Mechanisms of Evolution

How Does Variety Give Rise To New Species?

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Mechanisms of Evolution (Part 2): How does variety arise in the genomes of individuals and a group? How does variety give rise to new species?

Speciation is the evolutionary process by which new biological species arise. In order for continuing evolution there must be mechanisms to increase or create genetic variation and mechanisms to decrease it. The mechanisms of evolution are mutation, natural selection, genetic drift, recombination and gene flow.

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1. Does The Evidence Support Evolution?
2. Vitamin C And Common Ancestry
3. Are We Descended From Viruses?
4. Does The Fossil Record Support Evolution?
5. Where Are The Transitional Forms?


1. Introduction
2. Universal Common Descent
3. Good Design, Bad Design
4. Speciation And Extinction
5. How Fast Is Evolution?
6. What Can Embryos Tell Us About Evolution?
7. The Molecules Of Life
8. Molecular Evolution: Genes And Proteins
9. Retroviruses And Pseudogenes


The Importance of Evolution in Biology

"Nothing in biology makes sense except in the light of evolution." -- Theodosius Dobzhansky

Evolution has been called the cornerstone of biology, and for good reasons. It is possible to do research in biology with little or no knowledge of evolution. Most biologists do. But, without evolution biology becomes a disparate set of fields. Evolutionary explanations pervade all fields in biology and brings them together under one theoretical umbrella.

We know from microevolutionary theory that natural selection should optimize the existing genetic variation in a population to maximize reproductive success. This provides a framework for interpreting a variety of biological traits and their relative importance. For example, a signal intended to attract a mate could be intercepted by predators. Natural selection has caused a trade- off between attracting mates and getting preyed upon. If you assume something other than reproductive success is optimized, many things in biology would make little sense. Without the theory of evolution, life history strategies would be poorly understood.

Macroevolutionary theory also helps explain many things about how living things work. Organisms are modified over time by cumulative natural selection. The numerous examples of jury- rigged design in nature are a direct result of this. The distribution of genetically based traits across groups is explained by splitting of lineages and the continued production of new traits by mutation. The traits are restricted to the lineages they arise in.

Details of the past also hold explanatory power in biology. Plants obtain their carbon by joining carbon dioxide gas to an organic molecule within their cells. This is called carbon fixation. The enzyme that fixes carbon is RuBP carboxlyase. Plants using C3 photosynthesis lose 1/3 to 1/2 of the carbon dioxide they originally fix. RuBP carboxlyase works well in the absence of oxygen, but poorly in its presence. This is because photosynthesis evolved when there was little gaseous oxygen present. Later, when oxygen became more abundant, the efficiency of photosynthesis decreased. Photosynthetic organisms compensated by making more of the enzyme. RuBP carboxylase is the most abundant protein on the planet partially because it is one of the least efficient.

Ecosystems, species, organisms and their genes all have long histories. A complete explanation of any biological trait must have two components. First, a proximal explanation -- how does it work? And second, an ultimate explanation -- what was it modified from? For centuries humans have asked, "Why are we here?" The answer to that question lies outside the realm of science. Biologists, however, can provide an elegant answer to the question, "How did we get here?"