Why are dogs descendants of Wolves but humans are not descendants of chimpanzees?

Question

From here

The dog, Canis familiaris, is a direct descendent of the gray wolf, Canis lupus:

But from here

Human and chimp DNA is so similar because the two species are so closely related. Humans, chimps and bonobos descended from a single ancestor species that lived six or seven million years ago. As humans and chimps gradually evolved from a common ancestor, their DNA, passed from generation to generation, changed too.

Same is said for cats and dogs that they evolved from a common ancestor that is neither dog nor cat.
Why are dogs "friendly wolves"? but humans not " intelligent chimps"? Why are dogs descendants of wolves (with wolf ancestor) but humans and chimpanzees different species (with common ancestor)?

Dogs and wolves do create fertile offspring in the wild, whereas chimpanzees and humans do not. Is that the basis?

Answer 1

The very simplistic answer is that dogs and wolves belong to the same genus and are so closely related that they are often considered to be parts of the same species. The genus is Canis (Latin for dog) and the species are lupus (Latin for wolf) with domestic dogs being the subspecies familiaris (...the familiar one) to make the dog's name Canis lupus familiaris and the wolf's Canis lupus lupus. Being this closely related, dogs and wolves can interbreed to produce a hybrid wolfdog, which can themselves be fertile. Fertile interbreeds is one of the characteristics that are used to determine the separation of species. This means that things like mules, which are a cross between a horse (Equus ferus) and donkey (Equus africanus), and are different species within a genus aren't fertile.

Wikipedia has a good illustration of the relationships between dogs and wolves on the page on the genus Canis. Basically the genomes of dogs and wolves will be very very similar, much more similar than that of humans compared to chimpanzees. The last common ancestor (LCA) of dogs and wolves is about 10,000 years ago, at the domestication of dogs.

On the other hand Humans; Homo sapiens (Latin for "man" (as in mankind) and "wise-one") and chimpanzees; Pan troglodites (Pan was a god of the forest in mythology and Troglodites were mythical cave dwellers), are not even in the same genus, though we are in the same family grouping, known as the Hominidae, meaning that we are closely related in terms of body shape.

We don't actually have fossil evidence of the LCA for chimps and humans, so we don't know exactly what it looked like. However, for some frame of reference, I refer you to the excellent and informative A Short History of Nearly Everything by Bill Bryson, which has a line on hominid remains which goes something like this:

If you took all the ancient hominid remains you could comfortably fit them into the back of a pickup truck with room to spare.

While our genomes are similar, the genetic similarity is about 98.8% - which in a genome of about 3.2 billion bases, this equates to about 35 million differences. The similarity between wolves and dogs is 99.9%, which, with a genome of 2.4 billion bases, gives about 2.4 million differences, far fewer than between humans and chimpanzees.

The LCA of humans and chimpanzees is about 10-13 million years ago, which is about 1000x longer than that for dogs and wolves. If you could go forward about another 10 million years, dogs and wolves might be similarly separated to humans and chimpanzees.

Another problem here is the concept of relatedness - the LCA of humans and chimpanzees isn't a chimpanzee or a human, rather it is a species with similarities to both. On the other hand, we know the LCA of dogs and wolves, and know that it was a wolf, because of their close relationship. Thus we can say that dogs are the wolf's little sibling or are friendly wolves, but we can't say that humans are brainy chimps (or that chimps are less intelligent humans)

Answer 2

The original poster is correct in being concerned about the apparent contradiction in principle between the two statements. That is because one of them is incorrect — or at least misleading. The statement:

The dog, Canis familiaris, is a direct descendent of the gray wolf, Canis lupus

is misleading. To clarify, one should write something like:

The contemporary dog, Canis familiaris, and the contemporary gray wolf, Canis lupus, share a common ancestor, which is thought to be more similar to the contemporary wolf than the contemporary dog, and is generally considered a member of the species Canis lupus.

(This is an oversimplification, in that domestication of ancient wolves may have occurred on more than one occasion.)

The idea of phylogenic trees of species and extinct common ancestors, as in the case of different primates such as man and chimp, is the standard scientific interpretation of the fossil record and (more recently) powerful DNA sequence analysis, and the reader unfamiliar with this is left to read, e.g., the linked Wikipedia article on the topic.

It is more important to emphasize that even though the divergence of dogs and wolves is only estimated to have occurred about 120,000 years ago, their common ancestor differed from both contemporary animals, and that Canis lupus has also evolved in that time, despite the fact that certain distinguishing traits — particularly ‘wildness’ — are thought to have been present in the ancestor.

A relatively recent (2022) paper on the topic of the evolution of wolves — “Grey wolf genomic history reveals a dual ancestry of dogs” — documents these assertions.

Answer 3

Have a look at this diagram here.

Even though we have an ancestor in common with chimps and bonobos, we aren't directly descended from them - the one species that gave rise to chimps, bonobos, and us diverged into two ape species roughly 6 million years ago.

One species gave rise to the hominids, of which we are the only living example.

The other proto-ape kept ticking along until about 1-1.5 million years ago, when the newly widening Congo River split a population of these apes in two; the apes north of the river became what we know today as chimpanzees, while the southern ones became bonobos.

You can now see why scientists say the chimp is our closest relative - there are fewer evolutionary branches between us and them(2), then there are between us and gorillas(3)