Meerkats keep a lookout even though it clearly offers no survival benefit when there are no predators. This behavior is an instinct, not learned, and therefore difficult to get rid of. Assuming this instinct is currently neutral with respect to fitness, it might take a long while for it to disappear. But that might be beneficial in the long run, because the environment might change and their vigilance again become adaptive.
Giraffes are smaller when they are young (surprise!), so it seems unlikely that leaves on high branches that adults could barely reach would result in the selection pressure that eventually led to their long necks (and legs - that the legs are long too is a much overlooked fact, I think). Rather, sexual selection looks like a much better explanation. Males fight not just using their necks, but they also kick each other.
This is some serious, serious headbutting. Imagine if they evolved sharper horns.
Chimpanzees within a group are violent at dinner time, but disputes over the right to mate is settled in a much more peaceful fashion. A male and a very beautiful female were grooming and hugging each other (people watching going "hnnn, so sweet"), then the male stood up and did a brief dance (people watching going "oh wow, look!"), and then she put up her ass they had sex (people watching going "oh, erhm"). Then the much older male came over and interrupted them with his presence. He did the same dance, and the female got scared and ran away. The younger male pretended nothing had happened. Then the old one left, and the female returned. They repeated all of this a couple of times, with a lot of grooming in between. But why? If the old male had any power, why did he allow them to be close at all? If the other male was higher in the hierarchy, why did he not defend the female from him? At one point the old male attempted to mate with the female, but she moved a little bit, and that was enough to discourage him. Again the other male did nothing. I know from other primates that hierarchies are often very tight with everyone aware of their place in it. But here it seems like the hierarchy is in dispute, and yet it doesn't lead to fighting between the males.
Apparently, male chimpanzees prefer older females.
"Chimpanzee males may not find the wrinkled skin, ragged ears, irregular bald patches, and elongated nipples of their aged females as alluring as human men find the full lips and smooth complexions of young women, but they are clearly not reacting negatively to such cues," the researchers concluded.