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The Berkeley Evolution Site The Berkeley site contains resources that can help students and teachers to understand and teach about evolution. The materials are organized into optional learning paths like “What did T. rex taste like?” Charles Darwin's theory of natural selection explains how animals who are better equipped to adapt biologically to a changing environments survive longer and those who do not end up becoming extinct. Science is about this process of evolution. What is Evolution? The term “evolution” could have many nonscientific meanings. For example it could mean “progress” and “descent with modifications.” Scientifically it is a term used to describe a change in the characteristics of organisms (or species) over time. This change is based in biological terms on natural drift and selection. Evolution is an important principle in the field of biology today. It is an established theory that has stood up to the test of time and thousands of scientific tests. In contrast to other theories in science like the Copernican theory or the germ theory of disease, the evolution theory does not address questions of religious belief or God's existence. Early evolutionists, including Jean-Baptiste Lamarck and Erasmus Darwin (Charles's grandfather), believed that certain physical traits were predetermined to change in a gradual way, over time. click through the up coming website page referred to this as the “Ladder of Nature” or scala naturae. Charles Lyell first used this term in 1833 in his Principles of Geology. 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 have an ancestry that can be traced by fossils and other evidence. This is the current understanding of evolution, and is supported by many lines of scientific research which includes molecular genetics. While scientists don't know exactly how organisms developed but they are certain that the evolution of life on earth is the result of natural selection and genetic drift. People with advantages are more likely than others to survive and reproduce. These individuals pass on their genes to the next generation. As time passes the gene pool slowly changes and develops into new species. Some scientists also employ the term”evolution” to describe large-scale evolutionary changes like the creation of the new species from an ancestral species. Other scientists, like population geneticists, define evolution more broadly by referring an overall change in allele frequencies over generations. Both definitions are acceptable and accurate however, some scientists claim 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 evolve at the micro level – within cells, for example. The origins of life are an important topic in many fields, including biology and the field of chemistry. The question of how living things got their start is a major topic in science because it is an important challenge to the theory of evolution. It is sometimes referred to “the mystery” of life or “abiogenesis.” Traditionally, the belief that life can arise from nonliving objects 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 still think it is possible to go from nonliving to living substances. However, the conditions needed are extremely difficult to reproduce in the laboratory. Researchers investigating the origins of life are also interested in understanding the physical properties of the early Earth and other planets. The development of life is dependent on a number of complex chemical reactions which cannot be predicted by the basic physical laws. These include the reading of long information-rich molecules (DNA or RNA) into proteins that perform some function as well as the replication of these intricate molecules to produce new DNA or RNA sequences. These chemical reactions can be compared to the chicken-and-egg problem that is the emergence and growth of DNA/RNA, protein-based cell machinery, is necessary for the onset life. However, without life, the chemistry that is required to make it possible does appear to work. Abiogenesis research requires collaboration between scientists from various fields. This includes prebiotic scientists, astrobiologists, and planetary scientists. Evolutionary Changes The term “evolution” is commonly used today to refer to the accumulated changes in genetic characteristics of populations over time. These changes could result from adaptation to environmental pressures as discussed in the entry on Darwinism (see the entry on Charles Darwin for background) or natural selection. This is a process that increases the frequency of genes in a species that offer an advantage in survival over other species which results in a gradual change in the appearance of a particular population. These evolutionary changes are caused by mutations, reshuffling genes in the process of sexual reproduction, and also by gene flow. Natural selection is the process that makes beneficial mutations more common. All organisms undergo mutations and reshuffles of their genes. This occurs because, as mentioned above those with the beneficial trait tend to have a higher fertility rate than those without it. Over the course of many generations, this differential in the numbers of offspring produced can result in an inclination towards a shift in the amount of desirable traits in a population. A good example of this is the growing beak size on various species of finches on the Galapagos Islands, which have evolved different shaped beaks that allow them to easily access food in their new habitat. These changes in shape and form could also help create new organisms. Most of the changes that occur are caused by one mutation, however occasionally, multiple mutations occur simultaneously. Most of these changes can be harmful or neutral, but a small number could have a positive impact on the survival of the species and reproduce and increase their frequency over time. This is the way of natural selection, and it can be a time-consuming process that produces the accumulating changes that ultimately lead to the creation of a new species. Many people mistakenly associate evolution with the concept of soft inheritance which is the notion that inherited traits can be changed through conscious choice or by abuse. This is a misunderstanding of the biological processes that lead up to the process of evolution. A more precise description is that evolution is a two-step process that involves the distinct and often conflicting forces of natural selection and mutation. Origins of Humans Modern humans (Homo sapiens) evolved from primates – a species of mammals that includes chimpanzees and gorillas and bonobos. Our predecessors walked on two legs, as demonstrated by the first fossils. Biological and genetic similarities indicate that we have a close relationship with Chimpanzees. In reality, we are most closely with chimpanzees in the Pan Genus, which includes pygmy chimpanzees and bonobos. The last common ancestor shared between modern humans and chimpanzees was between 8 and 6 million years old. As time has passed, humans have developed a number of characteristics, including bipedalism and the use of fire. They also developed advanced tools. But it's only in the last 100,000 years or so that most of the traits that distinguish us from other species have emerged. These include a large brain that is complex human ability to build and use tools, as well as cultural diversity. Evolution is when genetic changes allow members of the group to better adapt to the environment. Natural selection is the mechanism that drives this change. Certain traits are preferred over others. The ones with the best adaptations are more likely to pass their genes to the next generation. This is how all species evolve, and it is the basis of the theory of evolution. Scientists refer to this as the “law of natural selection.” The law states species that share an ancestor will tend to acquire similar traits in the course of time. This is because these traits make it easier to reproduce and survive within their environment. Every organism has a DNA molecule that is the source of information that helps control their growth and development. The structure of DNA is composed of base pairs which are arranged in a spiral, around sugar and phosphate molecules. The sequence of bases within each strand determines phenotype or the individual's unique appearance and behavior. Variations in a population can be caused by mutations and reshufflings of genetic material (known collectively as alleles). Fossils of the first human species, Homo erectus and Homo neanderthalensis, have been found in Africa, Asia, and Europe. These fossils, despite some differences in their appearance, all support the hypothesis of modern humans' origins in Africa. The fossil and genetic evidence suggests that early humans left Africa and migrated to Asia and Europe.