Hi, this is Kate from MinuteEarth.
And my dog Watson looks like this.
But there are also dogs that look like this.
And this.
And this and this and this.
They’re so different that they barely seem like the same species.
While there are some definite weirdos in the feline world, cats generally look - and act
- much more similar to each other than dogs.
So yeah, doggos are way more diverse than cattos...except they also aren’t.
Because under all those superficial differences - what scientists call “phenotypic diversity”
- domestic dogs are surprisingly un-diverse in the DNA department.
On average, only a tiny fraction of dogs’ DNA differs from each other - that’s about
as much as their owners, and several times less than cats generally differ genetically
from each other.
So why do dogs look and act so doggone distinctive, compared to humans or cats?
Well, because it matters how genetic differences are distributed within a species.
Instead of genetic differences, let’s look at colored dots.
Say you have a bunch of dots - equal numbers of four different colors.
Now divide those dots up into four groups.
Within each group, you could have all the colors represented - each of these smaller
groups, then, would include all the diversity that exists among the dots as a whole.
Alternatively, each group could consist of dots of just one color - in this scenario,
all the individuals in each group are really similar to each other, but they’re really
different from individuals in the other groups.
This is kind of like what we’ve done with dogs.
Over centuries of careful breeding, we’ve partitioned different genes and variants of
genes into different groups of dogs.
As a result, dogs in different groups - which we call “breeds” - are genetically really
similar to each other, and really different from dogs of other breeds.
That’s how - even without a ton of genetic variation - we’ve ended up with dogs with
such distinct characteristics: think stubby legs in weiner dogs versus ridiculous stilts
in greyhounds.
Compared to dogs, cats have more genetic diversity overall, but since we haven’t been breeding
cats as long or as carefully, their cat-egories are less well-defined.
Each breed still contains a lot of the genetic diversity that exists in the species as a
whole, so cats within a breed aren’t all that genetically similar - and cats of different
breeds ARE somewhat similar.
And as for us humans?
Well, people within any one “population” of humans don’t have much more in common
genetically than they do with people from other populations.
On top of all this, for reasons we don’t exactly understand, a few spots in the dog
genome have outsize effects on a dog’s outside.
As far as we can tell, variation in just 14 genes causes almost all the variation in dogs’
size - compare that to the several hundred genes that contribute to humans’ height
and BMI.
So it’s pretty straightforward to create dogs with a forty-fold size difference.
But dogs aren’t total outliers - we’ve bred chickens with a 15-fold size difference
and turned a humble plant called Brassica oleracea into a diverse - and delicious - plethora
of forms.
So even though cats today all seem pretty similar, given another hundred years of careful
selection, we could probably breed cats that vary as much as dogs.
But first, we might want to consider whether breeding giant cats might be a giant cat-astrophe.
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