The Berkeley Evolution Site
Students and teachers who explore the Berkeley site will find resources to assist them in understanding and teaching evolution. The materials are arranged in various learning paths that can be used in a variety of ways like "What does T. rex look like?"
Charles Darwin's theory of natural selection explains how animals who are better able to adapt to changes in their environments survive longer and those that do not become extinct. This process of biological evolution is the main focus of science.
What is Evolution?
The word evolution has many nonscientific meanings, including "progress" or "descent with modification." Scientifically, it refers to a process of changing the characteristics of living things (or species) over time. The reason for this change is biological terms on natural selection and drift.
Evolution is the central tenet of modern biology. It is an established theory that has stood the test of time and a multitude of scientific experiments. In contrast to other theories in science, such as the Copernican theory or the germ theory of disease, evolution does not address issues of religious belief or God's existence.
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, as time passes. They referred to this as the "Ladder of Nature" or the 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 states that all species of organisms have common ancestors that can be traced through fossils and other evidence. This is the current view of evolution, which is supported by many research lines in science which includes molecular genetics.
While scientists don't know exactly how organisms developed however they are sure that the evolution of life on earth is a result of natural selection and genetic drift. Individuals with advantageous traits are more likely to live and reproduce, and these individuals transmit their genes to the next generation. As time passes, this results in gradual changes to the gene pool that gradually create new species and forms.
Some scientists also employ the term evolution to refer to large-scale evolutionary changes such as the creation of an entirely new species from an ancestral species. Other scientists, such as population geneticists, define evolution more broadly by referring to the net change in allele frequencies over generations. Both definitions are acceptable and accurate however some scientists believe that the allele-frequency definition omits important features of the evolutionary process.
Origins of Life
A key step in evolution is the appearance of life. The emergence of life happens when living systems start to develop at a microscopic level, like within cells.
The origin of life is an important subject in many fields such as biology and chemical. The question of how living things started has a special place in science since it poses an important challenge to the theory of evolution. It is often described as "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 common belief before Louis Pasteur's experiments proved that it was impossible for the creation of life to occur by a purely natural process.
Many scientists believe that it is possible to make the transition from nonliving materials to living. The conditions needed to make life are not easy to replicate in a laboratory. Researchers who are interested in the origins and evolution of life are also eager to understand the physical properties of the early Earth as well as other planets.
Additionally, the evolution of life depends on an intricate sequence of chemical reactions that cannot be predicted based on basic physical laws on their own. These include the reading of long information-rich molecules (DNA or RNA) into proteins that carry out a function as well as the replication of these intricate molecules to generate new DNA or RNA sequences. These chemical reactions are often compared to the chicken-and-egg dilemma of how life began: The emergence of DNA/RNA and protein-based cell machinery is crucial to the birth of life, but without the development of life, the chemical process that allows it isn't working.
Abiogenesis research requires collaboration between researchers from different disciplines. This includes prebiotic scientists, astrobiologists, and planet scientists.
Evolutionary Changes
The word evolution is usually used to describe the accumulated changes in the genetic traits of an entire population over time. These changes can result from adaptation to environmental pressures as described in the entry on Darwinism (see the entry on Charles Darwin for background) or may result from natural selection.
This is a method that increases the frequency of those genes which confer an advantage in survival over others, resulting in an ongoing change in the overall appearance of a group. The specific mechanisms responsible for these evolutionary changes include mutation, reshuffling of genes during sexual reproduction, and gene flow between populations.
Natural selection is the process that makes beneficial mutations more common. All organisms undergo mutations and reshuffles in their genes. This occurs because, as noted above those who have the advantageous trait are likely to have a higher fertility rate than those without it. Over many generations, this difference in the number of offspring produced can result in a gradual shift in the average number of beneficial traits in a population.
This is evident in the evolution of various beak designs on finches that are found in the Galapagos Islands. They have developed these beaks so that they can eat more easily in their new environment. These changes in the shape and form of organisms can also help create new species.
The majority of changes are caused by a single mutation, although sometimes multiple occur at once. The majority of these changes are neutral or even harmful to the organism but a small percentage can have an advantageous impact on the survival of the organism and its reproduction, thereby increasing the frequency of these changes in the population over time. Natural selection is a process that causes the accumulating change over time that leads to a new species.
Some people confuse the notion of evolution with the idea that the traits inherited from parents can be altered through conscious choice or use and abuse, a concept called soft inheritance. This is a misunderstood understanding of the nature of evolution, and of the actual biological processes that cause it. A more accurate 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 mammal species that includes chimpanzees and gorillas. Our ancestors walked on two legs, as evidenced by the oldest fossils. Genetic and biological similarities suggest that we are closely related to the chimpanzees. In fact, we are most closely connected to chimpanzees belonging to the Pan Genus that includes pygmy and bonobos and pygmy-chimpanzees. The last common ancestor of humans and chimpanzees was 8 to 6 million years old.
Humans have evolved a wide range of traits throughout time such as bipedalism, use of fire and advanced tools. It's only within the last 100,000 years that we've developed the majority of our essential traits. They include a huge brain that is complex human ability to build and use tools, as well as cultural diversity.
Evolution happens when genetic changes allow individuals of a population to better adapt to their environment. Natural selection is the process that drives this adaptation. Certain traits are preferred over others. People with better adaptations are more likely to pass their genes to the next generation. This is the way that 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 says that species that share a common ancestor tend to develop similar traits over time. This is because these traits allow them to survive and reproduce in their environment.
Every organism has a DNA molecule that contains the information needed to guide their growth. The DNA structure is made of base pairs that are arranged in a spiral around sugar and phosphate molecules. The sequence of bases within each strand determines the phenotype, the characteristic appearance and behavior of a person. Different changes and reshuffling of genetic material (known as alleles) during sexual reproduction can cause variation in a population.
Fossils of 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 modern humans' origins in Africa. The genetic and fossil evidence suggests that early humans left Africa and moved to Asia and Europe.