Having just completed the 30th anniversary edition of _The Selfish Gene_, I don't see why this should surprise anyone. I don't have a copy of the original, but in this edition Dawkins quite clearly discusses the the notion of absorbing viral and other bits of DNA into the genome when the DNA and the host share the same replication path. Perhaps I've miss-remembered something from the endnotes as part of the original material.

NOTE: I write software for a living, and consider myself a layman in the biological sciences (though I had the good sense to marry a biochemist ;-).

New Yorker magazine had an interesting online article on viruses/retroviruses back in December 2007:

"Darwin's Surprise"

http://www.newyorker.com/ reporti...fa_fact_specter

Probably old news to most of you here, and perhaps even "too basic" for many, but as a "layman" also, it was a good read!

It seems like retroviruses could carry genes across species boundaries in some cases. Is there some reason why this couldn't happen? It seems like this would be pretty similar to how oncogenes wound up in retroviruses, but moving across species.

"Connecting the dots, it's quite plausible that these particular ancient retroviruses have been recruited into the mammalian genome and serve as local immunosuppressors in the uterus during development. In fact, we already know that syncytin, a protein crucial in placenta formation, is the product of a retroviral gene (Knerr et al. 2004), so there's nothing at all far-fetched about this."

My casual reading says the syncytin question is murky. Syncytin 1 (HERV-W-derived) is active in hominoids but not old world monkeys (Cáceres and Thomas, 2006). ERV-3 (HERV-R) is expressed in the human placenta and has apparent syncytial and immunosuppressive domains, but 1% of Caucasians are fertile despite being natural homozygous knockouts (de Parseval and Heidmann, 1998).

Hmmm. Thanks for the pointers Daniel, hadn't read those.

http://www.nature.com/ng/ journal...ng.2007.51.html