No one knows for sure the exact origins of Homo Canidae, or the "breeds" thereof.  However, below are some proposed theories.

Theory 1: Created by government military agencies.
Some researchers speculate that Dogman is not a creature of nature, but rather a product of science. They propose that Dogman was created by the U.S. government and maybe other governments to serve as a military weapon.  The idea is that Dogmen/Dogwomen, perhaps, could have escaped or were set free from the facility(ies) that they were created in and have since been procreating in the wild. The only idea that refutes this theory is that Homo Canidae have been noted throughout history and people of that era could not have had the technology to have created the species scientifically.

Theory 2: A natural creature.
It is also proposed that Homo Canidae is simply a being of nature, just as any other human, mammal, bird, or reptile that has evolved. Some say that Dogman is "one of God's creatures". However, the species has simply not been documented officially by science due to the fact that they choose to remain elusive .

Theory 3: Dogman is a Nephilim.
​What is a Nephilim? According to the Biblical text, the Nephilim are the offspring of the Sons of God, who are described as celestial beings. The Sons of God can be better understood as angels or rather, fallen angels. Their job was to serve as "watchers" of humanity, but instead chose to have sexual relations with human women. Their angel/human offspring were the giants described in the Bible.

And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them, That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose...There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
                                                                                                                                  - Genesis 6:1–4, KJV

This verse can be cross referenced with the whole context of the Book of Enoch which is a non-Biblical text. Although not part of the Biblical canon, this apocryphal book was held in high regard to ancient Jews. In fact, The Book of Enoch was found along with the Jewish texts of the Old Testament in the Dead Sea Scrolls. Today, many modern Jews and Christians hold it as highly important because the world view it portrays is seen throughout the entire Bible. It tells the same story as Genesis 6 but goes into greater detail. 

And when the sons of men had multiplied, in those days, beautiful and comely daughters were born to them.  And the watchers, the sons of heaven, saw them and desired them. And they said to one another, “Come, let us choose for ourselves wives from the daughters of men, let us and beget for ourselves children.”
                                                                                                                                                         - Enoch 6:1-2

​How does this relate to Dogman? There is Enochian textual evidence that the Nephilim, the offspring of the fallen celestial beings, had relations with animals.

And all the others (fallen angels) together with them took unto themselves wives...And they became pregnant, and they bare great giants...And they began to sin against birds, and beasts, and reptiles, and fish..
                                                                                                                                                         - Enoch 7:1-5

In the above text, "to sin against" the list of animals, is regarded to mean sexual relations. The theory is that the Dogman, Sasquatch and some other cryptids are the offspring of the offspring of rebellious celestial beings. The Nephilim themselves are described as giants. This would explain the large size and height of these cryptids who are part angel, human, and animal.

Dr. Melba S. Ketchum, DVM, the director of DNA Diagnostics Inc. has done DNA testing on Sasquatch hair and found that the mitochondrial DNA, the DNA passed down from mother to child, is from a human woman. She states:

"The genome sequencing shows that Sasquatch [mitochondreal DNA] is identical to modern Homo sapiens, but Sasquatch  [nuclear DNA] is a novel, unknown hominin related to Homo sapiens and other primate species. Our data indicate that the North American Sasquatch is a hybrid species, the result of males of an unknown hominin species crossing with female Homo sapiens.”

Sasquatch and Dogman fit the Nephilim profile and Dr. Ketchum's DNA study corroborates the theory . More on her study here. 

How an angelic/spiritual being may transform into a physical being with working genetics is unknown.  However, the Nephilim theory may also the explain the legends of Minotaurs, Centaurs, Mermaids and other animal hybrids in history.