Unnatural Selection: What Time Lords, Changelings, and Mickey Mouse Have in Common

Question: If changelings can choose their forms at will, why in the world would they choose to look like technicolor moose-bugs?

The answer to that may have its roots entangled with several other natural and social phenomena. Take, for example, Mickey Mouse. In his earliest days, he was-- well, mouse-shaped. To an extent, he still is. However, in the many years since his genesis, the cheeks have grown chubbier. He's put on some kid gloves. He has grown shorter and a little wider. In essence, he has been made to more closely resemble a human infant. This is the effect of anthropomorphism; the more human something seems, the more we can relate to it. For the purposes of this argument, we will ignore the uncanny valley. But really, from Aesop's Fables to My Little Pony, creatures that appear more humanoid appeal to us much more.

There are real-life examples of this as well. For instance, most mammal infants cry at roughly the same frequency. So if a kitten is lost in the woods, it hopes that its cries will summon a) its own mother, b) another cat, or c) like maybe a lynx or something.

Time Lords may have made use of this principle. Why do they appear humanoid when they could be great big multidimensional squids? Because they don't want to freak aliens out, and for some reason they really wanted to appeal to the bipeds. There's another theory that Rassilon attempted to wipe out all non-bipedal sapients in the early days of Gallifrey, but... well, if he tried, I don't know that it worked. The number of times the Doctor has faced talking dogs, for instance, is evidence to the contrary.

So, why did the changelings switch to the bright color scheme and cute forms? After all, they don't need to look like anything, per se. When they transform into something, they gain all the abilities that something has, as evidenced by Ocellus's ability to breathe underwater while changed into a seapony to save Yona from drowning. This is quite important because I'd always sort of assumed it was all just a very good illusion. Apparently not. Back to the point, though, why the change?

Answer: To appeal to the ponies and most of the rest of the world. They are colorful, as ponies are colorful. They have hooves and two eyes and a muzzle, as ponies do. As, indeed, do the hippocampi. Some of these qualities are also shared with the donkeys, the zebras, and to some extent the minotaurs and griffons and dragons. And what happens when we encounter a being that appears closer to how we are ourselves? We are more likely to relate to it, perhaps. That may be why puppies are a more popular pet than snakes, and why the Doctor is so fond of Earth; they can relate to and be related to by those around them.