Confused on some things for evolution?

Evolution is the result of variation, inheritance, and selection. Variation happens with each new generation - offspring aren't exactly like their parents. One of the sources of the variation is mutation, which are random, permanent changes in DNA sequence.

The important thing here is that variation is basically random. An individual fish in a cave might be born without fully-formed eyes... but the chances of that happening are the same as a fish on the surface being born with that same mutation. The difference is in selection. The eyeless fish on the surface will be at a disadvantage, so it will be much less likely to survive and reproduce - so it probably won't have many offspring that it can pass its faulty eyeless genes on to.

The fish in the cave won't be at a disadvantage, though, so it won't get weeded out. On the contrary, it might even be at a slight advantage, since growing and maintaining eyes would use up resources but not give any benefit. The eyeless fish won't be less likely to survive, reproduce, and have lots of offspring to inherit its condition. The fact that it is slightly more efficient might even give it a small statistical advantage, so its eyeless offspring will "out-reproduce" everyone else in the population, and after many generations, everyone will have inherited the trait.

The evolution of fur is a little bit trickier. New traits can and do evolve (contrary to what CRR claims - he's been parroting that lie for a long time now), but it's harder to predict than the loss of a trait. It's more accurate to say that a species in a cold environment will evolve a way to deal with the cold. This MIGHT be fur. Then again, it might be subcutaneous fat. Or it could be feathers. Or it could evolve to migrate to warmer climates. Usually, when a new trait evolves, it's a modification of an existing trait. Feathers are a modification of scales, which is a modification of skin, for example. Hair is thought to be a modification of sensory whiskers. Sometimes this results in the loss of the original trait, but sometimes a gene can get duplicated, allowing one copy to remain the same, and other copy to mutate and lead to new traits.

Evolution isn't a guided, planning process, so it can sometimes go in weird and unexpected ways. It usually takes the path of least resistance, though. If a species gets stuck in a cooling climate and needs to evolve to fit the changing conditions it might evolve fur, especially if it already has some other sort of hair or fur, but it could also adapt in any number of other ways.

Well then go ask a biologist about your confusions. You might get help here but funzies will just tell you that he'll awaits and the educated need your question to be a little more specific. Kk just saw your deets. The trait (in this case the eyes) becomes useless. Because it requires energy to function individuals who tend put less energy into their eyes and are able to use that energy elsewhere will tend have an easier time surviving. With time they will produce more offspring who will also vary amoung individuals. Therefore the variants who use even less energy on their eyes will still be able to use that excess energy for more useful survival methods and again the process will repeat until the eyes are completely vestigial. It's important to remember that just because something is useful in one environment doesn't mean it won't be a hindrance in another. If there's no light it's better to not waste energy trying to sense it. Variation amoung species and reproduction are the keys.

I'll explain the concept using your example of creatures that grow fur:

In a cold environment the creatures with the most fur have a greater chance of survival and furthermore will be a better selection for their mate. Their own body heat will keep their mate warmer, so it makes them preferable in that regard. That type of evolution is known as natural selection and occurs over many generations.

Gradually each successive generation grows more hair just like one or both parents. The offspring that don't grow extra hair will have a reduced chance of survival or selection by a mate once they reach adulthood.

With the fish, eyes are of no use in a perpetually-dark environment but are one more organ that (1) has to be maintained and (2) may become injured or diseased. Therefore, the mutations for eye reduction or eyelessness will be selected for. With the fur, it works in the opposite direction, with the furrier mammal selected FOR.

Mutations are more or less random but there is a factor called canalization that makes it easier for the phenotype to change after a generation or two. Unless your teacher has read Waddington, he or she has probably not heard about it.

Eyes are a considerable disadvantage in a totally black cave because they are easily damaged. A mutation that makes the eyes more resistant to damage even though it degrades sight will therefore be an advantage and be favourably selected. The end result is blind cave fish.

Fish from different caves have been crossed and produced some sighted offspring showing that different mutations are responsible in different populations.

Adaptations occur by selection from existing variations in the gene pool. In a cold environment an animal will develop longer fur by elimination of the alleles that produce short fur. It will not start growing fur if that did not exist in the original population. The genetic diversity is reduced, thus adaptation is a step toward extinction.

High school Biology will clear that up. There is nothing confusing about evolution.

Mutations happen randomly. When there is light, mutations that cause eyes to function worse are selected against. When there is no light, mutations that cause the eyes to function worse are not selected against. The net result is that cave dwellers evolve away from functioning eyes.

The mechanism in the ocean is different. Ocean creatures have bio-luminescence.

You might take a class or read a book, but that would be a sin. God does not forgive those who ask questions!

Ask in biology and you will probably get an educated answer.

If you have a question, y need to ask it. If you're too stupid, give up.

Edit.

If you don't understand we can't teach you tonight.

About fish eyes. Any function is expensive. It takes energy and nutrients to make and maintain. Whatever supporting structures are also expensive.

If a mutation occurs where, say, eyes aren't built, and the organism needs them to thrive, that individual won't reproduce. But, if that mutation occurs in a fish that's in darkness, the lack of sight doesn't hurt but actually helps, as that fish has a better chance of doing better than its peers. It doesn't have to devote resources to growing and maintaining eyes and supporting systems.

So that individual has a better chance of leaving more offspring.

If you understand nothing about evolution this won't help. But if you get any of it, that should help.

You can't learn everything the night before a test.