Vampires are no exception to the phenomenon of evolution. In my world various species or races or breeds of these creatures can be observed. They can interbred as much as neanderthals can breed with sapiens or French men with Saxons or coyotes with wolves. Which means easily and with no ill effects.
They are not mystical creatures, lacking the magical powers usually portrayed in books and movies.
Yet some cultures of vampire can do feats which might seem impossible to the top level elite human.
One city in my world, a multicultural human-vampire city has a formidable military force of vampires. They make for excellent warriors due to their innate tolerance to cold climates, endurance, night vision and being able to quench their thirst and fill their bellies with the flesh and blood of enemy lines. And some say that an army marches on their belly. On top of everything, the weakest vampires can also surpass top human athletes both in strength and power.
But in time of peace warrior vampires still need to be fed. They require only 350 grams of blood per week to maintain idle activities. Fighting and other heavy work increases the thirst.
Vampires in this city are not slaves, they can decide to not be warriors. But there's little to no incentive to not go to war, especially since warriors are paid in both coin and blood taxes.
These vampires are weaker than other "breeds" of vampires but require less resources. Conflicts between warrior vampires and other vampires are rare but it's always a fight of numbers versus quality. Outcomes are never easily predictable.
I have many questions to make, but I'll split it in multiple threads.
What is the ratio of human citizens and vampire citizens the city must have in order to feed all warriors? The more vampire warriors, the better is the city protected from foes. This also increases the blood requirements thus human cost of shelter and feed.
Also consider that in cold climates blood can be stored for an entire year, but there's a weaker agricultural production.
Vampires can breed only with other breeds, races, cultures, species of vampires not with humans. The first section might be confusing but I thought it will be useful in the fure to connect the next questions I'm planning to make.
Vampires can ingest other foods as a hobby to savor the taste, but they only require human blood to survive. Human flesh is often eaten as filler food during war.
Vampires are born from sexual reproduction, not created.
Vampires are humanoids but not related to humans. They look like humans due to convergent evolution. The same way the ancient reptile Ichthyosaur looks and behaves similarly to the mammal dolphin even though they are not closely related or how bats and pterodactyls evolved similarly.
Some types of vampires are photosensitive and nocturnal, but those vampire warrior specifically can sunbathe if they want.