If you have any other comments or suggestions, please let us know at comment yourgenome. Can you spare minutes to tell us what you think of this website? Open survey. In: Facts Society and Behaviour. The theory of evolution is based on the idea that all species are related and gradually change over time. Evolution relies on there being genetic variation in a population which affects the physical characteristics phenotype of an organism.
Some of these characteristics may give the individual an advantage over other individuals which they can then pass on to their offspring. What is natural selection? Individuals in a species show variation in physical characteristics. This variation is because of differences in their genes. Individuals with characteristics best suited to their environment are more likely to survive, finding food, avoiding predators and resisting disease. These individuals are more likely to reproduce and pass their genes on to their children.
Individuals that are poorly adapted to their environment are less likely to survive and reproduce. Therefore their genes are less likely to be passed on to the next generation. As a consequence those individuals most suited to their environment survive and, given enough time, the species will gradually evolve. Natural selection in action: the Peppered moth Before the industrial revolution in the mids, the peppered moth was most commonly a pale whitish colour with black spots.
The idea didn't go over very well with the public or with other scientists. Darwin was so embarrassed by the ridicule he received that the swimming-bear passage was removed from later editions of the book. Scientists now know that Darwin had the right idea but the wrong animal. Instead of looking at bears, he should have been looking at cows and hippopotamuses. The story of the origin of whales is one of evolution's most fascinating tales and one of the best examples scientists have of natural selection.
To understand the origin of whales, you need a basic understanding of how natural selection works. Natural selection can alter a species in small ways, causing a population to change color or size over the course of several generations. When this process happens over a relatively short period of time and in a species or small group of organisms, scientists call it "microevolution. But when given enough time and accumulated changes, natural selection can create entirely new species, a process known as "macroevolution.
Take the example of whales: By using evolution as a guide and understanding how natural selection works, biologists knew that the transition of early whales from land to water occurred in a series of predictable steps.
The evolution of the blowhole, for example, might have started with random genetic changes that resulted in at least one whale having its nostrils farther back on its head. The whales with this adaptation would have been better suited to a marine lifestyle, since they would not have had to completely surface to breathe.
Such individuals were more successful and had more offspring. In later generations, more genetic changes occurred, moving the nose farther back on the head. Other body parts of early whales also changed. Front legs became flippers. Back legs disappeared. Their bodies became more streamlined, and they developed tail flukes to better propel themselves through water.
Darwin also described a form of natural selection that depends on an organism's success at attracting a mate — a process known as sexual selection. The colorful plumage of peacocks and the antlers of male deer are both examples of traits that evolved under this type of selection. But Darwin wasn't the first or only scientist to develop a theory of evolution.
Around the same time as Darwin, British biologist Alfred Russel Wallace independently came up with the theory of evolution by natural selection, while French biologist Jean-Baptiste Lamarck proposed that an organism could pass on traits to its offspring, though he was wrong about some of the details.
Like Darwin, Lamarck believed that organisms adapted to their environments and passed on those adaptations. He thought organisms did this by changing their behavior and, therefore, their bodies — like an athlete working out and getting buff — and that those changes were passed on to offspring. For example, Lamarck thought that giraffes originally had shorter necks but that, as trees around them grew taller, they stretched their necks to reach the tasty leaves and their offspring gradually evolved longer and longer necks.
Lamarck also believed that life was somehow driven to evolve through the generations from simple to more complex forms, according to Understanding Evolution , an educational resource from the University of California Museum of Paleontology.
Though Darwin wasn't sure of the mechanism by which traits were passed on, he did not believe that evolution necessarily moved toward greater complexity, according to Understanding Evolution; rather, he believed that complexity arose through natural selection. A Darwinian view of giraffe evolution, according to Quanta , would be that giraffes had natural variation in their neck lengths, and that those with longer necks were better able to survive and reproduce in environments full of tall trees, so that subsequent generations had more and more long-necked giraffes.
The main difference between the Lamarckian and Darwinian ideas of giraffe evolution is that there's nothing in theDarwinian explanation about giraffes stretching their necks and passing on an acquired characteristic.
Darwin didn't know anything about genetics, Pobiner said. That came later, with the discovery of how genes encode different biological or behavioral traits, and how genes are passed down from parents to offspring. The incorporation of genetics into Darwin's theory is known as "modern evolutionary synthesis.
The physical and behavioral changes that make natural selection possible happen at the level of DNA and genes within the gametes, the sperm or egg cells through which parents pass on genetic material to their offspring. In contrast, genetic drift produces random changes in the frequency of traits in a population.
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