Species are constantly changing. They must continuously adapt to the changing world around them. Animals that are successful can reproduce more, and their babies go on to have more babies. This is Evolution.
Natural Selection
Humans have known that plants and animals could change for a long time. Ancient farmers bred better crops by taking seeds from the best plants in each season and replanting them. Humans selected the best hunting dogs for breeding.
It was not until Charles Darwin traveled the world, on a research ship known as The Beagle that the Theory of Evolution was well understood.
Darwin wrote his theory in a book, On The Origin of Species, published 1872. This book was a complete explanation of how and why new species come into existence over time.
In his book, Darwin introduced the concept of Natural Selection. Much like humans selected dogs that were the best hunters, plants that produced the biggest vegetables, nature itself was also selecting different organisms. Sometimes the strongest organisms survived. Other times it was the fastest organism that survived. In other environments, it may have simply been the organism that could hide from predators the best.
His point: Only organisms that survive can reproduce.
Since all animals in a population have slightly different traits, nature is constantly selecting the organisms that are able to survive and reproduce the most in a given environment.
Galapagos Islands
On his travels to the Galapagos Islands, Darwin observed how finches on some islands were very similar to finches he had seen on other islands. Depending on the island, some finches had to eat cactus, while others specialized in eating seeds.
Some finches had long beaks to reach into cactus blossoms, while other finches had shorter beaks that could help pick seeds out of the soil. Over time each island environment and the food it contained was selecting the finches best able to survive there.
Genetic mutations and natural selection
Sometimes when an organism reproduces, a mistake is made. These mistakes – called mutations – can be good or bad depending on the environment. If this mutation can help an organism survive and be passed down to offspring, it can spread through natural selection and become a new trait.
Darwin’s theory is one of gradual change. Small changes or mutations accumulate over time until a whole new species evolves. This way of looking at evolution is called gradualism.
Scientists now believe that evolution can also happen quickly. In the theory of punctuated equilibrium, species stay the same for long periods of time. These periods of equilibrium are punctuated by bursts of rapid evolutionary change.
Written by Laura McCamy
Edited by Gabriel Buckley, MS Professional Natural Sciences
Illustrated by Meimo Siwapon