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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 resources are organized into a variety of learning paths such as “What did T. rex taste like?” Charles Darwin's theory of natural selection describes how species that are better equipped to adapt biologically to a changing environments over time, and those that do not become extinct. This process of biological evolution is what science is all about. What is Evolution? The word evolution has many nonscientific meanings. For instance “progress” or “descent with modification.” Scientifically, it refers to a changing the characteristics of organisms (or species) over time. This change is based in biological terms on natural drift and selection. Evolution is the central tenet of modern biology. It is an accepted theory that has stood up to the test of time and thousands of scientific experiments. Evolution does not deal with spiritual beliefs or God's presence in the same way as other scientific theories such as the Copernican or germ theory of diseases. Early evolutionists, such as Jean-Baptiste Lamarck and Erasmus Darwin (Charles's grandfather) believed that certain physical traits were predetermined to change in a gradual manner, over time. This was called the “Ladder of Nature” or scala naturae. Charles Lyell first used this term in 1833 in his Principles of Geology. Darwin presented his theory of evolution in his book On the Origin of Species, written in the early 1800s. It asserts that different species of organisms share the same ancestry, which can be traced through fossils and other lines of evidence. This is the current perspective on evolution, which is supported in a wide range of disciplines which include molecular biology. Scientists aren't sure how organisms evolved but they are sure that natural selection and genetic drift is responsible for the evolution of life. People with desirable traits are more likely to live and reproduce, and they transmit their genes to the next generation. Over time, the gene pool gradually changes and evolves into new species. Certain scientists also use the term”evolution” to describe large-scale evolutionary changes like the creation of the new species from an ancestral species. Some scientists, like population geneticists, define evolution in a broad sense, talking about the net change in the frequency of alleles across generations. Both definitions are accurate and palatable, but some scientists argue that allele-frequency definitions omit important features of evolutionary process. Origins of Life The development of life is a key step in the process of evolution. This occurs when living systems begin to evolve at the micro level – within cells, for instance. The origin of life is an issue in a variety of disciplines that include biology, chemistry and geology. The question of how living things got their start is of particular importance in science since it poses a major challenge to the theory of evolution. It is sometimes referred to “the mystery” of life or “abiogenesis.” The notion that life could arise from non-living matter was known as “spontaneous generation” or “spontaneous evolutionary”. It was a common belief prior to Louis Pasteur's tests proved that the creation of living organisms was not achievable through a natural process. Many scientists believe it is possible to move from living to nonliving substances. However, the conditions required are extremely difficult to replicate in labs. This is why researchers investigating the beginnings of life are also interested in determining the physical properties of the early Earth and other planets. The life-cycle of a living organism is dependent on a number of complex chemical reactions, which are not predicted by basic physical laws. These include the transformation of long, information-rich molecules (DNA or RNA) into proteins that perform a function as well as the replication of these intricate molecules to create new DNA or sequences of RNA. These chemical reactions can be compared to a chicken-and egg problem: the emergence and development of DNA/RNA, protein-based cell machinery, is required for the beginning of life. However, without life, the chemistry that is required to make it possible is working. Abiogenesis research requires collaboration between scientists from various disciplines. This includes prebiotic scientists, astrobiologists and planetary scientists. Evolutionary Changes The term “evolution” is commonly used today to describe the accumulated changes in the genetic characteristics of an entire population over time. These changes can result from adaptation to environmental pressures, as discussed in the entry on Darwinism (see the entry on Charles Darwin for background) or may result from natural selection. This process increases the number of genes that provide an advantage for survival in the species, leading to an overall change in the appearance of a group. The specific mechanisms that cause these changes in evolutionary process include mutation, reshuffling of genes during sexual reproduction, and gene flow between populations. Natural selection is the process that allows beneficial mutations to become more common. All organisms undergo mutations and reshuffles of their genes. This is because, as we've mentioned earlier those who have the beneficial trait tend to have a higher fertility rate than those who do not have it. This difference in the number of offspring born over many generations can result in a gradual shift in the average number advantageous characteristics in the group. This can be seen in the evolution of various beak shapes for finches from the Galapagos Islands. They have created these beaks to ensure that they can eat more quickly in their new home. These changes in the shape and appearance of living organisms may also help create new species. The majority of changes are caused by one mutation, however sometimes multiple occur simultaneously. Most of these changes are neutral or even harmful to the organism however a small portion of them could have a positive impact on survival and reproduction, thus increasing the frequency of these changes in the population over time. This is the way of natural selection and it is able to, over time, produce the cumulative changes that eventually lead to the creation of 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, which is known as soft inheritance. This is a misunderstanding of the biological processes that lead up to evolution. A more accurate description is that evolution is a two-step procedure that involves the distinct, and often competing, forces of natural selection and mutation. Origins of Humans Modern humans (Homo Sapiens) evolved from primates, which is a group of mammal species that includes chimpanzees as well as gorillas. The earliest human fossils show that our ancestors were bipeds. They were walkers with two legs. Genetic and biological similarities suggest that we are closely related to the chimpanzees. In reality, we are most closely related to the chimpanzees within the Pan Genus which includes pygmy chimpanzees and bonobos. The last common ancestor shared between humans and chimpanzees was between 8 and 6 million years old. Humans have evolved a wide range of characteristics over time such as bipedalism, use of fire and advanced tools. However, it is only in the last 100,000 years or so that the majority of the essential characteristics that differentiate us from other species have emerged. They include a huge, complex brain, the ability of humans to construct and use tools, and the diversity of our culture. Evolution occurs when genetic changes allow members of a population to better adapt to their environment. This adaptation is triggered by natural selection, a process that determines certain traits are favored over other s. The ones with the best adaptations are more likely to pass on their genes to the next generation. This is the way that all species evolve, and it is the foundation of the theory of evolution. Scientists refer to this as the “law of natural selection.” The law says that species that share a common ancestor tend to develop similar traits over time. It is because these traits allow them to survive and reproduce within their environment. Every organism has a DNA molecule that is the source of information that helps direct their growth and development. The DNA molecule is made up of base pairs that are spirally arranged around sugar molecules and phosphate molecules. The sequence of bases within each strand determines phenotype, or the individual's characteristic appearance and behavior. The variations in a population are caused by mutations and reshufflings of 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. These fossils, despite some differences in their appearance, all support the hypothesis of the origins of modern humans in Africa. Genetic and fossil evidence also suggest that early humans came out of Africa into Asia and then Europe.