Most of the "comments" I get on older posts are commercial spam, which I delete. But if you're interested in a creationist comment on Dave Wisker's guest post on peacocks, here it is. It seemed to be original rather than cut-and-paste, so I approved it, but did add some comments of my own.
I once heard PZ reply to this popular creationist question by pointing out that, although many Minnesotans are descended from Norwegians, there are still Norwegians. This isn't really a good analogy, however, because Minnesotans and Norwegians aren't separate species. We know this because they can interbreed, producing healthy children. At the end of this post I suggest a better answer, indirectly inspired by this week's paper.
Two of evolutionary biology's central questions are: how do species change over generations? and how does one species split into two? We have many detailed examples of small evolutionary changes occurring over days (in bacteria) or years (in animals and plants), so one would have to be very close-minded to deny major evolutionary change over millions of years. But major evolutionary change is not enough, by itself, to split one species into two. One subpopulation within a species must change, while the rest of the species either stays the same or changes in different ways. This divergence cannot happen if the two subpopulations continue to interbreed at high rates. In other words, speciation requires some reproductive isolation.
Often, reproductive isolation is a byproduct of geography. After a few individuals (or a pregnant female) cross a mountain range or are blown from the mainland to an island, they no longer interbreed with their ancestral population. Over many generations, random genetic drift or nonrandom natural selection can change the isolated population enough that they can no longer produce healthy offspring with the original population, even if they come back into contact.
Sometimes speciation can occur without a major geographic barrier, but reproductive isolation is still required. This week's paper shows that this has happened and is still happening in Europe.
"A continuum of genetic divergence from sympatric host races to species in the pea aphid complex", by Jean Peccoud and others, was just published online in the Proceedings of the National Academy of Science.
Photo by Jean Peccoud
Continue reading ""If evolution is true, why are there still chimps?"" »
“But if you believe that primates and guinea pigs [both of which have mutated, nonfunctional versions of a gene for making vitamin-C] were specially created, these facts don’t make sense. Why would a creator put a pathway for making vitamin C in all these species and then inactivate it? Wouldn’t it be easier simply to omit the pathway from the beginning? Why would the same inactivating mutation be present in all primates, and a different one in guinea pigs? Why would the sequences of the dead gene exactly mirror the pattern of resemblance predicted from the known ancestry of these species? And why do humans have thousands of pseudogenes [DNA sequences very similar to genes that are functional in other species, but with mutations that make them inactive] in the first place?” – Jerry Coyne, Why Evolution is True
I have been reading and enjoying “Why evolution is true”, by Jerry Coyne. Here are some thoughts on what I’ve read so far.
Continue reading "Facts and theory in Coyne’s “Why evolution is true”" »
Until I finish my book, Darwinian Agriculture, I am cutting back detailed posts to once or twice a month, but here are some links to papers that looked interesting this week.
Sustaining biodiversity in ancient tropical countryside
"arecanut palm (Areca catechu) production systems retain 90% of the bird species associated with regional native forest"
Selfish Genetic Elements Promote Polyandry in a Fly
[This "selfish gene" on the X chromosome refuses to share sperm with a Y chromosome. Female fruitflies mate with more males when more of them have this gene.]
Frequency-dependent selection maintains clonal diversity in an asexual organism
Finally, someone left a comment on an earlier post that used an out-of-context quote to claim evolutionary biologists are hiding from the fossil record. The truth is that fossils are less important to evolutionary biology today only because their contribution is diluted by new sources of information, especially comparisons of DNA sequences among species. But fossils are still a valued source of information. Here are two papers on fossils published this week in major journals. (How many papers did the "intelligent design" folks publish in major journals this week? This year? None?)
Variation in Evolutionary Patterns Across the Geographic Range of a Fossil Bivalve
This week's post is by Dave Wisker, a graduate student in Molecular Ecology at the University of Central Missouri.
It's the creationist's dream. If actual evidence of creation is too much to hope for, how about a peer-reviewed paper in a respected journal overturning one of the icons supporting a major element of Darwin's theory?. Sexual selection in peafowl is definitely one of those icons. There appeared to be ample empirical evidence that peahen's preference for more elaborate trains on their mates has led to the spectacular male tail displays we see today. A series of papers in the 1990's by behavioral ecologist Marion Petrie and others seemed to solidly support this, and there is also evidence that elaborate tails may indicate good genes (Petrie et al, 1991; Petrie and Williams, 1993;.Loyau et al, 2005a). This, in itself, is a challenge to an older idea that the peacock's tail shows how arbitrary female preferences can be amplified to extremes by a "runaway"? process (Fisher, 1958). But, whatever their evolutionary origin, the preference itself has rarely been questioned.
However, a recent paper published in Animal Behaviour (http://tinyurl.com/4t69v5), "Peahens do not prefer males with more elaborate trains"?, challenges the conventional wisdom.
I liked this essay comparing areas in evolutionary biology where there is genuine controversy -- i.e., where people who are actually collecting data and publishing on a topic disagree -- vs. the phony controversies imagined by creationists. Group selection may still almost qualify as a controversy, a question I may address in a later post, but age of the earth, common ancestry of all species (at least those studied so far!), and the power of natural selection to solve difficult problems are not at all controversial among those actively publishing on related topics.
The question of how much exposure high school students should have to genuine scientific controversies seems a bit more complex to me. I agree that helping students get enough of the basics to understand active controversies in any depth is a big challenge. On the other hand, I've been amazed how many high school students (and their parents) think that the only definition of "research" is looking up information in a library or on the web. If we want students to understand that scientific research is an exciting, ongoing activity, some kind of exposure to areas where scientists disagree seems essential. Areas of research that are easier to understand, like the mindless screening of drugs, don't convey the intellectual excitement of real science.
Here's a seminar class I've thought about for either high school seniors or first-year college students. First, let's set the minimum standard for a scientific controversy as: at least two conflicting points of view, each represented by data-containing papers from at least two nonoverlapping groups, in journals with an impact factor of at least 1.0. Each week we consider one question, such as:
1) What causes AIDS?
2) What is killing amphibians around the world?
3) How old is the earth (within 10%, say)?
4) What living species is the closest relative of chimpanzees?
Students get points for showing that each topic was controversial, at least at one time, with a big bonus for whoever shows controversy most recently. Then we could make a time-line, showing when each question was settled (pending new data, of course!).
Each generation tends to resemble the previous one, so evolution of whales from land animals, for example, took many generations. One limitation on the power of natural selection is that each generation must be viable. Some creationist suggested that the problem is analogous to "evolving" a sentence one letter at a time to make a substantially different sentence, while requiring that each intermediate step be a valid sentence. The Mosquito Eater has solved this challenge. Cool!
But we no longer need to rely on imperfect analogies to biological evolution. Molecular tools now make it possible to explore multistep evolution experimentally, as I discussed in an early post.
That's the title of an essay by my colleague Scott Lanyon. He notes that "development" refers to changes within an individual, whereas changes in the genetic composition of a population are known as "evolution." Apparently some public officials were afraid to say that a fish population could "evolve" resistance to a newly arrived pathogen, so they say they hope resistance will "develop." This is confusing, because individual susceptibility to pathogens can develop, increasing or decreasing with age, but that's not what they were talking about.
I used to run into a similar problem when I worked in an agronomy department. Some of the people I interacted with would say that an herbicide had "broken down", when actually the weed species it once killed had evolved resistance to it. The change was in the weeds, not in the pesticide. This misuse of the English language is particularly harmful because herbicides do break down (chemically degrade), which is usually a good thing; we don't want them polluting lakes, for example.
Populations evolve, but don't worry, fish and weeds didn't evolve from apes.
Reminder: generic comments on evolution not tied to a particular post, unsupported assertions, tirades, philosophical or religious discussions, etc. are welcome in the comments section of the Troll Refuge but not elsewhere. Repeat offenders will be banned. If anyone feels like arguing with a creationist, who claims that evolution can't create new KINDS -- is this an acronym, or is he just shouting? -- I just moved his comments there, along with my response.
Also in the Troll Refuge, Hermione Granger, founder of Save the Trolls, weighs in on the faith vs. skepticism debate.
There are hundreds of papers published each month whose authors find evolution useful in explaining their results. One would think that, if "intelligent design" has any scientific merit, there would be a significant number of papers each month presenting evidence of supernatural intervention by an intelligent designer. Surely the many religious scientists, in particular, wouldn't fail to publish results that turn out to support intelligent design, even if that wasn't the original focus of their research.
However, I haven't seen even one paper on intelligent design so far this year that meets the basic scientific criteria in my first post. Maybe I've missed some? Let's check the Discovery Institute web site.
This week’s paper, "Emergence of novel color vision in mice engineered to express human cone pigment", by Gerald Jacobs and colleagues at UC Santa Barbara and Johns Hopkins Medical School (Science 315:1723), is yet another experimental study that increases our understanding of how repeated cycles of natural selection, each producing a fairly small change, can lead to adaptations that may seem irreducibly complex.
Most humans have three different photopigment color sensors, as do our closest relatives. Many other mammals, including mice, have only two. Three-color vision is useful for many purposes, from identifying higher-protein leaves to eat (Nature 410:363) to telling which wire to cut to disarm the nuclear bomb buried under the stadium. But eventual usefulness isn’t enough for a trait to evolve. If a series of steps is required, each step must be beneficial, or at least not lethal. Such a series of steps has been worked out for the evolution of optically sophisticated eyes from light-sensitive spots (Proc. Roy. Soc. B 256:53), but what about color vision?
Continue reading "Evolution of color vision: transgenic mice see red" »
I reserve my blog-given right to delete off-topic comments -- except in this Troll Refuge. "Comments" whose only purpose is to link to a commercial or crackpot site will generally be deleted everywhere. This is a free service to people who may not realize they are crackpots.
Comments immune from deletion outside the Troll Refuge are either:
1) comments on the particular paper-of-the-week, or
2) suggestions for papers to discuss that meet the criteria in my first post.
"But", you may say, "I've got this great proof that evolution is all wrong! This scientist said something that could be interpreted as inconsistent with some aspect of evolutionary theory! That proves that both versions of the creation story in Genesis (cattle and trees created before and after humans) are literally true, doesn't it?"
If the scientist said it in a peer-reviewed paper published in the last month and containing new data, you can suggest it as a paper of the week. Otherwise, post your proof here in the Troll Refuge.
The comments section for this entry is also the place to whine about censorship, or to complain about my failure to delete someone else's comment that you think is off-topic. Off-topic comments attached to other entries are subject to deletion, or, if particularly amusing, transfer to this troll refuge, possibly with appropriate editing. Trolls repeatedly posting outside the refuge will be banished.
Troll hunters are welcome in the refuge, too. This may seem cruel, but we need to keep the population below carrying capacity. However, no firearms will be allowed, only sticks and stones. And words, of course.
A reader asked an interesting question about the difficulty of coordinated evolution of groups of genes. Although I welcome comments and questions, I won't usually have time for detailed responses. and I'd already discussed one paper this week. But then Huxley brought in a recent issue of Nature he'd been chewing on, and there it was: "Empirical fitness landscapes reveal accessible evolutionary paths" (Nature 445: 383-386). So I guess I should take this dog-given opportunity to talk about the evolution of multiple interacting genes. The Nature paper is a review article with no original data, so isn't eligible for my regular weekly paper discussion, but maybe it's OK as a bonus paper, especially since the most interesting papers it discusses were published within the last year and they do contain original data.
The exciting thing about these papers is that people are starting to use molecular methods in experiments that solve "you can't get there from here" problems in evolutionary biology.
Continue reading "Experiments with "fitness landscapes" explain evolution of interacting genes" »
In general, I don't want to waste time responding to tired old creationist criticisms of evolutionary theory that have already been refuted elsewhere (such as here or here) -- criticisms backed by new data would be another story -- but I do need to address one issue that could undermine my ability to find a paper to discuss each week. Some creationists have suggested that scientists are increasingly rejecting evolution. Actually they've been saying this for a long time. Is my paper pipeline drying up?