English Article:
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. The first eyes appeared about 543 million years ago - the very beginning of the Cambrian period - in a group of trilobites called the Redlichia. Their eyes were compound, similar to those of modern insects, and probably evolved from light-sensitive pits.
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. However, sight is not universal. Of 37 phyla of multicellular animals, only six have evolved it, so it might not look like such a great invention after all - until you stop to think. The six phyla that have vision (including our own, chordates, plus arthropods and molluscs) are the most abundant, widespread and successful animals on the planet.
Graham Lawton.
Graham Lawton.
2. The brainThe evolution of brains 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 have a nervous system that can control muscles, then you can actually move around and seek out food, sex and shelter. The simplest nervous systems are just ring-like circuits in cnidarians - the jellyfish, urchins and anemones. The next evolutionary step, which probably happened in flatworms in the Cambrian, was to add some sort of control system to give the movements more purpose. Armed with this, finding food would have been the top priority the earliest water-dwelling creatures. With brains come senses, to detect whether the world is good or bad, and a memory. Together, these let the animal monitor in real time whether things are getting better or worse. The more complex functions of the human brain - social interaction, decision-making and empathy, for example - seem to have evolved from these basic systems controlling food intake. The sensations that control what we decide to eat became the intuitive decisions we call gut instincts. The most highly developed parts of the human frontal cortex that deal with decisions and social interactions are right next to the parts that control taste and smell and movements of the mouth, tongue and gut. There is a reason we kiss potential mates - it's the most primitive way we know to check something out.
Helen Phillips.
