When organisms have to adapt to their environment through physical alterations, how is that passed down to their offspring in the long run?
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You’re thinking about this in the reverse order. Individuals don’t “adapt” in real time and “imprint” on genes. You also want to think about populations, not individuals, when you’re thinking about evolution.
In any given population there is a very wide variety of traits, and you can easily imagine how some of those traits are beneficial in specific environments, whereas the same treats maybe detrimental in others (e. g. polar bears fat & fur in tropics). Overtime, the beneficial traits spread throughout a population just by successfully reproducing more offspring (“the traits are “selected” for, which is a confusing term of art), whereas the maladaptive traits will decrease (“be selected against”.)
There are some more complex evolutionary ideas (epigenetics), where the environment can pass on traits, but only for a generation or two, but that doesn’t affect the DNA itself, just how the DNA is expressed.
It’s the other way around: genes (the genotype) determine, in the most part, physical characteristics (the fenotype).
Individuals, within a species, have genetic variation, because they’re different one from another. Individuals best adapted to their environment – often because of a genetic advantage translated to a physical advantage – tend to have more offspring, and more well-adapted, than the other individuals.
Fast-forward hundreds or thousands of generations. Those better-adapted descendants became the great majority, and the worse-adapted are going to be extinct. That’s a form of evolution.
https://en.wikipedia.org/wiki/Introduction_to_evolution
On the other hand, there’s epigenetics: heritable changes on fenotype that don’t require changes on genes, but in the genes’ activity and expression. More about it in
https://en.wikipedia.org/wiki/Epigenetics
You have it backwards – genes become physical adaptations.
Think of it like a car: each person needs to make a car from scratch, starting by copying the instructions for how to make a car from two different people, then making the car. However, sometimes you make a small mistake in the copying, and sometimes the instructions tell you to do things to the instructions (leave notes, erase notes, or actually changing the instructions themselves).
Those changes in the instruction manual over time results in different kinds of cars – maybe you miscopy a 2 as a 5, and now you have bigger wheels. Some of the changes might make the car not work – but fortunately, there’s a lot of error checking in those areas. And the better your car is, the more likely people will choose you to mentor them.
That’s life. The instruction manual is our DNA – and it slightly changes over time, some of it randomly, some of it as a result of DNA instructions (both from our DNA and outside sources). Those changes result in slight physical differences, some of which means the life form does slightly better – which means more offspring.
Imagine two people. One has by chance a genetical anomaly that makes him immune to malaria but makes the amount of oxygen his blood can carry lower.
He and his brother who doesn’t have this genetic anomaly live in a region with malaria: Brother one has a much higher chance to get old enough to produce a lot of offspring, brother 2 dies without having any. -> next generation some have the anomaly too and again, they will be the ones that have a high chance of surviving.
Now the same in a region without malaria and higher altitude:
Brother 1 suddenly has less capacity to transport oxygen and brother 2 is much fitter than him: high chance for brother 2 to produce more offspring. Now the tides have turned.
After some generations you have 2 groups of people and they are adapted to their environment.
But the important part is: the adaption was there first, the environment decides what adaption is actually usefull and which isn’t.
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