The Berkeley Evolution Site
Teachers and students who browse the Berkeley site will find a wealth of resources to assist them in understanding and teaching evolution. The resources are organized into a variety of learning paths such as "What did T. rex taste like?"
Charles Darwin's theory on natural selection describes how species who are better able to adapt biologically to changing environment survive over time and those who do not end up becoming extinct. This process of evolution in biology is the main focus of science.
What is Evolution?
The term "evolution" has a variety of nonscientific meanings. For instance "progress" or "descent with modification." Scientifically, it refers to a changing the characteristics of organisms (or species) over time. In page of biology, this change is based on natural selection and genetic drift.
Evolution is a key principle in the field of biology today. It is a concept that has been proven by a myriad of scientific tests. It does not address the existence of God or religious 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 step-like manner, over time. This was known 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 through fossils and other evidence. This is the current perspective on evolution, and is supported by a variety of areas of science which include molecular biology.
Although scientists aren't able to determine 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 desirable traits are more likely to survive and reproduce, and they transmit their genes to the next generation. Over time, this results in a gradual accumulation of changes in the gene pool that gradually lead to new species and forms.
Some scientists also employ the term evolution to refer to large-scale evolutionary changes, such as the formation of an entirely new species from an ancestral species. Certain scientists, including population geneticists, define evolution in a broader sense by using the term "net change" to refer to the variation in the frequency of alleles over generations. Both definitions are valid and reliable however some scientists believe that the allele-frequency definition is missing crucial aspects of the evolutionary process.
Origins of Life
The development of life is a crucial step in the process of evolution. The emergence of life occurs when living systems start to develop at a microscopic level, like within cells.
The origins of life are an issue in a variety of disciplines that include biology, chemistry, and geology. The origin of life is a subject of great interest in science, as 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 objects is known as spontaneous generation or "spontaneous evolution." This was a popular belief prior to Louis Pasteur's experiments showed that it was impossible for the emergence of life to be a result of a purely natural process.
Many scientists believe it is possible to move from nonliving substances to living ones. However, the conditions required are extremely difficult to replicate in labs. Researchers who are 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.
Furthermore, the growth of life is dependent on a sequence of very complex chemical reactions that cannot be predicted from basic physical laws on their own. These include the reading and replication of complex molecules, such as DNA or RNA, to produce proteins that serve a specific function. These chemical reactions are comparable to a chicken-and egg problem that is the emergence and growth of DNA/RNA, protein-based cell machinery, is necessary for the beginning of life. However without life, the chemistry that is required to enable it appears to be working.
Abiogenesis research requires collaboration with researchers from different fields. This includes prebiotic chemists, astrobiologists, planetary scientists geophysicists and geologists.
Evolutionary Changes
Today, the word evolution is used to describe the general changes in genetic traits over time. These changes can be the result of the adaptation to environmental pressures as described in Darwinism.
This mechanism also increases the number of genes that offer a survival advantage in the species, leading to an overall change in the appearance of an entire group. The specific mechanisms responsible for these evolutionary changes are mutation or reshuffling genes during 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. This occurs because, as we've mentioned earlier those with the beneficial trait tend to have a higher reproduction rate than those who do not have it. This variation in the number of offspring produced over a long period of time can result in a gradual change in the number of advantageous characteristics in a group.
A good example of this is the growing the size of the beaks on different species of finches found on the Galapagos Islands, which have evolved different shaped beaks that allow them to easily access food in their new environment. These changes in form and shape can also help create new organisms.
The majority of changes are caused by one mutation, but sometimes several occur at once. Most of these changes may be harmful or neutral however, a small percentage may have a positive effect on the survival of the species and reproduce and increase their frequency over time. This is the way of natural selection and it can eventually result in the accumulating changes that eventually result in a new species.
Some people confuse the notion of evolution with the idea that traits inherited can be altered by conscious choice or by use and abuse, which is called soft inheritance. This is a misunderstanding of the nature of evolution and of the actual biological processes that trigger it. It is more precise to say that evolution is a two-step independent process, which involves the forces of natural selection as well as mutation.
Origins of Humans
Humans of today (Homo Sapiens) evolved from primates, a species of mammal species that includes chimpanzees as well as gorillas. Our ancestors walked on two legs, as demonstrated by the oldest fossils. Genetic and biological similarities suggest that we are closely related to chimpanzees. In actual fact we are the closest with chimpanzees in the Pan genus that includes pygmy and pygmy chimpanzees and bonobos. The last common ancestor of modern humans and chimpanzees lived between 8 and 6 million years ago.
Humans have developed a range of characteristics over time including bipedalism, the use of fire and advanced tools. But it's only in the last 100,000 years or so that most of the essential traits that distinguish us from other species have emerged. These include a big brain that is sophisticated, the ability of humans to create and use tools, as well as cultural diversity.
Evolution occurs when genetic changes allow members of a population to better adapt to their environment. This adaptation is triggered by natural selection, which is a process by which certain traits are more desirable than other traits. The ones with the best adaptations are more likely to pass on their genes to the next generation. This is how all species evolve, and it is the foundation of the theory of evolution.
Scientists call this the "law of natural selection." The law states that species which have a common ancestor are likely to develop similar characteristics over time. This is because the traits allow them to live and reproduce in their environment.
Every living thing has an molecule called DNA that holds the information needed to guide their growth. The DNA molecule consists of base pairs that are arranged in a spiral around sugar molecules and phosphate molecules. The sequence of bases within each strand determines phenotype, or the individual's characteristic appearance and behavior. Different changes and reshuffling of genetic material (known as alleles) during sexual reproduction cause variations in a population.
Fossils of the first human species, Homo erectus and Homo neanderthalensis were discovered in Africa, Asia, and Europe. Despite some differences, these fossils all support the hypothesis that modern humans first came into existence in Africa. Genetic and fossil evidence also suggest that early humans moved out of Africa into Asia and then Europe.