The Berkeley Evolution Site

Teachers and students who browse the Berkeley site will find resources to help them understand and teach evolution. The materials are organized into a variety of learning paths like "What did T. rex taste like?"

Charles Darwin's theory of natural selection states that over time, animals that are better able to adapt biologically to changing environments survive and those that are not extinct. Science is concerned with this process of evolutionary change.

What is Evolution?

The word evolution has many nonscientific meanings. For instance "progress" or "descent with modification." Scientifically, it refers to a process of changes in the traits of organisms (or species) over time. In terms of biology, this change is caused by natural selection and genetic drift.

Evolution is a key tenet in the field of biology today. It is an established theory that has stood the test of time and a multitude of scientific tests. Evolution doesn't 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 like Erasmus Darwin (Charles’s grandfather) and Jean-Baptiste Lamarck believed that certain physical characteristics were predetermined to change in a gradual 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 different species of organisms have a common ancestry, which can be traced through fossils and other evidence. This is the current understanding of evolution that is supported by a variety of lines of research in science which includes molecular genetics.

Although scientists aren't able to determine the exact mechanism by which organisms evolved but they are certain that the evolution of life on earth is the result of natural selection and genetic drift. People with desirable traits are more likely to live and reproduce. These individuals pass on their genes to the next generation. As time passes the gene pool gradually changes and evolves into new species.

Certain scientists also use the term evolution to refer to large-scale evolutionary changes such as the creation of an entirely new species from an ancestral species. Some scientists, like population geneticists, define the term "evolution" in a more broad sense by referring to the net change in the frequency of alleles across generations. Both definitions are valid and reliable however, some scientists claim that the definition of allele frequency is lacking essential aspects of the evolution process.

Origins of Life

The birth of life is a crucial stage in evolution. This happens when living systems begin to evolve at a micro-level - within cells, for example.

The origins of life are an issue in a variety of disciplines such as biology, chemistry and geology. The question of how living things started is a major topic in science because it is an important challenge to the theory of evolution. It is sometimes referred to "the mystery" of life or "abiogenesis."

The notion that life could be born from non-living objects was referred to as "spontaneous generation" or "spontaneous evolutionary". It was a common belief prior to Louis Pasteur's tests showed that the creation of living organisms was not possible by the natural process.

Many scientists still believe it is possible to make the transition from nonliving substances to life. However, the conditions needed are extremely difficult to reproduce in labs. Researchers interested in the origins and evolution of life are also eager to know the physical properties of the early Earth as well as other planets.

The growth of life is also dependent on a series of complex chemical reactions that are not predicted by simple physical laws. These include the reading and the replication of complex molecules, such as DNA or RNA, to create proteins that serve a specific function. These chemical reactions are often compared to the chicken-and-egg problem of how life came into existence with the appearance of DNA/RNA and protein-based cell machinery is essential for the onset of life, but without the emergence of life the chemical reaction that is the basis for it is not working.

Research in the field of abiogenesis requires collaboration between scientists from various fields. This includes prebiotic chemists, the astrobiologists, the planet scientists, geologists and geophysicists.

Evolutionary Changes

The term "evolution" is typically used today to describe the accumulated changes in genetic characteristics of populations over time. These changes could be the result of the adaptation to environmental pressures as explained in Darwinism.

This is a method that increases the frequency of genes which confer an advantage in survival over other s and causes a gradual change in the appearance of a population. These changes in evolutionary patterns are caused by mutations, reshuffling genes in the process of sexual reproduction, and also by the flow of genes.

Natural selection is the process that makes beneficial mutations more common. All organisms undergo mutations and reshuffles of genes. As mentioned above, those with the beneficial characteristic have a higher reproduction rate than those who don't. Over the course of many generations, this differential in the numbers of offspring born could result in a gradual shift in the average amount of desirable characteristics in a particular population.

An excellent example is the growing the size of the beaks on different 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 form and shape can also help create new organisms.

The majority of the changes that occur are the result of one mutation, but occasionally, multiple mutations occur at the same time. Most of these changes can be neutral or even harmful, but a small number could have a positive impact on survival and reproduction with increasing frequency as time passes. This is the way of natural selection and it can, over time, produce the accumulating changes that ultimately lead to an entirely new species.

Many people confuse evolution with the idea of soft inheritance that is the belief that inherited traits can be changed through deliberate choice or misuse. This is a misunderstood understanding of the nature of evolution, and of the actual biological processes that cause it. It is more accurate to say that the process of evolution is a two-step independent process, that is influenced by the 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, walkers with two legs. Genetic and biological similarities suggest that we share a close relationship with chimpanzees. In actual fact we are the most closely connected to chimpanzees belonging to the Pan Genus which includes bonobos and pygmy-chimpanzees. The last common ancestor between modern humans and chimpanzees dated between 8 and 6 million years old.

Humans have developed a range of traits over time, including bipedalism, the use of fire, and the development of advanced tools. It is only within the last 100,000 years that we have developed the majority of our essential characteristics. These include a big, complex brain and the capacity of humans to construct and use tools, and cultural diversity.

Evolution happens when genetic changes allow individuals in a group to better adapt to their surroundings. This adaptation is driven by natural selection, a process whereby certain traits are preferred over other traits. The more adapted are more likely to pass on their genes to the next generation. This is how all species evolve, and the basis of the theory of evolution.

Scientists call this the "law of natural selection." The law says that species that have a common ancestor, tend to develop similar traits over time. This is because those traits allow them to live and reproduce in their environment.


All organisms have DNA molecules, which is the source of information that helps guide their growth and development. The DNA structure is made of base pairs which are arranged in a spiral, around sugar and phosphate molecules. The sequence of bases in each strand determines the phenotype, the characteristic appearance and behavior of a person. Variations in mutations and reshuffling of the genetic material (known as alleles) during sexual reproduction cause variations in a population.

Fossils of the earliest human species, Homo erectus and Homo neanderthalensis were discovered in Africa, Asia, and Europe. Although there are some differences they all support the hypothesis that modern humans first came into existence in Africa. The fossil and genetic evidence suggests that the first humans left Africa and moved to Asia and Europe.