Darwin visited a wide range of habitats in different continents and recorded what he had found. On his visits, he noticed that different, yet ecologically similar, animals species inhabited separated, but ecologically similar, habitats around the globe. For example, Darwin found flightless birds called Rhea’s living in the grasslands of South America. Rhea’s look and act a lot like ostriches yet ostriches only live in Africa and Rhea’s only live in South America.
Read MoreEvolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction.
Darwin’s Voyage
Darwin noticed that different, yet related, animal species often occupied different habitats within a local area. He observed that different islands such as the Galapagos Island had different varieties of the same animals such as mockingbirds and tortoises.
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Darwin noticed that some fossils of extinct animals were similar to living species. Darwin collected fossils of organisms that looked like living organisms. An example is an armadillo. Fossils from a long extinct glyptodont were found, and the similar animal living in the same area is an armadillo. The armadillo just happens to be a smaller version.
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Darwin’s journey began in 1831, when he was invited to sail on the HMS Beagle’s five year voyage. They mapped the coast line of Sough America and Darwin planned to collect specimens of plants and animals. Darwin collected an over abundance of organisms and recorded everything he found. He realized that there were three different patterns of biological diversity.
Read MoreNatural Selection
Darwin‘s contribution was to describe the process in nature that could operate like artificial selection
The Struggle for Existence:
Darwin realize that if more individuals are produced then can survive, members of a population must compete to obtain food, living space, and other limited necessities of life.
Variation and Adaptation:
Darwin knew that individuals have natural variation among their heritable traits. Some of those variants are better suited to life and their environment than others. Any heritable characteristics that increase an organisms ability to survive and reproduce in its environment is called an adaptation. Adaptations can involve body parts or structures. Adaptations also involve behaviors.
Survival of the Fittest:
individuals with adaptations that are well-suited to their environment can survive and reproduce and have high fitness. Individuals with characteristics that are not well-suited to their environment either die without reproducing or leave few offspring. The difference in rates of survival and reproduction is called survival of the fittest.
Natural Selection:
natural selection is the process by which organisms with variations most suited to their local environment survive and leave more offspring. Natural selection occurs in any situation in which more individuals are born then can survive.
Common Descent:
Darwin proposed that living species are descended, with modification, from common ancestors. This aspect of Darwins theory implies that life has been on earth for a very long time and far enough back are the common ancestors of all living things. According to the principle of common descent, all species, living and extinct, are descended from ancient common ancestors.
The Struggle for Existence:
Darwin realize that if more individuals are produced then can survive, members of a population must compete to obtain food, living space, and other limited necessities of life.
Variation and Adaptation:
Darwin knew that individuals have natural variation among their heritable traits. Some of those variants are better suited to life and their environment than others. Any heritable characteristics that increase an organisms ability to survive and reproduce in its environment is called an adaptation. Adaptations can involve body parts or structures. Adaptations also involve behaviors.
Survival of the Fittest:
individuals with adaptations that are well-suited to their environment can survive and reproduce and have high fitness. Individuals with characteristics that are not well-suited to their environment either die without reproducing or leave few offspring. The difference in rates of survival and reproduction is called survival of the fittest.
Natural Selection:
natural selection is the process by which organisms with variations most suited to their local environment survive and leave more offspring. Natural selection occurs in any situation in which more individuals are born then can survive.
Common Descent:
Darwin proposed that living species are descended, with modification, from common ancestors. This aspect of Darwins theory implies that life has been on earth for a very long time and far enough back are the common ancestors of all living things. According to the principle of common descent, all species, living and extinct, are descended from ancient common ancestors.
Ideas
- Hutton and Lyell concluded that earth is extremely old and that the processes that changed Earth in the past are the same processes that operate in the present. Hutton presented his hypotheses about how geological processes have shaped the Earth.
- Hutton recognized the connections between a number of geological processes and geological features like mountains and more.
- Lyell also argue that earth is much much older than a few thousand years. Darwin began to read Lyell’s books during his voyage and he was able to conclude that Lyell was correct.
- Lamarck suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies. he also suggested that individuals could pass these acquired traits onto their offspring, enabling species to change over time. Lamarck propose that all organisms have an inborn urge to become more complex and perfect. We know today that his hypotheses were incorrect in several ways however, his work paved the way for later biologist, including Darwin.
- Malthus noted that humans were being born faster than people were dying, causing overcrowding. Darwin realize that his reasoning applied even more to other organisms than it did to humans. This was important because Darwin became convinced that species evolved and he needed to figure out how evolution occurred.
- Inherited variation is used in artificial selection because in artificial selection, nature provides the variations, and humans select those they find useful.
Evidence
Biogeography
Biogeography is the study of where organisms live now and where are they and their ancestors lived in the past. The first pattern of bio geography is a pattern in which closely related species differentiate in slightly different climates. The second pattern is a pattern in which very distantly related species develop similarities in similar environments.
Homologous Structures
Structures that are shared by related species and that have been inherited from a common ancestor are called homologous structures. Biologist test whether structures are homologous by studying the way structures develop in embryos and the pattern in which they appeared over evolutionary history.
Analogous and Vestigial Structures
Analogous structures our body parts that share common function, but not structure. An example is the wing of a bee and the wing of a bird. Vestigial structures are inherited from ancestors but have lost much or all of their original function due to different selection pressures acting on the descendent. An example of a vestigial structure is the legs of the Italian three-toed skink.
Embryology
Similar patterns of embryological development provides further evidence that organisms have descended from a common ancestor. Researchers noticed that the early developmental stages of vertebrates look very similar. Observations make it clear that the same groups of embryonic cells develop in the same order and in similar patterns to produce many homologous tissues and organs in vertebrates. Darwin realize that similar patterns of development gives important clues to the ancestry of living organisms.
Genetics and Molecular Biology
At the molecular level, the universal genetic code and homologous molecules provide evidence of common descent. An example of molecular evidence for evolution is that all living cells use information coded in DNA and RNA to carry information from one generation to the next. This genetic code is nearly identical in almost all organisms.
