What is evolutionary theory

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Evolution of modern humans. Evolution of the human brain. Are humans still evolving? What is genetic variation? Fruit flies in the laboratory. What is inheritance? What is selective breeding?

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Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. In the mids, Charles Darwin famously described variation in the anatomy of finches from the Galapagos Islands. Alfred Russel Wallace noted the similarities and differences between nearby species and those separated by natural boundaries in the Amazon and Indonesia.

Independently they came to the same conclusion: over generations, natural selection of inherited traits could give rise to new species. Use the resources below to teach the theory of evolution in your classroom. When most of us think about natural selection, we attribute that theory to naturalist Charles Darwin. However, what most people do not know is that another scientist, Alfred Wallace, a naturalist, a geographer, and a socialist, also deserves some credit for the theory.

The main difference between the Lamarckian and Darwinian ideas of giraffe evolution is that there's nothing in theDarwinian explanation about giraffes stretching their necks and passing on an acquired characteristic. Darwin didn't know anything about genetics, Pobiner said. That came later, with the discovery of how genes encode different biological or behavioral traits, and how genes are passed down from parents to offspring. The incorporation of genetics into Darwin's theory is known as "modern evolutionary synthesis.

The physical and behavioral changes that make natural selection possible happen at the level of DNA and genes within the gametes, the sperm or egg cells through which parents pass on genetic material to their offspring.

Such changes are called mutations. Mutations can be caused by random errors in DNA replication or repair, or by chemical or radiation damage. Usually, mutations are either harmful or neutral, but in rare instances, a mutation might prove beneficial to the organism. If so, it will become more prevalent in the next generation and spread throughout the population.

In this way, natural selection guides the evolutionary process, preserving and adding up the beneficial mutations and rejecting the bad ones. But natural selection isn't the only mechanism by which organisms evolve, she said.

For example, genes can be transferred from one population to another when organisms migrate or immigrate — a process known as gene flow. And the frequency of certain genes can also change at random, which is called genetic drift. The reason Lamarck's theory of evolution is generally wrong is that acquired characteristics don't affect the DNA of sperm and eggs.

A giraffe's gametes, for example, aren't affected by whether it stretches its neck; they simply reflect the genes the giraffe inherited from its parents.

But as Quanta reported , some aspects of evolution are Lamarckian. For example, a Swedish study published in in the European Journal of Human Genetics found that the grandchildren of men who starved as children during a famine passed on better cardiovascular health to their grandchildren.

Researchers hypothesize that although experiences such as food deprivation don't change the DNA sequences in the gametes, they may result in external modifications to DNA that turn genes "on" or "off.

For instance, a chemical modification called methylation can affect which genes are turned on or off. Such epigenetic changes can be passed down to offspring. In this way, a person's experiences could affect the DNA he or she passes down, analogous to the way Lamarck thought a giraffe craning its neck would affect the neck length of its offspring. Even though scientists could predict what early whales should look like, they lacked the fossil evidence to back up their claim.

Creationists viewed this absence, not just with regard to whale evolution but more generally, as proof that evolution didn't occur, as pointed out in a Scientific American article. But since the early s, scientists have found evidence from paleontology, developmental biology and genetics to support the idea that whales evolved from land mammals.