Tag Archives: Stephen Jay Gould

Turnover pulse

Elizabeth Vrba, a South African paleontologist, coined the term “turnover pulse.” The idea is that most species most of the time are in an equilibrium with their physical and biotic environments, and not changing much. But every once in a while an environmental disturbance comes along, resulting in large scale extinctions, and a pulse of speciation. Most evolutionary change, on this theory, occurs during these pulses. Vrba saw evidence of a pulse 2.5 million years ago among South African antelopes (affecting specialized more than generalized feeders). The pulse was associated with a shift toward cooler weather, and a shrinking of forests and expansion of grasslands. Part of the turnover pulse hypothesis is that the same pulses should affect many different species at the same time: there is arguably a turnover among hominins as well, giving rise to a later generation of savannah-adapted australopithecines.

Vrba was one of a circle of paleontologists pushing the idea of punctuated equilibrium ¬– that during most of their existence species don’t change much (stasis), and evolutionary change is concentrated in the times and places when a new species branches off from another. Steven Jay Gould and Niles Eldredge were others pushing the idea. There are various possible explanations for why we might see a combination of stasis and punctuated equlibrium (assuming the theory is true in the first place). Environmental controls, as suggested by Vrba are one possibility. Or maybe species’ developmental systems are tightly integrated and resistant to change. Or (for sexually reproducing species) the need to find a similar-enough mate might foster stasis most of the time.

We’ve seen some enormous episodes of mass extinction before on Logarithmic History. The turnover pulse hypothesis implies that the same phenomenon on a smaller scale is behind most evolutionary change. Not everybody buys this though. Punctuated equilibrium is a hugely contentious topic. And plenty of evolutionary biologists think that arms races among (and within) species keep evolution running along pretty constantly even without environmental changes. We’ll see some of the same issues – punctuation versus gradualism, ecological forcing versus internal dynamics driven by arms races – when we take up human history.

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Planet of the horses

Horses have probably been the single most important domesticated animal in human history. Also, more than with other livestock, people get attached to horses as individuals. I’m guessing that in history and literature there are more horses with individual names than any other animal. (Alexander the Great’s horse was Bucephalus, “Ox-head”; Charlemagne’s was Tencendur; Don Quixote’s was Rocinante; Gandalf’s was Shadowfax.) We’ll be hearing a lot more about horses and horse folk on Logarithmic History once we get to human history.

Being so charismatic, horses have featured in a big way in arguments over evolution. Thomas Henry Huxley (1825-1895), “Darwin’s bulldog,” knew he needed to find good evidence for evolution. When he visited the United States in 1876, he was ready to give a lecture based on horse fossils from Europe. But visiting Yale, he was so impressed with O. C. Marsh’s collection of horse fossils from the western United States, that he rewrote his lecture around it.

Henry Fairfield Osborn (1857-1935) was director of the American Museum of Natural History and a huge presence in American paleontology. He was active at a time when most scientists accepted evolution, but many weren’t so keen on Darwin’s theory of natural selection. He thought horses were a fine example of “orthogenesis,” the tendency of species to follow a fixed line of evolution, reflecting internal forces, maybe related to willpower. He thought that humans shared a migratory spirit with horses, so that anywhere horse fossils were found would be a good place to look for human fossils. This theory didn’t pan out too well. A massive AMNH expedition to Central Asia led by Ray Chapman Andrews found all sorts of wonders – dinosaur eggs, baluchitheres – but no fossil “pro-men.” Orthogenesis leant itself naturally to diagrams showing evolution from early to modern horses going in a straight line.

horseladder

George Gaylord Simpson (1902-1984), paleontologist, was one of the great figures in the evolutionary Modern Synthesis that brought together Darwin’s theory of natural selection and Mendel’s genetics. There was no room for orthogenesis in the Modern Synthesis, and Simpson emphasized that the evolution of horses was a matter of adaptation to a changing environment – especially the spread of grasslands. Also that horse evolution looked more like a bush than a ladder.

horsebush

Stephen Jay Gould (1941-2002) was the most widely recognized American evolutionary biologist of recent times. (For example had a spot on The Simpson’s — “Lisa The Skeptic,” Season 9.) Gould had his own take on the modern synthesis, taking the “bushes not ladders” theme for horses and other animals (including human ancestors), and pushing it a step further. According to the theory of “punctuated equilibrium” (formulated in collaboration with Niles Eldredge), species mostly change relatively little during the time they exist (evolutionary stasis). Most evolutionary change happens when a small population buds off to form a new species and reproductive isolation allows it to conserve any evolutionary novelties it has developed. This opens up the possibility of “species selection.” Applied to horses, for example, this could mean that horses were evolutionarily successful for some time not so much because individual horses were well-adapted, but because something about horses collectively (their harem mating system, maybe) made one horse species especially likely to produce new species.

Opinions about Gould – as a theorist and a human being — are pretty divided. For a negative take, here’s a piece by Robert Trivers, one of the great figures in evolutionary biology.

The Burgess Shale and “Wonderful Life”

The Burgess Shale (about 510 Mya) is not the oldest Cambrian deposit known. There are deposits from China (Chengjiang) closer to the beginning of the era. But it is particularly rich and well studied. It also featured in debates about some Big Questions: How important are evolutionary laws versus historical accidents? Has the living world become more or less diverse over time?

Stephen Jay Gould (1941-2002) was one of the most widely known evolutionary biologists of his time. In 1989 he wrote a book about the Burgess Shale, called “Wonderful Life.” The title alluded to Frank Capra’s movie, “It’s a Wonderful Life,”* starring Jimmy Stewart. In the movie, the Stewart character, who thinks he’s wasted his life stuck in his home town, has a chance to see how things would have turned out if he had died young in an accident. He learns that his existence made a huge difference to his town.

Similarly, Gould argued that accidents of which Cambrian species survived and which went extinct made a huge difference to the later evolution of life. To make his case, he developed a subsidiary argument: that the Cambrian fauna displays a radical diversity of body plans in comparison with later eras. Gould made an analogy with the early development of automobiles, which featured diesel engines, steam engines, and electrical engines, before settling down on just gasoline engines. (He was writing before there were Priuses and Teslas, of course.)

This subsidiary argument has not fared well. Most of the supposedly radically different forms from the Burgess Shale turn out to be not that radically different from one another, or from modern forms. Most notorious was the case of a specimen called Hallucigenia. Paleontologists thought that this creature was like nothing that ever lived before. It turned out they were looking at it upside down; its “legs” were actually defensive spikes. It’s probably related to the ancestor of velvet worms, a group related to vertebrates and still living in Australia. A rather different perspective comes from Simon Conway Morris one of the experts on the Burgess Shale, in in his book “Crucible of Creation.”

That aside however, the question of accident versus necessity, in evolution and in history, will continue to come up throughout the Logarithmic History year.

*Not to be confused with Jerome Bixby’s short story “It’s a Good Life,” about a very different small town.

Turnover pulse

Elizabeth Vrba, a South African paleontologist, coined the term “turnover pulse.” The idea is that most species most of the time are in an equilibrium with their physical and biotic environments, and not changing much. But every once in a while an environmental disturbance comes along, resulting in large scale extinctions, and a pulse of speciation. Most evolutionary change, on this theory, occurs during these pulses. Vrba saw evidence of a pulse 2.5 million years ago among South African antelopes (affecting specialized more than generalized feeders). The pulse was associated with a shift toward cooler weather, and a shrinking of forests and expansion of grasslands. Part of the turnover pulse hypothesis is that the same pulses should affect many different species at the same time: there is arguably a turnover among hominins as well, giving rise to a later generation of savannah-adapted australopithecines.

Vrba was one of a circle of paleontologists pushing the idea of punctuated equilibrium ¬– that during most of their existence species don’t change much (stasis), and evolutionary change is concentrated in the times and places when a new species branches off from another. Steven Jay Gould and Niles Eldredge were others pushing the idea. There are various possible explanations for why we might see a combination of stasis and punctuated equlibrium (assuming the theory is true in the first place). Environmental controls, as suggested by Vrba are one possibility. Or maybe species’ developmental systems are tightly integrated and resistant to change. Or (for sexually reproducing species) the need to find a similar-enough mate might foster stasis most of the time.

We’ve seen some enormous episodes of mass extinction before on Logarithmic History. The turnover pulse hypothesis implies that the same phenomenon on a smaller scale is behind most evolutionary change. Not everybody buys this though. Punctuated equilibrium is a hugely contentious topic. And plenty of evolutionary biologists think that arms races among (and within) species keep evolution running along pretty constantly even without environmental changes. We’ll see some of the same issues – punctuation versus gradualism, ecological forcing versus internal dynamics driven by arms races – when we take up human history.

Planet of the horses

Horses have probably been the single most important domesticated animal in human history. Also, more than with other livestock, people get attached to horses as individuals. I’m guessing that in history and literature there are more horses with individual names than any other animal. (Alexander the Great’s horse was Bucephalus, “Ox-head”; Charlemagne’s was Tencendur; Don Quixote’s was Rocinante; Gandalf’s was Shadowfax.) We’ll be hearing a lot more about horses and horse folk on Logarithmic History once we get to human history.

Being so charismatic, horses have featured in a big way in arguments over evolution. Thomas Henry Huxley (1825-1895), “Darwin’s bulldog,” knew he needed to find good evidence for evolution. When he visited the United States in 1876, he was ready to give a lecture based on horse fossils from Europe. But visiting Yale, he was so impressed with O. C. Marsh’s collection of horse fossils from the western United States, that he rewrote his lecture around it.

Henry Fairfield Osborn (1857-1935) was director of the American Museum of Natural History and a huge presence in American paleontology. He was active at a time when most scientists accepted evolution, but many weren’t so keen on Darwin’s theory of natural selection. He thought horses were a fine example of “orthogenesis,” the tendency of species to follow a fixed line of evolution, reflecting internal forces, maybe related to willpower. He thought that humans shared a migratory spirit with horses, so that anywhere horse fossils were found would be a good place to look for human fossils. This theory didn’t pan out too well. A massive AMNH expedition to Central Asia led by Ray Chapman Andrews found all sorts of wonders – dinosaur eggs, baluchitheres – but no fossil “pro-men.” Orthogenesis leant itself naturally to diagrams showing evolution from early to modern horses going in a straight line.

horseladder

George Gaylord Simpson (1902-1984), paleontologist, was one of the great figures in the evolutionary Modern Synthesis that brought together Darwin’s theory of natural selection and Mendel’s genetics. There was no room for orthogenesis in the Modern Synthesis, and Simpson emphasized that the evolution of horses was a matter of adaptation to a changing environment – especially the spread of grasslands. Also that horse evolution looked more like a bush than a ladder.

horsebush

Stephen Jay Gould (1941-2002) was the most widely recognized American evolutionary biologist of recent times. (For example had a spot on The Simpson’s — “Lisa The Skeptic,” Season 9.) Gould had his own take on the modern synthesis, taking the “bushes not ladders” theme for horses and other animals (including human ancestors), and pushing it a step further. According to the theory of “punctuated equilibrium” (formulated in collaboration with Niles Eldredge), species mostly change relatively little during the time they exist (evolutionary stasis). Most evolutionary change happens when a small population buds off to form a new species and reproductive isolation allows it to conserve any evolutionary novelties it has developed. This opens up the possibility of “species selection.” Applied to horses, for example, this could mean that horses were evolutionarily successful for some time not so much because individual horses were well-adapted, but because something about horses collectively (their harem mating system, maybe) made one horse species especially likely to produce new species.

Opinions about Gould – as a theorist and a human being — are pretty divided. For a negative take, here’s a recent piece by Robert Trivers, one of the great figures in evolutionary biology.

The Burgess Shale and “Wonderful Life”

The Burgess Shale (about 510 Mya) is not the oldest Cambrian deposit known. There are deposits from China (Chengjiang) closer to the beginning of the era. But it is particularly rich and well studied. It also featured in debates about some Big Questions: How important are evolutionary laws versus historical accidents? Has the living world become more or less diverse over time?

Stephen Jay Gould (1941-2002) was one of the most widely known evolutionary biologists of his time. In 1989 he wrote a book about the Burgess Shale, called “Wonderful Life.” The title alluded to Frank Capra’s movie, “It’s a Wonderful Life,”* starring Jimmy Stewart. In the movie, the Stewart character, who thinks he’s wasted his life stuck in his home town, has a chance to see how things would have turned out if he had died young in an accident. He learns that his existence made a huge difference to his town.

Similarly, Gould argued that accidents of which Cambrian species survived and which went extinct made a huge difference to the later evolution of life. To make his case, he developed a subsidiary argument: that the Cambrian fauna displays a radical diversity of body plans in comparison with later eras. Gould made an analogy with the early development of automobiles, which featured diesel engines, steam engines, and electrical engines, before settling down on just gasoline engines. (He was writing before there were Priuses and Teslas, of course.)

This subsidiary argument has not fared well. Most of the supposedly radically different forms from the Burgess Shale turn out to be not that radically different from one another, or from modern forms. Most notorious was the case of a specimen called Hallucigenia. Paleontologists thought that this creature was like nothing that ever lived before. It turned out they were looking at it upside down; its “legs” were actually defensive spikes. It’s probably related to the ancestor of velvet worms, a group related to vertebrates and still living in Australia. A rather different perspective comes from Simon Conway Morris one of the experts on the Burgess Shale, in in his book “Crucible of Creation.”

That aside however, the question of accident versus necessity, in evolution and in history, will continue to come up throughout the Logarithmic History year.

*Not to be confused with Jerome Bixby’s short story “It’s a Good Life,” about a very different small town.