Classifying buttons vs. life

 
Buttons can be classified in many ways

Buttons can be classified in many ways

If you want to teach someone about classification, a pile of assorted buttons is a good tool. It is always interesting to have two or more groups working on a button classification and see what criteria they use. Buttons make a fine model and come in enough variations to make classifying them interesting and even challenging. However, there is more to classifying life than classifying buttons. Life has another dimension.

 Buttons are here-and-now objects. Big buttons don’t have little buttons and they don’t pass on information to offspring. They have no history that we can observe and they share no ancestors. Buttons carry no information about their past. Classifying them is a good model for what Linnaeus did when he classified life. He felt, at least for most of his career, that all life had been created instantaneously and had always been and would always be just as he saw it.

Life has important differences from buttons. Darwin’s work was very important in calling attention to life’s history and to the idea of evolution, which he called descent with modification. We now have overwhelming evidence that life changes through time and all living species have a long history. Fossils tell a good deal of the story, but the “second fossil record,” the DNA in each organism, is what has allowed us discover much more of the story.

Each species had ancestors that stretch back in time. For the story of the many human ancestors, see The Ancestor’s Tale by Richard Dawkins. This inspiring book has its own Wikipedia entry, in which the ancestors it visits are listed. http://en.wikipedia.org/wiki/The_Ancestor’s_Tale Connie Barlow describes associated experiential activities for children at The Great Story website. http://thegreatstory.org/ancestors-tale.html

Two species may be descendents of a common ancestor that lived in the not-so-distant past. Biologists strive to place these sorts of close cousins in the same group, a lineage that includes the ancestor and its descendents. Other life may have shared an ancestor with our cousin species, but much further back in time, with many more lineages also sharing that far past ancestor. This may be shown on a Tree-of-Life diagram as a deeper branch from earlier in life’s history.

How can we model descent with modification? Once at a teacher’s workshop I used chocolate candy. We had plain miniature chocolate bars, bars with nuts, Hershey’s Kisses, and Hershey’s Hugs. We made a branching diagram that illustrated our hypothesis of the descent of these candies. The best part was eating the samples after we had finished with our phylogeny.

Maybe there is no suitable model for classifying life other than life itself. It certainly won’t be boring.

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