GENETICS AND EVOLUTION
Eyes, by at least 40 million years. The only invertebrates with ears are land arthropods and they didn’t emerge until about 480 million years ago. Older invertebrates had antennae that would have been able to sense vibrations in the water, but that’s not quite the same thing as hearing. Trilobites already had complex compound eyes 521 million years ago, and simple eyespots without a lens probably date back to 570 million years ago, when the first multicellular animals appeared.
Why did humans evolve a sense of humour? A recent theory holds that humour evolved because it encourages us to perform the arduous task of fact-checking our assumptions about other people’s intentions and perspectives. By this account, mirth is the reward we get when we debunk one of our presumptions and see things suddenly in a new light – jokes are ‘super-normal stimuli’ that
exploit this system. Once it evolved, humour became a social signal – we assume funny people are intelligent and friendly, and men and women alike prefer witty partners. On average, however, men tend to be more concerned that would-be partners will find their jokes funny, whereas women are more attracted to people who make them laugh.
PHOTOS: GETTY X3, SCIENCE PHOTO LIBRARY, ALAMY
WHAT EVOLVED FIRST: EYES OR EARS?
The eyes can clearly be seen on this fossilised trilobite
WHY DID WE EVOLVE WARM BLOOD? Being warm blooded means that your body is maintained at a fixed temperature, regardless of how cold your surroundings are. The term for this is homeothermy. Less than one per cent of animals are homeothermic – it’s basically confined to mammals and birds. Homeothermic animals burn more fuel and need about 10 times as much food. However, chemical reactions generally happen faster at warmer temperatures and a warm body can work at the same activity level even in cold environments, such as at night, underground or in winter. Insects often can’t fly when it is too cold because their flight muscles can’t contract fast enough and many reptiles
have to bask in the sun for several hours each morning to warm up. A regulated body temperature also allows you to evolve enzymes that are tuned to work efficiently within a precise temperature range. The downside of this is that hypothermia or heatstroke are enough to render our enzymes inactive and kill us. Another possibility is that homeothermy may have evolved as a strategy for fighting infection. A 2010 study found that a body temperature of 36.7°C was enough to protect against most fungal infections. Mammals and birds rarely get fungal diseases, but they are a problem for fish.