Humans (also known as "Colonials") were a sentient mammalian bipedal species originally from the planet Kobol. They were an outwardly indistinguishable from Homo sapiens extraterrestrial race with compatible DNA to Homo sapiens as a result of a parallel evolution of hominids on both Kobol and Earth. The Colonial humans were a Kobol-evolved Homo sapiens analogue.
There are no longer "pure" Kobol-evolved humans living, meaning that "humanity," as it was defined by people in the Twelve Colonies of Kobol has gone extinct. The modern humans of Earth are a product of hybridization of them, the humanoid Cylons that arrived on Earth with the Colonal humans 150,000 years ago, and the original indigenous native Earth-evolved Homo sapiens.
A notable physiological distinction of Kobol-evolved humans from Earth-evolved humans was a lacking of a universal donor blood type -- Type O Negative.
Kobol-evolved humans possessed a capacity for genetic memory, which has now been bred into modern humans. This genetic memory does not take the form of passing on personal memories, but the passing on of an unconscious knowledge of certain invented concepts and ideas such as technology, language, engineering and even fashion and music along with various other aesthetic cultural aspects.
When the Kobol-evolved human Colonials settled on Earth and interbred with Earth-evolved humans 150,000 years ago, the genetic memory capacity was diluted and became latent. It took more than 140,000 years before it became active again. After the end of the Stone Age, the capacity began to reemerge and certain Colonial human cultural ideas and concepts reemerged. However, they reappeared only in rudimentary, fragmented and even modified forms. For example, the Colonial religion gradually reconstituted in the minds of the people of ancient Greece - but in a modified form (e.g. the "Lords of Kobol" became the "Gods of Olympus).
Over a period of several millennia, a multitude of Colonial ideas, concepts, and cultural aspects reemerged because of genetic memory. Although they would continue to reemerge in rudimentary, modified and fragmented forms, eventually these fragments coalesced into complete reconstitution of Colonial aspects.
As a result of genetic memory, by the early 21st century virtually every cultural aspect of human Colonial society has reemerged: language, names, fashion, engineering, architecture, furniture, music, art, cuisine, household appliances, television, automobiles, federalized government, judicial systems, labor unions, military protocols, firearms etc. Countries such as the United States, Canada, Australia and the United Kingdom collectively form a near perfect replication of the society of the Twelve Colonies of Kobol (an ostensibly alien civilization) more than 150,000 years ago – just without advanced technology such as jump drive and sentient machines. So even though genetically "pure" Colonial humans are extinct, their society has been reborn on Earth; the legacy of Kobol-evolved humans lives on.