientifically accurate while still being digestible to a general audience? Perhaps, if we have the time and I survive my tenure review, we may do so and take your input into consideration. Why respond and risk another snarky post from you guys? I could care less about your trivial blog critiques when I’ve received plenty of grants and paper rejections that cut much deeper into my existence as a young academic struggling to survive when the academic track has never been more challenging (<10% grant success rates at NIH, NSF, CIHR, etc).
I’m responding to ask that both of you reflect on the message your posts are sending to students and postdocs. As a young scientist, having a chat with my university PR rep, I have to now think twice about two senior tenured professors slamming my scientific credibility on your internet soapbox without a single direct email to me. How passive-aggressive!
Your message is saying that Academic science even less inviting to young scientists as it is, with faculty positions and grants falling way short of demand, and the tough sacrifices every young scientist is already making for the craft that we love. If we condone this type of sniping behavior, why would any young scientist want to learn and discuss with the older scientists of your generation?
A direct email from you to me expressing your scientific concerns of our commentary would have been a better way to go. I am willing to stand corrected. Your blog posts, however, are disappointing and appear petty to me. Let’s all set a better example here for our trainees.
If you wish to post this response verbatim on your blogs, go ahead, since I had thought of posting this response on your blog’s comments section. But to follow my own advice, I’ll try a direct email to you first. And if I don’t hear back from you, I may then ask my friend Bjorn to help me post this on his blog.
This time it's Assistant Professor of Biology Nelson Lau. He studies Piwi proteins and PiRNAs.
Lau was interviewed by Lawrence Goodman, a science communication officer at Brandeis University: DNA dumpster diving. The subject is junk DNA and you will be astonished at how ignorant Nelson Lau is about a subject that's supposed to be important in his work.
How does this happen? Aren't scientists supposed to be up-to-date on the scientific literature before they pass themselves off as experts? How can an Assistant Professor make such blatantly false and misleading statements about his own area of research expertise? Has he never encountered graduate students, post-docs, or mentors who would have corrected his misconceptions?
Here's the introduction to the interview,
Since the 1960s, it's largely been assumed that most of the DNA in the human genome was junk. It didn't encode proteins -- the main activity of our genes-- so it was assumed to serve no purpose. But Assistant Professor of Biology Nelson Lau is among a new generation of scientists questioning that hypothesis. His findings suggest we've been wrong about junk DNA and it may be time for a reappraisal. If we want to understand how our bodies work, we need to start picking through our genetic garbage.
BrandeisNow sat down with Lau to ask him about his research.
There's nothing wrong with being a "new generation" who questions the wisdom of their elders. That's what all scientists are supposed to do.
But there are certain standards that apply. The most important standard is that when you are challenging other experts you'd better be an expert yourself.
First off, what is junk DNA?
About two percent of our genome carries out functions we know about, things like building our bones or keeping the heart beating. What the rest of our DNA does is still a mystery. Twenty years ago, for want of a better term, some scientists decided to call it junk DNA.
Dan has already addressed this response but let me throw in my own two cents.
There was never, ever, a time when knowledgeable scientists said that all 98% of the DNA that wasn't part of a gene was junk. Not today, not twenty years ago (1996), and not 45 years ago.
There has never been at time since the 1960s when all non-gene DNA was a mystery. It certainly isn't a mystery today. If you don't know this then you better do some reading ... quickly. Google could be your friend, Prof. Lau, it will save you from further embarrassment. Search on "junk DNA" and read everything ... not just the entries that you agree with.
I added a bunch of links at the bottom of this post to help you out.
Is it really junk?
There’s two camps in the scientific community, one that believes it doesn’t do anything and another that believes it’s there for a purpose.
And you’re in the second camp?
Yes. It's true that sometimes organisms carry around excess DNA, but usually it is there for a purpose. Perhaps junk DNA has been coopted for a deeper purpose that we have yet to fully unravel.
It is possible that the extra DNA in our genome has an unknown deeper purpose but right now we have more than enough information to be confident that it's junk. You have to refute or discredit all the work that's been done in the past 40 years in order to be in the second camp.
Maybe when junk DNA moves to the right place in our DNA, this could cause better or faster evolution. Maybe when junk genes interacts with the non-junk ones, it causes a mutation to occur so humans can better adapt to changes in the environment.
Most of the undergraduates who took my course could easily refute that argument. I'm guessing that undergraduates in biology at Brandeis aren't as smart. Or maybe they're just too complacent to challenge a professor?
We've got a serious problem here folks. There are scientists being hired at respectable universities who aren't keeping up with the scientific literature in their own field. How does this happen? Are there newly hired biology professors who don't understand evolution?
Niu, D. K., and Jiang, L. (2012) Can ENCODE tell us how much junk DNA we carry in our genome?. Biochemical and biophysical research communications 430:1340-1343. [doi: 10.1016/j.bbrc.2012.12.074]
Doolittle, W.F. (2013) Is junk DNA bunk? A critique of ENCODE. Proc. Natl. Acad. Sci. (USA) published online March 11, 2013. [PubMed] [doi: 10.1073/pnas.1221376110]
Graur, D., Zheng, Y., Price, N., Azevedo, R. B., Zufall, R. A., and Elhaik, E. (2013) On the immortality of television sets: "function" in the human genome according to the evolution-free gospel of ENCODE. Genome Biology and Evolution published online: February 20, 2013 [doi: 10.1093/gbe/evt028
Eddy, S.R. (2013) The ENCODE project: missteps overshadowing a success. Current Biology, 23:R259-R261. [10.1016/j.cub.2013.03.023]
Hurst, L.D. (2013) Open questions: A logic (or lack thereof) of genome organization. BMC biology, 11:58. [doi:10.1186/1741-7007-11-58]
Kellis, M., Wold, B., Snyder, M.P., Bernstein, B.E., Kundaje, A., Marinov, G.K., Ward, L.D., Birney, E., Crawford, G. E., and Dekker, J. (2014) Defining functional DNA elements in the human genome. Proc. Natl. Acad. Sci. (USA) 111:6131-6138. [doi: 10.1073/pnas.1318948111]
Morange, M. (2014) Genome as a Multipurpose Structure Built by Evolution. Perspectives in biology and medicine, 57:162-171. [doi: 10.1353/pbm.2014.000]
I'm taking Ms. Sandwalk and hope to show her Down House. She loves old English houses.
She'll also be really excited to see Darwin's tomb in Westminster Abbey and tour the Natural History Museum. We'll make it a fun-filled week of science and evolution! Why don't you join us?
If Behe & Snoke are correct then modern evolutionary theory cannot explain the formation of new functions that require multiple mutations.
Cassey Luskin is aware of the fact that this result has not been widely accepted. He mentions one specific criticism:
In 2008, Behe and Snoke's would-be critics tried to refute them in the journal Genetics, but found that to obtain only two specific mutations via Darwinian evolution "for humans with a much smaller effective population size, this type of change would take > 100 million years." The critics admitted this was "very unlikely to occur on a reasonable timescale."
He's referring to a paper by Durrett and Schmidt (2008). Those authors examined the situation where one transcription factor binding site was disrupted by mutation and another one nearby is created by mutation. The event requires two prespecified coordinated mutations.
Another article about evolution and the attainment of perfection has appeared. This one was published by Nathaniel Scharping on the Discover website [Could Evolution Ever Yield a ‘Perfect’ Organism?].
The article focuses on a recent paper from Richard Lenski's group at Michigan State University (Lenski et al., 2015). Lenski's group asked a different question. They wanted to know whether there was a limit to the increase in fitness in their evolving E. coli populations in the Long-Term Evolution Experiment (LTEE). It's a different question than whether evolution can select for a "perfect" organism because Lenski and his collaborators understand modern evolutionary theory. They know that mutations causing small fitness increases are beyond the reach of natural selection in their evolving populations and they know that deleterious mutations can be fixed by random genetic drift.
They know that real evolving populations can never reach the summit of an adaptive peak or, if they do, they can never stay there.
I just re-read a 1997 paper by Francis Ayala and Walter Fitch (Ayala and Fitch, 1997). The opening two paragraphs describe the Modern Synthesis of Evolution in a very interesting way. The emphasis is on the history and the contributions of Theodosius Dobzhansky (1900-1975) but it makes another point that I'd like to mention.
Theodosius Dobzhansky (1900–1975) was a key author of the Synthetic Theory of Evolution, also known as the Modern Synthesis of Evolutionary Theory, which embodies a complex array of biological knowledge centered around Darwin’s theory of evolution by natural selection couched in genetic terms. The epithet ‘‘synthetic’’ primarily alludes to the artful combination of Darwin’s natural selection with Mendelian genetics, but also to the incorporation of relevant knowledge from biological disciplines. In the 1920s and 1930s several theorists had developed mathematical accounts of natural selection as a genetic process. Dobzhansky’s Genetics and the Origin of Species, published in 1937 (1), refashioned their formulations in language that biologists could understand, dressed the equations with natural history and experimental population genetics, and extended the synthesis to speciation and other cardinal problems omitted by the mathematicians.
The current Synthetic Theory has grown around that original synthesis. It is not just one single hypothesis (or theory) with its corroborating evidence, but a multidisciplinary body of knowledge bearing on biological evolution, an amalgam of well-established theories and working hypotheses, together with the observations and experiments that support accepted hypotheses (and falsify rejected ones), which jointly seek to explain the evolutionary process and its outcomes. These hypotheses, observations, and experiments often originate in disciplines such as genetics, embryology, zoology, botany, paleontology, and molecular biology. Currently, the ‘‘synthetic’’ epithet is often omitted and the compilation of relevant knowledge is simply known as the Theory of Evolution. This is still expanding, just like one of those ‘‘holding’’ business corporations that have grown around an original enterprise, but continue incorporating new profitable enterprises and discarding unprofitable ones.
The important point here is that evolutionary theory is a complex synthesis of sub-theories, hypotheses, and observations. While it may be convenient to refer to this synthetic version as the "Theory of Evolution," it's also very misleading.
I strongly recommend that we abandon that term and use "evolutionary theory" instead. Furthermore, we should be careful about using the term "Modern Synthesis" unless we are specifically referring to the version of evolutionary theory that was popular in the 1950s.
It's true that Ayala and Fitch would like to retain the term "Synthetic Theory" to refer to the expanded version of the Modern Synthesis. They want to emphasize that there have been important extensions to the original Modern Synthesis but these are merely add-ons. Darwin's basic idea of evolution by natural selection remains at the core of their version of the "Theory of Evolution."
That seems like a very pluralistic view but I'd like to note several things about this paper.
The word "drift" appears only once and it's in the form "neutral drift." There's no mention of random genetic drift as a mechanism of evolution that's been incorporated into the synthetic version of evolutionary theory.
The word "neutral" appears five times but "Neutral Theory" is not mentioned. The authors do concede that "the neutral-selection controversy rages on."
There are 50 references but not a single paper by Mootoo Kimura is mentioned. They do, however, discuss molecular clocks and discuss whether amino acid substitutions are really of "no adaptive consequence."
There's a fairly well-known paper by Gould and Lewontin that might be relevant in a discussion about the synthetic version modern evolutionary theory. They neglected to mention it.
Ayala, F.J., and Fitch, W.M. (1997) Genetics and the origin of species: an introduction. Proc. Natl. Acad. Sci. (USA) 94:7691-7697. [PDF]
Gould, S.J., and Lewontin, R.C. (1979) The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme. Proc. Roy. Soc. (London) Series B. Biological Sciences 205:581-598. [doi: 10.1098/rspb.1979.0086]
All living organisms have developed highly accurate DNA replication complexes and sophisticated mechanisms for repairing DNA damage. The combination results in DNA replication errors that are about 1 per 10 billion base pairs (10-10 per bp). DNA damage due to other factors is effectively repaired with an error rate of 1 in 100 per base pair (10-2 per bp).
Mutations can be beneficial, deleterious, or neutral. In organisms with large genomes there are many more neutral mutations than the other two classes but in organisms with smaller genomes a higher percentage of mutations are either beneficial or deleterious. In all cases, there are more deleterious mutations than beneficial ones.
If deleterious mutations are harmful to the individual then natural selection should favor a low mutation rate in order to minimize that effect. This is especially true in large multicellular organisms where somatic cell mutations cause cancer and other problems. It seems logical that the optimal mutation rate should be zero in order to maximize the survival of the individual and its offspring.
Nothing in biology makes sense except in the light of population genetics.
Michael Lynch But even though the number of beneficial mutations is low compared to those that are deleterious, this is the stuff of adaptive evolution. In the long run the population will become more fit if beneficial mutations occur and become fixed by natural selection. Eliminating mutations might provide a short-term advantage but eventually the population will go extinct if it can't adapt to new environments. (Neutral and deleterious mutations can also contribute to adaptation over the long term.)
The simplest explanation for this apparent paradox is that there's a trade-off between selection to minimize deleterious mutations and selection for long-term evolutionary advantage. The problem with that explanation is that it is very difficult to show how you can select for the future benefit of mutations to the species (population). It seems as though you have to invoke two bogeymen; group selection and teleology.
Maybe there's a better explanation?
Jerry Coyne recently thought about this problem and posted his analysis under the provocative title: The irony of natural selection. He concludes that there's some constraint that limits the ability of natural selection to achieve a zero mutation rate.
The most probable explanation is that evolution does not produce perfect adaptations. In the case of mutations, though natural selection favors individuals most able to repair any changes in DNA (although a small percentage of these might be adaptive), this level of perfection cannot be achieved because of constraints: the cost of achieving perfection, the fact that all errors are impossible to detect or remove, or that some cells (i.e., sperm or eggs) may not even have DNA-repair mechanisms because of genetic or physiological constraints.
I used to think that this was the best explanation. I taught my students that the accuracy of DNA replication, for example, comes at the cost of speed. The more accurate the polymerization process, the slower it takes. This makes a lot of sense and there's experimental support for the claim. Slowing down the time it takes to replicate the genome will affect the time it takes for cell divisions and that could be harmful ... or so the argument goes.
Unfortunately, I ran into Michael Lynch at an evolution meeting and he quickly destroyed that argument. There's no evidence that the speed of DNA replication is limiting the rate of cell divisions and, besides, there are easy ways for selection to get around such a limitation if it ever occurred. (This is a photo of Michael Lynch looking at me right after setting me straight. He's wondering how I could have been so stupid.)
When you think about it, there doesn't seem to be any biochemical or physiological constraints that could prevent the mutation rate from getting to zero ... or at least a lot closer than it is now.
Michael Lynch has a better answer and he explains it in a paper titled: "The Lower Bound to the Evolution of Mutation Rates" (Lynch, 2011).
As the mutation rate is driven to lower and lower levels by selection, a point must eventually be reached where the advantage of any further increase in replication fidelity is smaller than the power of random genetic drift (Lynch 2008, 2010). The goal here is to evaluate the extent to which such an intrinsic barrier can provide an adequate explanation for the patterns of mutation rates known to have evolved in natural populations.
The main "constraint" is the limited power of natural selection in the presence of random genetic drift. This will depend to some extent of the size of the population.
This idea is called the "drift-barrier hypothesis. It is described in Sung et al. (2012):
... the drift-barrier hypothesis predicts that the level of refinement of molecular attributes, including DNA replication fidelity and repair, that can be accomplished by natural selection will be negatively correlated with the effective population size (Ne) of a species. Under this hypothesis, as natural selection pushes a trait toward perfection, further improvements are expected to have diminishing fitness advantages. Once the point is reached beyond which the effects of subsequent beneficial mutations are unlikely to be large enough to overcome the power of random genetic drift, adaptive progress is expected to come to a standstill. Because selection is generally expected to favor lower mutation rates as a result of the associated load of deleterious mutations, and because the power of drift is inversely proportional to Ne, lower mutation rates are expected in species with larger Ne.
The Lynch lab has produced lots of evidence in support of the hypothesis although there may be some confounding factors in some populations.
The bottom line is that the real irony of natural selection is that it's just not powerful enough to reduce the error rate of replication and repair below the values we currently see.
In a sense, it's the "error rate" of fixation by natural selection in the face of random genetic drift that allows evolution to occur.
The more we learn about biology the more we learn that it's messy and sloppy at every level. Evolution is not a watchmaker and it's not even a blind watchmaker. It's a tinkerer1 and the "watch" barely keeps time.
1. Jacob, F. (1977) Evolution and tinkering. Science (New York, NY), 196:1161. [PDF]
Lynch, M. (2011) The lower bound to the evolution of mutation rates. Genome Biology and Evolution, 3:1107. [doi: 10.1093/gbe/evr066]
Sung, W., Ackerman, M.S., Miller, S.F., Doak, T.G., and Lynch, M. (2012) Drift-barrier hypothesis and mutation-rate evolution. Proc. Natl. Acad. Sci. (USA) 109:18488-18492. [doi: 10.1073/pnas.1216223109]
Sometime back in the pre-Cambrian (before blogs) there was a newsgroup called talk.origins—it still exists. In 1993 I wrote a little essay that tried to convince creationists1 of the difference between facts of evolution and evolutionary theory [Evolution is a Fact and a Theory]. I relied heavily on Stephen Jay Gould's essay on "Evolution as Fact and Theory" originally published in Discover magazine in 1981 and re-printed in Hen's Teeth and Horse's Toes.
I recently had occasion to re-read a paper by Motoo Kimura from 1968. (Kimura, 1968). I noticed, for the first time, that he estimates a mutation rate based on his understanding of the error rate of DNA replication. He also makes a comment about creationists.
Remember, this was in 1968 and we didn't know as much then as we do now. Kimura took note of the fact that evolutionary trees based on comparing amino acid sequences gave rates of amino acid substitutions that seemed far too high. His conclusion is in the abstract.
A few months ago I highlighted a paper by Casane et al. (2015) where they said ...
In September 2012, a batch of more than 30 articles presenting the results of the ENCODE (Encyclopaedia of DNA Elements) project was released. Many of these articles appeared in Nature and Science, the two most prestigious interdisciplinary scientific journals. Since that time, hundreds of other articles dedicated to the further analyses of the Encode data have been published. The time of hundreds of scientists and hundreds of millions of dollars were not invested in vain since this project had led to an apparent paradigm shift: contrary to the classical view, 80% of the human genome is not junk DNA, but is functional. This hypothesis has been criticized by evolutionary biologists, sometimes eagerly, and detailed refutations have been published in specialized journals with impact factors far below those that published the main contribution of the Encode project to our understanding of genome architecture. In 2014, the Encode consortium released a new batch of articles that neither suggested that 80% of the genome is functional nor commented on the disappearance of their 2012 scientific breakthrough. Unfortunately, by that time many biologists had accepted the idea that 80% of the genome is functional, or at least, that this idea is a valid alternative to the long held evolutionary genetic view that it is not. In order to understand the dynamics of the genome, it is necessary to re-examine the basics of evolutionary genetics because, not only are they well established, they also will allow us to avoid the pitfall of a panglossian interpretation of Encode. Actually, the architecture of the genome and its dynamics are the product of trade-offs between various evolutionary forces, and many structural features are not related to functional properties. In other words, evolution does not produce the best of all worlds, not even the best of all possible worlds, but only one possible world.
How did we get to this stage where the most publicized result of papers published by leading scientists in the best journals turns out to be wrong, but hardly anyone knows it?
Back in September 2012, the ENCODE Consortium was preparing to publish dozens of papers on their analysis of the human genome. Most of the results were quite boring but that doesn't mean they were useless. The leaders of the Consortium must have been worried that science journalists would not give them the publicity they craved so they came up with a strategy and a publicity campaign to promote their work.
Their leader was Ewan Birney, a scientist with valuable skills as a herder of cats but little experience in evolutionary biology and the history of the junk DNA debate.
The ENCODE Consortium decided to add up all the transcription factor binding sites—spurious or not—and all the chromatin makers—whether or not they meant anything—and all the transcripts—even if they were junk. With a little judicious juggling of numbers they came up with the following summary of their results (Birney et al., 2012) ..
The human genome encodes the blueprint of life, but the function of the vast majority of its nearly three billion bases is unknown. The Encyclopedia of DNA Elements (ENCODE) project has systematically mapped regions of transcription, transcription factor association, chromatin structure and histone modification. These data enabled us to assign biochemical functions for 80% of the genome, in particular outside of the well-studied protein-coding regions. Many discovered candidate regulatory elements are physically associated with one another and with expressed genes, providing new insights into the mechanisms of gene regulation. The newly identified elements also show a statistical correspondence to sequence variants linked to human disease, and can thereby guide interpretation of this variation. Overall, the project provides new insights into the organization and regulation of our genes and genome, and is an expansive resource of functional annotations for biomedical research.
The bottom line is that these leaders knew exactly what they were doing and why. By saying they have assigned biochemical functions for 80% of the genome they knew that this would be the headline. They knew that journalists and publicists would interpret this to mean the end of junk DNA. Most of ENCODE leaders actually believed it.
That's exactly what happened ... aided and abetted by the ENCODE Consortium, the journals Nature and Science, and gullible science journalists all over the world. (Ryan Gregory has published a list of articles that appeared in the popular press: The ENCODE media hype machine..)
Almost immediately the knowledgeable scientists and science writers tried to expose this publicity campaign hype. The first criticisms appeared on various science blogs and this was followed by a series of papers in the published scientific literature. Ed Yong, an experienced science journalist, interviewed Ewan Birney and blogged about ENCODE on the first day. Yong reported the standard publicity hype that most of our genome is functional and this interpretation is confirmed by Ewan Birney and other senior scientists. Two days later, Ed Yong started adding updates to his blog posting after reading the blogs of many scientists including some who were well-recognized experts on genomes and evolution [ENCODE: the rough guide to the human genome].
Within a few days of publishing their results the ENCODE Consortium was coming under intense criticism from all sides. A few journalists, like John Timmer, recongized right away what the problem was ...
Yet the third sentence of the lead ENCODE paper contains an eye-catching figure that ended up being reported widely: "These data enabled us to assign biochemical functions for 80 percent of the genome." Unfortunately, the significance of that statement hinged on a much less widely reported item: the definition of "biochemical function" used by the authors.
This was more than a matter of semantics. Many press reports that resulted painted an entirely fictitious history of biology's past, along with a misleading picture of its present. As a result, the public that relied on those press reports now has a completely mistaken view of our current state of knowledge (this happens to be the exact opposite of what journalism is intended to accomplish). But you can't entirely blame the press in this case. They were egged on by the journals and university press offices that promoted the work—and, in some cases, the scientists themselves.
Nature may have begun to realize that it made a mistake in promoting the idea that most of our genome was functional. Two days after the papers appeared, Brendan Maher, a Feature Editor for Nature, tried to get the journal off the hook but only succeeded in making matters worse [see Brendan Maher Writes About the ENCODE/Junk DNA Publicity Fiasco].
Meanwhile, two private for-profit companies, illumina and Nature, team up to promote the ENCODE results. They even hire Tim Minchin to narrate it. This is what hype looks like ...
Soon articles began to appear in the scientific literature challenging the ENCODE Consortium's interpretation of function and explaining the difference between an effect—such as the binding of a transcription factor to a random piece of DNA—and a true biological function.
Niu, D. K., and Jiang, L. (2012) Can ENCODE tell us how much junk DNA we carry in our genome?. Biochemical and biophysical research communications 430:1340-1343. [doi: 10.1016/j.bbrc.2012.12.074]
Doolittle, W.F. (2013) Is junk DNA bunk? A critique of ENCODE. Proc. Natl. Acad. Sci. (USA) published online March 11, 2013. [PubMed] [doi: 10.1073/pnas.1221376110]
Graur, D., Zheng, Y., Price, N., Azevedo, R. B., Zufall, R. A., and Elhaik, E. (2013) On the immortality of television sets: "function" in the human genome according to the evolution-free gospel of ENCODE. Genome Biology and Evolution published online: February 20, 2013 [doi: 10.1093/gbe/evt028
Eddy, S.R. (2013) The ENCODE project: missteps overshadowing a success. Current Biology, 23:R259-R261. [10.1016/j.cub.2013.03.023]
Hurst, L.D. (2013) Open questions: A logic (or lack thereof) of genome organization. BMC biology, 11:58. [doi:10.1186/1741-7007-11-58]
Morange, M. (2014) Genome as a Multipurpose Structure Built by Evolution. Perspectives in biology and medicine, 57:162-171. [doi: 10.1353/pbm.2014.000]
By March 2013—six months after publication of the ENCODE papers—some editors at Nature decided that they had better say something else [see Anonymous Nature Editors Respond to ENCODE Criticism]. Here's the closest thing to an apology that they have ever written ....
The debate over ENCODE’s definition of function retreads some old battles, dating back perhaps to geneticist Susumu Ohno’s coinage of the term junk DNA in the 1970s. The phrase has had a polarizing effect on the life-sciences community ever since, despite several revisions of its meaning. Indeed, many news reports and press releases describing ENCODE’s work claimed that by showing that most of the genome was ‘functional’, the project had killed the concept of junk DNA. This claim annoyed both those who thought it a premature obituary and those who considered it old news.
There is a valuable and genuine debate here. To define what, if anything, the billions of non-protein-coding base pairs in the human genome do, and how they affect cellular and system-level processes, remains an important, open and debatable question. Ironically, it is a question that the language of the current debate may detract from. As Ewan Birney, co-director of the ENCODE project, noted on his blog: “Hindsight is a cruel and wonderful thing, and probably we could have achieved the same thing without generating this unneeded, confusing discussion on what we meant and how we said it”.
Oops! The importance of junk DNA is still an "important, open and debatable question" in spite of what the video sponsored by Nature might imply.
(To this day, neither Nature nor Science have actually apologized for misleading the public about the ENCODE results. [see Science still doesn't get it ])
The ENCODE Consortium leaders responded in April 2014—eighteen months after their original papers were published.
Kellis, M., Wold, B., Snyder, M.P., Bernstein, B.E., Kundaje, A., Marinov, G.K., Ward, L.D., Birney, E., Crawford, G. E., and Dekker, J. (2014) Defining functional DNA elements in the human genome. Proc. Natl. Acad. Sci. (USA) 111:6131-6138. [doi: 10.1073/pnas.1318948111]
In that paper they acknowledge that there are multiple meanings of the word function and their choice of "biochemical" function may not have been the best choice ....
However, biochemical signatures are often a consequence of function, rather than causal. They are also not always deterministic evidence of function, but can occur stochastically.
This is exactly what many scientists have been telling them. Apparently they did not know this in September 2012.
They also include in their paper a section on "Case for Abundant Junk DNA." It summarizes the evidence for junk DNA, evidence that the ENCODE Consortium did not acknowledge in 2012 and certainly didn't refute.
In answer to the question, "What Fraction of the Human Genome Is Functional?" they now conclude that ENCODE hasn't answered that question and more work is needed. They now claim that the real value of ENCODE is to provide "high-resolution, highly-reproducible maps of DNA segments with biochemical signatures associate with diverse molecular functions."
We believe that this public resource is far more important than any interim estimate of the fraction of the human genome that is functional.
There you have it, straight from the horse's mouth. The ENCODE Consortium now believes that you should NOT interpret their results to mean that 80% of the genome is functional and therefore not junk DNA. There is good evidence for abundant junk DNA and the issue is still debatable.
I hope everyone pays attention and stops referring to the promotional hype saying that ENCODE has refuted junk DNA. That's not what the ENCODE Consortium leaders now say about their results.
Casane, D., Fumey, J., et Laurenti, P. (2015) L’apophénie d’ENCODE ou Pangloss examine le génome humain. Med. Sci. (Paris) 31: 680-686. [doi: 10.1051/medsci/20153106023]
The answers are the platypus and the opossum. The overall impression she conveys to the general public is that these species have not evolved for millions and millions of years.
I don't agree. I think it's important to teach the general public that such statements flatly contradict modern evolutionary theory. If, in fact, we discovered modern species that showed no signs of having evolved for millions of years, this would refute modern evolutionary theory.
The accepted minimal definition of evolution is ... [What Is Evolution?]
Evolution is a process that results in heritable changes in a population spread over many generations.
... or something similar like "change in the frequency of alleles in a population."
The main accepted mechanisms of evolution are natural selection and random genetic drift.
The only way positive natural selection1 can stop is if an organism is so perfectly adapted to its current environment (external and internal) that every possible mutation is either deleterious or neutral. That includes all metabolic processes and every structure in the cell.
Nobody could rationally advocate such a claim.
The only way to stop random genetic drift is if there's no such thing as a new neutral or nearly neutral mutation and all such variation in the population has been eliminated.
No evolutionary biologist could possibly make such a claim with a straight face.
It's easy to test such ridiculous claims by looking at the genomes of the opossum and the platypus. The evidence shows that they have evolved at the same rate as all other species.
The article actually mentions this problem ...
“'Unchanged' is a tricky word,” Nizar Ibrahim, a paleontologist at the University of Chicago and 2014 National Geographic Explorer, says via email.
With only fossils to go by, scientists can examine an ancient animal's skeletal structure, but it's not the whole story. Physiology and DNA change somewhat over time, he says, both through the basic process of evolution as well as random genetic changes.
That said, two mammals that have undergone the fewest evolutionary shifts are the platypus and the opossum, says Samantha Hopkins, associate professor of geology at the University of Oregon.
Liz Langley did not pick up on this comment so she missed a wonderful teaching moment.
It's possible that Liz Langley isn't aware of modern evolutionary theory and that she actually believes that evolution comes to a halt as long as species live in a relatively constant environment. It's possible that she disagrees with the minimal definition of evolution and prefers a definition that only counts significant changes in external phenotype. Or, it's possible that she thinks that National Geographic readers can't handle modern evolutionary theory. If it's the latter, I disagree.
1. You can't stop negative natural selection unless there are no new deleterious mutations. That's also impossible.
I was alerted to this video by a post on Facebook. I had never seen it before. The occasion is the celebration of the 20th anniversary of McLean v. Arkansas— one of the legal victories of Americans who are fighting to keep creationism out of the classroom.
It's a 30 minute presentation by Stephen J. Gould on the fossil record. The event took place in February 2001, just a year before he died. You should watch it for many reasons—too many to mention them all here but here are some of the most important ones.
In my first post [Answering Barry Arrington's challenge: Darwinism] I established that Barry Arrington's version of "Darwinism" is actually "Neo-Darwinism" or the "Modern Synthesis." We all know why Intelligent Design Creationists would rather use "Darwinism"—this explains why they deliberately change the meaning to make it look like they understand evolution
Arrington's version of "Darwinism can be seen in the Uncommon Descentglossary. It focuses on natural selection as the mechanism of evolution and doesn't mention Neutral Theory of random genetic drift.
OK, Larry. I assume you mean to say that I do not understand the basics of Darwinism. I challenge you, therefore, to demonstrate your claim.
Today I'm feeling optimistic—life is good and this evening we're going to a nice restaurant for dinner with our favorite nephew.1 Let's try, once again, to convert this into a teaching moment. Hopefully, at least one or two ID proponents will learn something.2
Let's think about the biochemical cost associated with adding some new piece of DNA to an existing genome. Michael Lynch has been thinking about this for a long time. He notes that there certainly IS a cost (burden) because the new bit of DNA has to be replicated. That means extra nucleotides have to be synthesized and polymerized every time a cell replicates.
This burden might seem prohibitive for strict adaptationists1 since everything that's detrimental should be lost by negative selection. Lynch, and others, ague that the cost is usually quite small and if it's small enough the detrimental effect might be below the threshold that selection can detect. When this happens, new stretches of DNA become effectively neutral (nearly neutral) and they can be fixed in the genome by random genetic drift.
The key parameter is the size of the population since the power of selection increases as the population size increases. Populations with large numbers of individuals (e.g. more than one million) can respond to the small costs/burdens and eliminate excess DNA whereas populations with smaller numbers of individuals cannot.
For those of you who are interested in the evolution of the major animal phyla, let me introduce you to the topic.
See the little red circle on the phylogenetic tree on the right? That's what we're talking about.
Most of the major animal phyla are first observed as primitive fossils in the Cambrian about 540 million years ago. The fossils cluster around dates that only span a few million years (about 10 million years). This is the Cambrian Explosion (see little red circle).
There's considerable debate among evolutionary biologists about what caused this relatively rapid appearance of diverse and disparate large fossils. Intelligent Design Creationist, Stephen Meyer decided that such a debate casts serious doubt on evolution as an explanation for the history of life so he wrote a book called Darwin's Doubt.
Modern Salmonidae (salmon and its relatives) have genomes that show clear evidence of an ancient duplication event. Berthelot et al. (2014) sequenced the rainbow trout genome and constructed a phylogenetic tree of all teleost fish. The genome duplication event in the Salmonidae lineage can be dated to approximately 96 million years ago (96 ± 5.5 Mya).
This event provides an opportunity to track the fate of the duplicated protein-coding genes. How many of the original duplicates are left and what happened to them?
There were able to get reliable data on 9,040 of the original genes in the ancestral genome. (That's about one third of the estimated 31,000 genes in the genome of the original species.) Of those 9,040 genes, 4,728 (52%) are now single copy genes because one of the duplicated genes has been lost. Many of these original genes are still detectable as pseudogenes at the right position in the genome.
By combining these results with studies of more ancient genome duplications in the vertebrate lineage, it looks like the average rate of gene loss is about 170 genes per million years (Berthelot et al., 2004). It's likely that in the majority of cases one of the duplicates will eventually become inactivated by mutation and that allele will become fixed in the genome by random genetic drift. (Some early inactivation events may be selected.)
4,312 (42%) of the original duplications have been retained in the trout genome as a small family consisting of two paralogues. In some cases the two paralogues have diverged and in some cases they are expressed in different tissues or at different stages of development. This suggests that the two copies have evolved different functions.
However, most of the duplicated genes seem to be performing similar functions and it's likely that there is no selective pressure to retain two copies. There just hasn't been enough time to inactivate one copy.
The trout genome contains 241 ancient microRNA genes and 233 of them still have two copies, one from each of the duplicated genomes. The authors suggest that this is significant and it indicates that multiple copies on these microRNA genes are needed. I'm not sure if this is true since these genes are quite a bit smaller than the average protein-coding gene so they will take longer to inactivate by mutation.
In any case, the big picture provides us with lots of data on the birth of new genes by duplication and death of genes by pseudogene formation.
Berthelot, C., Brunet, F., Chalopin, D., Juanchich, A., Bernard, M., Noël, B., Bento, P., Da Silva, C., Labadie, K., and Alberti, A. (2014) The rainbow trout genome provides novel insights into evolution after whole-genome duplication in vertebrates. Nature communications, 5:3657 April 22, 2014 [doi:10.1038/ncomms4657]
