Seminar One
Biology, culture and psychology
What is evolution?

A Giant Red Hermit Crab at the Texas State Aquarium in Corpus Christi, Texas
Stalked eyes of a Giant Red Hermit Crab from the Gulf of Mexico, captive at the Texas State Aquarium in Corpus Christi, Texas.
Photography by Greg and Mary Beth Dimijian

Evolution is the change over time of living organisms from one kind, or species, into others. An earlier organism evolves, or changes over time, into one or more different ones. Evolution means that there has been a progression of different organisms that you can trace back on a “tree” to earlier ancestral ones. The time frame may be very long (hundreds of millions of years, as from dinosaurs to birds) or very short (only days, as with variants of the human immunodeficiency virus in the body of one person.)

You can trace ancestry using anatomy (form) as a guide, as with fossils, or using genes. The latest methods draw gene trees which show uncanny resemblances of recently evolved genes to very old ones. We used to think that species trees were stunning to behold; now we have gene trees too, and the view of the forest is jaw-dropping. All the trees ultimately unite in a common trunk which is believed to be the original primeval soup of freely-exchanged genes of the earliest microorganisms on Earth.

Bryce Canyon National Park in Utah
The beautiful séracs (jagged spires) of eroded mountains in Bryce Canyon National Park, Utah, speak to us of the long expanses of geological time which Darwin knew about when he crafted his theory of natural selection. Evolution occurring over millions, even hundreds of millions, of years is called “macroevolution,” in contrast to “microevolution,” which takes place over much shorter time periods—even as short as days or weeks, in the case of the “cloud” of HIV variants developing in a person with AIDS.
Photography by Greg and Mary Beth Dimijian

DNA is the carrier of the digital code, the genetic code, which guides the development of a body and its behavior from conception to old age. The words of the code, called codons, have only three letters each and are virtually identical from viruses to mammals, betraying the evolution of all life forms, one from the other, over the entire history of the planet.

It is a stunning fact that a gene taken from a mammal can be read by bacteria, and that the same protein is produced from the gene in either organism. This means that the living computer in a primitive organism can read the code in a modern organism's genes; our silicon computers, in contrast, are doing well if they can keep up with software that is ten years old!

A Polkadot Tree Frog
Polkadot Tree Frogs (Hyla punctata) are found throughout the Amazon Rain Forest of South America.
Photography by Greg and Mary Beth Dimijian
A Spider monkey from Costa Rica
The Spider monkey, found in lowland rain forests from Mexico to South America, has a prehensile tail that is muscular and tactile and is used as an extra hand. The tail is sometimes longer than the body. Both the underside and tip of the tail are used for climbing and grasping and so the spider monkey uses it like a fifth hand. When swinging by the tail, the hands are free to gather food.
Photography by Greg and Mary Beth Dimijian
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