At the center of the Epic of Evolution is biological evolution. Biological evolution is defined as the change in DNA sequences in a population over time.
Evolution is a fact. Vast and growing quantities of evidence from the fossil record, from comparative anatomy, from embryology, and from DNA sequencing shows beyond any doubt that evolution is a fact.
So how does biological evolution work? How did humans emerge from single celled microbes? Understanding how evolution works is called a theory. As an analogy, we all know that gravity is a fact. But how gravity works is a theory.
In his 1859 book, On the Origin of Species, Darwin gave an overview of how descent with modification (what we now call biological evolution) worked. Since Darwin’s time, people have fleshed out many of the missing details for how evolution works.
Today, we know that descent with modification requires 4 ingredients: Variation, Acquisition of genes, Selection, and Time. This is summarized by the acronym VAST.
Variation – Evolution requires that DNA sequences change over time. Because he didn’t know about DNA, Darwin didn’t know how changes in DNA came about. Thanks to rapid breakthrouhgs in DNA technology, today, we know about many ways that DNA changes over time.
- Random Point Mutations – The first observed kind of variation in DNA was found to be due to errors and damage due to radiation or chemicals.
- Mobile DNA – Variation can result from DNA mobilization via a host of mechanisms: Horizontal gene transfer; sex,; recombination; transposons; viruses; retroviruses; integrons; and/or chromosome rearrangements.
- Symbiosis – An important kind of variation occurs when two organisms merge their genomes in an endosymbiotic event. Although rare, this type of variation led to the emergence of eukaryotes which made possible the evolution of plants and animals including eventually us humans.
Acquisition – Darwin thought that genetic material was only transmitted from parent to child via inheritance. More recently, scientists have discovered that DNA can also be transferred horizontally, from one species to another. Horizontal gene transfer has major implications for evolution. While these horizontal transfer events are rare, they contribute to the creation of radically new capabilities.
Selection – Darwin observed artificial selection to help him devise the idea of Natural Selection. While Natural Selection is still an important aspect of biological evolution, we now know that not all evolution happens via natural selection. Sometimes, random genetic drift acts to change the genes in a population. Today, many scientists refer to selection as “Differential Reproductive Success.”
Selection operates as a purifying but not a creative force ~ James Shapiro, author, Evolution in the 21st Century
Time – Evolution requires vast amounts of time.
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