Why do some doggies (like shepherds) have straight, pointy ears while other doggies (like retrievers) have floppy ears?
The basic answer is that they were bred to have certain behavioral traits and those traits correlate with developmental progress of young dogs. Retrieving, which retrievers excel at, is a trait which wolf puppies of a certain age focus on as one aspect of their behavioral development. So to retain that unnatural focus on retrieving, breeders have over generations bred an animal that looks and acts ( in this particular instance and perhaps a few others, judging by the retrievers I have known ) like a giant puppy as an adult. This whole process is called neoteny - the retention of juvenile features in an adult.
German Shepards on the other hand were bred for guard work and didn’t require the same focus on juvenile behavior patterns.
It’s not always as cut and dried as all that, but that’s the gist of it.
Some dogs have pointy ears because the breed standard is for cropped ears (Dobermans, for example). When they’re puppies, the ears are cut to that shape and the tail is docked. There are different opinions about the procedure, from “standard procedure” to “cruel and unusual”.
Neoteny doesn’t really explain it, as wolf cubs have erect ears (though admittedly larger than adults’). While neoteny no doubt contributes to the generally larger ears of domestic dogs, it’s likely that early breeders intentionally bred for large floppy ears in some dogs; in some others, larger ears were deliberately avoided; in yet others, large ears were an accidental variation present in the desirable breeding cohorts, which then got passed on; and other breeds’ ears just never changed much.
It’s also far from clear that German Shepherds and other herding dogs are less infantile in behavior than gun dogs; full-on predatory behavior is suppressed in both types, and both use modified hunting instincts in their work. I suspect that trying to explain anything in particular via neoteny is as futile as most “why” questions in evolution.
And remembering that labs and retrievers were bred not just to retrieve, but often to retrieve water fowl, then one can see why breeding them to have floppy ears might be an advantage in helping to keep water out of the inner ear, which can cause all sorts of problems.
Well the physical basis is that the cartilage and muscles of the ear are not strong enough to hold up the weight of the ear. The Norfolk and Norwich terriers are the same breed in some Kennel Clubs, although the Norfolk has floppy ears and the Norwich pointy ears. Some individuals’ ears will flop over only at the tip if the ears are particularly hairy, as can happen in long-haired chihuahuas and papillons I believe. The ears do not have to be huge to flop over though, ie. bulldogs, and of course chihuahuas, corgis and papillons have huge ears that have few problems staying perky.
Considering that domestication itself caused a higher rate of floppy ears in the Farm Fox Experiment (http://www.scribd.com/doc/249407/trutfoxstudy), although granted not a huge boost in numbers, we likely had a wide variety of ultra-floppy (bloodhound/basset style) to ultra-perky (basenji/chihuahua style) ears, and only relatively recently, when developing dogs for more than just hunt-helping or bark-at-bears or tote-goods, found it worthwhile to breed for specific ear strengths & shapes, such as for water protection, scent-gathering (I THINK this is still valid?), or “looking scary and wild.” I would think that many breeds simply have perky or floppy ears because they naturally ended up that way when first developing the breed, and nobody particularly cared to breed it out of them.
More than possible. The paedomorphosis camp also argues that floppy ears ( and big eyes, large braincase, soft fur, etc. ) are also just naturally attractive to humans as a signal of youth. Very young wolf cubs do have floppy ears.
My understanding ( probably outdated, I think I picked all this up from Scientific American many years ago, I never did take mammalogy 
) is that there is supposedly a weak hiearchy of neotenic behavior among breeds with guarding herd dogs showing the greatest ( or perhaps youngest ) behavioral neoteny and sled dogs and the like the least. Now as I recall the authors of that article were correlating that with phenotypic neoteny as well. But your counter-arguments are reasonable enough.
Hmmm… I think it was Smithsonian, not Scientific American and I believe it was this fellow Raymond Coppinger. Like I said in my first post, not cut and dried, but I’ll quote a bit:
*Puppies change (remodel) from neonates to adults. Heads grow (remodel) from little short-faced puppy heads to big long-faced adult heads. Change is allometric, not isometric. To arrest an animal at a particular growth stage is in effect to continue the allometric changes that are occurring at that stage. Since allometric changes are not prolonged in the ancestral stage, the resulting dogs are anatomically bizarre. Indeed, dogs are anatomically bizarre (e.g., head shapes or size variation).
If their anatomy is novel in terms of their ancestor, then their behaviors will also be novel and not directly equivalent to that of their ancestor. For this reason, one discussion of the evolution of working dogs was ready to drop the notion of behavioral neoteny, simply because although it might account for the heterochronic processes resulting in dogs, it was a poor predictor of either anatomical or behavioral result. In the five years that have elapsed since the paper was written, optimism about the use of neoteny as a predictor of anatomy and behavior is returning.*
from here: Biologic Bases of Behavior of Domestic Dog Breeds
Well, floppier… http://www.signonsandiego.com/news/mexico/images/070620wolves.jpg
Err…okay, I may just have to retract a bit. Damn! :D.
We’ll just put ears in Coppinger’s anatomically bizarre category ;).
Hmmm…For example, the floppy ears that characterize most dog breeds may be paedeomorphic trait, as very young wolf pups have floppy ears, which straighten shortly after birth.
From here ( interesting brief discussion comparing recent domestication of foxes with possible domestication of dogs ) :
People seem to be mixing up appearance and behavior. Just because some types of dogs have been bred to act like puppies doesn’t mean they have to look like puppies.
I think bouv has the right answer: retrievers and water dogs were bred to keep water out of their ears. To add to this, erect ears help an animal locate sounds, which makes them useful for guard dogs and some other types of dogs (like terriers, many of which were bred to kill vermin).
Not meant to be a hijack, but…Ground scent hounds have been bred with long floppy ears and floppy jowls, which apparently aid in stirring up scent molecules on the ground as the dog tracks…at least according to several sites that I visited recently (If needed, I’m sure that I could look up the references). This seems to be an example of head characteristics that are not related to developmental stages in puppies as far as I know.
So which doggies have the juvenile feature? Are adult doggies supposed to have straight ears or floppy ears?