Category: evolution

A self-aggrandizing post concerning a paper on speciation I wrote with Allen Orr

August 24, 2026 • 9:30 am

What is an old, retired scientist to do but look back on his career and find satisfaction in the good ideas he once had? (I just finished a great novel in which a superannuated Cuban musician does the same thing.) In line with that, reader Nick called my attention to a two-year-old video by Zach Hancock lauding a paper I wrote with my student, Allen Orr, as “one of the ten most influential papers in evolution.”

First, though, in April I bragged about another video by Zach Hancock (a professor at Augusta University) that put my book Speciation (also co-written with Allen Orr), as one of the ten most influential books in evolutionary biology (we were #10). I have to admit that I consider this book my most significant accomplishment in science, as it distilled the field of speciation down to a research program that succeeded in influencing research in the origin of species. It took us six years (each) to write.

I rarely look at Speciation now, though, for when I do I realize that when we wrote it I was at the top of my neuronal game, able to read, write, and synthesize far better than I do now. And when I open it and sample a page or so from the chapters I wrote, I think to myself, “Who is that guy? He was really savvy?!” I could not write it now, nor will either of us revise it.

But Zack had another video that I missed,  one on the ten most influential papers in evolutionary biology. And again Allen and I made the list, coming it at #9 with the paper below we published in 1989 in Evolution. Note the dedication to Bruce Grant, under whom both of us studied at William and Mary (click title to read the paper):

I’ll add that this paper was at first rejected by Evolution on one reviewer’s claim that we could not use the method of correlation that we did, but the reviewer simply didn’t understand that method (it’s not rocket science). We argued with the editor, something I’d never done, and the paper was accepted.

Zack chooses papers in the field that have been cited more than a thousand times. and I’ll let him explain the findings in his video below (the discussion of our paper goes from 5:23 to 7:51).

A few corrections. To determine the relative divergence time between pairs of species or taxa, we used published data using genetic distance determined by gel electrophoresis; we did not “sequence genes”.  The purpose of the paper, as Zack says, is to determine how reproductive barriers between species arise with time by looking at the degree of reproductive isolation (measured only as hybrid sterility/inviability or as mate discrimination) between groups and correlating that with electrophoretic genetic distance, which is a measure of divergence time.

Also, Zack emphasizes the “reinforcement” aspect of the paper (I’ve put that conclusion in bold below), but that is only one of its findings—granted, a nice one. But the overall conclusions are several-fold, as the paper’s abstract notes below, including the relative rates of evolution of postzygotic isolation versus one form of prezygotic isolation (mate discrimination) as well as showing early evolution of male versus female postzygotic isolation, which explains the phenomenon of “Haldane’s Rule“, a generalization first noticed by J. B. S. Haldane in 1922, but neglected until I took it up in 1985.  This rule, pointing out the greater preponderance of sterility and inviability in heterogametic (XY or ZW) hybrids than in homogametic hybrids (XX and ZZ) is still subject to investigation and controversy, but has been a central focus of the genetics of speciation since 1985.

Here’s the abstract of our paper with the “reinforcement” finding shown in bold. Note the other findings, too:

To investigate the time course of speciation, we gathered literature data on 119 pairs of closely related Drosophila species with known genetic distances, mating discrimination, strength of hybrid sterility and inviability, and geographic ranges. Because genetic distance is correlated with divergence time, these data provide a cross-section of taxa at different stages of speciation.

Mating discrimination and the sterility or inviability of hybrids increase gradually with time. Hybrid sterility and inviability evolve at similar rates. Among allopatric species, mating discrimination and postzygotic isolation evolve at comparable rates, but among sympatric species strong mating discrimination appears well before severe sterility or inviability. This suggests that prezygotic reproductive isolation may be reinforced when allopatric taxa become sympatric.

Analysis of the evolution of postzygotic isolation shows that recently diverged taxa usually produce sterile or inviable male but not female hybrids. Moreover, there is a large temporal gap between the evolution of male-limited and female hybrid sterility or inviability. This gap, which is predicted by recent theories about the genetics of speciation, explains the overwhelming preponderance of hybridizations yielding male-limited hybrid sterility or inviability (Haldane’s rule).

Finally, Allen and I continued to collect data as new studies became available, eventually expanding the study to 171 taxon pairs—an increase of 41% in the amount of data. The results, published in Evolution in 1997, were similar to those of the earlier study, but stronger because they were based on more data. You can read the paper by clicking below.

Since electrophoretic analysis of species divergence is largely obsolete—everyone uses DNA sequencing now—the whole paper can’t be repeated with modern methods, but what has been done is analysis of a subset of species, and, as I recall (I’m not going to look up the papers), the results to date support those of our 1989 and 1997 papers.

A scientist is lucky if he or she has more than one or two good ideas in their career, and by that I mean an idea that influences their field in a substantial way. I’ve had about three, one of which is the analysis embodied in these two papers. And I have to pay tribute to Allen Orr (now retired, too): fiercely intelligent and hard-working—more a colleague than my graduate student. Both of us are honored to be included in the lists of ten books and ten papers discussed by Hancock. Josh and Esther Lederberg, W. D. Hamilton. Ronald Fisher, Sewall Wright—that is damn fine company!

More misguided critique of the modern theory of evolution—in Skeptic magazine

July 6, 2026 • 9:00 am

A recent Skeptic magazine features George Levine’s review of a new book by Jessica Riskin: The Power of Life: The Invention of Biology and the Revolutionary Science of Jean-Baptiste Lamarck. It’s about the life and accomplishments of Jean-Baptiste Lamarck (1744-1829), one of the first naturalists to suggest that life evolved from earlier (and simpler) ancestors, and by natural processes.

Biologists largely know Lamarck from his having been wrong. Yes, organisms did evolve, but Lamarck got what drove evolution completely wrong. Instead of the better-adapted individuals in a species leaving more offspring, which was Darwin’s theory, Lamarck posited that evolution proceeded by two means:

a.) A teleological drive in organisms to become more complex, and

b.) Via the inheritance of acquired traits. That is, organisms somehow became more adapted to the environment through their own activities, and these acquired adaptations were passed on to the next generation. The classic example Lamarck gave—and one now used to debunk him—is his scenario of how giraffe’s got long necks. Originally, he said, giraffes had shorter necks, and had to stretch their necks to reach leaves higher up on trees.  That stretching made their necks longer, and, as this process continued over generations, giraffes got their astoundingly long neck. Their striving to reach leaves had somehow become inherited.

We know now that Lamarck was wrong on both counts. First, there is no teleological “drive” to become more complex (nor do all lineages become more complex: tapeworms, for example, lost nearly all their organ systems). Further, acquired traits are not inherited. Although Darwin mentioned that briefly, his alternative theory of natural selection (see below) was pretty much on the mark.  New suggestions that epigenetically acquired modifications become inherited fail on two counts: they are erased from the genome in a few generations, and they do not lead to adaptations. In fact, as in the case of the “Dutch Hunger Winter” of 1944-1945, epigenetic modifications of the DNA acted in a way that was maladaptive, raising the incidence of disease among descendants. Eventually, those environmentally-induced epigenetic changes in DNA disappear, as they always do when epigenetic modification is not itself coded by the DNA.

In the end, Lamark’s “theory” of evolution came to nothing and his work was largely ignored.  According to the Skeptic article by George Levine, Riskin’s book tries to rehabilitate the ignored Frenchman, arguing that Lamarck and Darwin were both right in some ways and wrong in others, with Lamarck making seminal contributions to biology.  But anybody who knows the history of evolutionary biology must realized Darwin was more right than Lamarck—by far—and it’s a stretch to even say that Lamarck made any big contributions to modern biology.

I have not yet read Riskin’s book, but I can say that Levine’s comparison of Darwin with Lamarck is deeply misguided. If he’s characterizing the book accurately—and I don’t know if he is—then the book is also misguided. But I don’t want to criticize Riskin. Rather, I want to correct the errors purveyed by Levine’s review. Click the title below to see that review.

First here’s Levine’s short bio from Skeptic:

George Levine is the author of Darwin and the Novelists (Harvard University Press/Chicago University Press); Darwin Loves You (Princeton University Press); and Darwin the Writer (Oxford University Press). He was a longtime professor at Rutgers University until his retirement in 2006.

Let’s take Levin’s major points (and errors) one by one.

a.) Where Darwin and Lamarck were both right.

Both of them suggested that evolution occurred by naturalistic means.  But while Lamarck’s ideas never caught on, Darwin’s did: within a decade after he published On the Origin of Species in 1859, most biologists and many educated people embraced Darwin’s main theories (see below).

b.) Where Darwin and Lamarck were both wrong, and how they differed in wrongness.

Neither Darwin nor Lamarck understood how heredity worked, and both suggested that acquired changes could be inherited.  While Lamarck suggested that use of an organ of feature changed the physiology of an organism in a way that could be inherited, he didn’t specify how.  Unlike Lamarck, Darwin did not see the inheritance of acquired traits as the only or the overweening method of evolutionary change, though he did posit a mechanism: organs and other bodily parts transmitted their changes to the reproductive organs through the production of small “gemmules” that somehow made their way to the reproductive organs. Darwin’s theory is called pangenesis, and was also wrong. The inheritance of acquired traits as a means of adaptive change has been disproven by many experiments. As I’ve written in detail, epigenetic modification of the DNA by environmental change is not a mechanism of adaptive evolution.

Although both men were wrong about acquired traits changing inheritance for good, Lamarck was also wrong by positing a teleological process that, over time, drove species to become more complex.

c.) Why Darwin is revered and Lamarck ignored.

While Levine spends a lot of time arguing that Lamarck and Darwin were both wrong, and yet both made seminal contributions to biology, he largely ignores the reason why Darwin is lauded and Lamarck is ignored   There are two reasons for this:

1.) Darwin provided copious evidence for evolution and against creationism, and Lamarck did not. If you read The Origin, you will find chapter after chapter detailing evidence for why evolution was correct and Biblical creationism was not.  Darwin describes how features of development, vestigial organs, biogeography, and even the fossil record (very sketchy in Darwin’s time) militate against creationism and in favor of evolution. In this way, Darwin shoved aside the dominant theory of how life came to be in favor of a naturalistic theory driven by what he saw as his greatest idea, #2:

2.) Darwin was the first to suggest a plausible mechanism for evolution supported by evidence: natural selection. Lamarck’s mechanism was not plausible. The idea of natural selection is the theory that organisms with traits that made them more adapted to the environment left more offspring—and, if trait variation was heritable (as it usually is), enriched the next generation with more adaptations—was Darwin’s greatest contribution to biology. While the idea of evolution was “in the air” in the mid-19th century, if Darwin hadn’t come up with natural selection, the modern theory of evolution would have been delayed by decades.  Although Darwin did see “pangenesis” as one mechanism of evolution, another was the (correct) idea that individuals in a species were different from another and those differences were largely due to differences in their hereditary material.  Darwin proposed that these differences could be due to “mutations” coming from environmental changes. Though that wasn’t correct (mutations appear to be random), environmental causation isn’t necessary for natural selection to work. All we need to know is that something causes individuals to differ in their traits, and some of those differences could be inherited. That, combined with the idea that trait differences could affect reproduction, is all ye need to know.

Darwin supported this idea simply by drawing a parallel with artificial selection, which, as Darwin’s own experiments with pigeons showed, was hugely successful in modifying species in any direction the breeder wanted.  The importance of this argument is shown by Darwin’s devoting the first chapter of The Origin to it: “Variation Under Domestication.” My favorite quote in this chapter is this:

Breeders habitually speak of an animals’ organisation as something quite plastic, which they can model almost as they please.”

It works for plants, too, of course, as we know from almost all our domestic crops being extreme modifications of species found in nature, all effected by artificial selection.

The parallel is nearly exact, save that the breeder determines which traits are adaptive, while it happens by itself in nature. But in both cases more-adapted individuals leave more offspring, transforming the species. The argument is very convincing, and natural selection transforming species has now been demonstrated many times in nature. You don’t need a human breeder.

Darwin, then, is most revered for the twin achievements of demonstrating the truth of evolution and then providing a plausible mechanism for the production of “the endless forms most beautiful and most wonderful” limned in the last paragraph of The Origin. Lamarck did neither of these things.

d.) So what were Lamarch’s contributions to modern biology?  Levine mentions three.  “Lamarck was the first to use the word ‘biology’ and to conceive biology as a separate science.” And he “invented the category ‘vertebrates’, separating them off from ‘invertebrates’ in scientific study.” That’s about it, and it doesn’t even come close to what Darwin accomplished.  Besides, in many cases it’s not useful to separate vertebrates from invertebrates. Often we want to study phenomena seen in both groups.

e.) Levine’s  review has a lot of misconceptions about Lamarck.  For some reason that baffles me, Levine thinks that Lamarck contributed to modern biology the idea that, via their own behaviors, organisms can change how natural selection acts on them.  Lamarck, he said, added to modern biology the idea that agents are not just passive “victims” of natural selection imposed from without by the environment, but can promote their own evolution through their behavior.  Beavers, for example, evolved to build dams, and by evolving that behavior they made themselves subject to whole new areas of natural selection: finding the right places to build, developing sharper teeth and behaviors to gnaw down trees, and turning their dams into homes.

But that idea—that organisms can promote their further evolution through behavior—while correct, was not contributed by Lamarck. It’s a well-established part of the modern theory of evolution called niche construction. It was implied even by Darwin, who wrote in his book on earthworms that they modify their environments. But it was brought into evolutionary biology by my own advisor, Dick Lewontin, and then made more formal by John Odling-Smee and Mark Feldman.  Lamarck had nothing to do with this addition to the modern synthetic theory of evolution.

In fact, Levine goes even further, and jumps the rails when he seems to suggest that organisms want to evolve in certain directions, a view that borders on Lamarck’s teleology. (Bolding is mine,)

Natural selection and Lamarckian evolution are not necessarily incompatible theories. Riskin points out that in 1896, James Mark Baldwin published a paper called “Organic Selection,” which, after first being contested ferociously “had recently achieved widespread acceptance among biologists.” “Organic Selection means selection that an organism enacts upon itself by behaving in certain ways.” For example, once humans found that opposable thumbs could help in survival, natural selection did its work and those born with opposable thumbs had a greater chance to survive. In this case, natural selection and something like Lamarckian intention co-exist. In fact, they depend upon each other. Human desire and intention change what it is to adapt. So, as Riskin puts it, “organisms aren’t just the passive objects of natural selection but its active conductors.” Hey, that might be a way to make Lamarck’s poor abused giraffes respectable.

For Lamarck, via Riskin, organisms are active in their own adaptiveness. They are capable of changing the environment to make it compatible with their needs. And here Riskin introduced me to a powerful and crucial element of Lamarckism that we have all ignored to our peril: Organisms are capable of changing their own environments. Usually, they do it in what they take to be their own interest. As we have all too slowly become aware, we have been working toward a new era: after the Pleistocene has come the Holocene and now (though still disputed) the Anthropocene—the era “defined by significant human impact on Earth’s geology, climate, and ecosystems.”

How can we hack our way through this weedy patch of misunderstanding? First, how did humans get opposable thumbs in the first place, if not through natural selection? Did a hominim with a mutant thumb appear one day, observe it had opposable thumbs, and then say, “I must evolve in this way.” That sounds dumb, but here Levine has got the cause and effect reversed. Natural selection did its work on the ancestral hominin hand to form opposable thumbs which, as time passed, became stronger and more dextrous (we know this from the fossil record).  What does “intention” have to do with this? Nothing, as far as I can see. Nor can organisms evolve via “what they take to be their own interest.”  Natural selection has nothing to do with the “self interest’ of organisms, most of which don’t even have “self-interest”.  Yes, organisms can behave in ways that suit them, and that can lead to new selective pressures, as with beavers and earthworms, but “interest’ has nothing to do with it.  This idea borders on teleological, as it is in the wacky new “Third Way” of evolution, which also has teleological elements,

f.) As if this weren’t bad enough, Levine tars the modern theory of evolution by connecting it with eugenics and environmental despoliation. It’s another way of praising Lamarck because his theory wasn’t in any way connected with this bad stuff.  Levine says this:

One depressing and horrifying fact of which Riskin has made me aware is that just about every major figure in the development of the “modern synthesis” was a eugenicist. Clearly, this is no accident. Humans, from the perspective behind the Weismann barrier, are objects to be manipulated, coal mines to be dug out. Bad gene clusters to be eliminated. It is partly as a polemic against this view of the absence of agency in this world that Riskin devotes the later part of her book. But it never takes the shape of polemic.

. . . What Riskin shows is that for Lamarck the kind of thinking implicit in the modern synthesis was and remains a moral and physical disaster.

It’s a physical disaster presumably because Lamarck pointed out that humans were destroying the environment and Darwin didn’t. But again, this has nothing to do with Darwin’s theory, nor does it show that Darwin was “wrong. ”  Connecting Darwinism with eugenics and environmental depredation is the final error in a string of misconceptions and outright errors by Levine. Pity that this stuff was published in Skeptic magazine, which apparently didn’t get Levine’s review vetted by an evolutionary biologist. I emphasize again that because I haven’t read Riskin’s book, my criticisms are directed not at her but at the reviewer.

Caturday felids trifecta: kitten rescued after tornado; brave cat spooks bear; why cats can’t taste sweetness; and lagniappe

June 20, 2026 • 9:45 am

On May 9, the AP’s odd news site recounted a kitten rescue (click on screenshot to read):

An excerpt:

As storm chaser Ashton Lemley picked his way through a tornado-ravaged Mississippi trailer park, he heard the unmistakable meow of a kitten pierce the predawn darkness.

The homes were flattened just hours earlier as storms spawned at least three tornadoes across the bottom half of Mississippi, injuring a dozen at the trailer park in the rural community of Bogue Chitto.

Lemley had no idea where the kitten was, but he was determined to find it. After a few minutes, the meowing stopped, and Lemley feared the worst.

Then, five minutes later, he heard it again.

“I said, ‘Oh, he’s still alive!’” Lemley told The Associated Press on Thursday.

Lemley quickly dug under insulation from a flattened wall until his flashlight beam found the kitten — wet, scared and hiding between two wooden posts.

Lemley captured the moment on video: “Oh my goodness, I found him!” he says to the camera. “Are you OK? Come here – it’s OK. … We’ll get you cleaned up, baby. Don’t you worry.”

Lemley held the kitten in his arms for a few minutes before handing it off to the commander of the United Cajun Navy, a volunteer disaster-response group, who dried it off and took it to safety. Lemley marveled that it didn’t appear to be injured.“I’ve been in these situations so many times,” said Lemley, who has been chasing storms since 2010. “I don’t try to get overly emotional. But it is very heartbreaking to see any type of animal or human go through something like that.”

Lemley says there’s already a lot of interest from people who want to adopt the kitten if its owners are not located. Some, he said, want to name it Tornado.

It won’t be coming home with him, though: Lemley is allergic to cats.

Here’s a short video of the rescue. Look at that sodden little moggy! But it will be okay.

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From PetHelpful, we have a Tik Tok video and the video notes (indented below).

Little Bear Visits My Bedroom Window

An unexpected guest can make for a delightful surprise, and nothing illustrates this better than when I found a little black bear gazing curiously through my bedroom window. This moment was not only adorable but also a wonderful reminder of the beauty of wildlife right at our doorstep.

Bears are fascinating creatures known for their intelligence and curiosity. When a bear approaches residential areas, it often piques curiosity and concern among homeowners. Observing animals in their natural habitat can lead to valuable insights about their behavior. In this case, Little Bear seemed intrigued by what was happening inside the house, highlighting the need for a peaceful coexistence with wildlife..It’s important to remember that while these encounters can be entertaining, maintaining a safe distance from wild animals is essential for both human and animal safety. Living close to nature offers unique experiences, but it also requires responsibility. If you find yourself in a similar situation, enjoy the moment, take pictures if safe, but avoid feeding or trying to interact directly with wild animals.

In closing, this little bear visiting my window was a charming experience that reminded me of the vibrant wildlife that surrounds us. Have you had any wildlife encounters in your area? Share your stories or tips on safely observing animals in nature!

Here’s a very short video of the cat, safely inside, lashing out with its paw at the bear. Bear heads for the hills!

@missashleyrubes

I was reading in bed when I looked over to Little Bear looking into my window 🪟🐻 #bear #blackbear #animal #nature #wildlife

♬ Curious Animals – Eitan Epstein Music

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If you own a cat, you probably know that they can’t taste sweetness in food. This article from Space Daily (click on screenshot) explains why. Well, it’s not rocket science: cats don’t have the rcceptors to taste sweetness. Or rather, they have the genes that allowed their ancestors (and their living mammalian relatives) to taste sweetness, but the genes are broken. (This is, of course, proof of evolution: why else would a cat have genes that function in its relatives, but that are broken in felids?

An excerpt:

Cats are notoriously indifferent to sweet things. Pour syrup near a dog and the dog will investigate. Pour syrup near a cat and the cat will ignore it. Veterinarians and cat-food companies have long noted that cats show no preference for sugar in feeding tests, no matter how much sugar is presented. The reason is not a behavioural quirk or a learned aversion. It is genetic, and it traces back tens of millions of years to the point at which the ancestors of modern cats became obligate carnivores, eating only meat. The gene that produces a working sweet receptor on the tongue, called Tas1r2, has been broken in cats for so long that it no longer functions at all. A cat looking at a sugar cube is in the same sensory position as a human looking at an ultraviolet light source: the signal exists, but the receptor that would detect it does not.

The molecular discovery came in 2005 from a team led by Xia Li and Joseph Brand at the Monell Chemical Senses Center in Philadelphia, in collaboration with colleagues at the Waltham Centre for Pet Nutrition in the United Kingdom. Their paper in PLOS Genetics, titled “Pseudogenization of a Sweet-Receptor Gene Accounts for Cats’ Indifference toward Sugar,” established that the cat sweet receptor is not just inefficient. It is, at the genetic level, non-functional.

. . . The animals affected included the California sea lion, the southern fur seal, the Pacific harbor seal, the Asian small-clawed otter, the spotted hyena, the fossa (Madagascar’s largest carnivore), and the banded linsang. Crucially, the disabling mutations in each of these species occurred in different places within the Tas1r2 gene, indicating that the losses happened independently in each lineage, not via inheritance from a common ancestor. The same evolutionary pressure that turned off the gene in cats turned it off, separately, in at least seven other carnivorous lineages over the same broad timeframe. Behavioural testing of two of the genotyped species — the Asian small-clawed otter (broken Tas1r2) and the spectacled bear (intact Tas1r2, and predominantly herbivorous despite its order) — confirmed the pattern. The otter showed no preference for sweet compounds. The bear preferred sugars and even some non-caloric sweeteners.

. . . The animals affected included the California sea lion, the southern fur seal, the Pacific harbor seal, the Asian small-clawed otter, the spotted hyena, the fossa (Madagascar’s largest carnivore), and the banded linsang. Crucially, the disabling mutations in each of these species occurred in different places within the Tas1r2 gene, indicating that the losses happened independently in each lineage, not via inheritance from a common ancestor. The same evolutionary pressure that turned off the gene in cats turned it off, separately, in at least seven other carnivorous lineages over the same broad timeframe. Behavioural testing of two of the genotyped species — the Asian small-clawed otter (broken Tas1r2) and the spectacled bear (intact Tas1r2, and predominantly herbivorous despite its order) — confirmed the pattern. The otter showed no preference for sweet compounds. The bear preferred sugars and even some non-caloric sweeteners.

And since people here should know some science, you’ll be able to understand this from the paper’s abstract:

Because the mammalian sweet-taste receptor is formed by the dimerization of two proteins (T1R2 and T1R3; gene symbols Tas1r2 and Tas1r3), we identified and sequenced both genes in the cat by screening a feline genomic BAC library and by performing PCR with degenerate primers on cat genomic DNA. Gene expression was assessed by RT-PCR of taste tissue, in situ hybridization, and immunohistochemistry. The cat Tas1r3 gene shows high sequence similarity with functional Tas1r3 genes of other species. Message from Tas1r3 was detected by RT-PCR of taste tissue. In situ hybridization and immunohistochemical studies demonstrate that Tas1r3 is expressed, as expected, in taste buds. However, the cat Tas1r2 gene shows a 247-base pair microdeletion in exon 3 and stop codons in exons 4 and 6. There was no evidence of detectable mRNA from cat Tas1r2 by RT-PCR or in situ hybridization, and no evidence of protein expression by immunohistochemistry. Tas1r2 in tiger and cheetah and in six healthy adult domestic cats all show the similar deletion and stop codons. We conclude that cat Tas1r3 is an apparently functional and expressed receptor but that cat Tas1r2 is an unexpressed pseudogene. A functional sweet-taste receptor heteromer cannot form, and thus the cat lacks the receptor likely necessary for detection of sweet stimuli. This molecular change was very likely an important event in the evolution of the cat’s carnivorous behavior.

The upshot: tasting sweetness in mammals requires a protein that is a dimer made from the product of two genes. In house cats (and some other carnivores), one of the genes is expressed normally but the other is nonfunctional because of a large deletion of the DNA sequence, so that the dimer itself isn’t formed. Ergo cats can’t detect sweetness, and thus you shouldn’t expect your cats to like sweets (they shouldn’t get them anyway). If your cat licks ice cream, it is tasting not the sweetness but the dairy-ness: fats and proteins.  Cheetahs and tigers also lack the dimeric protein.

Why do dogs taste sweetness and cats don’t? Because dogs produce the dimer and cats don’t.  Somewhere in the ancestor of all felids, the gene for Tastr2 experienced a deletion.  Because all cats are obligate carnivores, and don’t eat stuff like berries, they have no “need” to taste sweetness, so a deleted gene is not a deleterious gene. It just continued to mutate, staying in the DNA but doing nothing.

I suppose d*g ancestors, and mammals like bears and hedgehogs, do benefit from sugar in their diet and so have retained the genes to detect it. (We do, too: sugars were valuable components of the diet in us and our primate relatives, and so our taste chemistry evolved to not only detect sweetness, but also find it pleasurable so that we seek out a needed nutrient. Unfortunately, sugars are much more common now than in the millions of years of our ancestry since we diverged from the chimp/bonobo lineage; and so we eat too many of them and get cavities and grow obese.)

The alternative theory is that God decided to make cats obligate meat-eaters, and so he left out their ability to detect sugar. But that doesn’t work because why would God give cats genes that are very similar to those of their sweetness-tasting relatives, but don’t work?  The creation-by-God theory fails, and we’re left only with common ancestry, i.e., evolution.

We have a similar broken gene, as I describe in Why Evolution is True:

The most famous human pseudogene is GLO, so called because in other species it produces an enzyme called L-gulono-γ-lactone oxidase. This enzyme is used in making vitamin C (ascorbic acid) from the simple sugar glucose. Vitamin C is essential for proper metabolism, and virtually all mammals have the pathway to make it—all, that is, except for primates, fruit bats, and guinea pigs. In these species, vitamin C is obtained directly from their food, and normal diets usually have enough. If we don’t ingest enough vitamin C, we get sick: scurvy was common among fruit-deprived seamen of the nineteenth century.

The reason why primates and these few other mammals don’t make their own vitamin C is because they don’t need to. Yet DNA sequencing tells us that primates still carry most of the genetic information needed to make the vitamin.

It turns out that the pathway for making vitamin C from glucose involves a sequence of four steps, each promoted by the product of a different gene. Primates and guinea pigs still have active genes for the first three steps, but the last step, which requires the GLO enzyme, doesn’t take place: GLO has been inactivated by a mutation. It has become a pseudogene, called ¯ψGLO” (ψ is the Greek letter psi, standing for “pseudo”). ψGLO doesn’t work because a single nucleotide in the gene’s DNA sequence is missing. And it’s exactly the same nucleotide that is missing in other primates. This shows that the mutation that destroyed our ability to make vitamin C was present in the ancestor of all primates, and was passed on to its descendants. The inactivation of GLO in guinea pigs happened independently, since it involves different mutations. It’s highly likely that since fruit bats, guinea pigs, and primates got plenty of vitamin C in their diet, there was no penalty for inactivating the pathway that made it. This could even have been beneficial since it eliminated a protein that might have been costly to produce.

A dead gene in one species that is active in its relatives is evidence for evolution, but there’s more. When you look at ψGLO in living primates, you find out that its sequence is more similar between close relatives than between more distant ones. The sequences of human and chimp ψGLO, for example, resemble each other closely, but differ more from the ψGLO of orangutans, which are more distant relatives. What’s more, the sequence of guinea pig ψGLO is very different from that of all primates.

Only evolution and common ancestry can explain these facts.

Inactive pseudogenes that are functional in relatives constitute some of the strongest evidence for evolution, as there is no alternative theory that explains them. The article above alludes to the gene loss being a product of evolution, but doesn’t mention something that I see as crucial given Americans’ reluctance to accept evolution: the nature of the gene loss and the sequence similarity among pseudogenes is strong evidence for evolution.

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Lagniappe:  From an Archaeology and Art Facebook post:  Draw a cat using only straight lines.  Here you go:

And extra lagniappe (is that redundant?). Only in Turkey will there be spectators!

h/t: Ginger K.,

Beauty is in the (evolved) eye of the beholder

May 18, 2026 • 9:45 am

Right now I’m reading Steve Stewart-Williams’s new book: A Billion Years of Sex Differences: How Evolution Shaped the Minds of Men and Women. It is neither a pure blank-slate social-constructivist book nor a hereditarian, genetic-deterministic book, but takes an evidence-based middle ground, asking to what extent behaviors and mindset are molded by evolution and to what extent social conditioning plays a role.  I won’t give a take on the book as I’m not yet finished, but it does make many arguments I’m familiar with.  One of these is the familiar and well-documented claim that, based on different degrees of parental investment, men concentrate more than women on beauty when looking for a mate, while women are less interested in appearance than are men but more interested in paternal behavior, status, and wealth of a prospective mate. These are not absolute differences, of course: many men want women who will invest a lot in their offspring (we are, after all, generally monogamous), and many women want men who are pleasing to the eye. This is a difference in average preferences, not absolute ones characterizing all individuals.

Although some of this average sex difference in behavior may reflect social conditioning, its evolutionary background is likely based in part on the differential investment between the sexes in offspring: although many societies are polyandrous and monogamous, on average males still have a potentially larger number of offspring than do females. This appears to be true in many societies, as well as in our closest relatives, the apes and in most species of animals. Women, who by virtue of their reproduction (as well as by both the evolutionary and social impetus to do most of the childcare) need fathers who will do their share of parental duties and provide for the offspring.  And of course men do share some of those duties, but are also more interested in casual sex and adultery—a way to spread more of their genes when they don’t invest as much in offspring.

If you want the evidence for this, read Stewart-Williams’s book or the references he cites.

Why am I pondering this? Because when I went to the library the other day, I caught a glimpse of myself in the entry door and thought, “Geez, look at that ugly old man!”  Whatever attractive physical features I once had—and I was never close to being a Robert Redford—have vanished, carried away by time’s wingéd chariot.  Women, too, worry about ageing, and are even more concerned about it because of a key difference between men and women: as women get older and become unable to reproduce, they become less desirable faster than do men.  A man can have offspring even in his eighties, while in their early fifties most women hit menopause, which means no more kids. Since men have largely evolved to be physically attracted to women who can give them children, women try harder than do men to retain the signs of youth: hair color, plastic surgery, botox, and the like. On average, they try harder to retain physical attractiveness because it is that rather than status that is a dominant way of attracting partners—and most people want a partner.

Which brings up a tangential point: what about gay men and women?  I don’t know their preferences but it would be interesting to study (and I’m sure people have) whether men attracted to other men for lasting partnerships are less concerned with looks than are women attracted to other women for partnerships.

Back to the point, which is this. It is my theory, which is mine (and likely many other people’s) that there is really no objective difference in physical attractiveness with age, in either men or women.  Old men and women look different from their younger selves (I now refrain from looking in mirrors), but the beauty associated with youth and the loss in attractiveness associated with age are not anything objective (beauty never is, of course).  We are simply evolved to think that those features associated with having more offspring on us are more “beautiful”, as those mindsets are the ones promoted by natural selection. This explains why women are more concerned with the physical ravages of time then are men, for their physical attractiveness to the other sex wanes faster with time. I’ve often heard older actresses say that by the time they hit forty, Hollywood no longer wants them, while that doesn’t happen so much with male actors.  Why is this difference retained past the age of reproduction in women? I suppose it’s because it’s largely innate and most women didn’t live past menopause during most of our evolution.

Thus beauty is in the eye of the beholder: it is subjective, like all standards of beauty, but the subjectivity is molded in certain directions by natural selection.

I am not, of course, saying that this is good—only that much of it is natural. I do not want to commit the naturalistic fallacy here, but simply consider what aspects of our minds and behaviors might be based on genes, to what extent, and whether those evolutionary bits have been molded by natural selection.

This parallels a point I’ve made before: other aspects of our senses, like tastes, are clearly molded by natural selection.  I have said, for example, that to a vulture rotten meat tastes as good as an ice-cream sundae does to us.  Animals have evolved to search for food that tastes good because, over time, our senses evolve to find the food we need to grow and reproduce to be tasty. In other words, natural selextion has molded our taste buds and our brains so we prefer what is nutritious and fosters reproduction.  This can be hijacked: we now eat too many fats and sweets because those substances were desirable to our ancestors as they were rare but promoted reproduction.  Now they no longer do so because of the surfeit of “bad” food on tap.  But our taste buds haven’t yet caught up to our health.

Why do feces and vomit repel us, smelling foul? It’s very likely that these substances were evolutionarily associated with the spread of disease, and so we evolved smell-detectors that find them repugnant. After all, dung beetles love the odor of feces!

I’ll draw one more parallel here. Anybody who thinks about it seriously must admit that male orgasms, intricate and immensely pleasurable physiological mechanisms associated with ejaculation, have evolved as a way of promoting reproduction (the evolutionary basis of female orgasms is more speculative, but there is no shortage of adaptive hypotheses).  Orgasms are a way of getting men to produce offspring, just as sweetness is a way of getting us to eat sugar. And, like eating too many sweets, orgasms can be hijacked—severed from their reproductive function by condoms, chemicals, or medication. Organizations like the Catholic Church have tried mightily to try to reconnect sex and reproduction, but it is largely in vain.

I have undoubtedly written this too fast, as I just had some thoughts and wanted to get them down on paper before I forget them. I’ve considered that I’m trying to dispel my idea that I’m unattractive, and in so doing thought about physical attraction in general. And yes, I’m also reading Stewart-Williams’s book, which considers in detail this and other aspects of human (and animal) mentation and behavior.

Once you get an evolutionary mindset, all sorts of behaviors now become more interesting. That doesn’t mean we should make up adaptive stories and consider those stories to be true, but neither should we ignore possible evolutionary explanations. To explain the evolutionary basis of human behaviors and minds will be hard, as most of them evolved in the unrecoverable distant past—in our ancestors.  But some of the explanations are testable, and here I must stop.

An evolutionary biologist lists and discusses the ten most influential books in the field

April 7, 2026 • 11:00 am

I would have missed this video had reader Doug not called my attention to it. It’s a very good half-hour discussion by evolutionary biologist Zach B. Hancock, a professor at Augusta University, in which he recommends the the top ten most influential books in evolutionary biology. Since Hancock is a population geneticist, the books deal largely with evolutionary genetics, but not all of them.

I slipped in at #10 with my book on Speciation with Allen Orr, but I won’t be too humble to claim our book wasn’t influential, for, as Hancock notes, it’s the only comprehensive book on the origin of species around. (Darwin’s big 1859 book was about the origin of adaptations, and had little that was useful about the origin of species.) Hancock regrets that Allen and I aren’t going to do a second edition, but Allen refuses to, and I don’t have the spoons (I do have 200 pages of notes on relevant papers that appeared after our book came out, but that will go nowhere.)

The rest of the list is stellar, and shows a keen judgement about the field. I’m not sure I would have put Lack’s book on the Galápagos finches in there, as it’s pretty much out of date. It should be replaced by a very important book by Ernst Mayr, his Systematics and the Origin of Species or the updated version in 1963,  Animal Species and Evolution. It was Mayr who codified the Biological Species Concept and paved the way for experimental and observational studies of speciation, and hence my book with Orr. 

I’d expect every graduate student in evolutionary genetics to have read  most of these books by the time they get their Ph.D. In fact, when I was on prelim hearings, judging whether students could be admitted to candidacy after a year or two, I and my colleague Doug Schemske made a habit of asking students to name the major accomplishments of several of the authors listed below. My impression is that the history of the field is not given so much weight now, so I wonder if students could still explain the major accomplishments of say, Theodosius Dobzhansky or Ronald Fisher. The books are of more than historical interest, for they raise questions that are still relevant. (I spent a lot of my career trying to understand the phenomenon of “Haldane’s Rule,” explained by J.B.S. Haldane in 1922. The paper was completely neglected until I read it in the early eighties and started a cottage industry of explanations [my own was largely wrong]).

Hancock’s explication of each book is excellent.  If you’re an academic teaching evolutionary biology, you might see how many of these books your students have read.

One commenter on YouTube gave the list and the time points in the video where each is discussed (the links go to those time point).

2:26 #10 Speciation – Jerry Coyne & Allen Orr
4:50 #9 Darwin’s Finches – David Lack
6:59#8 Evolution: The Modern Synthesis – Julian Huxley
9:15 #7 The Origins Of Genome Architecture – Michael Lynch
11:23 #6 Chance & Necessity – Jacques Monod
13:26 #5 The Selfish Gene – Richard Dawkins
16:54 #4 The Neutral Theory of Molecular Evolution – Motoo Kimura
19:34 #3 Genetics and the Origin of Species – Theodosius Dobzhansky
22:20 #2 The Genetical Theory Of Natural Selection – Ronald Fisher
26:35 #1 On The Origin Of Species – Charles Darwin

Two “Times” obituaries for Robert Trivers

April 7, 2026 • 9:45 am

Reader Simon called my attention to a new obituary in the Times of London of Robert Trivers, a giant in evolutionary biology (and a notorious eccentric) who died on March 12.  Because his death wasn’t announced immediately after he expired, this was bit late, but better late than never—especially given Trivers’s importance in the field. It’s a good obituary but the gold standard was Steve Pinker’s “in memoriam” article about Trivers published in Quillette on March 25.

Click the screenshot below to read, and if that doesn’t work,the article is archived here.

An excerpt:

In a burst of creativity in the early 1970s, Robert Trivers published a series of scientific papers that earned him a claim to being among the most important evolutionary theorists since Darwin. He was the first to fully appreciate how a gene-centric view of natural selection could explain some of the most puzzling and fundamental patterns in social life: the function of altruism, why males and females differ so much, the underpinnings of sibling rivalry and the delicate dynamic of conflict and co-operation that exists between parent and child.

Brilliantly original, Trivers was also an academic misfit: a foul-mouthed, pot-smoking individualist with a notable tendency to get into violent scrapes and an ungovernable character that eventually strained his relationship with the academy to breaking point.

Why do we ever behave altruistically? That is, why would an organism ever promote the reproductive success of another at some cost to its own? Since the work of the great evolutionist WD Hamilton, it had been appreciated that “kin selection” could explain why close relatives help one another out: doing so promotes an organism’s “inclusive fitness”, a measure accounting not only for an organism’s own genes but for copies of the same genes likely to be present in relatives. But why help non-kin? To Trivers, it was an obvious fact of life that we sometimes give priority to friends, and even strangers, over direct relatives.

Persuaded of the misguidedness of “group selectionist” theories that were fashionable at the time — according to which organisms sometimes sacrifice themselves for the “good of the species” — Trivers gave the central explanatory role to the gene. In his landmark 1971 paper, The Evolution of Reciprocal Altruism, Trivers argued that altruism depended on the possibility of reciprocity. As long as helping a non-relative is not too costly, and there is sufficient probability that the favour would one day be returned, genes coding for altruistic dispositions spread.

. . . Frustrated by the Harvard biology faculty’s delay in granting his tenure application in the late 1970s, he abruptly left with his young family to take up a position at the University of California, Santa Cruz, a decision he came to regard as a “once in a lifetime” mistake. There, he befriended Huey Newton, co-founder of the paramilitary Black Panther political party, who was a doctoral student at the university. They co-authored a paper on self-deception, and Trivers made Newton his daughter’s godfather. He joined the Panthers for a period and later confessed to doing “an illegal thing or two”, before Newton removed him from the group for his own safety.

In fact, what I recall in 1977 is that Harvard’s biology department recommended tenure for Trivers, but that recommendation was overturned by President Derek Bok.  I was there at the time and can vouch for that. Others say that Trivers asked for early tenure and was denied that, and then decided to leave Harvard. I also heard, and I can’t vouch for this, that Richard Lewontin (my Ph.D. advisor) and Dick Levins, both Marxists who despised sociobiology, went to President Bok to lobby him to deny Trivers tenure.  What we do know is that Trivers then moved to Santa Cruz, and later to Rutgers, where his academic turmoil continued:

. . . In 2015 he was suspended by Rutgers University for refusing to teach a course on human aggression, a field he claimed he was not expert in (despite its being a personal forte of his). He quit university life for good shortly after. Later, he was among the set of high-profile intellectuals pilloried for maintaining financial and social links to Jeffrey Epstein, even after the latter’s conviction for sex offences. Far from apologetic, Trivers, who accepted funding from Epstein to study the relationship between knee symmetry and sprinting ability, vouched for his integrity; in Trivers’s view, Epstein’s imprisonment was punishment enough and his crimes less “heinous” than they were made out to be.

It is testament to the depth and generality of Trivers’s discoveries that they could be applied so readily, as he unsparingly conceded, to his own case. As he understood, natural selection has built us, and it is to natural selection we must return “to understand the many roots of our suffering”.

Compared to Pinker’s piece, the Times obituary is light on Trivers’s scientific accomplishments, but all in all it’s pretty good.

Below is a NYT obituary, also delayed, that appeared on March 27 (click to read or find it archived here):

An excerpt (David Haig, who’s quoted, has written his own remembrance of Trivers, as the two were good friends; but I don’t think it’s yet been published):

“Robert Trivers was unlike any other academic I have known,” David A. Haig, an evolutionary biologist at Harvard, wrote in a remembrance of Professor Trivers for the journal Evolution and Human Behavior. “In another life, he might have been a hoodlum.”

Raised by a diplomat and a poet, and educated at Phillips Academy in Andover, Mass., and Harvard University, Professor Trivers thrived on challenging scientific orthodoxies, calling the field of psychology a “set of competing guesses.” (He also scorned physics, noting that its utility was “connected primarily to warfare.”)

In the early 1970s, as a graduate student at Harvard and later as an untenured professor there, he published a series of papers applying Darwin’s theory of natural selection to social behavior, arguing that science had failed to connect evolution to an understanding of everyday life.

“I was an intellectual opportunist,” he wrote in “Natural Selection and Social Theory: Selected Papers of Robert Trivers” (2002). “The inability of biologists to think clearly on matters of social behavior and evolution for over a hundred years had left a series of important problems untackled.”

The paper does a decent job in outlining Trivers’s contributions, the most important of which was his evolutionary explanation of “reciprocal altruism”, but again, see Pinker for a fuller explication.  A bit more about the situation at Harvard:

During this creative burst, Professor Trivers struggled with mental health issues and was hospitalized at least once for bipolar disorder. He applied for early tenure at Harvard, but the decision was postponed because of concerns about his mental health.

“He could be a brilliant and wonderful colleague,” Professor Haig said. “In a different mood, he could be unnecessarily hostile to those around him.”

That’s enough for now, save one I just found in Skeptic, a remembrance by Trivers’s only graduate student ever, Robert Lynch. Click below to read:

It ends this way:

One of the last times I spoke with Robert, a fall had left his right arm nearly useless. He described it as “two sausages connected by an elbow.” He was a chaotic and deeply imperfect man, but also one of the few people whose ideas permanently changed how we understand evolution, animal behavior, and ourselves. Steven Pinker wrote that “it would not be too much of an exaggeration to say that [Trivers] provided a scientific explanation for the human condition: the intricately complicated and endlessly fascinating relationships that bind us to one another.”  That seems just about right to me.

His ideas are some of the deepest insights we have into human nature, animal behavior, and our place in the web of life. The mark of a great person is someone who never reminds us of anyone else. I have never known anyone like him.

I’ll miss you, Robert. You asshole.

A transitional fauna shows that the “Cambrian explosion” was happening before the Cambrian

April 5, 2026 • 8:30 am

The Cambrian Period, beginning at 538.8 Ma (million years ago) and lasting about 52 million years, is famous for marking the transition from simple and largely unicellular animals to, beginning at the period’s inception, representatives of modern groups.  This apparently rapid onset of modern forms of multicellular animals constitutes the famous “Cambrian Explosion.”

The Cambrian was preceded by the 96-million-year-long Ediacaran period, extending from 635 million years ago to the beginning of the Cambrian. The Ediacaran fauna, consisting of some multicellular animals of unknown affinity and things looking like members of some modern groups like cnidarians (represented today by jellyfish, corals and anemone). But most of the Ediacaran groups appeared to have died out at the end of the Ediacaran, and for unknown reasons.

The boundary between the Ediacran and the Cambrian thus marks a major transition in animal life.   Many of the “modern” groups that first arose during the Cambrian don’t have apparent ancestors in the Ediacaran, and so those modern groups were thought to have evolved almost instantaneously (in geological time!). But surely modern groups had ancestors during the Ediacaran: unless you’re a Biblical fundamentalist, you realize that ancestors of modern groups had to have existed well before the Cambrian explosion.

Now a paper in Science, based on a fossil group called the Jiangchuan Biota that spans the period from 559-534 million years ago, shows that representatives of “modern” groups seen in the Cambrian explosion were indeed present in the late Ediacaran, pushing back the time of origin of modern phyla 4-5 million years.  This conclusion was possible because of the remarkable preservation of the animals (and some algae), all present as carbonaceous films on rocks—the same kind of films (presumably due to rapid burial) that enabled us to see the remarkable Burgess Shale fauna of the middle Cambrian. The new find was in the province of Yunnan in Southwestern China.

You can see the paper by clicking the screenshot below, reading the pdf here, or reading the shorter blurb at an Oxford University sit. at the bottom. All photos below are taken from the paper.

I won’t go into all the terminology involved in identifying the groups but will show a few fossils from the paper strongly suggesting that some “modern” groups arose in the late Ediacaran.

First, an anomalous animal that appears to be some kind of worm, but one with a “holdfast” disc on its butt. We don’t know what this one is, but it has oral projections or tentacles. The disc is very clear:

Another wormlike animal (note that these are small: a few millimeters) having a clear oral region. Again, we’re not sure what this is, but the preservation as a carbon film is remarkable:

A deuterostome (animals where the first opening in the embryo becomes the anus rather than the mouth), a group thought to have appeared in the Cambrian but here seen in the Ediacaran: this one resembles  Herpetogaster, known from the early Cambrian which, according to Wikipedia, “possessed a pair of branching tentacles and a tough but flexible body that curved helically to the right like a ram’s horn and was divided into at least 13 segments”. This one, like Herpetogaster, has tentacles (at leat four) and a stalk.  It’s interpreted as a relative of acorn worms, relatives of modern echinoderms which are hemichordates, the closest living group to modern chordates (animals with notochords and a dorsal nerve chord, which include all vertebrates).

The one below,described in the paper as “Margaretia-like animal now known as a dwelling tube for an enteropneust hemichordate worm”. It’s also described as having “regular, oval-shaped holes running along its length”. Again, we see what is likely an early hemichordate, showing that the relatives of modern chordates seem to have been present several million years before the Cambrian explosion began.

The one below is identified as a ctenophore, or comb jelly, a phylum of early animals previously known only from the mid-Cambrian. “OS” stands for “oral skirt”, described as “a specialized, often scalloped, muscular, or rigid structure surrounding the mouth, primarily found in Cambrian-era fossil comb jellies such as Ctenorhabdotus and Thalassostaphylos. Unlike modern ctenophores, these ancient species used the skirt for feeding, potentially to engulf large prey.”

Finally, this animal is thought to be an early cnidarian with tentacles and a holdfast (HF). Although one form identified as a cnidarian had already been recognized from the Ediacaran, here we have another that’s different, showing a radiation of cnidarians before the Cambrian.

These fossil data support already-existing molecular data suggesting that animal groups had already evolved and diversified before the Cambrian, though until now no fossils, or only a few suggestive fossils, were known.

The authors’ summary below, though written in scient-ese, basically says that a major radiation of animal phyla had already begun before the Ediacran/Cambrian boundary, but we did not know about it because the conditions for forming this kind of trace fossil, requiring rapid burial in marine sediment (and subsequent finding by investigators!) were infrequent:

The new Jiangchuan animal fossils, dominated by bilaterians of apparently diverse affinities, with rarer fossils more typical of late Ediacaran deposits, could be described as a “Cambrian-type” assemblage from the late Ediacaran. A dominantly bilaterian assemblage from the late Ediacaran may not have been discovered until now as a result of the paucity of carbonaceous compressions from this time, hinting at a broader taphonomic bias (51).

If you want a short, readable summary of the importance of this fine, click below to read a shorter summary from Oxford University.