Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
by Grania
It is a truth universally acknowledged that socks bought in pairs will be reduced to a motley collection of singletons once you introduce them to your home.
A few days ago, Jerry posted one Missing Sock Hypothesis, that of the Eater Of Socks Monster from Terry Pratchett’s Hogfather. Now the ever wonderful Matthew Inman from The Oatmeal has a new one. Click through on the picture to see the original.
It’s a great tragedy. Who knew that it was all so heart-rending?
Sophisticated Theologians™ tell us all the time that only Biblical literalists or fundamentalists believe the stories in the Bible. God is, they say, much more “nuanced,” and most believers are closer to Kierkegaard than to Ken Ham.
Well, I call bullshit on that. Look at a new Pew Poll giving “Five Facts about Christmas in America.” Most of the survey is about whether we see Christmas as a cultural or religious holiday, our views on gift-giving, how we wish people happy holidays, and so on, but there’s one bit of interest to readers. That’s encompassed in this figure:
Got that, David Bentley Hart and Karen Armstrong? Got that, Terry Eagleton? Got it, all you atheist atheist-bashers who say we’re attacking a straw man? 65% of US adults believe all four of these Christmas myths. No, not all Americans are Biblical literalists about everything, but nearly all Americans are literalists about something. Just remember, nearly 3 in four Americans believe that Jesus was born of a virgin. This poll was published today, so it reflects current beliefs.
h/t: Alan G.
This short video, about evolution in real time, is the best yet in the sequence of the “Twelve Days of Evolution” videos, produced by PBS and “It’s Okay to be Smart. ” I’ll be presenting, reviewing, and annotating these over the holidays:
The creationist canard dispelled here is the idea that if we can’t see evolution in real time, it doesn’t happen. (Never mind that the fossil record gives us tons of evidence for the process.) The example it gives is a nice one: the work of Marlene Zuk and her colleagues (she occasionally comments here) on the loss of sound-producing structures in crickets. You can read about it in detail at this site, but the upshot is that the invasion of a cricket-parasitizing fly in two Hawaiian Islands imposed strong selection on the resident crickets to lose their song, for the fly uses that song to detect its prey. Not only was evolution extremely fast in this case, but it involved only a single mutation on the X chromosome, one that ablated the stridulation combs of males. Soundless males survived, for the survival advantage more than outweighed their loss of ability to attract females through singing.
The example is not just evidence for evolution, but evolution via natural selection. Remember that there are other causes for evolution besides natural selection, most notably genetic drift.
But of course we’ve had examples of natural selection in real time for ages. John Endler’s book Natural Selection in the Wild gives several hundred, all from nature, and we’ve known about microbes evolving resistance to antibiotics for decades. Ditto for plants evolving resistance to herbicides, insects to insecticides, and plants to heavy metals brought to the surface by mining.
And most of you have heard of Peter and Rosemary Grant’s work on selection in the medium ground finch (Geospiza fortis), one of the best-documented examples of natural selection in vertebrates. A drought killed off small plants on the Galápagos island of Daphne Major, enabling only those individuals with larger beaks, who could crack the remaining big seeds, to survive. The population’s beak size increased by 10% in one generation, and the genetic and ecological basis of the trait change is well understood.
Section 5 of Douglas Theobald’s magnificent evidence-for-evolution website, 29+ Evidences for Macroevolution, gives other examples, though I can’t seem to access it now.
Well if this don’t beat all! My kishkes are in knots, for my own alma mater, Harvard University, has now joined the anti-free-speech squad. As the Guardian reports, its transgression took the form of a placemat given to the students by the university’s Office for Equity, Diversity, and Inclusion, with the collusion of the freshman dean’s office.
First have a look at the placemat, which is designed to tell students how to talk to their families and friends over holiday break about four pressing social issues. You might not be able to read it, but if you click twice in succession (with a pause between the clicks), you’ll be able to see what it says—unless you’re terribly myopic. The Guardian‘s summary (indented) is below the photo:
One section dealt with student activism and the recent trend of students challenging campus racism. “Why are black students complaining? Shouldn’t they be happy to be in college?”, one question asked. The suggested response stated that the students were not complaining and that “if non-black students get the privilege of that safe environment, I believe that same privilege should be given to all students”.
[JAC: The first section is also very poorly written and ungrammatical.]
A second section addressed the ongoing controversy over allowing Syrian refugees into the US, which family members could argue, Harvard suggested, was unsafe because the refugees might have ties to terrorists. The response provided said that “the US has been accepting refugees from the war-torn areas around the world for decades”. It specifically referenced the wars in Central America and said that despite accepting refugees then, they had “very strict vetting and not one incident of violence”. The section also misspelled Islamophobia.
The outgoing title of “house master” was addressed in the next section. The mat explained that the University had stopped using the phrase because the term master “is reminiscent of slave masters and the legacy of slavery”.
In the final section, the mats dealt with questions about the police killings of African Americans, and asked: “Why didn’t they just listen to the officer? If they had just obeyed the law this wouldn’t have happened”.
The response provided led in with a question: “Do you think the response would be the same if it was a white person being pulled over?” It said that the victims were “not breaking the law and are unarmed”. It then referenced Tamir Rice, the 12-year old boy who was shot to death in November 2014 by police officers two seconds after they arrived on the scene.
Now in general I agree with most of these sentiments, but that’s not the point. The point is that the Harvard administration is in effect telling the students what to think and say. And that’s inimical to the purpose of a good university, which is to expose students to a diversity of viewpoints, give them the tools to think, and then let them decide for themselves. It’s certainly not to propagandize the students with a set of politically acceptable and liberal viewpoints.
It’s telling, in fact, that the Harvard Undergraduate Council, a group of students still in school, distributed a statement excoriating the University for distributing these placemats:
And, on the same day, the administration—through two deans—apologized, though they qualified their apology by saying how laudable their goals were.
It’s a sad situation when the students are more savvy about free speech than the deans of their college. I’m heartened by the response of the students, but depressed by the administration. It’s time for Harvard to adopt the University of Chicago’s exemplary free speech policy.
h/t: Steve
Just a reminder: I’ll be accepting Christmas-themed photos of readers’ cats until Christmas Eve; they’ll be posted the next day. Rules: one photo per customer, must have a holiday theme, and the cat must be yours. Cats don’t have to be living; we do post pictures of cats from Christmases past. A few lines about your moggie (including its name) would be appreciated, but don’t be too verbose.
One thing I’ve learned from the nine pictures already submitted is that cats like to climb on Christmas trees. I should have realized it: they not only like to climb, but the trees are festooned with dangly and shiny things that are perfect for batting.
Posting will be lighter until the New Year as Professor Ceiling Cat (Emeritus) wants to have a break.
There are two species of “face mites,” Demodex, that live on humans. One, D. folliculorum, lives mostly on the hair follicles, and mostly on the face. It’s small (0.1-0.4 mm), has a transparent body with four pair of anterior legs (remember, mites are arachnids), and nearly all of us harbor them. They’re harmless, although in large numbers they can cause a form of mange. Here’s D. folliculorum; remember, they’re all over you!!! (Read Ed Yong’s popular piece about them here.)
The other species. D. brevis, lives in the sebaceous glands at the base of the hairs, so its niche is slightly different. Because those are buried in our pores, they’re less likely to be transmitted between people than are individuals of D. folliculorum.
Before we get to the new paper on D. folliculorum, I was interested in seeing if the two hair-inhabiting species on our bodies are sister species: each other’s closest relatives. That would imply that, since these species are limited to humans, they speciated on our bodies, i.e., a form of sympatric speciation (speciation in the same small area without the need for geographic barriers, so that species form while they’re still exchanging genes). Now it’s possible that they are sister species but still speciated allopatrically (in geographic isolation), with a common ancestor evolving into D. folliculorum in one part of the world, into D brevis in another part, and then later came to cohabit single humans when these isolated human populations came back together and swapped mite species.
But that’s not the way it happened. Our hair mites are not sister species, as the phylogeny below. The closest relatives of D. folliculorum are two species in the genus that inhabit white-tailed deer (WTD) and mice (D. musculi) respectively. A less-related species inhabits dogs, and D. brevis is even less closely related:
These two species, then, did not separate on the human body, but are the result of two separate invasions of distinct species from other animals. This is a common finding for parasites—relatd species on one host are almost never sister species—supporting the idea that speciation in parasites usually requires some kind of geographic separation (i.e., speciation on other hosts, which in effect are isolated “islands”.) See chapter 4 of Speciation, by Coyne and Orr, for more detailed discussion of this issue.
But that’s my own take; now on to a new paper on D. follicularum, published by Michael Palopoli and colleagues in the Proceedings of the National Academy 0f Sciences (USA). Reference is at bottom; download is free.
Since the “parasite” (it could be seen as a commensal since it rarely harms us) is an obligate resident on human bodies, Palopoli et al. wanted to see how its evolution mirrored that of its human hosts. So they sampled D. folliculorum from 70 humans distributed over the globe (except in North America), and looked at the evolutionary relationship between the mites by sequencing a segment of their mitochondrial DNA. Here’s how they cluster based on geographic origin and evolutionary relationship; the colors of the segments show where the hosts are from (key at top), and their evolutionary relationships are in the “tree graph” inside the circle:
What does this show? First, that there are four “clades” or evolutionarily-related groups, labeled A-D in the diagram. Second, these clades in general cluster according to geographic origin (As and Bs, for instance, come from Africa and Asia respectively, Cs are mostly African, and Ds are largely of European origin); but note that there is variation within each geographic area, as displayed in the map below:
This shows that, in general, these mites have evolved in geographic isolation from each other, as expected if they had a fairly ancient origin and co-evolved with humans as they migrated over the globe.
It also shows that the mites probably jumped onto humans in Africa, for that is where they are most genetically diverse, and thus probably older. As humans moved out over the planet from Africa, the genetic variation drops. That makes sense because only a limited number of people left Africa about 60,000 years ago; ergo a limited sample of their hair mites went with them.
There’s one exception to this, though: Latin Americans have a genetically diverse sample of mites—nearly as diverse as Africans. But that makes sense if you think about it, for Latin America harbors a human mixture of diverse origin: Europeans, Africans (most brought as slaves), and Native Americans. If they had sampled the U.S., I suspect they’d also find a diverse mixture, though not as diverse as Latin America (we have fewer Native Americans).
There are a few other results of interest. Mites are stable on individual humans for a long time, as found by sampling the mites on single people over several years. That makes sense too, since they reproduce on our bodies. Also, when an individual moves between continents, say someone born in Africa who moves to the US, the ancestral mite genotypes remain stable: such individuals harbor mites having DNA that’s found only in Africa. (An alternative hypothesis is that different human ethnic groups impose different selection pressures on their hair mites, so the close and persistent match between mite and human genotypes could reflects natural selection as well as evolutionary history.)
The notion that there’s not much movement between individuals, though, is supported by looking at mite DNA from human families. The authors found that mite genotypes were often shared between members of families, but rarely between ethnically similar individuals from different families. That also makes sense because humans in the same family have a lot more skin-to-skin or hair-to-skin contact than do humans of different families.
How old is the divergence between genetically different D. folliculorum mites? Using a “molecular clock” (i.e., the amount of DNA divergence coupled with the shaky assumption that, in these mites, DNA diverges at about the same linear rate it does in other arthropods), the authors calculate that the major mite clades diverged between 3 and 4 million years ago. That is, the mite groups above come from a common ancestor about as old as the genus Homo itself—or older. And that, in turn, implies that these little guys have been with us since we were small, hairy apelike denizens of the savanna. But even if the clock isn’t calibrated correctly, they’re still old, antedating our movement out of Africa.
After reading the paper and writing all this, I’m strongly tempted to go to the lab, pull out a few eyelashes, and examine them under the microscope. Like many biologists, I’m not squeamish about what I’ll find. After all, I did harbor a 1.5 inch botfly maggot in my head for almost two months!
___________________
Palopoli, M. F., D. J. Fergus, S. Minot, D. T. Pei, W. B. Simison, I. Fernandez-Silva, M. S. Thoemmes, R. R. Dunn, and M. Trautwein. 2015. Global divergence of the human follicle mite Demodex folliculorum: Persistent associations between host ancestry and mite lineages. Proceedings of the National Academy of Sciences (USA). Dec. 14, 2015, online; doi: 10.1073/pnas.1512609112
Be sure to send in your good wildlife photos for possible posting here. The level in the tank is okay, but its drop has made me a bit nervous.
Today we have some photographs taken by reader Damon Williford and sent to me on November 23. His notes:
Attached are some photos that I took this weekend. The first batch are from Estero Llano Grande State Park in the Lower Rio Grande Valley of Texas. Two are tyrant flycatchers, Tropical Kingbird (Tyrannus melanocholicus), and a Vermilion Flycatcher (Pyrocephalus rubinus, male). The other photos are a sleepy Yellow-crowned Night-heron (Nyctanassa violacea), Long-billed Thrasher (Toxostoma longirostre), and spiny softshell turtle (Apalone spinifera),
These photos are from the Santa Ana National Wildlife Refuge on the Texas-Mexico border, including a roseate skimmer (Orthemis ferruginea), rosebelly lizard (Sceloporus variabilis), and Texas indigo snakes (Drymarchon melanurus erebenus). I saw more indigo snakes on that refuge last Sunday than I have seen any where else. I found a total of 4. The head shot was of a small individual (2-3 ft). The second photo is the last indigo snake I came across that day and looked like it was 4-5 feet long. These snakes come across as very camera shy.
Welcome to the first day of Winter 2016! But it’s starting off warm this week (today’s temperatures at top, and predicted high and low temperatures for each day of the week given in Fahrenheit below); so there’s no chance of a white Christmas here. Global warming is already showing its insidious effects, and it’s gonna get worse.
On this day in 1968, Apollo 8 was launched from the Kennedy Space Center, leading to men walking on the moon for the first time in the following summer. I watched the moonwalk live, and I’ll never forget it: we won’t see that again in our lifetime! On this day in 1866, Maud Gonne was born (Yeats lovers will know who she is), and in 1937 Jane Fonda was born. On December 21, 1940, F. Scott Fitzgerald died of a heart attack at only 44; he is one of my favorite writers and prose stylists—though he couldn’t spell worth a damn—and if you can get hold of his collected letters to his daughter Scottie, do read it (I see that it’s rare and a bit pricey on Amazon). You can see one letter here. Meanwhile in Dobrzyn, Hili is looking extremely cute, and she knows it!:
Hili: Life is an extreme sport!
A: Why?
Hili: You never know whether you are going to look good in the photo.
Hili: Życie to sport ekstremalny!
Ja: Dlaczego?
Hili: Nigdy nie wiadomo, czy zdjęcie dobrze wyjdzie.
And in Wroclawek, Leon’s had his fill of walking, but he needs his fill of noms:
Leon: Let’s go home now. I will check whether my bowl is getting filled.
