If you believe Sitchin and his work of 35 years decoding the tablets form ancient Sumar then the Annunaki came here approximately 432,000 years ago and got tired of digging their own gold and to make a long story short they needed gold to pulverize and put into their atmosphere to block the suns rays or heat up their planet something like that....But anyway they got tired of "mining" and said hey why don't we mix some of our DNA with these Neandrathals over here and they can dig for us...Sounds like a plan and so we were born!