http://www.newscientist.com/article/dn9951-top-10-lifes-greatest-inventions.html?page=1
1. Multicellularity
2. The eye
3. The brain
4. Language
5. Photosynthesis
6. Sex
7. Death
8. Parasitism
9. Superorganism
10. Symbiosis
Very cool article! I was amazed by this one:
9. Superorganism: LARGE numbers of individuals living together in harmony, achieving a better life by dividing their workload and sharing the fruits of their labours. We call this blissful state utopia, and have been striving to achieve it for at least as long as recorded history. Alas, our efforts so far have been in vain. Evolution, however, has made a rather better job of it.
Take the Portuguese man-of-war. It may look like just another jellyfish blob floating on the high seas, but zoom in with a microscope and you see that
what seemed like one tentacled individual is in fact a colony of single-celled organisms (

). These "siphanophores" have got division of labour down to a fine art. Some are specialised for locomotion, some for feeding, some for distributing nutrients.