I am not very well-versed in Theory of Evolution.
Most of my understanding came from my own thinking and some science books.

When we say evolution, we are not saying a monkey which born as monkey, by growing bigger and older, the monkey start to lose its hair, learn to walk fully with 2 legs, drops its tail and become human. As we noticed not a single monkey in the zoo ever grow and evolved become humans.

We are talkin a big population of a species, which give birth to its species but with slight unique differentiation between each individuals. For example people. You look like your brothers and sisters. You also look like your father and mother. You also have similarity with your uncles, aunties and cousing. Not surprisingly you also more or less has same skin and hair colour with your neighbours and friends.

But obviously, you are unique and different from all of them in some way. Maybe you can run faster than you other brother. Maybe you are more dumb in math compare to your other sister. You are taller than your neighbour son. You might even have different type of blood compare to your own parent eg. you are type O , whereas your father is OA and Mother is OB . And this differentiation come from random combination and sometime accidental mutation gene during conception ... not during you are growing up.

The second factors that causes evolution is the external environment.

Presumably, a virus mutated and can kill all the people except people with blood type O ... and by times go by ... we will find a lot or almost all the people who lives on earth have blood type O . Mutation does occur during propagation, maybe once in while during ovulation, some part of the gene or amino acid failed to locked in probably and the baby produced might have blood type A again, or maybe type B ... or new type C !

Since, when the situation where all the type A and type B people has been wiped out, the virus that by itself would have ceased or maybe mutated to the different type, which might start to attack blood type O ?

This level of evolution still happening, like races features, G6PD deficient, Thalasemia, Sickle cell, etc.

Let say the whole earth is flooded, you will either start to grow gill like fish, or wing start to come out from your back .... this is another stupid ignorant statement or understanding by people who is .... you know what !

When talking about evolution and the first living organism ... there is a big different.

First organism is came about from chances.
It is a very simple organism, with just a few combination of shell of amino acids, some short strain of RNA and simple carbon material which come together by chances. The probability is very rare but make happen because of simplistic nature and vast number random chances that are involved. There is Billions of amino acid, carbon, maybe water, energy on One planet multiply by billions of planets in one galaxy, multiply by billions of galaxies out there making a so-call rare probability become not so rare anymore when compare to this Mega billions chances that is make available.

Variation of species came from evolution.
Evolution is not talking about chance anymore.
We are not talking about a probability of a very complex protein, happen to be together with a very complex carbohydrate, happen together with some complex collagen, DNA, RNA, and with everything else and suddenly pop-up a complex species like tiger, giraffe or even humans.

Evolution best seen thru bacteria as mention before because of its small size so we can have a big population of bacteria in a single cm square, short life span, and we can manipulate their environment.

In real life, we can see fossil and actually even life animals. Tiger, lion, leopard, cheetah are obviously came from same ancestor. Do you know that white tiger came from orange tiger ? Not that the orange tiger getting old and its orange fur start to gray like human hair and become white tiger. By some chances, the combination of 2 cells of Orange tigers give rise to a white tiger !

Have you see a sea-snail that have tentacles like squid ? I almost got a seizure when I saw it first time ! Its has shelf but it has a very small tentancle waving about ( for what I am not sure) and I can see a spurt of water pump up from it proppeled it forward at 1 feet per hour. Now I know why snail and clam are of the same families with squid and octopus ~ the Molusc.