Think of a paperclip as a metal bar.

As kids we would keep flipping the inner part of a paperclip. And kept folding it till it breaks.

So, when you bend the paperclip into plastic deformation. It is difficult/impossible to bend it back. You would have to melt it completly. without melting it. It bends at the point of lease resistance. So after 1 bend, there is a new structure and new point of least resistance is somewhere else near the original bend. So even if you try to bend it back, it won't be the same structure. In this case some of the bonds might have completly broken, but there is still enough to hold it together.

When you keep bend a paper clip, some areas will have elastic defirmation, some will have plastic, and some will break. So if you keep bending it back and forth around a certain area, eventually enough break around the point that you are bending it, that it just splits into 2 pieces.

[removed]

Punctuated equilibrium is possibly more likely than some kind of slowing down. As you understand natural selection, what is the driving force? Some selective pressure from the environment is what causes all mutations and all culling of statistically slightly-less advantageous traits from propagating to the next generation. The list of those potential pressures is rather long, no?

Others have given great answers. I wanted to point out that the “Red Queen hypothesis” (Wikipedia link) is relevant here. In Lenski’s experiment, conditions were intentionally kept pretty much constant, but in the real world

> species must constantly adapt, evolve, and proliferate in order to survive while pitted against ever-evolving opposing species.… the effective environment of any homogeneous group of organisms deteriorates at a stochastically constant rate. …the evolutionary progress (= increase in fitness) of one species deteriorates the fitness of coexisting species, but because coexisting species evolve as well, no one species gains a long-term increase in fitness

[removed]

Thanks for that. There is so little I know and so much I can learn from others.

From what I understand (my focus is Neuroscience, not Infectious Disease or Immunology), one of the main observed effects of COVID infection is inflammation of the vascular system [1]. Since the vascular system is responsible for maintaining pretty much all organs of the human body, infected individuals can exhibit a variety of symptoms based on the location of the inflammation. For example, neurological symptoms can indicate damage of the vessels around the brain [2].

This effect on the vascular system is not shared by the other pathogens/diseases you have listed, which (generally) target specific organs and/or tissues (respiratory, gastrointestinal, CNS) that are not as widespread and foundational as the vascular system. The variety of different possible targets (read: possible areas where the vascular system may suffer damage) is a very likely explanation for the variety of symptoms of COVID-19.

This is super interesting. Hopefully you don't mind if I continue one more! When you bend the bar and it undergoes plastic deformation, why is it that if you bend the bar enough it will eventually begin to degrade and eventually "fail"? Failure in this context is weaken at the bend or break completely in half.

Based on what I've learned from your posts, it would appear that something happens at the atomic level to the bonds if you overwork the metal.

I think the tricky nuance with determining what has caused someone’s cancer is that cancer emerges after a few pre-cancerous mutations rather than just the one - kind of like a slippery slope mutation cascade that increases the likelihood of full blown malignant cancer by massive amounts with each mutation. So whilst smoking might cause one of those mutations, it’ll take a few more to become malignant! And then another few more to become metastatic cancer, the biggest killer

I disagree with the people saying no here. Thanks to genome sequencing and tumour genome sequencing, we can definitely start chipping away at the cause of some cancers. Have a look at mutational signatures in human cancer on Google scholar. Some carcinogens can leave distinct signatures in tumour DNA, allowing determination of cause in some cases. Cigarette smoking is a good example of something that leaves a unique mutational signature. It’s a super interesting topic. There’s a great paper by Alexandrov et al (2020) in Nature.

[removed]

At low temperatures the thermal energy is too low to overcome the activation energy barrier required for the defect to migrate.

[removed]

The charge cancels out, but that doesn't mean they can't stay put. Imagine a positive charge in the middle of a triangle and three smaller identical negative charges in the corners, for instance.

In reality it's a bit more complex than that. Electrons are fermions, and that means that they experience so-called Pauli repulsion. This is what prevents two atoms from falling on top of one another, and what prevents you from inserting your hand into the table. On top of that there are dynamical electromagnetic effects, known as dispersion, that lead to electromagnetic attraction even between uncharged objects. For instance two atoms of argon, both neutral, will attract one another unless they are very close to one another.

In an iron lattice the cohesion is due to the electrons stabilizing the nuclei.

[removed]

well that and the structure of your respiratory system and shape of your nose and mouth. The slight differences in skeletal structure changes the length, width, diameter, etc. of muscles and tissues that are responsible for speech, making each person have a unique sound

That would be a stretch. It's more nature and nurture. Your physical characteristics will impact tonality and what not. You're upbringing will impact cadence, pronouncation, and other influences. Finally, your brain will make its own choices combining all this input into your own voice.

You can consciously influence some parts like pronouncation and accent if you work at it.

[removed]

Yes, this principle should apply in nature; but at the same time this only applies to a fairly restrictive case

namely, if you take a population of organisms and put it in a new environment, at first its adaptation to this environment will improve very quickly, then it will keep making progress but slower

however, in nature you have to consider that (1) most organisms have been in their usual environments for a while so they're all in the slow adaptation phase; yet that (2) environments actually change all the time, because climate isn't perfectly stable and because the surrounding ecosystems aren't stable either (ecosystems are complex systems that are constantly disrupted by new pathogens, new species, species going extinct or becoming less/more abundant, etc., on top of natural phenomena)

So there's always adaptation, because it occurs towards a forever-moving target. In most cases, it's more accurate to consider that evolution is a perpetual thing

Evolution is made up of two parts, broadly speaking: random variation and natural selection. (And sexual selection but I’m leaving that aside for now)

Random variation doesn’t slow down, it’s effectively always bubbling away making the next generation look and function slightly differently. These are effectively copying errors when the genetic code is replicated.

Natural selection can appear to slow down, or halt entirely. This is where organisms try to survive in the world long enough to reproduce, “may the best man win” so to speaks (all genders evolve, it’s just a phrase). As time goes by, the species either becomes better suited to its environment or goes extinct. And there is a limit to how well suited it can become (if nothing else, evolving can in principle get stuck at a dead end).

Such animals are called “living fossils”, and I believe alligators are an example of this. There are some plants also which have barely changed for millions of years, because they are very well suited to their environment and any variation tends to make them worse.

[removed]

[removed]

When an organism is adapted to its environment, and the environmental pressures are not changing, there will appear to be very little evolution going on. In actuality, the alleles of genes will continue to mix and recombine in new ways during sexual reproduction which means that with each new generation the organism is still putting out new versions of itself.

The DNA polymerase is also hardwired with a certain error rate which is very low, but just high enough to allow for a change in DNA here and there. Just rare enough to not really change much, but to allow for change to be possible. These changes too are put out in each new generation.

Typically if the species is excellently adapted to its environment, and the environment doesn't change all, these genetic changes in each new generation aren't likely to provide an improvement so you don't see much change. This is known as stabilizing pressure.

But as soon as a new selective pressure appears, it will become clear that that species never actually retired from the evolution game.

No, that isn't how age works.

Even for a forensic examiner, reading age from the body itself is rarely conclusive. The sole exeption is early childhood, which has specific stages of growth and therefore can be a little more telling. However, for adults or cases of malnutrition...determining an exact age is guesswork, not science. Humans do not grow uniformly.

So, the reason of our voices being different than each other is we actually choose our voices.