"But symbiosis shows us that such trees are idealised representations of the past. In reality the tree of life often grows in on itself. Species come together, fuse, and make new beings, who start again. Biologists call the coming together of branches - whether blood vessels, roots, or fungal threads, ANASTOSMOSIS. Anastosmosis, branches forming sets, is a wonderfully onomatopoetic word. One can hear the fusing. The tree of life is a twisted, tangled, pulsing entity with roots and branches meeting underground and in midair to form eccentric new fruits and hybrids. Anastosmosis, although less frequent, is as important as branching. Symbiosis, like sex, brings previously evolved beings together into new partnerships. Like sex, too, symbioses are protracted unions with stable, prolific futures. Others quickly dissolve. The interaction of each generation of genetically continuous beings calls into question any picture-book tree of life." Lynn Margulis - Symbiotic Planet: A New Look at Evolution