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The Berkeley Evolution Site The Berkeley site has resources that can assist students and teachers learn about and teach evolution. The materials are organized into a variety of learning paths such as “What did T. rex taste like?” Charles Darwin's theory of natural selection explains how in time, creatures better able to adapt biologically to changing environments thrive, and those that are not extinct. Science is about this process of biological evolution. What is Evolution? The word evolution can have a variety of meanings that are not scientific. For example it could refer to “progress” and “descent with modifications.” It is scientifically based and refers to the process of changing traits over time in organisms or species. This change is based in biological terms on natural drift and selection. Evolution is an important principle in modern biology. It is a concept that has been tested and verified by a myriad of scientific tests. Contrary to other theories of science, such as the Copernican theory or the germ theory of disease, evolution does not address issues of religious belief or the existence of God. Early evolutionists, like Jean-Baptiste Lamarck and Erasmus Darwin (Charles's grandfather), believed that certain physical characteristics were predetermined to change in a gradual manner, as time passes. This was referred to as 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. In the early 1800s, Darwin formulated his theory of evolution and published it in his book On the Origin of Species. It asserts that all species of organisms share a common ancestry which can be traced through fossils and other evidence. This is the modern view of evolution, which is supported in a wide range of areas of science which include molecular biology. While scientists do not know exactly how organisms developed 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 these individuals pass their genes on to the next generation. Over time the gene pool gradually changes and evolves into new species. Certain scientists also use the term”evolution” to refer to large-scale changes in evolutionary processes, such as the formation of the new species from an ancestral species. Other scientists, like population geneticists, define it more broadly, referring to an overall change in allele frequencies over generations. Both definitions are acceptable and accurate, although some scientists argue that the allele-frequency definition is missing crucial aspects of the evolutionary process. Origins of Life A key step in evolution is the emergence of life. This happens when living systems begin to develop at a micro-level – within individual cells, for instance. The origin of life is an important topic in a variety of disciplines such as biology and the field of chemistry. The question of how living things started is of particular importance in science due to it being an enormous challenge to the theory of evolution. It is often referred to as “the mystery of life,” or “abiogenesis.” Traditionally, the belief that life could emerge from nonliving things is known as spontaneous generation, or “spontaneous evolution.” This was a popular belief prior to Louis Pasteur's research showed that it was impossible for the creation of life to occur by the natural process. Many scientists believe it is possible to transition from nonliving to living substances. However, the conditions required are extremely difficult to replicate in a laboratory. Researchers interested in the evolution and origins 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 reading of long, information-rich molecules (DNA or RNA) into proteins that carry out a function, and the replication of these intricate molecules to generate new DNA or RNA sequences. These chemical reactions can be compared to the chicken-and-egg problem which is the development and emergence of DNA/RNA, protein-based cell machinery, is necessary for the onset life. However without life, the chemistry needed to enable it does appear to work. Research in the area of abiogenesis requires collaboration between scientists from various fields. This includes prebiotic scientists, astrobiologists and planetary scientists. Evolutionary Changes The term “evolution” is used to describe cumulative changes in genetic characteristics over time. These changes can be the result of the adaptation to environmental pressures as described in Darwinism. The latter is a mechanism that increases the frequency of genes that confer an advantage in survival over others and causes a gradual change in the overall appearance of a particular population. The specific mechanisms responsible for these evolutionary changes include mutation and reshuffling of genes in sexual reproduction, as well as gene flow between populations. Natural selection is the process that makes beneficial mutations more common. All organisms undergo changes and reshuffles in their genes. As previously mentioned, those with the beneficial characteristic have a higher reproduction rate than those that do not. Over the course of many generations, this variation in the numbers of offspring born could result in gradual changes in the average number of advantageous characteristics in a particular population. One good example is the increase in beak size on different species of finches found on the Galapagos Islands, which have developed beaks with different shapes to enable them to more easily access food in their new environment. These changes in shape and form can also aid in the creation of new species. The majority of changes are caused by a single mutation, but sometimes several occur at once. The majority of these changes could be neutral or even harmful however, a few could have a positive impact on the survival of the species and reproduce, increasing their frequency as time passes. Natural selection is a mechanism that causes the accumulating change over time that eventually leads to a new species. Many people confuse evolution with the idea of soft inheritance that is the belief that traits inherited from parents can be changed through deliberate choice or misuse. This is a misinterpretation of the biological processes that lead to the process of evolution. A more accurate description is that evolution involves a two-step process, that involves the distinct and often antagonistic forces of mutation and natural selection. Origins of Humans Modern humans (Homo Sapiens) evolved from primates, a group of mammal species which includes chimpanzees as well as gorillas. Our predecessors walked on two legs, as evidenced by the earliest fossils. Genetic and biological similarities show that we have a close relationship with the chimpanzees. In reality our closest relatives are chimpanzees from the Pan genus. This includes pygmy as well as bonobos. The last common ancestor shared between modern humans and chimpanzees was 8 to 6 million years old. Humans have developed a range of traits over time, including bipedalism, the use of fire, and the development of advanced tools. It's only within the last 100,000 years that we've developed the majority of our key characteristics. These include a big, complex brain and the capacity of humans to create and use tools, as well as cultural variety. Evolution occurs when genetic changes allow members of an organization to better adapt to the environment. Natural selection is the mechanism that drives this adaptation. Certain traits are preferred over others. The more adjusted are more likely to pass their genes on to the next generation. This is how all species evolve and is the basis for the theory of evolution. Scientists call this the “law of natural selection.” The law states species that have a common ancestor are likely to develop similar characteristics in the course of time. This is because these traits allow them to live and reproduce in their natural environment. Every living thing has the DNA molecule, which contains the information needed to control their growth. The DNA molecule consists of base pairs that are spirally arranged around phosphate molecules and sugar molecules. The sequence of bases found in each strand determines the phenotype – the appearance and behavior of an individual. The variations in a population are caused by mutations and reshufflings in genetic material (known collectively as alleles). Fossils from the earliest human species Homo erectus, and Homo neanderthalensis have been discovered in Africa, Asia and Europe. Despite some differences the fossils all support the notion that modern humans first appeared in Africa. Suggested Studying and genetic evidence suggest that early humans migrated out of Africa into Asia and then Europe.