"Many animals, including humans, acquired essential ‘foreign’ genes from microorganisms co-habiting their environment in ancient times"

Horizontal gene transfer is a process whereby organisms living within the same environment pass genes between one another. In contrast, conventional evolutionary genetics dictate that genes are passed on vertically down ancestral lines.

In single cell led organisms, this is a well known mechanism and thought to be the process whereby bacterial rapidly acquire antibiotic resistance. However, in a world first led by Alastair Crisp from the Department of Chemical Engineering and Biotechnology, University of Cambridge - a comparative study examined HGT in animals and humans, whereby 144 foreign genes were identified ie: human genes not from our ancestors

The study involved

Reference :

1: http://www.cam.ac.uk/research/news/human-genome-includes-foreign-genes-not-from-our-ancestors