The evolution we're all familiar with, traits passed on from parents to children with small genome errors that eventually can lead to new species is called vertical evolution. There is another type of evolution where gene sequences can be passed between organisms of different species, phylums, or even kingdoms which is called horizontal evolution.
Horizontal evolution is interesting and plays a larger role the further you go back in time. Horizontal evolution is not uncommon among bacteria and other prokaryotes (single cell organisms without nuclei), which were the dominant form of life for the first 3 billion years(maybe longer). In fact, it appears vertical evolution didn't start really shaking things up till the advent of sexual reproduction roughly 500 million years ago. That's 3.4 billion years where horizontal evolution played an important role.
The following article talks about a venom that appears only in a particular species of spider and bacteria and investigates if horizontal evolution plays a role. See link below:
http://www.sciencedaily.com/releases/2006/02/06020 2075525.htm
de- evolution
