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.
Here’s an old video from Vox that shows morphological evidence for evolution in the human body based on vestigial organs and traits. Most of these can be found in Why Evolution is True, but it’s good to see them in video like this.
This takes the website back to its original aim: giving the readers evidence for why evolution is true.
A new scientific paper from the Proceedings of the Royal Society Series B (first screenshot below) tells a rather complex story that I’ll deliberately simplify to save space. The paper is behind a paywall, but a pdf may be found via judicious inquiry, and the reference is at the bottom.
The article above is aptly summarized by Veronique Greenwood in the New York Times‘s “Trilobite” column
Three groups of birds have evolved a remarkable feature: the ability to remotely sense prey (i.e., detecting prey without touching them) by sticking their bills in the ground and sensing vibrations. These groups are the kiwis, the ibises, and some shorebirds. The detection can occur either through the direct sensing of vibrations of prey movement, or the reflection of sound waves off hard-shelled prey as the bird sticks its beak into the ground. This feature is called “remote touch.”
It turns out that the bill tips of “remote touch” birds are pitted with small depressions that contain cells called “Herbst corpuscles”, which are the motion-detecting organs. aThese birds also have an expanded area of the brain that is used to process the extremely important touch signals.
Other species have different ways of using their bills to detect prey by touch. Ducks and geese have a bony organ at the tip of their bills that also have pits with Herbst corpuscles, but they are organized differently, with mechanoreceptors beside them. These are what ducks use in “dabbling”—turning their butts up and sticking their beak into the dirt or sediments to forage. Finally, parrots have a different kind of bill-tip organ with receptors not located in the bone.
Below are photos from the paper showing the different types of bill tips. The authors also examined skulls of hundreds of living species and dissected beak tissue from many to see if there were Herbst cells associated with the bill pits.
First, a bird without remote sensing, as with most birds. It’s a kelp gull (Larus dominicus). There are a few pits at the tip of the bill, but soft tissue analysis showed no receptor cells. It does not forage by touch.
Here are two birds with remote sensing. First, the hadeda ibis (Bostrychia hagedash). Note the highly pitted bill tip organ (enlarged). It also has the Herbst cells as well as an enlarged bit of the brain for detecting touch. (This bird, like all other birds save the ratites and tinamous, falls into the large group of species called neognaths.)
Ditto for the kiwi, which falls into the other group of birds, the paleognaths, a small group that contains only the large flightless birds or ratites (emus, ostriches, etc.) plus the tinamous, which can fly, but not well. Its remote sensing organ with Herbst cells is located at the very tip of its long bill. Indeed, the ratio of bill length to skull size is one of several keys to diagnosing whether these birds have remote sensing.
Finally, the tinamou, a paleognath that= has a remote-sensing organ containing the pits but no Herbst corpuscles in them. But this species doesn’t feed by probing the ground. Other ratites, like the ostrich and emu, also have a pit-studded bill, but no vibration-detecting cells. The pits seem to be a leftover from an ancestor which had pits that were useful because they contained vibration-detecting cells. In other words, they’re a vestigial trait.
The other ratites also lack the expanded brain regions for processing information from the touch receptors. This makes sense, for while it may not cost much to retain some pits in the bill when you don’t need them, brain tissue is metabolically expensive, and if you’re not using it it would pay to divert those resources to other functions that would help you reproduce.
As I said, the presence of the pits in birds that don’t use them suggest that this trait is a vestigial trait carried over from an ancestor. One can distinguish the remote-touch birds from other species by a combination of bill length/skull size ratio, number of pits, and spacing between the pits.
But which ancestor? It turns out that we have fossil skulls of ancient extinct birds, the lithornithids, which are very early paleognaths. Although soft tissue wasn’t available for these birds, some of the species show the mechano-sensing organ—as evidenced from the number and spacing of the pits, as well as the bill/skull ratios characterized by remote foragers. Here’s a photo of the two lithornithid skulls; captions under the photos are from the paper (click to enlarge photo).
The conclusion is that putative ancestors of the paleognaths were remote-touch-sensing species. The fact that living paleognaths like emus and tinamous still retain the pits suggests that this nonfunctional “organ” is a useless remnant of a trait inherited by all paleognaths from a lithornithid ancestor. Indeed, the authors think that the ancestor of all birds might have been a remote-sensing prober (my emphasis):
Our analyses corroborate that the basal palaeognaths, the small, volant lithornithids, had a tactile bony bill-tip organ enabling them to use remote touch to locate buried invertebrate prey items. This finding, combined with our understanding of the evolution of the lithornithids, suggests a Cretaceous origin of the remote-touch sensory system in modern birds before the palaeognath–neognath split.
As for why among living paleognaths only the kiwi has a functional touch organ when it was present in an extinct ancestor, that could be explained by either of two scenarios. The first involves, the organ’s loss in a more recent ancestral species and then the re-acquisition of the organ in just the kiwi lineage. The second possibility is that the kiwi kept an ancestral remote-probing organ while all the other paleognaths lost it. The authors are unable to distinguish between these two scenarios.
What about the neognaths that have remote-sensing organs, like the ibis or shorebirds? Did they retain the ancestral touch organ while all other neognaths—the vast majority of living birds—lost it? Probably not; as the authors say, this is an independent case of evolution.
What is even more fascinating is the possibility that this ability to detect prey remotely may have been present in the reptilian ancestors of birds, which may scientists think are the theropod dinosaurs:
Interestingly, there is increasing evidence that some non-avian theropods had specialized sensory structures located on the distal portion of their rostra, based on a high degree of external foramina/pitting preserved on their mandibles. We speculate that perhaps such sensitive snouts in non-avian theropods may have been precursors to the evolution of remote touch in their avian relatives.
It’s interesting to note that alligators and crocodiles also have touch-sensitive “dome receptors” in their upper jaws, also associated with pitting in the bones. The archosaurs are a group of early reptiles ancestral to both birds and crocodilians, and maybe the receptors we see in crocs and gators are related, in some way, to the pits in the beak of the kiwi.
This is all speculative, but what seems pretty solid is that the bill pitting and useless “touch organs” in non-kiwi ratites and tinamous are vestigial remnants of a functional organ in an ancient ancestor. And that’s evidence for evolution.
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Toit, C. J. d., A. Chinsamy, and S. J. Cunningham. 2020. Cretaceous origins of the vibrotactile bill-tip organ in birds. Proceedings of the Royal Society B: Biological Sciences 287:20202322.
The other day I took a picture of this juvenile mallard—one of Honey’s babies—and a friend noticed it had what appeared to be an atavistic claw on its wing. At least I think it’s on its wing; it could be on a foot tucked behind the bird. But I doubt it.
Here I’ve circled it:
And enlarged it:
The question is whether this is an atavistic claw: the remnant of the claw that was on the reptilian forelimb, and was also prominent in early birds (ignore the labeling of Archaeopteryx as “the earliest known bird”.
Birds also have “spurs“, which are outgrowths of bone that aren’t developmentally homologous to a true claw. But the duckling above seems to have a true claw; it doesn’t look like a bone spur, but is recurved and apparently made of keratin.
Real bird claws, as in the hoatzin, grow from the digit that’s in the bird wing; in this case it would be the “thumb”. Here’s a “normal” bird.
But birds like hoatzins have true claws, especially in the chicks, which use them to climb back into trees when they fall in the water. I’ve put an Attenborough video of this behavior below the picture, and what it shows is that the claim that a “vestigial” character has to be nonfunctional to be considered vestigial is incorrect. Vestigial traits are simply remnants of traits that evolved earlier but have been coopted for a different function (“exaptations”, Steve Gould might call them). The hoatzin’s claw, very useful for the bird, is certainly a vestigial trait, and is just as much evidence for evolution (of birds from reptiles) as if it were completely nonfunctional.
Some species of waterfowl are known to have these claws (see here and here), but I can’t find something explicitly on mallards.
So we have a mystery here, and I’ve asked a few experts to weigh in. This is either a true atavistic claw in the wing, or one of the claws (nails) in the duck’s rear foot, which could be tucked behind it. You can weigh in, or wait for an answer. Stay tuned.
h/t: Nicole, Greg
In almost exactly one month, I’m speaking to the Tallahassee Scientific Society in Tallahassee, Florida. My talk is on Thursday, March 26, and I think the time and venue are the same as those for the previous speaker: 7 p.m. at Tallahassee Community College’s Center for Innovation on Kleman Plaza. The topic is “Why Evolution is Still True”, and I’ll give a brief rundown of the evidence for evolution (updated in light of new discoveries), followed by discussion of why Americans remain so resistant to this scientific truth.
I’ll give one more announcement in mid-March or so, and all are welcome to come. I believe they’ll also have my two trade books on sale, which I’ll be glad to autograph. And, if you tell me the genus and species of any felid besides the house cat, I’ll draw a cat in it.
Here’s a photo I sent them to use for advertising the talk; the picture is from Wikipedia so it’s in the public domain. Toes, teeth, and size!
When I started this website in 2009, my intention was just to publicize my new book, Why Evolution is True. On the advice of my publishers, I created a site with the idea of occasionally posting new evidence for evolution to complement what was in the book. I expected to post about once a month or so. Well, what a monster this has become!
But today I’m writing about some new work that fits perfectly with the original aim of this site. It’s a paper in the Proceedings of the Royal Society by Kathryn Kavanagh et al. that gives developmental evidence for the five-toed ancestry of modern one-toed horses. You can read the paper by clicking on the screenshot below or reading the pdf here ; a full reference is at the bottom. If you want a short but less informative piece, the New York Times has a report.
Lots of organisms show developmental evidence for their evolution from very different ancestors; I describe some of this in chapter 3 of Why Evolution is True. Embryonic dolphins, for example, develop hindlimb buds, which in their four-legged ancestors went on to become legs, but in the dolphin the buds regress before birth, leaving newborns with no hind limbs. We humans, like all terrestrial vertebrates, begin development by forming what go on to become gill slits in our fishy ancestors. In reptiles, amphibians, and mammals, though, those gill slits are transformed into other stuctures, like our esophagus.
In my evolution class I talk about the lanugo: the thick coat of hair that human fetuses develop at about six months after conception. It’s shed before birth—but not in chimps, our closest relatives, who are born hairy (remember: we are the “naked ape”). The transitory formation of that coat of hair in our species, which is of no use to the embryo, can be explained only by our descent from a primate with hair.
So if these transitory features disappear, why do we see them at all? We’re not sure, but their appearance may be necessary to provide developmental “cues” for the appearance of features that do remain. Remember, development is a very complex process which requires a nexus of coordinated features appearing at the right times. In the dolphin, for instance, the hind limb buds may provide cues for the development of other skeletal structures, and then disappear because they are no longer needed, for natural selection would remove them because they’re cumbersome, a waste of resources, and unnecessary in a marine mammal.
Horses are another example. We know from the fossil record that modern horses evolved from five-toed ancestors, but what we have left, the lower leg and hoof, are the remnants of only the middle toe. The other four toes disappeared over time (we can see this in the fossil record), though the two toes flanking the middle one remain as vestigial “splint bones” on the horse’s leg. The outer two toes are gone completely. Here’s a drawing of one of the vestigial toes in a modern horse: a splint bone (lateral view; there’s one on the other side, too):
But you can see all five toes if you look closely during development, as reported in this new paper. If you get horse embryos at the right early stage of development, you can see the primordia for all five toes forming, with the outer ones fusing and shrinking to leave only the middle toe, which becomes the lower leg and hoof. Previously, nobody had been able to see this evidence of ancestry in embryos, but Kavanagh et al. managed to get the right material.
The authors procured (don’t ask me how) horse embryos from artificially inseminated mares, and analyzed four of them by making tissue sections of embryos between days 29 and 35 after copulation. (There is a very narrow window of time to see the primordia for all five digits, as shrinkage and disappearance of the four superfluous ones is fast.)
First, here’s a diagram of what the primordia look like. On the right side you see the evolutionary progression of horse ancestors (also shown below), starting with five, then four, and then three, with the two side toes gradually being reduced to the splint bones. We’re not sure why this happened, but a likely explanation is that at the time these horses were evolving—and they evolved in what is now North America—the climate was drying up and the forests of the West were giving way to grasslands. While toes are good for running fast around trees and vegetation, if you’re escaping predators in a featureless grassland, you want a hoof to run fast and straight.
On the left side, in blue, are the toe primordia in four embryos; those blue bits are regions where cartilage would normally condense and then bone would form. (“FL is “foreleg” and “HL” is “hindleg”). You can see that two of the embryos have five primordia early on, with the central one, which becomes the lower leg, being the largest, as it’s the toe that will become the hoof. The other two embryos have three primordia, with the central one the largest.
Now of course we don’t need this kind of evidence to show evolution, or even to show evolution of toe loss in horses, as we have an excellent fossil record of horses and a good idea of their “family tree”. Here’s a figure from the Encyclopedia Brittanica:
But the developmental evidence is a nice confirmation of what the fossils tell us, and add the information that the evolutionary sequence of toe loss is mirrored in the developmental sequence of modern one-toed horses. This is a version of the “biogenetic law” stating that “ontogeny recapitulates phylogeny” (i.e., development mimics evolutionary history). That law has many exceptions, for sometimes the ancestral stages are competely lost in embryos, but it does hold for horse toes. First five, then three, then one—in both development and in the fossil record.
By the way, sometimes the side toes don’t disappear, but, probably through a screwup in development, form rudimentary adult toes, producing polydactylous horses like this one:
Similarly, sometimes the dolphin’s hind limbs don’t disappear and we get dolphins with little legs sticking out of its rear, like this one that I show in my “evidence for evolution” talk:
UPDATE: I forgot to include the authors’ point that many vertebrates have lost toes from the ancestral five, and that these species are ripe for embryological investigations of the type shown here. They give a table of some of these animals. Would embryos of the camel or the three-toed jerboa, for instances, show five toe primordia that are then lost? We don’t know if this is the case, and the absence of five primordia wouldn’t disprove evolution, for the retention of toe primordia is a lucky (for us) feature of development, but isn’t expected in every case.
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Kavanagh, K. D., C. S. Bailey, and K. E. Sears. 2020. Evidence of five digits in embryonic horses and developmental stabilization of tetrapod digit number. Proceedings of the Royal Society B: Biological Sciences 287:20192756.
UPDATE: I found out that the well-known evolutionary geneticist John C. Avise published a related book in 2010, but one that concentrates on a different line of evidence for evolution. John’s book (screenshot of cover below with link to Amazon) lays out the many suboptimal features of the human genome. He thus concentrates on molecular evidence, noting the many features in that bailiwick whose imperfection gives evidence for evolution and against intelligent design. Lents’s and Avise’s books thus make a good pair, since the former seems to deal mostly with anatomy and physiology and the latter with molecular data. I’ll be reading both of them.
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Biologist Nathan Lents, whose abbreviated c.v. is given below, has been featured on this site before, both as a critic of creationism (good), but also as a defender of the Adam-and-Eve apologetics pushed by his religious friend Josh Swamidass (bad). But chalk up another two marks on Lents’s “good” side. First, he’s written a book (click on screenshot below) that lays out all the suboptimal features of the human body—features whose imperfection gives evidence for evolution. I’m getting the book for teaching purposes, and here’s the Amazon summary:
Dating back to Darwin himself, the “argument from poor design” holds that examples of suboptimal structure/function demonstrate that nature does not have a designer. Perhaps surprisingly, human beings have more than our share of quirks and glitches. Besides speaking to our shared ancestry, these evolutionary “seams” reveal interesting things about our past. This offers a unique accounting of our evolutionary legacy and sheds new light on how to live in better harmony with our bodies, in all their flawed glory.
Nathan Lents is Professor of Biology at John Jay College and author of two recent books: Not So Different and Human Errors. With degrees in molecular biology and human physiology, and a postdoctoral fellowship in computational genomics, Lents tackles the evolution of human biology from a broad and interdisciplinary perspective. In addition to his research and teaching, he can be found defending sound evolutionary science in the pages of Science, Skeptic Magazine, the Wall Street Journal, The Guardian, and others.
And here’s a half-hour Center for Inquiry talk, clearly based on his book, in which Lents discusses how the flaws in the human body instantiate evolution. It’s not just that there are flaws—which support the notion that natural selection doesn’t produce absolute perfection, but simply the best result available given the existing genetic variation—but, more important: those flaws are understandable as the result of our evolution from ancestors who were different from us.
Some of Lents’s examples (like our broken gene in the Vitamin C synthesis pathway), are discussed in WEIT, but others, like the bizarre configuration of our nasal sinuses, aren’t. I haven’t seen the book, but it looks like a good compendium of evidence for evolution using something that everyone’s familiar with: the glitches and bugs in the human body.
It’s a good talk, and Lents is an energetic and lucid lecturer. I recommend that you listen to this, for you’ll learn stuff that will stay with you, and also serve to help you argue with creationists.
h/t: Michael
There are three kinds of vestiges that constitute evidence for evolution, or rather its sub-claim that modern species share common ancestors. I discuss all three in Why Evolution is True:
1.) Vestigial traits that persist in modern species but either have no adaptive function in a species or a function different from the one served in that species’ ancestors. The vestigial ear muscles of humans are one, the flippers of penguins (functional, but not for flying in the air) is another, and the coccyx in humans (sometimes with attached “tail muscles” that can’t move it) is a third.
2.) Vestigial genes that are functional in our relatives (and presumably in our ancestors) that have been inactivated in some modern species. There is no explanation for these “dead genes” save that they were useful in ancestors but aren’t useful any longer. Examples are “dead” genes that code for egg yolk proteins in humans (but don’t produce them); a dead gene for vitamin C synthesis in humans (we don’t make the vitamin because that gene is inactivated, but rather get it from our diet; and the many dead “olfactory receptor” genes in cetaceans (whales, dolphins, etc.)—genes that were active in their terrestrial ancestors but became inactivated because “smelling” underwater uses different genes and traits.
3.) Features in development that are transitory, and whose appearance makes sense only under the supposition that those features were present in common ancestors and persist in some descendants but not others. The lanugo (a transitory coat of hair in human embryos) is one.
Today’s paper, which just appeared in the journal Development, shows several other “transitory” evolution-attesting features. Diogo et al. show that human embryos develop muscles that disappear as development proceeds, but those muscles don’t disappear in some of our relatives, including closely related ones like other primates as well as distant relatives like reptiles.
Moreover, these muscles, which disappear in most human embryos, sometimes don’t disappear, persisting in adults as rare and nonfunctional variants. Or they appear in malformed individuals, with both phenomena often seen in “vestigial traits”. For example, some people are born without wisdom teeth, considered a vestigial holdover from our ancestors; and the functionality of human vestigial ear muscles that move the ears in our relatives, like cats and dogs, is variable: some people like me are able to move those muscles and wiggle their ears, while others can’t.
Click on the screenshot below to access the paper, and the pdf is here (reference at the bottom of this post).
The authors visualized the muscles in the embryonic arm and leg by doing immunostaining—using antibodies that would affix to proteins in the muscles and also carried ancillary molecules that would make those muscles more easily visualized under the microscope in a three-dimensional way. The authors used 70 antibodies, but the main ones bound to muscle-specific proteins like myosin and myogenin.
They stained the mounted limb sections of 13 embryos (presumably from abortions) ranging from nine to thirteen weeks after gestation (quantified as “gestational weeks”, or GWs), and with the standard measurement “crown-rump length” (CR) ranging from 2.5 cm to 8.0 cm (about 1 to 3 inches). These were thus very small embryos, but the sophistication of the technique, and the efficacy of the stain, combined with our knowledge of embryonic development and tetrapod muscle anatomy, enabled the authors to produce pictures like these: the muscles in the hands of a 10 and 11-GW fetus:
What they found is that human embryos show a number of muscles present in the adults of some other tetrapods (including our closest relatives, the chimps), but that disappear during human development, with a few of these “atavistic muscles” fusing with other muscles in human fetuses although remaining distinct in our tetrapod relatives.
Here’s how the authors describe the main results, listing some of the atavistic muscles in the embryos (I’ve put them in bold):
As summarized in Tables 2-5 and also noted above, various atavistic muscles that were present in the normal phenotype of our ancestors are present as the normal phenotype during early human ontogenetic stages and then disappear or become reduced and completely fused with other muscles, thus not being present/distinguishable in human adults. These include the upper limb muscles epitrochleoanconeus (Fig. 3), dorsoepitrochlearis, contrahentes 3-5 (Fig. 4) and dorsometacarpales 1-4 (Figs 3-5), and the lower limb muscles contrahentes 3-5, dorsometatarsales 1-4 (Fig. 6) and opponens digiti minimi (Fig. 6). These muscles are present in some other tetrapods, as shown in Tables 6 and 7, which summarize the comparisons with other limbed vertebrates. Of all these muscles, only the dorsometacarpales often remain in adults, fused with other muscles: all the others are normally completely absent in human adults. Fascinatingly, all these atavistic muscles are found both as rare variations of the normal adult population and as anomalies in individuals with congenital malformations such as those associated with trisomies 13, 18 and 21, reinforcing the idea that such variations and anomalies can be related to delayed or arrested development.
Here are two of the fetal atavistic muscles. First, the dorsometacarpales in the hand, which are present in modern adult amphibians and reptiles but absent in adult mammals. The transitory presence of these muscles in human embryos is an evolutionary remnant of the time we diverged from our common ancestor with the reptiles: about 300 million years ago. Clearly, the genetic information for making this muscle is still in the human genome, but since the muscle is not needed in adult humans (when it appears, as I note below, it seems to have no function), its development was suppressed:
Here’s a cool one, the jawbreaking “epitrochleoanconeus” muscle, which is present in chimpanzees but not in adult humans. It appears transitorily in our fetuses. Here’s a 2.5 cm (9 GW) embryo’s hand and forearm; the muscle is labeled “epi” in the diagram and I’ve circled it:
This muscle must have become nonfunctional, and reduced in development, over the last six million years or so, when the common ancestor of humans and chimps gave rise to our separate lineages.
An interesting sidelight of this study is that some of these vestigial muscles occur as rare variants in adult humans, either via developmental “accidents” or as part of congenital malformations. Presumably these screwups in development block the genetic changes that normally lead to the suppression and disappearance of muscles in embryos. Variable expression of vestigial traits is common in organisms where the traits haven’t evolved into something else that’s useful. (For more on human vestigial traits, see the Wikipedia article on “human vestigiality”). The authors note that when the muscles do appear in adults, they are “functionally neutral, not providing any type of major functional advantage or disadvantage.”
The presence of these vestigial muscles is pretty irrefutable evidence of evolution and common ancestry, for there’s no reason why either God or an Intelligent Designer (a pseudonym for “God” to ID advocates) would put a transitory muscle in a human fetus that’s of no use whatsoever, but just happens to resemble the fetal muscles that goes on to develop into adult muscles in our relatives. I wonder how creationists, including IDers, will explain this as the work of a designer. Will they say the muscles are really functional in a fetus? If so, why do they disappear? And doesn’t the fact that they go on to develop into functional muscles in our relatives like chimps and reptiles say something about common ancestry?
Two more points:
1.) The order of appearance of these muscles in development doesn’t completely comport with their order of evolution. This shows that the “recapitulation theory”—that the order of development mimics the order of evolution—isn’t completely obeyed. But we’ve known that for a long time. The time of appearance of a trait in development can be changed by other factors, like its usefulness in “priming” the development of other features. But this doesn’t overturn the very strong conclusion that the presence of transitory muscles in the human fetus that remain in adults of our relatives is evidence for evolution.
2.) Finally, muscles in the arms and legs that appear “homologous” (i.e., have the same evolutionary origin) may have had independent evolutionary origins, and may involve different genes, so they’re not really “homologous” in the way evolutionists use that term. As the authors note,
These differences support the emerging idea that the topological similarities between the hand and foot of tetrapods, such as humans, are mainly secondary (see recent reviews by Diogo et al., 2013, 2018; Diogo and Molnar, 2014; Sears et al., 2015; Miyashita and Diogo, 2016). This idea is further supported by the fact that the order of developmental appearance of the hand muscles is markedly different from that of the corresponding foot muscles (Tables 6, 7). As an illustrative example, whereas the lumbricales are the first muscles to differentiate in the hand, together with the contrahentes (Table 6), in the foot the lumbricales differentiate only after most other foot muscles are already differentiated (Table 7). Thus, these developmental data and evidence from comparative anatomy and from the evolutionary history of human limb muscles (see Tables 6, 7) indicate that several of the muscles that seem to be topologically similar in the human upper and lower limbs actually appeared at different evolutionary times; appear in a markedly different ontogenetic order; derive from different primordia; and/or are formed by the fusion of different developmental units in each limb.
Now the authors didn’t do this study to demonstrate evolution; like most rational people, they accepted it long ago. Rather, their stated aim was to “build an atlas of human development comprising 3D images. . . that can be used by developmental biologists and comparative anatomists, as well as by professors, students, physicians/pathologists and the broader public.” But one of the bonuses, especially for the broader public, is the very clear demonstration of the common-ancestry tenet of modern evolutionary theory.
h/t: Liz
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Diogo, R., N. Siomava, and Y. Gitton. 2019. Development of human limb muscles based on whole-mount immunostaining and the links between ontogeny and evolution. Development 146: