sorry to keep hijacking the thread y'all...
adaptations are things that ensure survival so we can procreate. structural adaptations are physical changes (genetic mutations) within a species. the wider the gene variation, the more likely that if something crazy happens in the environment, the species will not die out completely. like i said with the giraffes, if they all had short necks and the only food is leaves on the trees, they'd all die out. but if some of them happened to have long necks, they would survive, so the entire species wouldn't die out. (there are also behavioral and psychological adaptations, but for simplicity i won't get into that right now.)
evolution is a change in the gene pool over time. some structural adaptations are better suited for a certain environment, so you will see the genes for that adaptation the most in a population. if something about the environment changes, the species must adapt to survive. that means some individuals will die off but some will survive. for example the giraffes' food shortage came about because a nomadic group of small short animals came thru and ate up all the grass and shrubbery. now the environment is different, so only those with long necks who can eat tree leaves can survive. the short-necked giraffes die out, only the long-neck giraffes live and they have more long-necked giraffe babies generation after generation. the gene pool went from being a short-necked majority to a long-necked majority.
see, adaptation and evolution are tied together, but they are not the same thing. now my nerdy self is going to go eat breakfast...