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what would cause these species to have a need to evolve?
Species do not evolve because there is a "need". In any population, the individuals vary in their physical characterists. Some physical characteristics make it more likely for an individual to survive or to mate (and thus pass on these characteristics to its offspring), some make it less likely that an individual will survive or mate, and thus it characteristics will not be passed to the next generation. So the next generation will have slightly more individuals with the "good" characteristic, and slightly fewer individuals with the "bad" characteristic. There is no teleology here -- if you look at all the coyotes that live in a certain area, each one will be slightly different that any of the others, and perhaps these slight differences will allow one a better chance to avoid a predator, catch prey, or find a mate than another individual.
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giraffes with long necks to reach leaves on higher trees
So a pre-giraffe with a slightly longer neck could reach food that a pre-giraffe with a shorter neck cannot. So a longer necked pre-giraffe can not only survive in dense forests where there is plenty of underbrush, but can range into more open grassland, where it can reach the leaves of short trees and the bottom leaves of slightly taller trees. A shorter necked individual is pretty much stuck in the forest, where there might be more competition for other individuals -- the longer necked individual can find food that no one else can reach, so it is less likely to go hungry. Thus, in the next generation, there are fewer short-necked pre-giraffes and more long-necked giraffes.
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H.Sapiens developping the level of intelligence
Primates are social animals. They live in groups and act cooperative. Often, there are hierarchies among the individuals. Those in the upper levels in the hierarchies are more likely to get first dibs on available food as well as have more access to mates. A slightly more intelligent ape will be better able to keep track of alliances and perhaps figure out the consequences of its actions in regard to the reactions of the others in the tribe. So a "smarter" individual is more likely to produce offspring than a "dumb" one. (Eventually, of course, we get a positive feed back case where a smart individual is more likely to able to make long term plans, make tools, and use more sophisticated communication).
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Why hasnt higher intelligent developped in other species....
Like dolphins (which, incidently, are also social species)?
At any rate, intelligence is
not an automatic advantage to the one that possesses it. Higher intelligence requires a larger brain, which then requires more energy, energy that cannot be used to run faster, climb higher, or breed more often. Also, why would intelligence be an advantage to, say, aardvarks? It wouldn't: all anthills are pretty much the same, the same techniques will always suffice to get into them, aardvarks do not have hands so tools would be unavailable to them -- pure instinct will suffice for the relatively simple aardvark world, so more intelligent aardvarks would not necessarily replace less intelligent ones.
The question is
not "why aren't all species, or all species of apes, intellgent?" The question is, "why did intelligence prove to be advantageous to human ancestors?" And we may never know the answer to that. If we suppose that natural selection is the main driving force of evolution, then all we can say is that a population of our pre-Australopithecine ancestors were in an environment that larger brains and more intelligent gave the individuals with those traits an advantage over the others. Quite possibly, in that environment there would have been a number of different traits that would have been advantageous; however, since mutations are random, it was the mutations that led to greater intelligence that appeared first, and so this is the direction that our species took.
"Intellectually, scientifically, even artistically, fundamentalism -- biblical literalism -- is a road to nowhere, because it insists on fidelity to revealed truths that are not true." -- Katha Pollitt
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