The Berkeley Evolution Site The Berkeley site contains resources that can help students and teachers to understand and teach about evolution. The materials are arranged in optional learning paths for example "What does T. rex look like?" Charles Darwin's theory of natural selection explains how over time creatures that are better able to adapt biologically to changing environments do better than those that are not extinct. This process of evolution in biology is the basis of science. What is Evolution? The term "evolution" could have a variety of meanings that are not scientific. For example it could mean "progress" and "descent with modifications." It is a scientific term that refers to the process of changing traits over time in organisms or species. In terms of biology, this change is caused by natural selection and genetic drift. Evolution is a central tenet of modern biology. It is a concept that has been proven by thousands of scientific tests. Unlike many other scientific theories like the Copernican theory or the germ theory of disease, the evolution theory is not a discussion of spiritual belief or God's existence. Early evolutionists, like Jean-Baptiste Lamarck and Erasmus Darwin (Charles's grandfather) believed that certain physical traits were predetermined to change in a step-like manner, over time. This was called the "Ladder of Nature" or scala naturae. Charles Lyell used the term to describe this idea in his Principles of Geology, first published in 1833. Darwin published his theory of evolution in his book On the Origin of Species which was written in the early 1800s. It asserts that different species of organisms have a common ancestry, which can be determined through fossils and other evidence. This is the current understanding of evolution, and is supported by numerous research lines in science that include molecular genetics. While scientists don't know exactly how organisms evolved however they are sure that the evolution of life on earth is the result of natural selection and genetic drift. People with traits that are advantageous are more likely to survive and reproduce, and these individuals transmit their genes to the next generation. As time passes the gene pool gradually changes and develops into new species. Some scientists use the term evolution in reference to large-scale changes, like the evolution of one species from an ancestral one. Certain scientists, such as population geneticists, define evolution in a broad sense, using the term "net change" to refer to the change in the frequency of alleles across generations. Both definitions are valid and reliable however some scientists believe that the allele-frequency definition is missing important features of the evolutionary process. Origins of Life The most important step in evolution is the appearance of life. ???? ??? ??? happens when living systems begin to evolve at the micro level, within individual cells, for instance. The origins of life is an issue in a variety of disciplines such as geology, chemistry, biology and chemistry. The origin of life is a subject of interest in science, as it challenges the theory of evolution. It is often described as "the mystery of life," or "abiogenesis." The notion that life could be born from non-living matter was known as "spontaneous generation" or "spontaneous evolutionary". This was a popular belief before Louis Pasteur's tests showed that the creation of living organisms was not possible by the natural process. Many scientists believe it is possible to transition from living to nonliving substances. The conditions needed to create life are difficult to replicate in a laboratory. This is why researchers studying the beginnings of life are also keen to understand the physical properties of the early Earth and other planets. Furthermore, the growth of life is dependent on the sequence of extremely complex chemical reactions that cannot be predicted based on basic physical laws on their own. These include the reading of long information-rich molecules (DNA or RNA) into proteins that perform functions, and the replication of these intricate molecules to generate new DNA or sequences of RNA. These chemical reactions are often compared with the chicken-and-egg dilemma of how life began in the first place. The appearance of DNA/RNA and proteins-based cell machinery is vital for the beginning of life, but without the emergence of life the chemistry that makes it possible does not appear to work. Research in the area of abiogenesis requires collaboration between scientists from a variety of fields. This includes prebiotic chemists, the astrobiologists, the planet scientists geophysicists, geologists, and geophysicists. Evolutionary Changes Today, the word evolution is used to describe general changes in genetic traits over time. These changes may result from the response to environmental pressures as explained in the article on Darwinism (see the entry on Charles Darwin for background) or may result from natural selection. This mechanism also increases the frequency of genes that offer a survival advantage in a species, resulting in an overall change in the appearance of the group. The specific mechanisms responsible for these evolutionary changes are mutation or reshuffling genes during sexual reproduction, and gene flow between populations. While mutation and reshuffling of genes are common in all organisms, the process by which beneficial mutations are more frequent is called natural selection. This is because, as we've mentioned earlier, those individuals with the advantageous trait are likely to have a higher fertility rate than those with it. Over the course of several generations, this differential in the number of offspring born can result in an inclination towards a shift in the average amount of desirable characteristics in a particular population. A good example of this is the growth of beak size on various species of finches in the Galapagos Islands, which have developed different beak shapes to enable them to more easily access food in their new habitat. These changes in shape and form can also help create new organisms. The majority of the changes that occur are the result of one mutation, however occasionally, multiple mutations occur at the same time. The majority of these changes are neither harmful nor even detrimental to the organism, however, a small proportion of them can be beneficial to survival and reproduction, thus increasing their frequency in the population over time. Natural selection is a process that could result in the accumulation of changes over time that lead to a new species. Many people confuse the concept of evolution with the idea that traits inherited can be changed through conscious choice or use and abuse, a notion called soft inheritance. This is a misunderstanding of the nature of evolution, and of the actual biological processes that cause it. It is more precise to say that evolution is a two-step, independent process that involves the forces of natural selection and mutation. Origins of Humans Modern humans (Homo sapiens) evolved from primates, a group of mammals that includes chimpanzees and gorillas and bonobos. The earliest human fossils show that our ancestors were bipeds. They were walkers with two legs. Biological and genetic similarities indicate that we have an intimate relationship with Chimpanzees. In reality, our closest relatives are chimpanzees belonging to the Pan genus. This includes pygmy and bonobos. The last common ancestor of modern humans and chimpanzees dated 8 to 6 million years old. Over time, humans have developed a variety of characteristics, such as bipedalism and the use of fire. They also invented advanced tools. However, it is only in the last 100,000 years or so that the majority of the essential traits that distinguish us from other species have developed. These include a big brain that is sophisticated, the ability of humans to create and use tools, as well as cultural variety. The process of evolution occurs when genetic changes enable members of the group to better adapt to the environment. Natural selection is the process that triggers this adaptation. Certain characteristics are more desirable than others. The ones with the best adaptations are more likely to pass their genes to the next generation. This is the way that all species evolve and forms the foundation of the theory of evolution. Scientists refer to this as the "law of natural selection." The law states that species that have an ancestor in common will tend to develop similar traits over time. This is because the traits allow them to live and reproduce in their environments. Every organism has a DNA molecule that provides the information necessary to control their growth and development. The DNA structure is made of base pairs that are arranged in a spiral around phosphate and sugar molecules. The sequence of bases in each string determines the phenotype or the distinctive appearance and behavior of a person. The variations in a population are caused by mutations and reshufflings of genetic material (known collectively as alleles). Fossils of the earliest human species, Homo erectus and Homo neanderthalensis, have been found in Africa, Asia, and Europe. These fossils, despite differences in their appearance all support the hypothesis of the origins of modern humans in Africa. The genetic and fossil evidence suggests that the first humans left Africa and moved to Asia and Europe.
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