I have always heard that when a species evolves a "new" trait, it is due to some form of mutation (when the mutation occurs in the animal is irrelevant, provided it pass the "new" trait on to it's offspring). Whether that "new" trait is useful, or not, is supposed to be basically up to chance (except when sexual selection is involved). However, it appears to me that a lot of people think of these animals as evolving these new traits, because of the necessity.

Should I be thinking of it this way as well? If so, what is it that "tells" the animal that it should evolve, and what is it that causes the animal to do so appropriately? Also (and this point is the reason for the title of the thread), why are there so many seemingly "unnecessary" traits, that would not have evolved out of necessity?

Any help on this would be appreciated.

What unneccessary traits? Characteristics randomly emerge. Characteristics are discriminated against when they have an disadvantage in terms of additional resources etc. It takes longer for it to disappear than to appear...

Life forms don't envision a need and then evolve toward that need. They radiate in many directions and the environmental conditions dictate which group does the best. The conditions sculpt (direct) the evolution.

When someone is describing past events non-technically, they may say something like "the ice age began so creature X evolved thicker fur". They don't mean it was the creature's idea to do so. They mean that among the population of creature X there was already variation in fur thickness and the cooler temperatures resulted in the furrier ones to fare better than the less furry ones. The result was that over time, the population's average specimen had thicker fur than the population's average ancestor.

* - well, not literally "all"....some paths are more likely than others

By the way, mutation is not the only way to obtain new traits. There's also recombination (sexual mixing among a population) and gene flow (sudden mixing of previously separated populations).

I may not have all the details perfect, so bare with me. A population of a certain type of bacteria were placed in a growth medium rich in two kinds of simple sugars (a glucose and a fructose, I believe). The type of bacteria used was known to be capable of metabolizing only one type of sugar (the glucose, let's say). When all the glucose was used up, and the population began to starve, reproduction of DNA strands became unstable. This resulted in a sudden "burst" of mutations. Some of these were able to metabolize fructose, and became a new species.

Is anyone else here are familiar with the experiment to which I'm referring?

Since Fructose catabolism is not too different from glucose metabolism, it is reasonable to expect at least one bacteria to aquire this mutation.

And the idea of mutations to increase in frequency during times of hardship also seems quite reasonable on its own merits. Under starvation a lot changes in all cells. It would be evolutionarily advantages to adapt to stresses by allowing your species to evolve faster as such....

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Originally posted by Phobos:
Think of it this way, mutation (being essentially random) sets life forms down paths in all* directions, but natural selection (non-random) is a seive that only allows some paths to succeed.

Life forms don't envision a need and then evolve toward that need. They radiate in many directions and the environmental conditions dictate which group does the best. The conditions sculpt (direct) the evolution.

When someone is describing past events non-technically, they may say something like "the ice age began so creature X evolved thicker fur". They don't mean it was the creature's idea to do so. They mean that among the population of creature X there was already variation in fur thickness and the cooler temperatures resulted in the furrier ones to fare better than the less furry ones. The result was that over time, the population's average specimen had thicker fur than the population's average ancestor.

* - well, not literally "all"....some paths are more likely than others

By the way, mutation is not the only way to obtain new traits. There's also recombination (sexual mixing among a population) and gene flow (sudden mixing of previously separated populations).

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In the fabric of space and in the nature of matter, as in a great work of art, there is, written small, the artist’s signature. (from Sagan's "Contact")

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That's how I've always looked at it. However, some of the members start asking question about why we still do something (or enjoy something) if it has not advantage for us, and these questions throw me off.