A novel study published in the journal Genome Biology has questioned the long-held belief that evolution is completely dependent on genes passed down. The researchers have challenged the assumption as humans contain alien genes that have not been passed from our ancestors.

The research has focused on the use of horizontal gene transfer, which means the transfer of genes between organisms living in the same environment. Study's lead researcher Alastair Crisp from the University of Cambridge shared that we have acquired important 'foreign' genes from the micro-organisms that co-habited in their environment in ancient times.

Crisp was of the view that it is the first study that has shown the level at which horizontal gene transfer (HGT) takes place in animals, including humans. Crisp affirmed that the transfer has led to tens or hundreds of active 'foreign genes'.

"Surprisingly, far from being a rare occurrence, it appears that HGT has contributed to the evolution of many, perhaps all, animals and that the process is ongoing, meaning that we may need to re-evaluate how we think about evolution", affirmed Crisp.

In the study, the researchers have evaluated the genomes of 12 species of fruit fly, four species of nematode worm, and ten species of primate, including humans. By studying them, the researchers calculated how well the genes align to the similar genes in other species to know the chances of them being foreign in origin.

The researchers affirmed that by carrying out comparative analysis with other groups of species, they were able to predict when the genes were most probably acquired. The researchers said 17 previously-reported genes were acquired through horizontal gene transfer.

They have also identified 128 additional foreign genes in the human genome that were not previously reported.