From the Bassett Hound to the St. Bernard, many dog breeds have ears that don't stand up. Floppy ears are super cute, but you might wonder if there's a deeper reason why some dogs' ears droop. The question has puzzled some of history's top minds – seriously, Charles Darwin considered the issue (among other issues concerning the differences between domesticated animals and their wild counterparts) way back in the 1800s. Thankfully modern science has shed some light on the conundrum. So, let's get science-y!
Genetic studies have shown that dogs first started hanging out with humans some 10,000 years ago. Dogs were essentially wolves then – complete with ears that stood up tall. Over years and millennia, humans selectively bred dogs to have more desirable traits (like being friendlier or tamer). Floppy ears, while adorable, were simply a byproduct of this domestication and breeding for tameness. Scientists have even given this phenomenon a name: domestication syndrome. It's something that was first noticed by Charles Darwin, who wondered why domesticated animals (not just pet dogs) have features and traits that differ from related wild animals.
A recent study published in Genetics has explored domestication syndrome in depth. In addition to floppy ears, side effects of domestication include smaller jaws and teeth, white fur patches, and juvenile faces, among other traits. The syndrome isn't unique to dogs – it affects domesticated pigs, horses, sheep, rabbits, and foxes as well.
So what's going on exactly? The first wolves to join up with humans thousands of years ago must have been different from other wolves – they most likely had less adrenalin which meant they were less prone to attack or take flight when near humans. Adrenalin comes from the adrenal gland, which is formed by stem cells called neural crest cells. Humans selectively bred dogs for tameness, and by doing so they bred dogs with small neural crest deficits (these deficits are why the wolves were less afraid of humans in the first place). These stem cells don't just affect adrenaline and the adrenal gland, though – they also go to other parts of animals, like ears. Because of these neural crest deficits, embryonic stem cells malfunction or get lost on their way to build tissue (dogs' ears droop because of malformed cartilage), and this causes the physical differences you see between domesticated and wild animals (like dogs and wolves, for instance).
Floppy ears and the other side effects of selective breeding for tameness don't seem to harm dogs or other domesticated animals, and they're not even present in every animal – remember, not all dogs have floppy ears. Humans might not have intentionally bred dogs to have droopy ears, but the trait is undeniably cute, even if floppy ears are technically a deformity. We wouldn't want our floppy-eared dogs any other way.