Biodiversity

Chapter 3 | Genes and genetic diversityForces ofevolutionThere hasn’t always been as much genetic diversity on Earth as there is today. It evolvedfrom practically nothing. There are four ingredients to evolution: natural selection,variation, inheritability and time. The combination of these ingredients accounts forthe evolution of species – everything from whales to drug-resistant bacteria!Let’s go back to eye colour, onlylet’s imagine there is a forestthat is home to a populationof pigeons with different eyecolours – let’s say some havegreen eyes and others greyeyes. By chance, the green-eyedpigeons are particularly goodat seeing in the dark. In thisimaginary forest, the pigeonsfeed all day on delicious figsonly available on a smallnumber of fig trees. Duringthe night, the birds rest. But achange in the climate drives anew species of pigeon-huntingeagle into the area. The eagle’stalent for diving from a greatheight onto pigeons feeding inthe fruit trees depends on gooddaytime visibility.The pigeons soon begin tohide in the daytime andfeed at night. The greyeyedpigeons have troublefinding fruit at night and arecaught by the eagle duringthe day. The pigeons withgreen eyes, however, are ableto eat without the threat ofthe eagle because they canfeed at night. The greeneyedpigeons’ green-eyedoffspring are more successful!They live longer and havemore offspring. As the greyeyedpigeons disappear, thepigeon population starts tochange. Over time, most ofthe newborn pigeons have thesame eye colour – green!This story illustrates thatwhere there is variation in apopulation (e.g. in eye colour),new or existing pressures(e.g. eagles) select specificinheritable traits passed onfrom one generation to the next(e.g. green eyes) that conveyan advantage. Over time (e.g.several generations of pigeons)the population changes and thespecies evolves. Where thereare no pigeon-hunting eagles,the pigeons can still thrivewhatever their eye colour.Eventually after much time haspassed, the green-eyed pigeons,with their skills at feeding inthe night and avoiding eagles,could become a completelyindependent species.28Youth and United Nations Global Alliance