Tag Archives: Natural Selection

Pagel on Darwin

ResearchBlogging.orgMark Pagel, evolutionary theorist extraordinaire, has published an Insight piece in Nature on Natural selection 150 years on. Pagel, well known for myriad projects in natural selecition theory and adaptation, and for developing with Harvey the widely used statistical phylogenetic method (and for being a reader of my thesis) wishes Charles Darwin a happy 200th birthday, and assesses this question:

How has Darwin’s theory of Natural Selection fared over the last 150 years, and what needs to be done to bring this theoretical approach to bear as we increasingly examine complex systems, including human society?
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Elephants and Horses

In 1833, Darwin spent a fair amount of time on the East Coast of South America, including in the Pampas, where he had access to abundant fossil material. Here I’d like to examine his writings about some of the megafauna, including Toxodon, Mastodon, and horses, and his further considerations of biogeography and evolution.

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Rheas and the Birth of Evolutionary Theory

Everyone knows about Darwin’s Finches, of the Galapagos Islands. But of course, Darwin made observations of birds throughout his travels on The Beagle. Here, I present a number of passages from The Voyage that include some of these observations.

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Fossil Quadrupeds

Charles Darwin wrote a book called Geological Observations on South America. Since Fitzroy needed to carry out intensive and extensive coastal mapping in South America, and Darwin was, at heart, a geologist more than anything else (at least during the Beagle’s voyage), this meant that Darwin would become the world’s expert on South American geology. Much of The Voyage is about his expeditions and observations. Part of this, of course, was figuring out the paleontology of the region.
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The Modes of Natural Selection

There many ways of dividing up and categorizing Natural Selection. For example, there are the Natural Selection, Sexual Selection and Artificial Selection, and then there is the Modes of Selection (Stabilizing, Directional, and Disruptive) trichotomy.

We sense that these are good because they are “threes” and “three” is a magic number. Here, I’m focusing on the Mode Trichotomy, and asking that we consider that there are not three, but four modes of Natural Selection. This will cause tremors throughout the Evolutionary Theory community because Four is not a magic number, but so be it.

In Stabilizing Selection the extremes of a trait are selected against and the mean value of the trait remains the same. Mutations constantly introduced into the population tht produce traits out at the extremes are selected against. In Directional Selection the values of a trait at one end of the distribution are selected against and/or values at the other end are selected for, so that the distribution of values, and it’s mean, move in one direction. In Disruptive Selection the average values are selected against so that the distribution of the trait becomes bimodal.

That was pretty simple, but Continue reading The Modes of Natural Selection

The Three Necessary and Sufficient Conditions of Natural Selection

Natural Selection is the key creative force in evolution. Natural selection, together with specific histories of populations (species) and adaptations, is responsible for the design of organisms. Most people have some idea of what Natural Selection is. However, it is easy to make conceptual errors when thinking about this important force of nature. One way to improve how we think about a concept like this is to carefully exam its formal definition.

In this post, we will do the following:

  • Discuss historical and contextual aspects of the term “Natural Selection” in order to make clear exactly what it might mean (and not mean).
  • Provide what I feel is the best exact set of terms to use for these “three conditions,” because the words one uses are very important (there are probably some wrong ways to do it one would like to avoid).
  • Discuss why the terms should be put in a certain order (for pedagogical reasons, mainly) and how they relate and don’t related to each other.

When you are done reading this post you should be able to:

  • Make erudite and opaque comments to creationists that will get you points with your web friends.
  • Write really tricky Multiple Choice Exam Questions if you are a teacher.
  • Evolve more efficiently towards your ultimate goal because you will be more in control of the Random Evolutionary Process (only kidding on this third one…)

Continue reading The Three Necessary and Sufficient Conditions of Natural Selection