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Most mutations are not good, or downright lethal, leading to miscarriage, cancer and other awful outcomes. Especially in multicellular organisms, advantageous mutations occur quite rarely. That organism also has to be lucky enough to survive long enough to reproduce (you might have an incredibly advantageous mutation but just be unlucky and get struck by lightning before you reproduce for example). It may be something more akin to flipping 50 or 100 heads in a row.

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Fatigue is sort of a mix of plastic and elastic deformation. It can happen when a material is only being elastically stressed - but the mechanism of operation is still dislocation motion (like plastic deformation).

The dislocations that move in this case require much lower stress to move - ie. not all dislocations move at exactly the yield stress of the material (that's sort of an average). But in this case, dislocations move back and forth along the same path (the path of low resistance), and eventually form a slip band which can eventually lead to failure of the material.

This is referred to generally as high-cycle fatigue, ie. it takes a lt of cycles to cause failure, because the stresses are low, and SN (stress vs #cycles) curves are used to assess damage and predict time to failure (compared with a stress/strain curve used to predict failure from overstress).

Even recessive traits are selected for in the natural environment over time. However, they remain recessive for various reasons. This could include the recessive trait being advantageous in certain circumstances, but not others. Or that is only an advantage if other traits are also expressed at the same time. Many times a recessive trait can be an advantage but exacts a biological cost as well. If these traits remain recessive, evolutionary pressures cause them to become more common in the "required" circumstances, while allowing them to swiftly become less common when the environment is not suitable for that trait.

Have you thought about the modality of disease vectors with this conversation? Maybe disease is a more efficient form of life. Maybe parasitism would be recursive and self contained in a computational mind frame. Other commenters have mentioned evolutions “discernment” of a modality and this is a flawed frame.

Mutations are random. You can't make a gene mutate in the wild.

When a gene mutation does occur, it is still largely unrelated random factors that will determine if the individual with that mutation survives to pass on the gene. Only once that mutation has spread to a large enough portion of the population, will statistical tends become significant.

If an established gene is not harmful enough to survival and mating, then diffusion will sustain it in the population. Random mating means that any sufficiently established gene will reach an equilibrium between selective pressure reducing its prevalence and diffusion bringing all alleles into equality.

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https://en.wikipedia.org/wiki/X_chromosome

Tldr - they noticed the X chromosome was weird, so they called it X. Then Y was the next letter. Then Z and W came about to distinguish between the ZW system and the XY system (also it's important to note that the X chromosome is the X chromosome, period, whether it's in a mouse or a human or whatever--it refers to a specific thing that plays a specific role).

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Why don't they use XY? Is it just alphanumeric numbering starting with the A chromosome? How do they pick the order of the chromosomes?

The chances of a random mutation being adaptive is far far lower than 50%. It's more like getting heads ten times in a row.

No all genes are working against the force of entropy to exist. If there isn't a pressure keeping something from mutating like it being adaptive or changing it being maladaptive then it will eventually be replaced.

> Is it an advantage or just “this happened to work out slightly better than the alternatives present at the time”?

It doesn't even have to be better or provide and advantage, it just has to not be negative enough to cause them to go extinct. Fitter/better only applies to competitive situations where there's selective pressure. It's possible for a trait to have no impact on fitness and just be one way that works among others.

Even neutral mutations are working against entropy if there isn't a pressure keeping it around. Sure you could have a three generation neutral->advantageous or even a twenty generation disadvantageous->advantageous. In the same sense you could phase through a wall if your electrons all randomly lined up.

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I doubt that's true, that's like saying it's unlikely to get 3 head coin flips in a row.

As long as it's not so much worse that the individual dies before mating, the gene will spread through a population. Over a long enough period, if it is less productive at surviving, it may eventually die out, but that takes many generations.

You: > Is it an advantage or just “this happened to work out slightly better than the alternatives present at the time”?

Evolution: I don't understand the difference?

>needs to be at least as good if not better than other siblings.

>If it's going to take three generations of mutations to get to an advantage, they probably won't make it.

This is largely up to chance, unless the mutation is both dominant and a significant disadvantage early in life. Many mutations that are recessive, neutral, or only slightly disadvantageous spread through populations just through chance. For example, just look at human traits like hair color or clinodactyly.

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It’s a great question and you’re exactly right! There are even some cases of fish having multiple sex chromosome systems interacting together to be XYZ. Cichlid fish in particular, well known for rapid speciation, show incredible evolution of sex chromosomes. In which case, you’re unlikely to find a single degenerate Y chromosome like you find in mammals.

no but in order for water to boil the kinetic energy of the water molecules has to be strong enough to resist the cohesive force of other water molecules+ that of air . so while there is no difference in a normal region , in a mountainous area where the air pressure is low it takes more time to boil the water in a stove and the same time in a oven because its closed