Your colour vision and night vision grew from one ancient gene
The human eye senses light with four genes: three handle colour and one handles dim light at night. All four descend from a single ancestral gene that was copied, and the copies drifted into new jobs. Gene duplication like this is one of evolution's main workshops for building something new out of spare parts.
Evolution is change in the inherited traits of populations over generations. It happens when forces such as natural selection and random genetic drift act on variation, making some traits more common and others rarer. Charles Darwin and Alfred Russel Wallace independently conceived natural selection in the mid-nineteenth century, and Darwin laid it out in On the Origin of Species. The logic rests on four observations: more young are born than can survive, individuals differ, some differences help survival and reproduction, and those differences can be inherited.
In the early twentieth century, the theory merged with Mendelian inheritance and population genetics. Heredity runs through DNA, a long molecule whose sequence of four bases spells out instructions somewhat like letters in a sentence. Mutations are the ultimate source of new variation. Roughly half of those in protein-coding regions are harmful and the rest mostly neutral, with a small share helpful; outside those regions the great majority are neutral.
Duplication matters because a spare copy frees one version to experiment while the other keeps doing the original job. Sometimes fragments of several genes recombine into fresh combinations, and occasionally entirely new genes emerge from stretches of DNA that previously coded for nothing. Polyketide synthases, large enzymes that make antibiotics, show the modular approach, containing up to 100 separate domains that each perform one step, like stations on an assembly line.
Small genetic tweaks can have visible results. Wild boar piglets wear camouflage stripes, but mutations in a gene called MC1R break up that pattern, and most domestic pig breeds carry such mutations. Not every trait is inherited, though: a suntan comes from genes interacting with sunlight and is not passed on. All living things, humans included, share a last universal common ancestor that lived roughly 3.5 to 3.8 billion years ago.
Source: Evolution
