Recent comments in /f/askscience

mxjuno t1_j5ky5qq wrote

Reply to comment by Zeebuss in Do other animals have dangerous pregnancies just like humans? by Level_Shift_7516

I was actually going to include that caveat but I tried to keep it simple. There are so many generations of wisdom in midwifery, and I’m absolutely sure it has made a difference over the generations. I used midwives myself for my births. I wish I could find the article that refuted that our anatomy would’ve changed that much due to interventions that humans use and animals do not.

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Any-Broccoli-3911 t1_j5kqon3 wrote

Reply to comment by CrackpipeStickman999 in How do we know that the biggest known stars are actually so big and not just regular sized ones at the end of their "life"? by realzanji

Yes, we can put the stars in the diagram based on their brightness and their temperature.

If they are in the main diagonal, they burn core hydrogen and will last a while.

If they are brighter than the main diagonal, they burn shell hydrogen and either core or shell helium, they are close to their death.

If they are less bright than the main diagonal, they don't burn anything and are just slowly cooling down.

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Zeebuss t1_j5koxla wrote

Reply to comment by mxjuno in Do other animals have dangerous pregnancies just like humans? by Level_Shift_7516

For humans, midwifery is one the oldest and most ubiquitous professions in history, we've been intervening in birth for as long as know anything about.

Animal birth as well, animal husbandry is at least as old as agricultural, but domestication was already well underway among pre-agricultural nomadic societies.

Neither of these practices of artificial selection and assisted birth are "a few generations" old. They are ancient and absolutely have had enough generations for significant adaptation to occur. Also human artificial selection can happen much faster than that.

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lmxbftw t1_j5km6bo wrote

Reply to How do we know that the biggest known stars are actually so big and not just regular sized ones at the end of their "life"? by realzanji

Are you talking about volume here, or mass? If volume, then the biggest ones we know ARE indeed at the end of their "life", up at the top-right corner of the Hertzsprung-Russell diagram. To know the radius of a star, you need to know its distance, which there are different ways of working out, some more precise than others. In the case of VY Canis Majoris, one of the largest stars known, there's a very precise radio parallax distance measure from the VLBI. Once you know distance, how bright it appears to be, and the temperature (these second two are relatively straight-forward and easy to measure from Earth) you can work out how physically large the star has to be to produce the observed amount of light from the Stephan-Boltzmann law.

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Citrownklown t1_j5kdjzt wrote

Reply to comment by curiousnboredd in What is a neurotransmitter "turnover rate", with reference to acetylcholine? What does it mean if the turnover rate is increased or decreased? by yungPH

It looks like the mode of action of botox is a bit more complex (here’s from one of my favorite webpages drugs@fda)

12.1 Mechanism of Action BOTOX blocks neuromuscular transmission by binding to acceptor sites on motor or sympathetic nerve terminals, entering the nerve terminals, and inhibiting the release of acetylcholine. This inhibition occurs as the neurotoxin cleaves SNAP-25, a protein integral to the successful docking and release of acetylcholine from vesicles situated within nerve endings. When injected intramuscularly at therapeutic doses, BOTOX produces partial chemical denervation of the muscle resulting in a localized reduction in muscle activity. In addition, the muscle may atrophy, axonal sprouting may occur, and extrajunctional acetylcholine receptors may develop. There is evidence that reinnervation of the muscle may occur, thus slowly reversing muscle denervation produced by BOTOX.

https://www.accessdata.fda.gov/drugsatfda_docs/label/2011/103000s5236lbl.pdf#page13

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