The Berkeley Evolution Site
Teachers and students who browse the Berkeley site will find a wealth of resources to help them understand and teach evolution. The materials are arranged in optional learning paths for example "What does T. rex look like?"
Charles Darwin's theory of natural selection states that over time creatures that are more able to adapt to changing environments survive and those that are not extinct. Science is concerned with this process of evolution.
What is Evolution?
The term "evolution" can be used to refer to a variety of nonscientific meanings. For instance, it can 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 well-supported theory that has stood the test of time and a multitude of scientific studies. Evolution does not deal with God's presence or spiritual beliefs like other theories in science, like the Copernican or germ theory of disease.
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 way, over time. 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.
Darwin revealed his theory of evolution in his book On the Origin of Species published in the early 1800s. It asserts that different species of organisms have a common ancestry, which can be proven through fossils and other evidence. This is the modern view of evolution, which is supported in many areas of science that include molecular biology.
Scientists do not know how organisms evolved but they are sure that natural selection and genetic drift is the primary reason for the evolution of life. Individuals with advantageous characteristics are more likely than others to live and reproduce. These individuals then 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 in reference to large-scale change, such as the evolution of a species from an ancestral one. Some scientists, like population geneticists, define the term "evolution" in a broad sense, talking about the net change in allele frequency over generations. Both definitions are valid and reliable however some scientists believe that the allele-frequency definition omits important features of the evolutionary process.
Origins of Life
The emergence of life is an essential step in evolution. The emergence of life occurs when living systems begin to evolve at a micro scale, for instance within cells.
The origins of life are an important subject in many areas such as biology and the field of chemistry. The nature of life is an area that is of immense interest to scientists because it challenges the theory of evolution. It is often called "the mystery of life," or "abiogenesis."
Traditionally, the belief that life can arise from nonliving things is called spontaneous generation or "spontaneous evolution." This was a popular belief prior to Louis Pasteur's research showed that it was impossible for the development of life to happen through an entirely natural process.
see this site believe it is possible to transition from nonliving materials to living. However, the conditions required are extremely difficult to reproduce in a laboratory. Researchers studying the origins of life are also keen to understand the physical properties of early Earth and other planets.
The development of life is also dependent on a series of complex chemical reactions which cannot be predicted by basic physical laws. This includes the conversion of long, information-rich molecules (DNA or RNA) into proteins that perform a function, and 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 that is the emergence and growth of DNA/RNA, a protein-based cell machinery, is necessary to begin the process of becoming a living organism. However without life, the chemistry needed to make it possible appears to be working.
Research in the area of abiogenesis requires collaboration between scientists from various disciplines. This includes prebiotic chemists, astrobiologists, planetary scientists geophysicists and geologists.
Evolutionary Changes
Today, the word evolution is used to describe the cumulative changes in genetic characteristics over time. These changes can be the result of the adaptation to environmental pressures as discussed in Darwinism.
This process increases the number of genes that confer an advantage for survival in the species, leading to an overall change in the appearance of an entire group. The specific mechanisms responsible for 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. As noted above, individuals who possess the desirable trait have a higher reproductive rate than those that do not. This difference in the number of offspring born over a number of generations could cause a gradual change in the average number advantageous characteristics in the group.
A good example of this is the growing beak size on various species of finches in the Galapagos Islands, which have evolved different shaped beaks to allow them to more easily access food in their new habitat. These changes in the shape and form of organisms could also aid in the creation of new species.
The majority of changes are caused by a single mutation, but sometimes several occur simultaneously. Most of these changes may be negative or even harmful however, a few may have a positive effect on the survival of the species and reproduce and increase their frequency as time passes. Natural selection is a process that causes the accumulating change over time that eventually leads to the creation of a new species.
Many people mistakenly associate evolution with the concept of soft inheritance that is the belief that inherited traits can be changed by deliberate choice or misuse. This is a misunderstood understanding of the nature of evolution and of the actual biological processes that trigger it. A more precise description is that evolution involves a two-step process, involving the independent and often conflicting forces of natural selection and mutation.
Origins of Humans
Humans today (Homo sapiens) evolved from primates, a group of mammals that also includes chimpanzees and gorillas and bonobos. The earliest human fossils show that our ancestors were bipeds - walking on two legs. Biological and genetic similarities indicate that we share the same ancestry with chimpanzees. In actual fact our closest relatives are chimpanzees from the Pan genus. This includes pygmy and bonobos. The last common ancestor shared between humans and chimpanzees was 8 to 6 million years old.
Humans have developed a range of characteristics over time including bipedalism, the use of fire and advanced tools. It's only in the last 100,000 years that we have developed the majority of our essential characteristics. They include language, a large brain, the ability to construct and use complex tools, and cultural diversity.
Evolution happens when genetic changes allow individuals in a group to better adapt to their environment. Natural selection is the process that triggers this adaptation. Certain characteristics are more desirable than others. The ones who are better adjusted are more likely to pass on their genes to the next generation. This is how all species evolve and is the basis for the theory of evolution.
Scientists refer to this as the "law of natural selection." The law states that species which share an ancestor will tend to develop similar traits over time. It is because these traits make it easier to survive and reproduce within their environment.
Every organism has a DNA molecule that contains the information needed to control their growth. The DNA molecule is made up of base pairs that are arranged in a spiral around phosphate molecules and sugar molecules. The sequence of bases within each strand determines the phenotype or the individual's unique appearance and behavior. The variations in a population are caused by reshufflings and mutations 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 variations in their appearance, all support the theory of modern humans' origins in Africa. Genetic and fossil evidence also suggest that early humans came out of Africa into Asia and then Europe.