I dont know who the first human was, the people made on the 6th day were told to be fruitful and spread out. Then God planted a Garden eastward in Eden and took a/the man he had made there to work. How can those people from the 6th day be fruitful and spread out if the man was taken to the Garden and why would God need Eve when male and female were already made on the 6th day? The 6th day people were a group, they were not two people... And Adam was taken from among them or from among their descendants to the Garden at a later point in time. These people from the 6th day had hominid ancestors, "let us make man in our image" echoes the Sumerian myth.
According to the myth the gods were upset at having to work and they rebelled. Enki proposed creating a race of primitive workers (there was no adam to till the land, God took the adam to work in the Garden). He announced that a creature roaming his Abzu (southern domain) could be given the image of the gods so he and Ninhursag set out to achieve that goal. This ties in with a Zulu myth, they have a legend about the artificial ones (their ancestors) waging a war on the ape men.
The Genesis story is also describing our transition from an earlier creature, one that was unashamed of their nakedness, one so 'primitive' a mate was first sought from among the other animals before Eve was made. This being was 'innocent', they did not understand good and evil, and apparently had not procreated yet. One that would suffer increased pain in child birth.
Thats another important clue, how would Eve know anything about how much pain was involved in child birth? Why would God tell her she will suffer even more? More than who? Her hominid ancestors. If its true anatomically 'modern' women saw increased difficulty giving birth maybe 200kya, and our genetic Eve dates to that time, the Bible may be a record of events that happened back then.
So what were the 6th day people doing while Adam and Eve were considering the Serpent's offer of knowledge? They were being fruitful and spreading out. From where? Ethiopia, westward of Eden. One need only follow the Arabian coastline to find Eden. Thats why Cain was able to find a wife and why he was worried about being killed, there were other people in the world.