Rachel Nowak in the New Scientist:
The eye
THEY appeared in an evolutionary blink and changed the rules of life forever. Before eyes, life was gentler and tamer, dominated by sluggish soft-bodied worms lolling around in the sea. The invention of the eye ushered in a more brutal and competitive world. Vision made it possible for animals to become active hunters, and sparked an evolutionary arms race that transformed the planet. And what a difference it made. In the sightless world of the early Cambrian, vision was tantamount to a super-power. Trilobites’ eyes allowed them to become the first active predators, able to seek out and chase down food like no animal before them. And, unsurprisingly, their prey counter-evolved. Just a few million years later, eyes were commonplace and animals were more active, bristling with defensive armour. This burst of evolutionary innovation is what we now know as the Cambrian explosion.
Sex
BIRDS do it, bees do it – for the vast majority of species, sexual reproduction is the only option. And it is responsible for some of the most impressive biological spectacles on the planet, from mass spawnings of coral so vast that they are visible from space, to elaborate sexual displays such as the dance of the bower bird, the antlers of a stag and – according to some biologists – poetry, music and art. Sex may even be responsible for keeping life itself going: species that give it up almost always go extinct within a few hundred generations.
The enduring success of sex is usually put down to the fact that it shuffles the genetic pack, introducing variation and allowing harmful mutations to be purged (mutations are what eventually snuffs out most asexual species). Variation is important because it allows life to respond to changing environments, including interactions with predators, prey and – particularly – parasites. Reproducing asexually is sometimes compared to buying 100 tickets in a raffle, all with the same number. Far better to have only 50 tickets, each with a different number.
The brain
BRAINS are often seen as a crowning achievement of evolution – bestowing the ultimate human traits such as language, intelligence and consciousness. But before all that, the evolution of brains did something just as striking: it lifted life beyond vegetation. Brains provided, for the first time, a way for organisms to deal with environmental change on a timescale shorter than generations. A nervous system allows two extremely useful things to happen: movement and memory. If you’re a plant and your food source disappears, that’s just tough. But if you have a nervous system that can control muscles, then you can actually move around and seek out food, sex and shelter.
Superorganisms
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.
Read more here.