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The Berkeley Evolution Site Teachers and students who browse the Berkeley site will find resources to help them understand and teach evolution. The resources are organized into optional learning paths such as “What did T. rex taste like?” 에볼루션게이밍 of natural selection explains that over time creatures that are more able to adapt to changing environments thrive, and those that do not become extinct. This process of evolution is the basis of science. What is Evolution? The term “evolution” can have a variety of meanings that are not scientific. For instance it could mean “progress” and “descent with modifications.” It is a scientific term that refers to the process of changing characteristics over time in organisms or species. In biological terms this change is based on natural selection and genetic drift. Evolution is a key principle in modern biology. It is a well-supported theory that has stood up to the test of time and a multitude of scientific tests. Unlike many other scientific theories like the Copernican theory or the germ theory of disease, evolution is not a discussion of spiritual belief or God's existence. Early evolutionists, such as Erasmus Darwin (Charles’s grandfather) and Jean-Baptiste Lamarck believed that certain physical traits were predetermined to change in a step-like fashion over time. This was known as the “Ladder of Nature” or scala naturae. Charles Lyell first used this term in 1833 in his Principles of Geology. Darwin published his theory of evolution in his book On the Origin of Species published in the early 1800s. It states that all species of organisms have a common ancestry, which can be traced through fossils and other lines of evidence. This is the current view of evolution, which is supported by numerous lines of research in science, including molecular genetics. Although scientists aren't able to determine 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 desirable traits are more likely to live and reproduce, and they pass their genes on to the next generation. As time passes, the gene pool gradually changes and evolves into new species. Certain scientists use the term”evolution” to refer to large-scale changes, such the formation of one species from an ancestral one. Some scientists, like population geneticists, define the term “evolution” in a more broad sense by referring to the net change in allele frequency over generations. Both definitions are valid and reliable however, some scientists claim 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. The beginning of life takes place when living systems begin to develop at a micro level, like within individual cells. The origins of life are an issue in a variety of disciplines such as biology, chemistry and geology. The question of how living things started is a major topic in science because it is an important challenge to the theory of evolution. It is often described as “the mystery of life,” or “abiogenesis.” Traditionally, the idea that life can arise from nonliving objects is known as spontaneous generation or “spontaneous evolution.” This was a common belief before Louis Pasteur's experiments showed that it was impossible for the development of life to be a result of the natural process. Many scientists believe that it is possible to transition from nonliving materials to living. However, the conditions required are extremely difficult to reproduce in labs. Researchers who are interested in the origins and development of life are also keen to learn about the physical characteristics of the early Earth as well as other planets. The growth of life is dependent on a number of complex chemical reactions, which cannot be predicted by simple physical laws. These include the transformation of long, information-rich molecules (DNA or RNA) into proteins that carry out functions and the replication of these complex molecules to create new DNA or sequences of RNA. These chemical reactions are often compared to the chicken-and-egg issue of how life first appeared: The appearance of DNA/RNA and protein-based cell machinery is essential to the birth of life, however, without the appearance of life, the chemistry that makes it possible does not appear to work. Abiogenesis research requires collaboration with researchers from different disciplines. This includes prebiotic scientists, astrobiologists and planet scientists. Evolutionary Changes The term “evolution” is typically used today to describe the cumulative changes in genetic characteristics of populations over time. These changes could result from the response to environmental pressures as described in the entry on Darwinism (see the entry on Charles Darwin for background), or from natural selection. This is a process that increases the frequency of those genes which confer an advantage in survival over others, resulting in gradual changes in the appearance of a particular population. These evolutionary changes are triggered by mutations, reshuffling genes during sexual reproduction, and gene flow. Natural selection is the process that makes beneficial mutations more common. All organisms undergo changes and reshuffles in their genes. This is because, as mentioned above, those individuals with the beneficial trait tend to have a higher reproduction rate than those with it. Over many generations, this differential in the numbers of offspring born can result in gradual changes in the average number of beneficial traits within a group of. A good example of this is the increase in beak size on different species of finches in the Galapagos Islands, which have developed beaks with different shapes to enable them to more easily access food in their new home. These changes in shape and form can aid in the creation of new organisms. The majority of changes are caused by one mutation, although sometimes multiple occur at the same time. Most of these changes are neutral or even detrimental to the organism, however, a small proportion of them can have an advantageous impact on the survival of the organism and its reproduction, thereby increasing the frequency of these changes in the population over time. This is the process of natural selection and it is able to be a time-consuming process that produces the cumulative changes that eventually lead to a new species. Some people confuse the notion of evolution with the notion that traits inherited can be altered by conscious choice or use and abuse, a concept called soft inheritance. This is a misunderstanding of the biological processes that lead to evolution. It is more accurate to say that the process of evolution is a two-step, separate process, that is influenced by the forces of natural selection as well as mutation. Origins of Humans Humans today (Homo sapiens) evolved from primates – a species of mammals that also includes chimpanzees and gorillas and bonobos. Our predecessors walked on two legs, as evidenced by the earliest fossils. Genetic and biological similarities show that we share a close relationship with Chimpanzees. In reality we are the closest related to the chimpanzees within the Pan genus that includes pygmy and bonobos and pygmy chimpanzees. The last common ancestor between modern humans and chimpanzees dated between 8 and 6 million years old. Over time humans have developed a variety of traits, including bipedalism and the use of fire. They also created advanced tools. It's only within the last 100,000 years that we have developed the majority of our key characteristics. These include a large, complex brain, the ability of humans to build and use tools, and cultural diversity. The process of evolution occurs when genetic changes enable members of a group to better adapt to their environment. Natural selection is the process that drives this change. Certain traits are preferred over others. People with better adaptations are more likely to pass on their genes to the next generation. This is the way all species evolve and the basis of the theory of evolution. Scientists call this the “law of natural selection.” The law states that species which have a common ancestor are more likely to develop similar traits over time. This is because these traits make it easier to reproduce and survive within their environment. Every organism has an molecule called DNA that holds the information necessary to direct their growth. The DNA molecule consists of base pairs arranged spirally around phosphate molecules and sugar molecules. The sequence of bases in each strand determines the phenotype, the appearance and behavior of a person. Variations in mutations and reshuffling of the genetic material (known as alleles) during reproduction causes variation in a population. Fossils from the early 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 fossil and genetic evidence suggests that early humans left Africa and moved to Asia and Europe.