djublonskopf OP t1_je4mnrz wrote

Okay, I just looked it up. In the USA a full-size Snickers is 57g, in Spain it's 50g, so my "full size" is slightly smaller than a USA full size.

A USA "Fun Size" is 17g. A USA mini is 9g, and a Spain mini is 10.3g.

So while my full size is slightly smaller than a USA full size, and my mini is slightly larger than a USA mini, they aren't Fun Size.


djublonskopf t1_jdjofch wrote

The idea is, if protons do indeed randomly decay (over extremely long periods of time), then a neutron star will very slowly lose mass via this process, with protons in its thin outer crust very occasionally evaporating. After about 10^(38) years, enough mass will have been lost that the neutron star finally reaches a tipping point where it is light enough to not be a neutron star anymore. So it explodes into a white dwarf.


djublonskopf t1_jbk2vmg wrote

>Temperature-based determination existed before genetic one.

Specifically, there is a hypothesis that the very first amniotes (reptiles, birds, and mammals are all amniotes) used temperature-dependent sex signalling, and only evolved genetic sex signalling later. There is some good support (phylogenetically) that the first amniotes did not have sex chromosomes but used temperature instead...and that sex chromosomes independently evolved multiple times within the amniotes.

The best model for why any species would adopt temperature-determined sex is probably the Charnov-Bull model. Simply put, the model predicts that in some species, the temperature at which they develop and hatch has a different effect on males and females, so temperature-dependent sex signalling gives you the best possible fitness in your males and females. For example, maybe a species lives in a place with cold winters, and lays eggs early in the spring. And let's say that species is best served by more females surviving the winter than males. If females develop in colder eggs, then eggs laid earlier in the springtime nesting season will all be female. That head start means the females will be bigger in the fall when the first frost hits. Males might then develop later in the nesting season and be smaller when the first frost hits, and a few more males may die during the winter, but the species as a whole preserves more females overwinter this way and improves its odds of surviving.

Of course, both can be true; Charnov-Bull could be the reason why the first amniotes used temperature as a sex selector, and part of the reason that some species have kept it to this day...but obviously many later evolved sex chromosomes (including us warm-blooded mammals).


djublonskopf t1_jb4tcd3 wrote

Correct. Lungs evolved completely separately from gills. Our ancestors repurposed gills into inner ears, the cartilage of the trachea, and the hyoid bone, all structures still around our jaws/throat.

(Technically, our even earlier ancestors repurposed parts of their gills into the first jaws, too.)

Early in embryonic development, however, our gill arches and their major blood vessels still appear…and the recurrent laryngeal nerve grows out to that embryonic gill tissue. Later in development, the “gills” stay basically in place and become those other structures in the ear and throat. So instead of innervating gills, the nerve is now innervating…all the things we repurposed our gills into.


djublonskopf t1_jb3x5ws wrote

In fish, the homologous nerve innervates the gills.

The difference is that in fish, the aorta doesn't come out of the heart. The heart pumps blood to the gills, and from the gills the oxygenated blood flows into the fish-aorta, which runs alongside the spine and carries blood to the rest of the body. Any nerve running in a straight line from the brain to the gills would pass between several major gill blood vessels to get there.

So once our ancestors developed lungs, we didn't need the blood from our hearts to run all the way up to where our gills used to be before reaching the aorta. Instead, one of the blood vessels that used to service the gills gets repurposed into our "aortic arch", and stays down close to the heart so it can connect up with the rest of the aorta down there.

So the nerve that in fish (and tetrapod embryos) runs directly from the brain to the gills (or what we've repurposed gill tissue into, various structures around our ears and throats) ends up between the heart and the aortic arch. So since the aortic arch stays down in the torso, and our necks develop in between our skulls and our torsos, the recurrent laryngeal nerve ends up stretched all the way down to where the aortic arch ends up, and then comes all the way back to where the "gills" are.


djublonskopf t1_jb2a0kb wrote

It actually varies by species! Penguins, on one extreme, have zero hollow bones, keeping a heavy, marrow-filled skeleton to help with deep diving.

For most other birds, the skeleton is actually quite marrow-rich when they are just hatchlings. As they grow into adulthood, the skeleton gradually becomes pneumatized, with air sacs displacing red marrow in many bones. However, this displacement is not 100%...small spots of marrow persist into adulthood in many bones that researchers would otherwise call "pneumatized" or "hollow".

A few bones tend to escape pneumatization entirely, especially the femur and the tibiotarsus. In most birds these red-marrow-filled leg bones will make up the bulk of blood cell production. Other common red-marrow sites in birds are the radius/ulna in the wing, and certain sections of vertebrae (especially the caudal vertebrae in the tail). Many other bones will retain just a small amount of marrow in some birds, and none in others, so there is variation from species to species...but in general those three sites (fibia/tibiotarsus in legs, radius/ulna in wings, vertebrae in tail) will play a big role in making red blood cells for most birds.


djublonskopf t1_ja2ax32 wrote

The Platyhelminthes (or flatworms) might be what you're looking for. They have no circulatory system, instead relying on diffusion through their skin and tissues to obtain the oxygen they need and expel waste CO2. They also have no respiratory organs, nor blood, lymph, or any other body fluid...the simple flatness of their bodies is sufficient to ensure that oxygen can reach their innermost cells. But they do have a primitive brain, a two-lobed cortex of nerve cells and a core of nerve fibers that take in sensory information and coordinate movement for the rest of the body.


djublonskopf t1_j9w2x9f wrote

This is true. In the 6-week case, the eye has probably been intentionally filled with octafluoropropane (C3F8) to keep the gas from being reabsorbed too quickly…this gives the retina more time to remain dry to allow more healing before the gas is absorbed and replaced by fluid.

If the eye is filled with normal air, the air should be reabsorbed in a much shorter time (2-10 days).


djublonskopf t1_j9u5sbk wrote

Reply to comment by derioderio in How did the placenta evolve? by fil-

Yes. Marsupial fossils would represent mammals that gave live birth, but aren’t placental mammals either.

Multituberculates are a lineage of mammal that is completely extinct today, but they were closer to therians (placentals+marsupials) than monotremes. Some of them had incredibly narrow pelvic openings too, hinting that they may also have been live-birthers (of tiny, underdeveloped offspring like the marsupials.)


djublonskopf t1_j9tbhh0 wrote

It is absorbed by the body cavity lining, makes its way into the blood stream, and is exhaled. The absorption happens pretty much exactly the way it happens in your lungs (diffusion), there's just less surface area to work with than in the highly-branched lung interior, so it takes a bit longer.

O2 and CO2 are absorbed pretty quickly into the blood compared to the nitrogen gas (N2) that makes up the majority of air. So when laproscopic surgeons insuflate a surgical area with gas to give them a little more room to see and work, they intentionally use CO2...which helps any gas left behind after the surgery to be absorbed more quickly, and also protects the patient in case a (small) bubble got into the bloodstream (as a bubble of pure CO2 will be absorbed into the blood faster and thus might do less damage than a longer-lasting nitrogen bubble.) But even a regular air mix at an incision site will be absorbed before too long.


djublonskopf t1_j9oso0h wrote

Specifically, the syncytins are important because they keep the mother's immune cells from being able to reach "through" the placenta into the developing fetus.

There are certain immune cells that are able to slip between other epithelial cells. If the mother's immune cells were to slip past the cells of placenta, they would almost certainly attack the fetus. Placental mammals solve this by having a "boundary layer" between the placenta and the mother. The cells of the boundary layer use those viral syncytins to "fuse" together, becoming one giant solid mega-cell with lots of nuclei. Because there are no longer any individual cells to slip between, the mother's immune cells are unable to get past this boundary layer (the syncytiotrophoblast) and thus the rest of the placenta and fetus are protected from the mother's immune system.


djublonskopf t1_j9orcrt wrote

Placental mammals (like us) basically start with 3 precursor tubes that fuse together early in development.

In marsupials, the ureters (which transport urine from kidneys to the bladder) pass in between the 3 vaginas, so it would be pretty much impossible for them to fuse without cutting off the transport of urine to the bladder. In placental mammals, the ureters develop differently and no longer pass between the tubes, which is why it's possible for us to fuse the 3 precursor tubes into one.


djublonskopf t1_j71ffx9 wrote

In 1693, the Dutch anatomist Philip Verheyden performed a dissection of his own leg (after it was amputated). Upon reaching the tendon we now call the Achilles Tendon, he jokingly (or poetically) referred to it as chorda Achillis, or "Achilles' sinew". This was the first recorded connection between a real part of human anatomy and the myth of Achilles, and several sources credit Verheyden with coining the association. (EDIT: This account appears to be apocryphal; apparently in his writings he credits several colleagues with coming up with the name.)

As for specifically calling it the Achilles tendon, that name was coined (in Latin, as tendo Achillis) in the early eighteenth century by German anatomy professor Lorenz Heister.

As to other mythological body parts:

  • The atlas vertebrae holds up the skull, just as the titan Atlas held up the sky in Greek mythology
  • The Latin lympha is derived from the Greek nymphe; lympha meaning "clean and pure water" after the Greek story of the nymphs. Our bodies' own lymph is so named.
  • See this paper investigating (with good citations) a whole bunch more.

djublonskopf t1_j6mlod3 wrote

True hibernation is a long-term period of dormancy...weeks, or even months of continuous metabolic slowdown. Going into and out of it takes hours. Very few animals actually hibernate—certain snakes, bees, and bats, as a few examples. They generally stay "asleep" for the entire period, perhaps waking up only rarely to relieve themselves.

Torpor, instead, is much more short-lived, and generally involuntary...when it's cold their metabolism slows down and they conk out, if it warms up they get up and stretch and move around, maybe go find a snack. A lot of "hibernating" animals really just experience torpor during cold nights for a season, but are still somewhat active most days.


djublonskopf t1_j6mk8fl wrote

Asthma, allergic rhinitis, and eczema are all statistically more prevalent in children of households with animals present than without. This was a hospital-based study that looked at Qatari children, so the mix of animals (cats, goats, birds) weren't exactly the same mix as you'd find in, say, the USA, but the statistical significance was very strong (p=0.008 to p=0.0001)

This study of Dutch children was a little more interesting, as it looked at both current and past pet ownership (dogs, cats, rodents, or birds). People who have always had pets (and still do) were actually the healthiest, followed by people who had never had pets. So if you stopped reading the paper there, you might think "oh, maybe having pets is actually good for your respiratory health!" But the researchers also asked about respiratory symptoms (asthma, coughing, wheezing, etc.) in people who used to have pets but no longer have pets...and often, those households no longer have pets because the children had developed respiratory issues. And some of the people who never had pets made that choice precisely because they had pre-existing respiratory issues that they did not want to aggravate. So it's not enough to look just at who currently has animals, because people change their behavior over time, and sometimes in response to the very variables you're trying to study.

In short, yes, it appears that living with animals (especially cats) increases the risk of developing respiratory symptoms like asthma, allergies, wheezing, etc...and that those symptoms persist at a higher rate than experienced by non-animal-owners even if the household goes animal-free.