How repeatedly mating the same domesticated wolves gave us all these different dog breeds?
In: Biology
We didn’t mate the same wolves, we selected for certain traits, and bred to exaggerate those traits. Natural variation leads to small changes, we just exploited those small changes to amplify them
This is much the same way that broccoli, cauliflower, cabbage, and brussel sprouts are all the same plant, bred to have a different edible part of the plant.
There’s a bit of variation in every individual, some are bigger, some are smarter, some are cuter. When they identify a trait they like they start breeding individuals that show that trait more with other ones who also display that trait. By doing this the trait gets reinforced in the puppies that are born. Do this over enough generations and you start to get the different breeds of dog.
There’s supposedly a bit of fox in some breeds, too.
But mostly it’s selective breeding over a very long time.
You know how natural selection can make a species evolve? Dogs evolved using artificial selection.
Let’s say you want a very small dog that can go into badger den. You take the smallest wolves you can find and breed them together.
From the offspring you again take the smallest and breed them together.
From that offspring you again take the smallest and breed them together.
And so forth.. after many generations you’ll have a very small dog.
Want a Saint Bernhard? Do the opposite and breed the biggest wolves you can find and their biggest offspring.
Over tens of thousands of yours, you can create quite the variety!
Breeding dogs with dogs for traits gave us all of our numerous dog breeds.
Domesticating wolves gave us our first dogs.
How did that happen? We don’t actually know. In fact it might’ve happened more than once in different parts of the world.
What we do know is if you selectively breed for traits like friendliness, being docile, etc. you produce more youthful, puppy-looking animals over time. This has been done with experiments with foxes over decades.
There are doninant genes and indominant genes. When different genes combine, the dominant one decides the phenotype. If there is no dominant, the indominants decide what will the phenotype be like. When you mate the same wolves, these indominant genes combine and make a new phenotype (you can think of that as physical appearance).
So let’s mate the same wolves:
Aa × Aa —> AA, Aa, Aa, **aa**
_Note: I oversimplifed the process so it is easy to understand._
These all are different genes. And there is a wolf with a different phenotype.
This process happens repeatedly for years and new breeds show up.
It’s pretty cool! By breeding wolves with certain traits over generations, we get new dog breeds. It’s like picking the traits you want and passing them on.
Every litter of wolf cubs has some large ones and small ones, more aggressive and less aggressive ones, ones with thicker or less thick fur, ones with darker or lighter colours. Random mutations occasionally occur that may add some alteration. You keep the ones you like, and kill or neuter or abandon the ones you don’t want.
Humans probably did not do any *intentional* selective breeding on wolves. What happened is this:
1. Wolves and humans shared an ecosystem.
2. The wolves that were less scared by humans and fire would be bolder and benefit, possibly from getting extra access to scrap food, extra protection from weather and extra warmth from our fires/shelters.
3. Those more-human friendly wolves had more successful kids because it was easier for them to survive
4. Those friendlier wolves would outcompete scared wolves in areas around humans.
This process continued for many generations until wolves were trusting humans outright. At that point, they’re basically the first dogs. It’s really only once you reach this stage that humans are intentionally choosing which ones to breed for specific tasks, probably many thousands or tens of thousands of years after wolves and humans first started co-domesticating.
It’s important to realize domestication isn’t a thing that *humans* do to *animals*. It’s a thing that can happen both ways. Wolves domesticated humans as much as humans domesticated wolves.
The humans who weren’t too afraid to have wolves around benefitted from the protection, hunting assistance, and waste disposal that wolves provided. That means they outcompeted humans who did not have wolves.
The same process in reverse. We are two species which have molded each other to mutual benefit.
This is not exactly ELI5, but gets at the core of your question. *One* of the many reasons is that dogs have a lot of Short Interspersed Nuclear Elements (SINEs). SINEs are short bits of DNA that because of the way they are coded, get copied and reinserted elsewhere in the genome. They are not genes because they don’t make a protein, they are just sequences with instructions that say “duplicate me and put me back somewhere else on the genome” but don’t specify where. As a result you will have multiple copies of different SINEs floating around. Over generations these SINEs will also “evolve” away from one another and become slightly different in their sequences and lengths.
When these SINEs get inserted into genes, they will affect the gene based on where in the gene it is inserted. So you could have the same SINE inserted into different locations on the same gene in different dogs, which leads to different physiological outcomes. For example, all of the different merle colorations (think leopard dogs, australian shepherds, cardigan welsh corgies, etc.) are due to the SILV SINE. There is variation in the merle coloration because of the length of the different SILV SINE inserts and their placements on one gene responsible for depositing melanin (PMEL).
Because dogs have an abundance of these SINEs, there is also more occasion for SINEs to be copied and inserted. Then, when you couple that with breeding and the fact that each individual gets one copy of DNA from each parent, you can get a lot of variation.
Fun fact about SINEs, primates have a SINE family called the ALU sequence, and the number of copies and their positions on the genomes are different between primate species and also within populations of the same species, so they can be used as population markers.
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