Tag Archives: Natural Selection

New study: natural selection can act to impede speciation

Australian Walking Stick
Australian Walking Stick

My friend KL sent me this press release from the University of Colorado at Boulder.

It says:

An intriguing study involving walking stick insects led by the University of Sheffield in England and the University of Colorado Boulder shows how natural selection, the engine of evolution, can also impede the formation of new species.

The team studied a plant-eating stick insect species from California called Timema cristinae known for its cryptic camouflage that allows it to hide from hungry birds, said CU-Boulder Assistant Professor Samuel Flaxman. T. cristinae comes in several different types — one is green and blends in with the broad green leaves of a particular shrub species, while a second green variant sports a white, vertical stripe that helps disguise it on a different species of shrub with narrow, needle-like leaves.

While Darwinian natural selection has begun pushing the two green forms of walking sticks down separate paths that could lead to the formation of two new species, the team found that a third melanistic, or brown variation of T. cristinae appears to be thwarting the process, said Flaxman. The brown version is known to successfully camouflage itself among the stems of both shrub species inhabited by its green brethren, he said.

Using field investigations, laboratory genetics, modern genome sequencing and computer simulations, the team concluded the brown version of T. cristinae is shuttling enough genes between the green stick insects living on different shrubs to prevent strong divergent adaptation and speciation. The brown variant of the walking stick species also is favored by natural selection because it has a slight advantage in mate selection and a stronger resistance to fungal infections than its green counterparts.

“This is one of the best demonstrations we know of regarding the counteractive effects of natural selection on speciation,” said Flaxman of CU-Boulder’s Department of Ecology and Evolutionary Biology, second author on the new study. “We show how the brown population essentially carries genes back and forth between the green populations, acting as a genetic bridge that causes a slowdown in divergence.”

A paper on the subject appeared in a recent issue of the journal Current Biology. 

[…]“This movement of genes between environments slows down the genetic divergence of these stick insect populations, impeding the formation of new species,” said Aaron Comeault, a former CU-Boulder graduate student and lead study author who conducted the research while at the University of Sheffield.

So, in the past I had read that natural selection can act as a stabilizing force in nature – keeping the organism operating within a type. This study seems to be confirmation of that. But there are other problems with generating macro-evolutionary change.

Also related to the problem raised by the study is this problem of genetic drift, which also works against the preservation of beneficial mutations.

Evolution News explains the genetic drift problem:

Evolutionary biologists often assume that once mutations produce a functionally advantageous trait, it will easily spread (become “fixed”) throughout a population by natural selection. For example, imagine a population of brown-haired foxes that lives in a snowy region. One fox is born with a mutation that turns its fur coat white, rather than brown. This fox now has an advantage in hunting prey and escaping predators, because its white fur provides it with camouflage. The white fox survives, passing its genes on to its offspring, which are also adept at surviving and reproducing. Over time, the white-haired trait spreads throughout the population.

This is how it’s supposed to work — in theory. In the real world, however, merely generating a functionally advantageous trait does not guarantee it will persist, or become fixed. For example, what if by chance the white fox trips, breaks a leg, and gets eaten by a predator — never passing on its genes? Random forces or events can prevent a trait from spreading through a population, even if it provides an advantage. These random forces are lumped together under the name “genetic drift.” When biologists run the mathematics of natural selection, they find that unless a trait gives an extremely strong selective advantage, genetic drift will tend to overwhelm the force of selection and prevent adaptations from gaining a foothold in a population.

This underappreciated problem has been recognized by some evolutionary scientists who are skeptical of the ability of natural selection to drive the evolutionary process. One of those scientists is Michael Lynch, an evolutionary biologist at Indiana University, who writes that “random genetic drift can impose a strong barrier to the advancement of molecular refinements by adaptive processes.”2 He notes that the effect of drift is “encouraging the fixation of mildly deleterious mutations and discouraging the promotion of beneficial mutations.”3

I guess the point of this is that if someone wants to convince you that macro-evolution is possible through the mechanisms of random mutation and natural selection, then they have some work to do. And it’s more work than just asserting that it happened.

People who are technical may benefit from reading Michael Behe’s book “The Edge of Evolution”, which studies how likely it is to get several positive adaptations in a row within a reasonable period of time.

UPDATE: A biologist friend tells me that “whether natural selection is driving speciation or preventing it, in neither case is it explaining how these organisms came to be in the first place. It only explains how existing organisms interact with their environment. And this can be explained at least as well through intelligent design as through naturalistic processes.” She also says that natural selection can drive speciation, but still within a kind.

Can Darwinian evolution create new functional biological information?

Here’s a great article from Evolution News that explains the trouble that Darwinian evolution has in building up to functional new biological information by using a process of random mutation and natural selection.

Casey Luskin takes a look at a peer-reviewed paper that claims that Darwinian evolution can do the job of creating new information, then he explains what’s wrong with the paper.

Excerpt:

In Wilf and Ewens’s evolutionary scheme there is a smooth fitness function. Under this view, there is no epistasis, where one mutation can effectively interact with another to affect (whether positively or negatively) fitness. As a result, any mutations that move the search toward its “target” are assumed to provide an immediate and irrevocable advantage, and are thus highly likely to become fixed. Ewert et al. compare the model to playing Wheel of Fortune:

The evolutionary model that Wilf and Ewens have chosen is similar to the problem of guessing letters in a word or phrase, as on the television game show Wheel of Fortune. They specify a phrase 20,000 letters long, with each letter in the phrase corresponding to a gene locus that can be transformed from its initial “primitive” state to a more advanced state. Finding the correct letter for a particular position in the target phrase roughly corresponds to finding a beneficial mutation in the corresponding gene. During each round of mutation all positions in the phrase are subject to mutation, and the results are selected based on whether the individual positions match the final target phrase. Those that match are preserved for the next round. … After each round, all “advanced” alleles in the population are treated as fixed, and therefore preserved in the next round. Evolution to the fully “advanced” state is complete when all 20,000 positions match the target phrase.

The problem with this approach is that a string of biological information that has only some letters that are part of a useful sequence has no present function, and therefore cannot survive and reproduce.

Look:

Thus, Wilf and Ewens ignore the problem of non-functional intermediates. They assume that all intermediate stages will be functional, or lead to some functional advantage. But is this how all fitness functions look? Not necessarily. It’s well known that in many instances, no benefit is derived until multiple mutations are present all at once. In such a case, there’s no evolutionary advantage until multiple mutations are present. The “correct” mutations might occur in parallel, but the odds of this happening are extremely low. Ewert et al. illustrate this problem in the model by using the example of the difficulty of one phrase evolving into another:

Suppose it would be beneficial for the phrase

“all_the_world_is_a_stage___”

to evolve into the phrase

“methinks_it_is_like_a_weasel.”

What phrase do we get if we simply alternate letters from the two phrases?

“mlt_ihk__otli__siaesaaw_a_e_.”

Under the assumptions in the Wilf and Ewens model, the “fitness” of this nonsense phrase ought to be exactly half-way between the fitnesses of “all the world is a stage” and “methinks it is like a weasel.” Such a result only makes sense if we are measuring the fitness of the current phrase by its proximity to the target phrase.

But the gibberish of the intermediate phrase doesn’t cause any problem under Wilf and Ewens’s model. Not unlikeRichard Dawkins, they assume that intermediate stages will always yield some functional advantage. And as more and more characters in the phrase match the target, it becomes more and more fit. This yields a nice, smooth fitness function — rich in active information — not truly a blind search.

Not only is there that first problem, but here’s a second:

Wilf and Ewens endowed their mathematical model of evolution with foresight. It is directed toward a target — an advantage that natural selection conspicuously lacks. And what, in our experience, is the only known cause that is goal-directed and has foresight? It’s intelligence. This means that once again, the Evolutionary Informatics Lab has shown that simulations of evolution seem to work only because they’ve been intelligently designed.

This is worth the read. If Darwinian mechanisms really could generate code, then there would be no software engineers. The truth is, the mechanisms don’t work to create new information. For that, you need an intelligent designer.

Peer-reviewed paper in medical journal challenges Darwinian evolution

Casey Luskin explains over at Evolution News.

Summary: (links removed)

A new article by Dr. Joseph Kuhn of the Department of Surgery at Baylor University Medical Center, appearing in the peer-reviewed journal Baylor University Medical Center Proceedings, poses a number of challenges to both chemical and biological evolution. Titled “Dissecting Darwinism,” the paper begins by recounting some of the arguments raised during the Texas State Board of Education debate that challenged chemical and biological evolution. Those challenges include:

1. Limitations of the chemical origin of life data to explain the origin of DNA
2. Limitations of mutation and natural selection theories to address the irreducible complexity of the cell
3. Limitations of transitional species data to account for the multitude of changes involved in the transition.

(Joseph A. Kuhn, “Dissecting Darwinism,” Baylor University Medical Center Proceedings, Vol. 25(1): 41-47 (2012).)

It’s a good little introduction to where the action is on the origins debate but regular readers will have read it all before.

But there was one thing I found interesting.

The naturalistic response to this paper:  (links removed)

The journal also published a rebuttal to Dr. Kuhn by Charles Stewart Roberts, a cardiovascular surgeon in Virginia. Dr. Roberts’s rebuttal simply asserted, as if it were a truth that required no scientific backing, that all biological features could be produced by evolution:

The notion of “irreducible complexity” in a cell, as an argument against evolution, is beyond my present understanding. Knowing that life has existed on planet earth for billions of years, however, I suspect that there has been time enough for evolution, no matter how complex, with reducibility.

I was having a debate with an atheist on Facebook and this guy did nothing but duck and dodge by citations of peer-reviewed evidence, like the paper from December 2011 on the oxygen in the early Earth’s atmosphere, which destroys naturalistic origin of life scenarios. My favorite of his speculations was when he responded to the Big Bang cosmology by saying “one can easily envision a scenario in which the universe has existed eternally”. Or something like that. Atheists – always easily envisioning things that are falsified by the available experimental evidence.

Casey comments on Roberts’ “rebuttal”: (links removed)

We’ve addressed this sort of unsophisticated and poorly articulated argument in defense of defending Darwinian evolution many times. You can’t just vaguely appeal to vast and unending amounts of time (and other probabilistic resources) and assume that Darwinian evolution can produce anything “no matter how complex.” Rather, you have to demonstrate that sufficient probabilistic resources exist to produce the feature.

Rather than making assumptions, proponents of intelligent design ask what the Darwinian mechanism can, or cannot, do. For example, a 2010 peer-reviewed research paper by pro-ID scientist Doug Axe modeled a population of evolving bacteria, and found that there are severe limits on the ability of Darwinian evolution to produce multi-mutation features. (A multi-mutation feature is one that requires multiple mutations to be present before there is any advantage given to the organism.)

Axe’s research makes assumptions very generously favoring Darwinian evolution. He assumed the existence of a huge population of asexually reproducing bacteria that could replicate quickly — perhaps nearly 3 times per day — over the course of billions of years. But he found that complex adaptations requiring more than six neutral mutations would exhaust the probabilistic resources available over the entire history of the earth.

[…]Axe’s work suggests that we cannot assume, as Roberts does, that sufficient probabilistic resources exist to produce all the features we see in life, “no matter how complex.” Indeed, follow-up research by Axe and Ann Gauger suggests that many features might require more mutations before conferring an advantage than could arise in the history of the earth. Their 2011 study attempted to convert one protein into another, closely related protein — the kind of transformation that evolutionists claim happened easily in the history of life. Through mutational analysis, they found that a minimum of seven independent mutations — and probably many more — would be necessary to convert the protein and its function into that of its allegedly close relative.

Evolutionary theory certainly can explain some things. It works up to a point. But there is only so much time available, so much material to react, and so many reactions per second. Hand-waving is not going to prove the neo-Darwinian hypothesis. It’s going to take published experimental results. Like the results of Doug Axe and Ann Gauger.

Oh by the way, there’s another peer-reviewed article confirming the inability of naturalistic mechanisms to create first life discussed on Evolution News. (David L. Abel, “Is Life Unique?,” Life, Vol. 2:106-134 (2012)). I can’t blog on all of them!

Prominent atheist philosopher gives mixed review of intelligent design

Consider this report on a peer-reviewed assessment of intelligent design by the prominent atheist philosopher Thomas Nagel.

Excerpt:

Prof. Thomas Nagel, a self-declared atheist who earned his PhD. in philosophy at Harvard 45 years ago, who has been a professor at U.C. Berkeley, Princeton, and the last 28 years at New York University, and who has published ten books and more than 60 articles, has published an important essay, “Public Education and Intelligent Design,” in the Wiley InterScience Journal Philosophy & Public Affairs, Vol. 36, issue 2…

[…]Prof. Nagel’s paper is a significant and substantial opening, at America’s highest intellectual level, that encourages all intelligent, educated, informed individuals — particularly those whose interest in this issue derives from intellectual curiosity, not the emotional advocacy excitement for any side — that it is legitimate as a matter of data, science, and logic, divorced from all religious texts and doctrines, to consider that intelligent design may be a valid scientific approach to understanding how DNA and the complex chemical systems of life came to attain their present form. Prof. Nagel’s article is well worth the price to put it in the library of any inquiring mind.

The actual paper is here.

Now for the summary of the paper, with supporting quotes:

Professor Nagel has read ID-supportive works such as Dr. Behe’s Edge of Evolution (p. 192). He reports that based on his examination of their work, ID “does not seem to depend on massive distortions of the evidence and hopeless incoherencies in its interpretation” (pp. 196-197). He reports that ID does not depend on any assumption that ID is “immune to empirical evidence” in the way that believers in biblical literalism believe the bible is immune to disproof by evidence (p. 197). Thus, he says “ID is very different from creation science” (p. 196).

Prof. Nagel tells us that he “has for a long time been skeptical of the claims of traditional evolutionary theory to be the whole story about the history of life” (p. 202). He reports that it is “difficult to find in the accessible literature the grounds” for these claims.

Moreover, he goes farther. He reports that the “presently available evidence” comes “nothing close” to establishing “the sufficiency of standard evolutionary mechanisms to account for the entire evolution of life” (p. 199).

He notes that his judgment is supported by two prominent scientists (Marc Kirschner and John Gerhart, writing in the Oct. 2005 book Plausibility of Life), who also recognized that (prior to offering their own theory, at least) the “available evidence” did not “decisively settle[]” whether mutations in DNA “are entirely due to chance” (p. 191). And he cites one Stuart Kauffman, a “complexity theorist who defends a naturalistic theory of emergence,” that random mutation “is not sufficient” to explain DNA (p. 192).

Prof. Nagel acknowledges that “evolutionary biologists” regularly say that they are “confiden[t]” that “random mutations in DNA” are sufficient to account for “the complex chemical systems we observe” in living things (p. 199) — but he disagrees. “Rhetoric” is the word Professor Nagel uses to rejects these statements of credentialed evolutionary biologists. He judges that the evidence is NOT sufficient to rule out ID (p. 199).

He does not, however, say that the evidence compels acceptance of ID; instead, some may consider as an alternative to ID that an “as-yet undiscovered, purely naturalistic theory” will supply the deficiency, rather than some form of intelligence (p. 203).

In light of these considerations, Prof. Nagel says that “some part of the high school curriculum” “should” include “a frank discussion of the relation of evolutionary theory to religion” but that this need not occur in biology classes if the biology teachers would find this too much of a “burden” (p. 204). Significantly, Prof. Nagel — who is a professor of law as well as a professor of philosophy — concludes that, so long as the proposal is not introduced by religiously-motivated persons “as a fallback from something stronger,” but by persons “more neutral” or “without noticeable religious beliefs,” it would be constitutional to “mention” ID in public school science classes, because doing so genuinely furthers “the secular purpose of providing a better understanding of evolutionary theory and of the evidence for and against it” (p. 203). He makes clear that the “mention” must be a “noncommittal discussion of some of the issues” (p. 205).

So Nagel does NOT think that ID is a slam dunk, just that it is worth considering in science classrooms. Teach the controversy, that’s always the right approach. Be open-minded. Look at the evidence before you decide.

New study finds that advantageous traits don’t easily infuse in populations

A new study in Nature (September 30,2010) has found something interesting. (H/T WgButler777)

Excerpt:

Our work provides a new perspective on the genetic basis of adaptation. Despite decades of sustained selection in relatively small, sexually reproducing laboratory populations, selection did not lead to the fixation of newly arising unconditionally advantageous alleles. This is notable because in wild populations we expect the strength of natural selection to be less intense and the environment unlikely to remain constant for ~600 generations.”

Consequently, the probability of fixation in wild populations should be even lower than its likelihood in these experiments. This suggests that selection does not readily expunge genetic variation in sexual populations, a finding which in turn should motivate efforts to discover why this is seemingly the case.”

What does it mean?

It means that good traits that evolve in a single individual do not necessarily “take” in the entire population, so that will live on in successive generations. If the accumulation of beneficial mutations is required for Darwinism to create all of these new body plans and organ types, then what are we to make of the creative power of Darwinian mechanisms?

Read more about it here at Uncommon Descent.