Recent comments in /f/askscience

allahyokdinyalan t1_j9gwc6a wrote

Reply to when a limb gets amputated, how do they stop the flow of blood? by EnchantedCatto

Medical student with expressed interest in surgery here.

Amputation is not simply chopping off a limb. If planned well, it involves several steps of careful surgical interventions.

The most important thing to note about amputations is that, you would want to keep the mobility as high as possible. Depending on the amount of tissue left, you would generally want to keep joints and a bit more tissue distal to the joint.

So let's start with the innermost part, the bone. You would not want to expose the bone or leave a thin layer of tissue around it. That would lead to pain using prosthetics and during daily life even without the use of prosthetics.

In order to prevent this, the surrounding soft tissues, muscle and fat and skin needs to be slightly longer than the bone so that it can cover the bone well enough.

As stated above by a surgeon, directly connecting big arteries and veins leads to poor cardiovascular outcomes. It certainly depends on the type of trauma and the amount of salvagable tissue but you would want to rely on capillaries and angiogenesis (new vessel formation) for venous return in the long run.

There must also be enough skin to cover the resulting "stump" of a tissue without puckering the skin and while trying to achieve the best cosmesis and surgical outcomes.

I have explained all these steps because many people imagine sawing a leg off when someone says amputation but in modern surgical practice, that's far from truth.

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HumanistHippy t1_j9gs3bl wrote

Reply to How did Paul Dirac predict the existence of a positron before the actual discovery? by bazongaenthusiast

It was the result of his equation that combined quantum mechanics with special relativity in order to describe the behavior of an electron moving at a relativistic speed.

The equation necessitated a "positron" mathematically. Unless the math was incorrect (which it wasn't), the "positron" had to be there even if we were unable to observe it at the time.

Source: CERN

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GeriatricHydralisk t1_j9gpv7o wrote

Reply to What are more accepted hypotheses that similarly explain the aspects of hominid evolution that the "pseudoscientific" aquatic ape theory does? by KEVLAR60442

Rather than cover what's already covered elsewhere, it's worth pointing out why the AAH fails:

  • First, it considered traits "piecemeal", rather than looking at the organism as an integrated whole. This allows it to engage in the common fallacy of "remembering the hits and forgetting the misses" - it points to things like the diving reflex or subcutaneous fat that are consistent with diving, but "conveniently" ignores traits completely inconsistent with aquatic life, such as lack of reflexive swimming (babies show a diving reflex, but cannot actively swim) or valvular nostrils.
  • Second, it's completely at odds with comparative data. Lots of mammals have become semiaquatic and aquatic, and none of them have done so in the manner postulated by AAH. Nostril valves and webbed digits are near-universal in semiaquatic mammals, but absent in us, nothing else has become bipedal to move in water like AAH proposes. There are even several monkeys which swim and dive on a VERY regular basis (Allen's Swamp Monkey, Japanese Macaque, Proboscis Monkey), and a) don't display anywhere near the strength of adaptations claimed by AAH and b) have the sort of adaptations you would expect from a typical swimming/diving mammal.
  • Lastly, back when AAH was proposed, and when all the major books/articles/talks in favor of it came out, we knew almost nothing about our ancestors, particularly their habitats and ecology. The Leakeys had only just begun their work, and wouldn't find Lucy until the 70's.

Getting dragged into the particulars of this or that trait is a mistake, operating on too low of a level. Considring organisms are integrates wholes, and considering trait evolution in a comparative context, AAH makes not a damn bit of sense.

It's also why nearly nobody with a PhD in a relevant field takes it even remotely seriously, and the only exception was a plankton ecologist with no training in anthropology.

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DorkRockGalactic t1_j9gouep wrote

Reply to comment by Felted_Grape in Why are fevers cyclical? by Key-Marionberry-9854

That's a good analogy really.

With all the random stuff happening, it's possible for things to order themselves by random chance. Earth life happened to order itself just the right way to self replicate and thrive on our island of stability where there are energy gradients to exploit.

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