Recently in Evolution Category

Agrilus planipennis Fairmaire

Emerald ash borer traces, by Richard Meiss.

Photography contest, Finalist.


Larval feeding galleries of Agrilus planipennis Fairmaire – emerald ash borer. They are an invasive species in the American Upper Midwest (arriving here from Asia some fifteen years ago) that poses a serious threat to the native population of ash trees (genus Fraxinus). Some of their opportunistic enemies (e.g., woodpeckers and squirrels) inflict their own damage on the trees as they search for the larvae. Their spread is aided by human transport of infected wood, especially as firewood.

Partial eclipse of the sun


Partial eclipse of the sun by Marilyn Susek.

Photography Contest, Finalist.

Susek.Parcial_Solar_Eclips_March_3rd_2015 (600x450).jpg

Partial eclipse of the Sun, Ravenfield, Rotherham, S. Yorks., UK.

New hominin species discovered


And Science has just posted an interesting piece by Ann Gibbons, describing how the principal investigator, paleoanthropologist Lee Berger, advertised first for “tiny and small, specialised cavers and spelunkers with excellent archaeological, palaeontological and excavation skills” and later for “early career scientists” to come to Johannesburg and study the fossils. Gibbons reports that there was a certain amount of grumbling over Berger’s approach. The approach, however, apparently paid off: Gibbons and his team have discovered a new hominin, Homo naledi.


The fossils have not yet been dated, but Science reports that they display a round skull but a small brain, a wrist that suggests toolmaking, fingers that suggest tree climbing, and a foot that suggests upright walking. The Times article here quotes Ian Tattersall of the American Museum of Natural History to the effect that it is certainly a new species, but possibly not of the genus Homo. You may find a technical article here in the open-access journal eLIFE.

Berger’s team, which seems to number about 50, will now set about dating the fossils and trying to extract DNA. To these ends, Gibbons reports that Berger will attempt to recruit yet more young scientists.

Not to be outdone, Ken Ham of Answers in Genesis reports that his colleague Elizabeth Mitchell is working on an article on Berger’s discovery. Ham adds,

But we can say with confidence that this discovery changes nothing about our understanding of human history.

Truer words were never spoken.

The September issue of Natural History magazine is devoted almost entirely to essays concerning Alfred Russel Wallace. I usually turn the pages of NH, look at the pictures, and read many of the captions – but I read this issue almost in its entirety (and therefore cannot resist writing about it). Unfortunately, it looks as though none of the articles is available on the Web, but you can get your own copy for $3.95 (US), presumably on the newsstand.

The issue was edited by Richard Milner, head of the Wallace Centenary Celebration. According to the second comment below, he also edited a special issue of Skeptic magazine, and you may request a free copy of either or both magazines by writing Mr. Milner an e-mail.

The first article, by the distinguished naturalist David Attenborough, outlines Wallace’s career. I did not know that, as Wallace returned from South America, his ship caught fire, and he lost all his notes and his specimens; I think I learned that fact 2 more times in subsequent articles. Attenborough outlines how Wallace got the idea of natural selection while studying birds of paradise. As is widely known, he sent an essay to Darwin. Lyell and Hooker arranged to have Wallace’s paper presented alongside a paper by Darwin, who then rushed his own book, On the Origin of Species, into print. Attenborough remarks, “You might have thought there was an embarrassment or perhaps hostility or resentment” between Darwin and Wallace. “Not at all. The two men had great respect for each other, untinged by any sign of jealousy.”

An article by geneticist Andrew Berry goes over some of the same material, though in more detail and more biographically. Berry observes that Wallace’s 1865 definition of “species” is identical to the “biological species concept” that is usually attributed to Ernst Mayr 80 or so years later. There is a certain amount of redundancy in these articles, each of which was written as if the authors thought they would have to stand alone: Berry introduces us to Wallace’s Line, apparently unaware that Attenborough has already done so in the preceding article and Gary Noel Ross will do so later. Wallace originally went abroad, says naturalist Errol Fuller, to earn money by supplying stuffed animals to middle- and upper-class England; evidently such products were in considerable demand at the time, and Attenborough estimates that Wallace collected 110,000 insects, 7500 shells, 8050 bird skins, and over 400 mammals and reptiles. Fuller shows us some stuffed specimens that remain in remarkably good condition today.

But for someone who just wants to look at the pictures, the high point of the issue might be a series of photographs of birds of paradise by Tim Laman with a narrative by Edwin Scholes. An article by Ross describes (sort of) following in Wallace’s footsteps and searching for the golden birdwing butterfly; this article likewise displays excellent photographs, some by the author and including what seems to be a selfie taken from a distance of several meters.

The final article is a reprint of a 1980 article by Stephen Jay Gould. Gould discusses the fact, noted in an earlier article as well, that Wallace and Darwin disagreed on sexual selection, and also on the origin of the human brain. Wallace, according to Gould, took the “hyperselectionist” position that everything that evolved is an adaptation. The brain, however, can do much that it is not adapted to do, like write symphonies. Such reasoning, says Gould, leads Wallace “right back to the basic belief of an earlier creationism that it [Wallace’s hyperselectionism] meant to replace—a faith in the rightness of things, a definite place for each object in an integrated whole.”

If you want to know more, I am afraid that you will have to buy the magazine. And cheer up! The pictures are better in print than on your monitor.

Felis catus


Photograph by Andrey Pavlov.

Photography contest, Finalist.


Felis catus – domesticated cat. Mr. Pavlov tells us, “The photo of the cat is my cat Rosie, short for Rosen of Einstein-Podolsky-Rosen (her sister is named Electron, not pictured). She is a daughter of a feral cat, rescued from a swamp in central Louisiana.”

Eumorpha achemon


Photograph by Gabrielle Hovinen.


Eumorpha achemon – achemon sphinx moth.

Noncircular pupils explained


Several years ago, I reviewed the book Evolution’s Witness: How Eyes Evolved, by Ivan Schwab. The book is downright encyclopedic, and I could not praise it highly enough. But in my review I wondered about elongated pupils, such as those of a cat, which are barely discussed the book. I remember reading somewhere that the elongated pupil could be stopped down farther than a circular pupil, but that explanation does not account for the problem that horizontal structures will be more clearly resolved than vertical structures (presuming that the pupil is elongated vertically and the eye is nearly diffraction limited).

A team from Berkeley and Durham University now proposes a better explanation. Without going into detail, they find that predators that ambush their prey, like cats, typically have vertically elongated pupils. From the abstract:

Vertically elongated pupils create astigmatic depth of field such that images of vertical contours nearer or farther than the distance to which the eye is focused are sharp, whereas images of horizontal contours at different distances are blurred. This is advantageous for ambush predators to use stereopsis to estimate distances of vertical contours and defocus blur to estimate distances of horizontal contours.

One way to put it: All the blur due to defocus is in the vertical direction, so horizontal contours are blurred when defocused, whereas vertical contours are not, because the blur is parallel to the contour; see their Figure 2(A). I do not want to go into detail, but they demonstrate that ambush predators, like the cat, that prowl close to the ground benefit from having good stereo vision for vertical contours. Prey animals, like the goat, often have horizontal pupils, which supposedly facilitate wide-angle views. Curiously, their pupils remain horizontal regardless of the orientation of their heads.

This paper goes a long way toward explaining why different animals have differently oriented pupils. You may see a video and a short article here and an NPR report here.

The paper does not explain how, when I was an elongating pupil in fourth grade, my teacher, an ambush predator if ever there was one, managed to see through 360°.

Who? The Chevalier de Lamarck, that’s who. Born 1 August 1744, he was the first evolutionary biologist who gave a mechanism that could, in principle, explain adaptation. Even though his mechanism was wrong, he was a true pioneer and a great biologist. (I’ll leave this post short, so as not to push Matt’s photo contest off the page).

Actias luna

Photograph by Tom Gillespie.

Photography Contest, Second Place.


Actias luna – Luna moth, Duluth, Georgia. Shot from underneath, as it was resting upside-down in my azalea bush.

Domesticated: Book review


A number of years ago, I found a family of raccoons living in my chimney.1 I got them out by dropping a trouble light down the flue and turning it on for a few days. According to Richard C. Francis, in his splendid book, Domesticated, animals such as raccoons living in urbanized areas represent the first step toward domesticating those animals.

The full title of the book is Domesticated: Evolution in a Man-Made World, and Francis shows in considerable detail how various animals became domesticated: dogs, cats, pigs, sheep and goats, reindeer, camels, horses, rodents, and perhaps humans, as well as other predators such as raccoons and ferrets. Each scenario is slightly different, each seems well documented, and each has just a little bit of just-so story in it.

Melting of polar ice


Photograph by Dan Moore.

Photography Contest VII: Winner.


Melting of polar ice. Mr. Moore writes, “Our ship got caught in the ice and had to be freed by a Canadian ice breaker. Global warming – what?? Actually, yes – we could not get through because so much ice broke free further north near the polar ice cap and was blown south into the shipping channels.” Mr. Moore will receive a signed copy of Why Evolution Works (and Creationism Fails), which has been donated by one of the authors.

Here are the finalists of the 2015 photography contest. We received 16 photographs from 7 photographers, somewhat fewer than in previous years. This year we decided to choose 1 picture from each entrant and enlisted our wife to help with the choices. The text was written by the photographers and lightly edited for consistency.

The finalists are given below the proverbial fold, in alphabetical order of last name. Please look through their photographs before voting for your favorite. You will have to be logged in to vote on the poll. We know it is possible to game these polls. Please be responsible and vote only once. If we think that the results are invalid, we will cancel the contest.

Polling will close Friday, July 17, at approximately 12:00 CST.

Reed Cartwright contributed to this post.

Zenaida macroura


Zenaida macroura – mourning dove, Walden Ponds Wildlife Habitat, Boulder, Colorado, spring, 2015. I have not seen nor heard a mourning dove within the city limits since the collared doves took over.

Photography contest finalists next week, July 6, noon, CST.

Unidentified fossil


David MacMillan, who wrote an 8-part series on creationism for us, sent us these 4 photographs, along with the following request:

“I recently moved back to central Kentucky. One of the things I came across while visiting my family was this fossilized object I discovered near my home here when I was about 9 or 10 years old.

“Back in the late 90s, we were living in a new development and there was a lot of excavation going on near our house. I believe I found this half-buried in the bottom of a rain-fed creek just after a particularly heavy period of excavation followed by some heavy rainstorms.

“It appears to be a vertebra, due to the shape and orientation of the various spurs, and what seems to be a very large nerve opening going in the side. The exterior is dotted with what appear to be marine fossil concretions, including scallops and similar creatures.

“This region of Kentucky comprises primarily Ordovician limestone and shales, which is puzzling because this would have to be a pretty large marine vertebrate, and there were virtually no large bony vertebrates in the Ordovician. Perhaps this is actually not a vertebra at all and is rather some sort of oddly-shaped shell?

“The largest human lumbar vertebrae are around 13 mm thick, while this measures over 5 cm thick. If it is a vertebra, it would have to come from an animal with a spinal column at least five times the length of a human spine.

“Basically, I’m stumped. Any idea whether any of the readers of Panda’s Thumb might be able to identify it?”

Ondatra zibethicus


Ondatra zibethicus – muskrat, Elmer’s Two-Mile Creek, Boulder, Colorado, May, 2015. The muskrat shown here disappeared after the 2013 flood, and I did not see any muskrats again till this spring.

Don’t forget to enter the photography contest – 1 week remaining!

Photography Contest VII


Polish your lenses, oil your tripods, search your archives – the seventh Panda’s Thumb photography contest, begins – now!


Polaroid Land Camera, Model 160, 1962-1965. Apologies for the moiré pattern on the face of camera!

We will accept entries from 12:00 CST, June 8, through 12:00 CST, June 22. We encourage pictures of just about anything of scientific interest. If we get enough entries, consistently with Rules 11 and 12, we may assign entries to different categories and award additional prizes, presuming, of course, that we can find more prizes.

The first-place winner will receive a signed copy of Why Evolution Works (and Creationism Fails), which has been donated by one of the authors. The second-place winner will receive a copy of The Devil in Dover, which has been generously donated by the National Center for Science Education.

Selasphorus platycercus


Photograph by David Young.


Selasphorus platycercus – broad-tailed hummingbird, Boulder, Colorado, May, 2015.

… June 8. That is, we will accept entries from noon, June 8, to noon, June 22, where noon is defined by the Panda’s Thumb server, which thinks it is still in Central Standard Time, or UTC(GMT) – 5 h. The rules will be essentially the same as previous years’. We have not chosen categories yet, but please be assured that they (or it) will be all-inclusive. So wipe your lenses, grease your shutters, and be ready!

Chrysemys picta


Chrysemys picta – painted turtle, Walden Ponds Wildlife Habitat, Boulder, yesterday. See also here.

The majority of U.S. medical schools do not require evolutionary biology as a prerequisite for acceptance and do not offer courses dedicated to the subject. But as we talked about last time, adopting an evolutionary perspective on medical issues can potentially give new insights into disease treatment, prevention, and diagnosis. Where do we and should we begin to teach this kind of thinking? What resources are available to teachers and students to learn about evolution and its application to modern day problems?

Evolutionary training can help doctors look at diseases in a different light (Nesse et al, 2006). Take, for instance, sickle cell anemia: carriers of the sickle cell trait, a disease which is highly prevalent in tropical regions, are resistant to malaria, likely as a result of natural selection. This knowledge is helpful in developing ways to prevent malaria and perhaps similar evolutionary links between other diseases or infections and protective traits exist, but examining this hypothesis requires a thorough understanding of evolution and population genetics. Based on examples like this proponents of evolutionary medicine believe evolutionary biology should be considered a core subject for medical students, side by side with anatomy, physiology, biochemistry, and embryology, and that medical license exams should include questions about evolutionary biology.

People with sickle-cell anemia, whose bodies produce abnormal, crescent-shaped red blood cells, also carry genes that protect against malaria. This is most likely the reason sickle cell anemia is so common in areas where malaria is highly prevalent.

Image source: National Health Service

But while most medical schools do not offer much in the way of evolutionary education, there are some resources available for K-12 students and teachers as well as college undergraduates and graduates. One example is the BEACON Center for the Study of Evolution in Action at Michigan State, an interdisciplinary research team working on applying evolutionary principles to a wide range of problems in fields such as medicine, computer science, ecology, and engineering. Along with research, BEACON is focused on evolution outreach and education: researchers are conducting studies to see if integrating undergraduate cellular and molecular biology courses with evolution improves evolutionary understanding. The center also organizes K-12 summer programs, activities for K-12 teachers, and undergraduate and graduate-level courses.

While BEACON is enjoying great success, the NESCent (National Evolutionary Synthesis) Center, a center in North Carolina promoting multidisciplinary evolutionary research, will be closing this year after a decade of operation. Like BEACON, NEScent was also active in public outreach and education, organizing events like Darwin Day for K-12 students and training workshops for graduate students and teachers. But a new center is opening in the wake of NESCent: the Triangle Center for Evolutionary Medicine (TriCEM), which will focus on the partnership of evolutionary biology with human and veterinary medicine.

We’ve made the case for why an evolutionary understanding can improve research in medicine. But if we want to shift the paradigm of medical thought to one that emphasizes evolutionary biology, we need to reevaluate how we teach evolution from the earliest levels of education through medical school.

This series is supported by NSF Grant #DBI-1356548 to RA Cartwright.

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This page is an archive of recent entries in the Evolution category.

Eugenics is the previous category.

Evolution Education is the next category.

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