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+--- Thread: Research From dinosaur to bird: origin of feathers + Humans descended from 2 ancestral groups (/thread-17628.html)
From dinosaur to bird: origin of feathers + Humans descended from 2 ancestral groups - C C - Mar 20, 2025
From dinosaurs to birds: the origins of feather formation
https://www.unige.ch/medias/en/2025/des-dinosaures-aux-oiseaux-lorigine-de-la-formation-des-plumes
PRESS RELEASE: Feathers are among the most complex cutaneous appendages in the animal kingdom. While their evolutionary origin has been widely debated, paleontological discoveries and developmental biology studies suggest that feathers evolved from simple structures known as proto-feathers. These primitive structures, composed of a single tubular filament, emerged around 200 million years ago in certain dinosaurs. Paleontologists continue to discuss the possibility of their even earlier presence in the common ancestor of dinosaurs and pterosaurs (the first flying vertebrates with membranous wings) around 240 million years ago.
Proto-feathers are simple, cylindrical filaments. They differ from modern feathers by the absence of barbs and barbules, and by the lack of a follicle—an invagination at their base. The emergence of proto-feathers likely marked the first key step in feather evolution, initially providing thermal insulation and ornamentation before being progressively modified under natural selection to give rise to the more complex structures that enabled flight.
The laboratory of Michel Milinkovitch, professor at the Department of Genetics and Evolution in the Faculty of Science at UNIGE, studies the role of molecular signaling pathways (communication systems that transmit messages within and between cells), such as the Sonic Hedgehog (Shh) pathway, in the embryonic development of scales, hair, and feathers in modern vertebrates. In a previous study, the Swiss scientists stimulated the Shh pathway by injecting an activating molecule into the blood vessels of chicken embryos and observed the complete and permanent transformation of scales into feathers on the bird’s feet.
Recreating the first dinosaur proto-feathers. ‘‘Since the Shh pathway plays a crucial role in feather development, we wanted to observe what happens when it is inhibited,’’ explains Rory Cooper, a postdoctoral researcher in Michel Milinkovitch’s lab and co-author of the study. By injecting a molecule that blocks the Shh signaling pathway on the 9th day of embryonic development – just before feather buds appear on the wings – the two researchers observed the formation of unbranched and non-invaginated buds, resembling the putative early stages of proto-feathers.
However, from the 14th day of embryonic development, feather morphogenesis partially recovered. Furthermore, although the chicks hatched with patches of naked skin, dormant subcutaneous follicles were autonomously reactivated, eventually producing chickens with normal plumage.
‘‘Our experiments show that while a transient disturbance in the development of foot scales can permanently turn them into feathers, it is much harder to permanently disrupt feather development itself,’’ concludes Michel Milinkovitch. ‘‘Clearly, over the course of evolution, the network of interacting genes has become extremely robust, ensuring the proper development offeathers even under substantial genetic or environmental perturbations. The big challenge now is to understand how genetic interactions evolve to allow for the emergence of morphological novelties such as proto-feathers.’’
PAPER: http://dx.doi.org/10.1371/journal.pbio.3003061
Modern humans may have descended from at least two ancestral populations
https://www.cam.ac.uk/research/news/genetic-study-reveals-hidden-chapter-in-human-evolution
PRESS RELEASE: Modern humans descended from not one, but at least two ancestral populations that drifted apart and later reconnected, long before modern humans spread across the globe.
Using advanced analysis based on full genome sequences, researchers from the University of Cambridge have found evidence that modern humans are the result of a genetic mixing event between two ancient populations that diverged around 1.5 million years ago. About 300,000 years ago, these groups came back together, with one group contributing 80% of the genetic makeup of modern humans and the other contributing 20%.
For the last two decades, the prevailing view in human evolutionary genetics has been that Homo sapiens first appeared in Africa around 200,000 to 300,000 years ago, and descended from a single lineage. However, these latest results, reported in the journal Nature Genetics, suggest a more complex story.
“The question of where we come from is one that has fascinated humans for centuries,” said first author Dr Trevor Cousins from Cambridge’s Department of Genetics. “For a long time, it’s been assumed that we evolved from a single continuous ancestral lineage, but the exact details of our origins are uncertain.”
“Our research shows clear signs that our evolutionary origins are more complex, involving different groups that developed separately for more than a million years, then came back to form the modern human species,” said co-author Professor Richard Durbin, also from the Department of Genetics.
While earlier research has already shown that Neanderthals and Denisovans – two now-extinct human relatives – interbred with Homo sapiens around 50,000 years ago, this new research suggests that long before those interactions – around 300,000 years ago – a much more substantial genetic mixing took place. Unlike Neanderthal DNA, which makes up roughly 2% of the genome of non-African modern humans, this ancient mixing event contributed as much as 10 times that amount and is found in all modern humans.
The team’s method relied on analysing modern human DNA, rather than extracting genetic material from ancient bones, and enabled them to infer the presence of ancestral populations that may have otherwise left no physical trace. The data used in the study is from the 1000 Genomes Project, a global initiative that sequenced DNA from populations across Africa, Asia, Europe, and the Americas.
The team developed a computational algorithm called cobraa that models how ancient human populations split apart and later merged back together. They tested the algorithm using simulated data and applied it to real human genetic data from the 1000 Genomes Project.
While the researchers were able to identify these two ancestral populations, they also identified some striking changes that happened after the two populations initially broke apart.
“Immediately after the two ancestral populations split, we see a severe bottleneck in one of them—suggesting it shrank to a very small size before slowly growing over a period of one million years,” said co-author Professor Aylwyn Scally, also from the Department of Genetics. “This population would later contribute about 80% of the genetic material of modern humans, and also seems to have been the ancestral population from which Neanderthals and Denisovans diverged.”
“However, some of the genes from the population which contributed a minority of our genetic material, particularly those related to brain function and neural processing, may have played a crucial role in human evolution,” said Cousins.
The study also found that genes inherited from the second population were often located away from regions of the genome linked to gene functions, suggesting that they may have been less compatible with the majority genetic background. This hints at a process known as purifying selection, where natural selection removes harmful mutations over time.
Beyond human ancestry, the researchers say their method could help to transform how scientists study the evolution of other species. In addition to their analysis of human evolutionary history, they applied the cobraa model to genetic data from bats, dolphins, chimpanzees, and gorillas, finding evidence of ancestral population structure in some but not all of these.
“What’s becoming clear is that the idea of species evolving in clean, distinct lineages is too simplistic,” said Cousins. “Interbreeding and genetic exchange have likely played a major role in the emergence of new species repeatedly across the animal kingdom.”
So who were our mysterious human ancestors? Fossil evidence suggests that species such as Homo erectus and Homo heidelbergensis lived both in Africa and other regions during this period, making them potential candidates for these ancestral populations, although more research (and perhaps more evidence) will be needed to identify which genetic ancestors corresponded to which fossil group.
Looking ahead, the team hopes to refine their model to account for more gradual genetic exchanges between populations, rather than sharp splits and reunions. They also plan to explore how their findings relate to other discoveries in anthropology, such as fossil evidence from Africa that suggests early humans may have been far more diverse than previously thought.
“The fact that we can reconstruct events from hundreds of thousands or millions of years ago just by looking at DNA today is astonishing,” said Scally. “And it tells us that our history is far richer and more complex than we imagined.”
The research was supported by Wellcome. Aylwyn Scally is a Fellow of Darwin College, Cambridge. Trevor Cousins is a member of Darwin College, Cambridge.