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Unlock This CourseCharles Darwin revolutionised our understanding of life on Earth with his theory of evolution by natural selection. Published in 1859 in "On the Origin of Species", Darwin's ideas explained how all living things have descended from common ancestors and how species change over time through a process of natural selection.
Key Definitions:
Darwin developed his theory during a five-year voyage on HMS Beagle (1831-1836). His observations of finches on the Galápagos Islands were particularly important. He noticed that finches on different islands had different beak shapes, perfectly suited to their food sources.
Darwin's theory is based on four main observations that lead to one inevitable conclusion - evolution by natural selection.
Understanding these principles is crucial to grasping how evolution works in nature.
All individuals in a population show variation in their characteristics. This variation can be in size, colour, behaviour, or any other trait. Some of this variation is inherited from parents.
More offspring are produced than can survive to adulthood. This creates competition for limited resources like food, water, shelter and mates. Only some individuals will survive this struggle.
Individuals with characteristics that give them an advantage in their environment are more likely to survive and reproduce. This is "survival of the fittest" - but fittest means best adapted, not strongest.
Before the Industrial Revolution, light-coloured peppered moths were common because they camouflaged well against light tree bark. During industrialisation, pollution darkened tree trunks, making dark moths better camouflaged. The dark moth population increased dramatically. After pollution controls were introduced, light moths became common again. This shows natural selection in action over just 100 years!
Darwin's theory is supported by multiple lines of evidence from different scientific fields. This evidence has grown stronger since Darwin's time with new discoveries and technologies.
Scientists use various types of evidence to support the theory of evolution, each providing a different piece of the puzzle.
Fossils show a progression of life forms over time. Simple organisms appear in older rock layers, while more complex organisms appear in newer layers. Transitional fossils show intermediate forms between different groups of organisms.
Homologous structures are similar bone arrangements in different species (like human arms, bat wings and whale flippers). These suggest common ancestry. Vestigial organs like human tailbones are remnants of structures that were useful in ancestors.
For natural selection to work, there must be variation within populations. This variation comes from several sources and understanding these is key to understanding evolution.
Variation is the raw material of evolution. Without it, populations cannot adapt to changing environments.
The Galápagos finches that inspired Darwin show remarkable variation in beak shape and size. Ground finches have large, strong beaks for cracking seeds. Tree finches have smaller, pointed beaks for eating insects. Cactus finches have long, curved beaks for reaching nectar. Each beak shape is perfectly adapted to the bird's food source, demonstrating how natural selection shapes organisms to fit their environment.
Since Darwin's time, our understanding of evolution has expanded greatly. We now know about genes, DNA and the molecular basis of inheritance, which has strengthened and refined Darwin's original theory.
Evolution isn't just something that happened in the past - it's happening all around us today. We can observe it in real time in many organisms.
Bacteria evolve resistance to antibiotics through natural selection. When antibiotics are used, susceptible bacteria die, but resistant ones survive and multiply. This is why it's important to complete antibiotic courses and not overuse them.
Insects can evolve resistance to pesticides in the same way. Farmers must rotate different pesticides or use integrated pest management to prevent resistance from developing.
There are several common misunderstandings about how evolution works. Clearing these up helps us better understand the process.
Understanding what evolution doesn't do is just as important as understanding what it does do.
Humans share a common ancestor with other primates. Evidence includes similar DNA sequences (98.8% identical to chimpanzees), similar bone structures and fossil evidence showing gradual changes in skull shape, brain size and posture over millions of years. Features like bipedalism (walking upright) evolved because they provided advantages in the African savanna environment where early humans lived.
Darwin's theory has profound implications for how we understand life on Earth and our place in it. It explains the incredible diversity of life and predicts how organisms might change in the future.
Understanding evolution helps us solve modern problems and make predictions about the future.
Evolution explains why we get sick (pathogens evolve to infect us), why we age and how to develop new treatments. Understanding evolution helps doctors fight antibiotic resistance and develop vaccines.
Evolution helps us understand how species might adapt to climate change and habitat loss. This knowledge is crucial for conservation efforts and protecting biodiversity.
Darwin's theory of evolution by natural selection remains one of the most important scientific theories ever developed. It unifies all of biology and continues to guide scientific research today. By understanding evolution, we gain insight into the history of life on Earth and our own place in the natural world.