Sapere Aude
Tag: evolution
Some viruses can replicate without passing all their genes into any 1 cell.
A classical view in virology assumes that the viral replication cycle occurs within individual cells. But in the case of this “multipartite” virus, it seems that this is not true. The segments infect cells independently and accumulate independently in the plant host cells. It really shows that the virus doesn’t work at a single-cell level, but at a multicellular level.
breeds represented as working, hunting, or pet groups don’t represent real dogs. So-called stray dogs, street dogs, neighborhood dogs, village dogs, and even feral dogs of the world are the real, naturally evolved, self-selected dogs
I had long suspected that Denisovans represented a substantial portion of the already-known Chinese fossil record; they just hadn’t been identified. The Xiahe jaw, we hoped, could bridge the gap. The Xiahe mandible is complete enough to now revisit the rich Chinese hominin fossil collection and identify other fossils as Denisovan, even without DNA evidence. I have no doubt that in the future the sequencing of ancient proteins will complement these morphological analyses. But the most extraordinary aspect of our findings is the demonstration that such archaic hominins could successfully live in this challenging high-altitude environment, more than 120 ka before modern H. sapiens settled on the Tibetan Plateau. It seems that a gene variant that helps modern populations on the Tibetan Plateau to adapt to high-altitude hypoxia was inherited from these Denisovans.
Fragile DNA Enables New Adaptations to Evolve Quickly
If highly repetitive gene-regulating sequences in DNA are easily lost, then that may explain why some adaptations evolve quickly and repeatedly
Researchers have discovered a new kind of organism that doesn’t fit into the plant, animal, or any other kingdom of known organisms. 2 species of the microscopic organisms, called hemimastigotes, were found in dirt. Hemimastigotes were first seen and described in the 19th century, and ~10 species have been described over the past 100 years. But up to now, no one could figure out how they fit into the evolutionary tree of life. Based on the new genetic analysis, it looks like you’d have to go back 1 ga before you could find a common ancestor of hemimastigotes and any other known living thing.
Sabercat extinction has been understood in terms of top-down ecological stress, a victim of ‘trophic cascade’, just as the top predators of the ocean today are dying off because populations of prey fishes are collapsing beneath them. The plight of today’s big cats also seems to echo the downfall of Smilodon: we know that leopards, tigers, jaguars and other big cats require large swathes of habitat that are connected through ecological corridors, providing them with plenty of ground to stalk, and enough prey to survive. Decrease the habitat and food supply, and the cats suffer. But what if we could trace the clues back the other way? What if the extinction of Smilodon could help us understand what wiped out so many of the species it relied upon for food? New research on this question could help us untangle the frighteningly mysterious nature of extinction — in the past and future — itself. For now, the exact reason why Smilodon disappeared remains unknown. Loss of food is a likely cause, but that answer only moves the question a step back to why Smilodon’s prey died out. The sabercat was a casualty in a wider extinction at the end of the Pleistocene that marked the end of the Ice Age and the beginning of a world over which our species has disproportionate influence. Some researchers like to call this the Anthropocene, but whether or not such a designation truly fits depends on how long our species lasts. What might the fossil record look like 100m years from now? The Pleistocene extinction could come to shade into the modern biodiversity crisis with little or no break in between. The close of the Ice Age might have been the beginning of a new age, or it could have been one dramatic blip in an ongoing mass extinction, tracking the rise of human dominance. Some of the garbage that ends up preserved in La Brea’s asphalt might help future archaeologists untangle this mystery.
Those who are trying to improve such systems have long wondered: what is the secret of human general intelligence? In this post I want to consider we can learn about this from fact that the brain evolved. How would an evolved brain be general? if we are looking to explain a surprising generality, flexibility, and rapid evolution in human brains, it makes sense to consider the possibility that human brain design took a different path, one more like that of single-celled metabolism. That is, 1 straightforward way to design a general evolvable brain is to use an extra large toolbox of mental modules that can be connected together in many different ways. While each tool might be a carefully constructed jewel, the whole set of tools would have less of an overall structure. Like a pile of logical gates that can be connected many ways, or metabolism sub-networks that can be connected together into many networks. In this case, the secret to general evolvable intelligence would be less in the particular tools and more in having an extra large set of tools, plus some simple general ways to search in the space of tool combinations. A tool set so large that the brain can do most tasks in a great many different ways.
2023-03-25: Intelligence is modular and extremely prevalent, for generous definitions of intelligence
One implication of this hierarchy of homeostatically stable, nested modules is that organisms became much more flexible while still maintaining a coherent ‘self’ in a hostile world. Evolution didn’t have to tweak everything at once in response to a new threat, because biological subunits were primed to find novel ways of compensating for changes and functioning within altered systems. For example, in planarian flatworms, which reliably regenerate every part of the body, using drugs to shift the bioelectrically stored pattern memory results in two-headed worms. Remarkably, fragments of these worms continue to regenerate two heads in perpetuity, without editing the genome. Moreover, flatworms can be induced, by brief modulation of the bioelectric circuit, to regrow heads with shape (and brain structure) appropriate to other known species of flatworms (at about 100 million years of evolutionary distance), despite their wild-type genome.
Each day, 800m viruses cascade onto every square meter of the planet. Unimpeded by friction with the surface of the Earth, you can travel great distances, and so intercontinental travel is quite easy for viruses. It wouldn’t be unusual to find things swept up in Africa being deposited in North America.
The case of the Ancient North Eurasians showed that while a tree is a good analogy for the relationships among species — because species rarely interbreed and so like real tree limbs are not expected to grow back together after they branch — it is a dangerous analogy for human populations. The genome revolution has taught us that great mixtures of highly divergent populations have occurred repeatedly. Instead of a tree, a better metaphor may be a trellis, branching and remixing far back into the past.
this seems to scale. humans didn’t use to travel more than 30 km from their place of birth in historical times.
When Combs looked closer, distinct rat subpopulations emerged. Manhattan has 2 genetically distinguishable groups of rats: the uptown rats and the downtown rats, separated by the geographic barrier that is midtown. It’s not that midtown is rat-free—such a notion is inconceivable—but the commercial district lacks the household trash (aka food) and backyards (aka shelter) that rats like. Since rats tend to move only a few blocks in their lifetimes, the uptown rats and downtown rats don’t mix much.
Gregor J. Rothfuss 