The Berkeley Evolution Site
The Berkeley site contains resources that can help students and educators learn about and teach evolution. The materials are organized in different learning paths like "What does T. rex look like?"
Charles Darwin's theory on natural selection explains how animals who are better equipped to adapt biologically to changing environments over time, and those that don't end up becoming extinct. This process of evolution is the basis of science.
What is Evolution?
The term "evolution" can have many nonscientific meanings, such as "progress" or "descent with modification." Scientifically, it refers to a process of change in the characteristics of living things (or species) over time. This change is based in biological terms on natural drift and selection.
Evolution is a key concept in modern biology. It is a concept that has been tested and verified by a myriad of scientific tests. Evolution does not deal with God's presence or spiritual beliefs, unlike many other theories of science, 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 step-wise manner, over time. This was referred to as 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 which was written in the early 1800s. It claims that different species of organisms have the same ancestry, which can be traced through fossils and other lines of evidence. This is the current perspective of evolution, which is supported in many areas of science which include molecular biology.
While scientists do not know exactly how organisms developed, they are confident that the evolution of life on earth is the result of natural selection and genetic drift. People with traits that are advantageous are more likely to survive and reproduce, and these individuals transmit their genes to the next generation. Over time, this results in a gradual accumulation of changes to the gene pool, which eventually result in new species and types.
Some scientists use the term evolution in reference to large-scale changes, such the formation of one species from an ancestral one. Certain scientists, such as population geneticists, define evolution in a more broad sense by using the term "net change" to refer to the variation in the frequency of alleles over generations. Both definitions are accurate and palatable, but some scientists believe that allele-frequency definitions do not include important aspects of evolutionary process.
Origins of Life
The emergence of life is an essential step in the process of evolution. The emergence of life happens when living systems start to develop at a micro scale, for instance within individual cells.
The origins of life is an issue in a variety of disciplines such as biology, chemistry and geology. The question of how living things started is of particular importance in science since it poses an enormous challenge to the theory of evolution. It is often referred to 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 popular belief prior to Louis Pasteur's experiments proved that it was impossible for the emergence of life to be a result of a purely natural process.
Many scientists still think it is possible to go from nonliving to living substances. However, the conditions that are required are extremely difficult to replicate in labs. This is why researchers investigating the nature of life are also keen to understand the physical properties of the early Earth and other planets.
Furthermore, the growth of life depends on a sequence of very complex chemical reactions that cannot be predicted from basic physical laws alone. These include the reading of long, information-rich molecules (DNA or RNA) into proteins that carry out functions as well as the replication of these intricate molecules to generate new DNA or sequences of RNA. These chemical reactions can be compared with the chicken-and-egg issue which is the development and emergence of DNA/RNA, the protein-based cell machinery, is necessary for the beginning of life. Although without life, the chemistry that is required to make it possible does appear to work.
Research in the field of abiogenesis requires collaboration among scientists from a variety of fields. This includes prebiotic chemists, the astrobiologists, the planet scientists, geologists and geophysicists.
Evolutionary Changes
The term "evolution" is typically used today to refer to the accumulated changes in the genetic characteristics of a population over time. These changes may result from adaptation to environmental pressures, as explained in the article on Darwinism (see the entry on Charles Darwin for background), or from natural selection.
This is a method that increases the frequency of genes in a species which confer an advantage in survival over others which results in a gradual change in the appearance of a particular population. The specific mechanisms that cause these evolutionary changes are mutation, reshuffling of genes during sexual reproduction, and also gene flow between populations.
While reshuffling and mutation of genes happen in all living things and the process by which beneficial mutations are more prevalent is called natural selection. This occurs because, as we've mentioned earlier those with the beneficial trait tend to have a higher reproduction rate than those without it. This difference in the number of offspring produced over a number of generations could result in a gradual change in the average number advantageous characteristics in the group.
A good example of this is the growing the size of the beaks on different species of finches in the Galapagos Islands, which have developed different beak shapes to enable them to more easily access food in their new home. These changes in shape and form can also aid in the creation of new species.
The majority of the changes that take place are caused by a single mutation, but sometimes, several changes occur at the same time. The majority of these changes could be neutral or even harmful however, a small percentage may have a positive effect on the survival of the species and reproduce with increasing frequency as time passes. Natural selection is a process that causes the accumulating change over time that eventually leads to a new species.
Some people think that evolution is a form of soft inheritance that is the belief that inherited traits can be altered by conscious choice or abuse. This is a misunderstanding of the biological processes that lead up to evolution. A more accurate description is that evolution involves a two-step process, involving the independent and often conflicting forces of natural selection and mutation.
Origins of Humans
Modern humans (Homo Sapiens) evolved from primates, a species of mammal species which includes chimpanzees as well as gorillas. The earliest human fossils show that our ancestors were bipeds, walking on two legs. Genetic and biological similarities suggest that we are closely related to the chimpanzees. In fact, we are most closely with chimpanzees in the Pan Genus that includes pygmy and bonobos and pygmy chimpanzees. The last common ancestor shared between modern humans and chimpanzees dated 8 to 6 million years old.
Over time humans have developed a range of characteristics, including bipedalism and the use of fire. They also developed advanced tools. It's only within the last 100,000 years that we've developed the majority of our important characteristics. These include a large brain that is sophisticated, the ability of humans to construct and use tools, as well as the diversity of our culture.
The process of evolution occurs when genetic changes allow members of a group to better adapt to their environment. This adaptation is driven by natural selection, a process whereby certain traits are favored over others. Those with the better adaptations are more likely to pass on their genes to the next generation. This is the way that all species evolve and is the foundation of the theory of evolution.
Scientists call it the "law of Natural Selection." The law states that species that have a common ancestor are likely to develop similar traits in the course of time. This is because these traits help them to live and reproduce in their environment.
Every living thing has the DNA molecule, which contains the information necessary to direct their growth. The DNA structure is composed of base pairs that are arranged in a spiral around sugar and phosphate molecules. The sequence of bases found in each string determines the phenotype or the appearance and behavior of an individual. 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 found in Africa, Asia and Europe. While there are some differences between them they all support the hypothesis that modern humans first came into existence in Africa. The genetic and fossil evidence suggests that early humans left Africa and moved to Asia and Europe.