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Unlock This CourseEvolution is one of the most important ideas in biology. It explains how all living things have changed over millions of years to become the species we see today. But how do we know evolution actually happened? Scientists have gathered loads of evidence from different sources that all point to the same conclusion - life on Earth has evolved!
Think of it like being a detective. When detectives solve a crime, they don't rely on just one piece of evidence. They collect fingerprints, DNA, witness statements and CCTV footage. In the same way, scientists have collected different types of evidence that all support evolution.
Key Definitions:
Evolution happens through natural selection. Organisms with traits that help them survive in their environment are more likely to reproduce and pass these traits to their offspring. Over many generations, these helpful traits become more common in the population.
Fossils are like nature's photo album - they show us what life was like millions of years ago. When organisms die, sometimes their bodies get buried quickly in mud or sand. Over time, the soft parts rot away, but the hard parts like bones and shells can turn into stone, creating fossils.
Fossils provide amazing evidence for evolution in several ways. First, they show us that life forms in the past were different from today's organisms. Second, when we look at fossils in rock layers (called strata), we can see how organisms changed over time. The deeper the rock layer, the older the fossils.
Fossil evidence shows horses evolved from small, dog-sized animals with multiple toes into the large, single-toed horses we know today. This took about 50 million years!
Fossils show that whales evolved from land mammals. Early whale fossils have legs and lived near water, whilst later fossils show the gradual loss of legs and development of flippers.
Archaeopteryx fossils show features of both dinosaurs (teeth, claws, long tail) and birds (feathers, wings). This supports the idea that birds evolved from dinosaurs.
Human fossils show our evolution from ape-like ancestors. Lucy, a 3.2 million-year-old fossil found in Africa, walked upright but had a small brain. Later fossils show gradual increases in brain size and changes in skull shape, leading to modern humans about 200,000 years ago.
DNA is like a instruction manual that tells cells how to build and run an organism. All living things use DNA and by comparing the DNA of different species, scientists can work out how closely related they are. The more similar the DNA, the more closely related the species.
When scientists compare DNA sequences between different species, they find that organisms that look similar also have similar DNA. For example, humans and chimpanzees share about 98% of their DNA, which suggests we evolved from a common ancestor relatively recently (about 6-7 million years ago).
Scientists also compare proteins between species. Proteins are made using instructions from DNA, so similar proteins suggest similar DNA. The protein cytochrome c is found in nearly all living things, but with small differences that show evolutionary relationships.
Embryos are developing organisms before they're born or hatched. Amazingly, embryos of different species often look very similar in their early stages, even if the adults look completely different. This suggests they evolved from common ancestors.
Early embryos of fish, birds and mammals all have gill slits and tails, even though adult mammals and birds don't have gills. As development continues, each embryo develops the features specific to its species. This pattern suggests all these animals evolved from a common ancestor that had gills and a tail.
The embryos of fish, chickens, pigs and humans look remarkably similar in early development. They all have a tail, gill slits and similar body segments. As they develop, fish keep their gills and tail, birds develop wings and beaks and mammals develop limbs and lose their tails (except for a tiny tailbone in humans).
The distribution of species around the world provides strong evidence for evolution. Islands are particularly interesting because they often have unique species that are similar to, but different from, species on nearby continents.
When a small group of organisms reaches an isolated island, they may evolve differently from their relatives on the mainland. Over time, this can lead to new species that are found nowhere else on Earth.
On the Galapagos Islands, Charles Darwin found 13 different species of finches. Each had a different beak shape suited to their food source - some had large beaks for cracking seeds, others had thin beaks for eating insects. They all evolved from one original finch species that reached the islands.
Humans have been changing organisms through selective breeding for thousands of years. This process, called artificial selection, shows how selection can produce dramatic changes in a relatively short time.
Farmers and breeders choose organisms with desirable traits and breed them together. Over many generations, this creates organisms that are very different from their wild ancestors.
All dog breeds, from tiny Chihuahuas to massive Great Danes, evolved from wolves through artificial selection. Humans bred dogs for different purposes - hunting, herding, or companionship.
Modern wheat, corn and rice look very different from their wild ancestors. Farmers selected plants with larger seeds, easier harvesting and better taste over thousands of years.
Darwin studied pigeon breeding and found that breeders could create birds with different colours, feather patterns and body shapes. This helped him understand how natural selection might work in the wild.
Bacteria evolve resistance to antibiotics through natural selection. When antibiotics are used, most bacteria die, but a few with resistance genes survive and reproduce. Over time, the population becomes mostly resistant bacteria. This is evolution happening in real time and shows why we need to use antibiotics carefully.
All these different types of evidence support the same conclusion - life on Earth has evolved over billions of years. Fossils show us the history of life, DNA reveals family relationships between species, embryos show common ancestry, geographical patterns explain how species spread and change and artificial selection demonstrates that selection can produce dramatic changes.
Evolution isn't just an idea - it's a scientific theory supported by mountains of evidence from many different fields of study. Understanding evolution helps us make sense of the incredible diversity of life on our planet and continues to help scientists in fields like medicine, agriculture and conservation.