Recent comments in /f/askscience

Marsdreamer t1_j9i2pi4 wrote

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

Not always. There's a great example of an evolutionary study on a bird species that had incredibly long tails. Like, tails that were so long that they often interfered with flight and made the bird significantly more likely to be caught by predators.

However, the females preferred males with longer tails. So, what essentially happened is that the male birds continued to grow their tails as long as they possibly could until they hit a sort of critical threshold of being maximally attractive for females, but juuuust short enough that it didn't completely hinder their ability to get away from predators and fly.

Researches assayed this by taking feathers and artificially elongating certain male bird's tails (basically bird hair extensions). They noted that these doctored birds had significantly higher mating rates than other birds, but on the flip side, they also got caught (and killed) by predators much more often.

There's tons of examples of this throughout nature, where sexual selection essentially overrides the fitness loss for 'deleterious' traits.

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Lets_Go_Why_Not t1_j9i1ik4 wrote

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

They certainly can be, for sure, though sometimes the mechanisms can be blurred - for example, is a sexual preference for greater height in place because taller people are inherently better at something because of the height OR is it simply that people with access to sufficient food and nutrients (through a variety of mechanisms) are taller, thus height is just an indicator, rather than a survival mechanism itself. And that doesn’t even begin to account for sexually selected traits that are theorized to be technically detrimental to day-to-day survival BUT that kind of indicate to potential mates “if I can afford to waste energy on this useless trait, imagine how awesome I am in everything else!” (eg peacock feathers).

In other words, sexual selection can be weird to untangle.

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SchlauFuchs t1_j9hzt24 wrote

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

it is not so much the amount of blood that is the problem but that the heart is used to pump against a given flow resistance and that resistance changes with the number of reduced "consumers". It is a little like with the electrical grid, when large consumers suddenly go offline/online, the power plants have to adjust their generation to not cause a systemic failure.

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dcs1289 t1_j9huya2 wrote

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

The blood cells don't actually leave the capillaries if everything is going fine. The capillary bed is basically a mesh of VERY tiny blood vessels - picture two sets of tree roots with the bottom portion of the roots aiming towards each other and connected - arteries (tree trunk on the left of your mental image) diverge into smaller arterioles which diverge more into capillaries.. which merge back together into venules, which merge into veins (tree trunk on the right).

When the blood is moving through the capillaries, exchange of oxygen and nutrients is able to occur through small pores in the cells (or straight across the cells in some cases). The blood cells don't leave the circulation, but the plasma that they float around in can move back and forth through the tiny gaps.

Here's a good picture to describe the mental image I'm trying to verbalize above.

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