“It’s been a profound mystery for many, many decades in biology, how cells are able to accomplish this task of almost magically knowing what their size is”. Shape and size regulation are important because they are closely tied to how a cell functions: Too large and it can be difficult for the cell to quickly retrieve information contained in its own DNA; too small and the cell doesn’t have enough space to split properly, causing errors in division and growth that could lead to disease. The secret to cell size regulation lies in the concentration of KRP4 in each new cell. Though the daughter cells inherit an equal amount of KRP4, because they might be different sizes, the concentration of this protein in each cell isn’t necessarily the same. Smaller cells started with a higher concentration of KRP4 and spent more time growing. For bigger cells, the concentration was diluted, so they grew less. Overall, this balanced out any asymmetries in cell size.
Tag: science
LSD lowers priors
An important aspect of predictive processing is that each hypothesis generated by a level in the hierarchy is associated with a notion of confidence in the hypothesis, which in turn is based on prior expectations. Could psychedelics be altering our perception of reality by messing with this process? Friston and Robin Carhart-Harris think so. If psychedelics mess with prior beliefs, that might also explain why they cause one to hallucinate a reality that’s untethered from real-world expectations.
The Human Family Tree
Our planet was very different 100 ka ago, and if we could survey that time, we would be astounded by the human diversity across its surface. To enumerate what little we know with certainty, there were at a minimum: modern humans, Neanderthals, at least 3-4 varieties of Denisovans, and 2 pygmy Homo populations in Southeast Asia. Likely there were still remnant Homo erectus in Southeast Asia as well, and other diverged lineages within Africa, and a new Homo in Nesher Ramla, Israel, in the Middle East with affinities to Neanderthals.
2023-02-04: More evidence of a much more distributed situation
“Cognitive revolutions”—such as the widespread shift some 300 ka BP from clunky, handheld stone tools to more refined blades and projectile points—were probably instances of different populations with distinctive cultural and biological features coming together and recombining their genes and ideas.
This mosaic evolution would explain certain seemingly unexplainable findings. For example, researchers found human fossils in the Democratic Republic of Congo that dated to 22 ka BP but physically resembled people living 300 ka BP. In Senegal, scientists uncovered 12 ka BP stone toolkits that could easily be transplanted to a situation 100 ka BP.
These finds probably resulted from periods of isolation where different populations in different parts of the continent each developed distinctive cultural and physical adaptations to their local environments. At the same time, instances of connectivity allowed different populations to acquire beneficial traits, behaviors, and technologies from one another, becoming better adapted and more flexible.
Homo Nesher
The bones of an early human, unknown to science, who lived in the Levant at least until 130 ka ago, were discovered in excavations near the city of Ramla. Recognizing similarity to other archaic Homo specimens from 400 ka ago, found in Israel and Eurasia, the researchers reached the conclusion that the Nesher Ramla fossils represent a unique Middle Pleistocene population, now identified for the first time.
Numbers inevitable?
Why do we use numbers so much? Is it something about the world? Or is it more something about us? We discussed above the example of fundamental physics. And we argued that even though at the most fundamental level numbers really aren’t involved, our sampling of what happens in the universe leads us to a description that does involve numbers. And in this case, the origin of the way we sample the universe has deep roots in the nature of our consciousness, and our fundamental way of experiencing the universe, with our particular sensory apparatus, place in the universe, etc. As long as we preserve core aspects of our experience as what we consider conscious observers some version of numbers will in the end be inevitable for us. We can aspire to generalize from numbers, and, for example, sample other representations of computational reducibility. But for now, numbers seem to be inextricably connected to core aspects of our existence.
Mesopelagic Fish
Mesopelagic fish that live 100-1000m below the surface constitute 95% of the world’s fish biomass, 10-30x more than previously thought. “This very large stock of fish that we have just discovered is untouched by fishers.”
2023-02-24: The seafloor is similarly underappreciated
The majority of the bottom of the ocean is covered in morbid ooze, 100m deep. This substance is made of the skeletons of an uncountable number of tiny creatures, raining down from above. The passage of material through this ooze is a substantial part of several biological, chemical, and geological cycles.
Retron Library Recombineering
RLR generates up to millions of mutations simultaneously, and “barcodes” mutant cells so that the entire pool can be screened at once, enabling massive amounts of data to be easily generated and analyzed. “RLR enabled us to do something that’s impossible to do with CRISPR: we randomly chopped up a bacterial genome, turned those genetic fragments into single-stranded DNA in situ, and used them to screen millions of sequences simultaneously. RLR is a simpler, more flexible gene editing tool that can be used for highly multiplexed experiments, which eliminates the toxicity often observed with CRISPR and improves researchers’ ability to explore mutations at the genome level.”
K/T extinction event
66 ma ago, maybe on a Tuesday afternoon, life was the same as it had been the day before or 1 ka before or pretty much 1 ma before. Things were good for our feathered dinosaur buddies. Until a tiny, tiny detail in the sky changed.
2021-04-06: Chicxulub created rainforest
the dinosaur extinction was also a massive reset event for neotropical ecosystems, putting their evolution on an entirely new path leading directly to the extraordinary, diverse, spectacular and gravely threatened rainforests in the region today.
2022-10-05: The Chicxulub Impact Produced a Powerful Global Tsunami
The Chicxulub asteroid impact produced a global tsunami 30k times more energetic than any modern-day tsunami produced by earthquakes. Here we model the first 10 min of the event with a crater impact model, and the subsequent propagation throughout the world oceans using 2 different global tsunami models. The Chicxulub tsunami approached most coastlines of the North Atlantic and South Pacific with waves of 10m high and flow velocities of 1 m/s offshore. The tsunami was strong enough to scour the seafloor in these regions, thus removing the sedimentary records of conditions before and during this cataclysmic event in Earth history and leaving either a gap in these records or a jumble of highly disturbed older sediments.
Representational Drift
Neurons that represented the smell of an apple in May and those that represented the same smell in June were as different from each other as those that represent the smells of apples and grass at any one time. Representational drift occurs in a variety of brain regions besides the piriform cortex. Its existence is clear; everything else is a mystery. How can animals possibly make any lasting sense of the world if their neural responses to that world are constantly in flux? If such flux is common, “there must be mechanisms in the brain that are undiscovered and even unimagined that allow it to keep up.”
Galactic Settlement
The simulation depicts the expansion of a technological civilization through the Milky Way, created along lines previously described in the literature. What we are looking at is the transition between a Kardashev Type II civilization, and a Type III, which has spread throughout the galaxy. This might be a fast process considering the motions of stars themselves, which would overcome the inertia of slower growing settlements and boost expansion rates. Issues like starship capabilities and the lifetime of colonies come into play, but the striking thing is how fast galactic settlement occurs and how the motions of stars factor into the settlement wave. The parameters are everything, and they’re interesting:
- Ships are launched no more frequently than every 100 ka;
- Technology persists in a given settlement for 100 ma before dying out;
- Ship range is 10 light years.
- Ship speeds are 10 km/s; Voyager-class speeds.
- The simulation covers 1 ga
Gregor J. Rothfuss 