In my theology, Adam & Eve, being from another world in the heavenly realm, had duel circulatory systems which allowed them to partake of the special energies of the "Tree of Life", a special shrub from heaven that would have allowed them to live on indefinitely. After the default they lost the use and became mortal.
The "Tree of Life" had been brought to earth much earlier accompanying the previous fallen administration of the planetary "Prince of this world" who became "the crafty beast". Some of the immortal volunteer staff of the Prince, ascendant humans like us but who came from other worlds, sons of God who came down from heaven, also lost the use of the tree due to the rebellion. Being stranded and now mortal these sons of God attempted to populate the earth with their progeny being genetically superior in intelligence: "The Nephilim were on the earth in those days—and also afterward—when the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men of renown."
In the jumbled chronology of the Bible the so called "Nephilim" predated Adam and Eves arrival but the authors of Genesis didn't realize this.
The bloodlines of the Jews are actually related to these supermen who came to earth.