Jul 19, 2022 04:44 PM
(This post was last modified: Jul 19, 2022 04:49 PM by C C.)
Tree of life: https://en.wikipedia.org/wiki/Tree_of_life_(biology)
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The Bizarre Bird That’s Breaking the Tree of Life
https://www.newyorker.com/science/elemen...ee-of-life
EXCERPTS: . . . Hoatzins, which live along oxbow lakes in tropical South America, have blood-red eyes, blue cheeks, and crests of spiky auburn feathers. Their chicks have primitive claws on their tiny wings and respond to danger by plunging into water and then clawing their way back to their nests—a trait that inspired some ornithologists to link them to dinosaurs. Other taxonomists argued that the hoatzin is closely related to pheasants, cuckoos, pigeons, and a group of African birds called turacos. Alejandro Grajal, the director of Seattle’s Woodland Park Zoo, said that the bird looks like a “punk-rock chicken,” and smells like manure because it digests leaves through bacterial fermentation, similar to a cow.
DNA research has not solved the mysteries of the hoatzin; it has deepened them. One 2014 analysis suggested that the bird’s closest living relatives are cranes and shorebirds such as gulls and plovers. Another, in 2020, concluded that this clumsy flier is a sister species to a group that includes tiny, hovering hummingbirds and high-speed swifts. “Frankly, there is no one in the world who knows what hoatzins are,” Cracraft, who is now a member of B10K, said. The hoatzin may be more than a missing piece of the evolutionary puzzle. It may be a sphinx with a riddle that many biologists are reluctant to consider: What if the pattern of evolution is not actually a tree?
[...] Scientists had long assumed, for example, that daytime hunters such as hawks, eagles, and falcons all descended from a single bird of prey. But, in the genetic tree, hawks and eagles shared a branch with vultures, yet falcons turned out to be closer relatives of passerines and parrots. This meant that the peregrine falcon is more closely related to colorful macaws and tiny sparrows than to any hawk or eagle. The traditional explanation for flightlessness in ratites—that a common ancestor diverged into ostriches, emus, rheas, cassowaries, and kiwis after the southern continents split apart—also collapsed. DNA showed that the ratites also included flying birds called tinamous, suggesting that the group evolved flightlessness at least three separate times. “That study revolutionized our understanding of how the major groups of living birds are related to each other,” Daniel J. Field, an avian paleontologist at the University of Cambridge, said. Bird-watching guides had to reorganize their contents to reflect the new relationships.
What the study could not settle was the early evolution of modern birds. It was easy to tell when pheasants and ostriches turned off the highway of avian evolution, but modern birds did not follow a simple off-ramp. They seemed to zoom off in different directions, as though each kind of bird took a different exit from a busy roundabout. From their common ancestor—perhaps a little ground bird that pecked seeds and insects out of the ash that the asteroid left behind—modern birds split quickly into more than half a dozen branches. But the fastest computers of the time weren’t fast enough to disentangle them. All but one of these branches diversified into about ten thousand bird species. The last belonged to the hoatzin alone. The strange bird likely made the journey to the present day all by itself. “The enigmatic Opisthocomus (hoatzin) still cannot be confidently placed,” Hackett’s team wrote.
[...] The conflicting signals in the hoatzin genome may not be analytical errors but biological realities—and they may require a different paradigm than the tree.
The tree is so ingrained in evolutionary biology that scientists encourage “tree thinking.” By learning to think in terms of trees, students can avoid the common fallacy of reading evolution as a ladder in which simpler organisms become more complex, as in the famous image “The Ascent of Man,” which shows a knuckle-walking ape evolving into an upright human. For all its pedagogical value, however, the tree also embeds subtle assumptions about evolution. The tree tends to downplay the genetic variation within species, which can obscure the fact that common ancestors are actually diverse populations that can pass on different versions of a gene to different descendants. It tells a story of endless partition and diversification, with branches that diverge and never reticulate.
[...] In 2016, Alexander Suh, a biologist on the forty-eight-genome team, superimposed all the different gene trees they had generated. The resulting image of the early evolution of modern birds, around the time the dinosaurs went extinct, was not a tidy series of diverging branches but a kind of web or fishnet, whose contours constantly crossed paths. In a paper, Suh urged his colleagues to consider other patterns of evolution—to argue “less about which species tree is ‘correct,’ and more about if there is such a thing” as a traditional tree of life for modern birds.
[...] Hybridization may have been rampant in the aftermath of the asteroid strike, when modern-bird lineages first emerged. Interbreeding would have passed genes from one branch of the tree to another, adding another layer of complexity on top of incomplete lineage sorting. “Lineages that split and never talk to each other again—that’s not how biology works,” Stiller said. Still, she remains hopeful that one day we may build an authoritative diagram of the past. “Our models are still comparatively simple,” she told me. “We should be able to reconstruct evolutionary history if we have the right models and the right data.”
The outlines of animal evolution still look a lot like a tree in many places, which is why scientists continue to spend so much time developing and debating different branches. But, if tree thinking taught biologists that everything is connected, genes are suggesting that the connections can run even deeper than a tree can capture... (MORE - missing details)
https://youtu.be/0HytWfqWYUQ
https://www.youtube-nocookie.com/embed/0HytWfqWYUQ
- - - - - -
The Bizarre Bird That’s Breaking the Tree of Life
https://www.newyorker.com/science/elemen...ee-of-life
EXCERPTS: . . . Hoatzins, which live along oxbow lakes in tropical South America, have blood-red eyes, blue cheeks, and crests of spiky auburn feathers. Their chicks have primitive claws on their tiny wings and respond to danger by plunging into water and then clawing their way back to their nests—a trait that inspired some ornithologists to link them to dinosaurs. Other taxonomists argued that the hoatzin is closely related to pheasants, cuckoos, pigeons, and a group of African birds called turacos. Alejandro Grajal, the director of Seattle’s Woodland Park Zoo, said that the bird looks like a “punk-rock chicken,” and smells like manure because it digests leaves through bacterial fermentation, similar to a cow.
DNA research has not solved the mysteries of the hoatzin; it has deepened them. One 2014 analysis suggested that the bird’s closest living relatives are cranes and shorebirds such as gulls and plovers. Another, in 2020, concluded that this clumsy flier is a sister species to a group that includes tiny, hovering hummingbirds and high-speed swifts. “Frankly, there is no one in the world who knows what hoatzins are,” Cracraft, who is now a member of B10K, said. The hoatzin may be more than a missing piece of the evolutionary puzzle. It may be a sphinx with a riddle that many biologists are reluctant to consider: What if the pattern of evolution is not actually a tree?
[...] Scientists had long assumed, for example, that daytime hunters such as hawks, eagles, and falcons all descended from a single bird of prey. But, in the genetic tree, hawks and eagles shared a branch with vultures, yet falcons turned out to be closer relatives of passerines and parrots. This meant that the peregrine falcon is more closely related to colorful macaws and tiny sparrows than to any hawk or eagle. The traditional explanation for flightlessness in ratites—that a common ancestor diverged into ostriches, emus, rheas, cassowaries, and kiwis after the southern continents split apart—also collapsed. DNA showed that the ratites also included flying birds called tinamous, suggesting that the group evolved flightlessness at least three separate times. “That study revolutionized our understanding of how the major groups of living birds are related to each other,” Daniel J. Field, an avian paleontologist at the University of Cambridge, said. Bird-watching guides had to reorganize their contents to reflect the new relationships.
What the study could not settle was the early evolution of modern birds. It was easy to tell when pheasants and ostriches turned off the highway of avian evolution, but modern birds did not follow a simple off-ramp. They seemed to zoom off in different directions, as though each kind of bird took a different exit from a busy roundabout. From their common ancestor—perhaps a little ground bird that pecked seeds and insects out of the ash that the asteroid left behind—modern birds split quickly into more than half a dozen branches. But the fastest computers of the time weren’t fast enough to disentangle them. All but one of these branches diversified into about ten thousand bird species. The last belonged to the hoatzin alone. The strange bird likely made the journey to the present day all by itself. “The enigmatic Opisthocomus (hoatzin) still cannot be confidently placed,” Hackett’s team wrote.
[...] The conflicting signals in the hoatzin genome may not be analytical errors but biological realities—and they may require a different paradigm than the tree.
The tree is so ingrained in evolutionary biology that scientists encourage “tree thinking.” By learning to think in terms of trees, students can avoid the common fallacy of reading evolution as a ladder in which simpler organisms become more complex, as in the famous image “The Ascent of Man,” which shows a knuckle-walking ape evolving into an upright human. For all its pedagogical value, however, the tree also embeds subtle assumptions about evolution. The tree tends to downplay the genetic variation within species, which can obscure the fact that common ancestors are actually diverse populations that can pass on different versions of a gene to different descendants. It tells a story of endless partition and diversification, with branches that diverge and never reticulate.
[...] In 2016, Alexander Suh, a biologist on the forty-eight-genome team, superimposed all the different gene trees they had generated. The resulting image of the early evolution of modern birds, around the time the dinosaurs went extinct, was not a tidy series of diverging branches but a kind of web or fishnet, whose contours constantly crossed paths. In a paper, Suh urged his colleagues to consider other patterns of evolution—to argue “less about which species tree is ‘correct,’ and more about if there is such a thing” as a traditional tree of life for modern birds.
[...] Hybridization may have been rampant in the aftermath of the asteroid strike, when modern-bird lineages first emerged. Interbreeding would have passed genes from one branch of the tree to another, adding another layer of complexity on top of incomplete lineage sorting. “Lineages that split and never talk to each other again—that’s not how biology works,” Stiller said. Still, she remains hopeful that one day we may build an authoritative diagram of the past. “Our models are still comparatively simple,” she told me. “We should be able to reconstruct evolutionary history if we have the right models and the right data.”
The outlines of animal evolution still look a lot like a tree in many places, which is why scientists continue to spend so much time developing and debating different branches. But, if tree thinking taught biologists that everything is connected, genes are suggesting that the connections can run even deeper than a tree can capture... (MORE - missing details)
https://youtu.be/0HytWfqWYUQ