In this struggle for existence, survival and reproduction do not come down to pure chance. Darwin and Wallace both realized that if an animal has some trait that helps it to withstand the elements or to breed more successfully, it may leave more offspring behind than others.
On average, the trait will become more common in the following generation, and the generation after that. As Darwin wrestled with natural selection he spent a great deal of time with pigeon breeders, learning their methods.
He found their work to be an analogy for evolution. A pigeon breeder selected individual birds to reproduce in order to produce a neck ruffle. Given enough time, Darwin and Wallace argued, natural selection might produce new types of body parts, from wings to eyes.
Darwin began formulating his theory of natural selection in the late s but he went on working quietly on it for twenty years. He wanted to amass a wealth of evidence before publicly presenting his idea.
During those years he corresponded briefly with Wallace right , who was exploring the wildlife of South America and Asia. Darwin had been working on a major book on evolution and used that to develop On the Origins of Species , which was published in Wallace, on the other hand, continued his travels and focused his study on the importance of biogeography.
The book was not only a best seller but also one of the most influential scientific books of all time. Yet it took time for its full argument to take hold. Within a few decades, most scientists accepted that evolution and the descent of species from common ancestors were real. But natural selection had a harder time finding acceptance.
In the late s many scientists who called themselves Darwinists actually preferred a Lamarckian explanation for the way life changed over time. Wallace worked around the world gathering evidence to support his evolutionary theory. He is best known for studying warning colouration in animals, one example being the golden birdwing butterfly Ornithoptera croesus , as well as his theory of speciation. After a variety of zoological discoveries, Wallace proposed a theory of evolution which matched the unpublished ideas Darwin had kept secret for nearly 20 years.
This encouraged Darwin to collect his scientific ideas and collaborate with Wallace. They published their scientific ideas jointly in The idea behind the theory of evolution through the process of natural selection is that all species of living things have evolved from simple life forms over a period of time. The Earth is about 4.
It explains how giraffes came to have such long necks, like those shown in the photo below. In the first chapter of his book On the Origin of Species , Charles Darwin discussed how artificial selection, also called selective breeding, had been successful in changing the traits of animals, including pigeons, cats, cattle, and dogs.
He used this discussion as a springboard to introduce his idea of natural selection as well as to provide support for it. The use of selective breeding to change the traits of other species has a very long history. In fact, archaeological evidence indicates that selective breeding of both plants and animals began as early as 10, years ago in the Middle East when previous hunter-gatherers began to domesticate animals and cultivate cereal plants.
Around this time, changes in climate led to increasing drought, which forced people to concentrate around permanent water sources. These population concentrations could not be supported by wild animals and plants in the vicinity, providing a stimulus for the invention of agriculture and the use of selective breeding to increase the amount of available food.
For thousands of years, species of plants such as wheat and rice and of animals such as goats and sheep were selectively bred and changed from their wild ancestors.
The result was modern maize commonly called corn , shown on the right in the same picture. Teosinte was very small with fewer grains on it.
The modern corn is bulky and with a lot more grain on it. After maize was created, it spread across the Americas and was introduced to Europe by European explorers and traders. Today, maize is still a dietary staple and the most widely grown grain crop in the Americas.
The wild ancestors of domesticated wheat and rice were easy to identify because the modern species resemble their wild counterparts. However, that wasn't the case with maize, which looks very different from teosinte. Maize also appeared quite suddenly in the archaeological record, so its origin has been of special interest.
Go online to learn more about the selective breeding of teosinte to maize. Use only reliable sources such as university websites to find answers to the following questions:. What is the Theory of Evolution by Natural Selection?
In other words, organisms change over time. Life on Earth has changed as descendants diverged from common ancestors in the past. The other idea is that evolution occurs by natural selection.
Natural selection is the process in which living things with beneficial traits produce more offspring than others do. This results in changes in the traits of living things over time. Voyage of the Beagle In , when Darwin was just 22 years old, he set sail on a scientific expedition on a ship called the HMS Beagle. Each stop along the way is labeled.
The route starts with Sydney. Darwin and the others on board eventually circled the globe. For example: He visited tropical rainforests and other new habitats where he saw many plants and animals he had never seen before, such as the giant iguana and booby bird pictured below. These observations impressed him with the great diversity of life. He experienced an earthquake that lifted the ocean floor 2. He also found rocks containing fossil seashells in mountains high above sea level.
These observations suggested that continents and oceans had changed dramatically over time and continue to change in dramatic ways.
He visited rock ledges that had clearly once were beaches that had gradually built up over time. He dug up fossils of gigantic extinct mammals, such as the ground sloth, fossils of which are also pictured below. This was hard evidence that organisms looked very different in the past. He also dug up the fossil skeleton of a giant ground sloth-like the one shown here. Tortoises with saddle-shaped shells can reach up to eat plant leaves above their head.
Tortoises with dome-shaped shells cannot reach up in this way. These two types of tortoises live on islands with different environments and food sources. How might this explain the differences in their shells? Other Influences on Darwin Science, like evolution, always builds on the past.
Jean Baptiste Lamarck — was an important French naturalist. He was one of the first scientists to propose that species change over time.
However, Lamarck was wrong about how species change. His idea of the inheritance of acquired characteristics is incorrect. Traits an organism develops during its own life cannot be passed on to offspring, as Lamarck believed.
Charles Lyell — was a well-known English geologist. Darwin took his book, Principles of Geology, with him on the Beagle. From this, Lyell inferred that Earth must be far older than most people believed.
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