What would cause pointed, elf-like ears to evolve in a humanoid species? Presumably cultural factors could help explain how they stuck if the species had already developed civilization, but what could give it a significant enough advantage to allow it to get to that point? What would make a humanoid with pointed ears more likely to be able to reproduce and pass the trait on in those first generations?
The founder effect is a way genetic traits with no particular adaptive value can spread in a population. From linked wikipedia:
In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.
Consider Stahl's ear.
Stahl's ear is a rare congenital auricular malformation in which an abnormal "third crus" traverses the upper pole of the scapha. This results in a deformation that flattens and steers the helical rim posteriorly and superiorly. This deformity was originally described by Stahl in the nineteenth century. It is more prevalent in Oriental societies, especially Japan. It is seen bilaterally in 20% of cases. It is also known as Spock's ear or Vulcan Ear.
Stahl's ear can happen. Suppose an individual was born that had a predisposition to that. This individual went on to be one of the founders of the elven race - probably not because of her ears, but because of some other genetic fitness advantage like being in the right place at the right time and not dying before having lots of kids. Her pointy ears come along for the ride.
The ancestors of humans used to have pointed ears. Elves just didn't evolve rounded ears, that's all.
We find symmetry attractive because it's an indicator of general good health and genetic stability whereas uncommon traits indicate a disparate lineage, so when we see someone with long pointed symmetrical ears we instinctively recognise them as being a good source of new and well vetted genes.
Imo the only reason eleven ears haven't evolved already is that there hasn't been the right combination of prosperity and selective pressure to cause humans to evolve to primarily be more attractive to other humans. With the right conditions and enough time human dimorphism could develop until women are all long legged, large breasted, slim waisted, doe eyed, flourescent haired anime-like elves, and men all look like Sephiroth complete with inexplicable air-intake fringes.
Or we could evolve into blobs, who knows?