Science Is a Process (2 of 4)


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In the marketplace of ideas, the simplest explanation has the advantage. This principle is referred to as parsimony.

Consider these observations:

  • A close look at snails, nautiloids, squids, octopuses and cuttlefish reveals the basic similarity of the body form of each (see below).

    Basic body form comparison

  • The shell of a nautilus and its extinct relatives, the ammonites, is very similar to the shell of a snail.
  • The tentacles of an octopus, when carefully examined, can be seen to be a modified snail's foot.

    octopus Common ancestry is the parsimonious explanation for the similarities between this octopus and its kin.

  • The stomachs of all members of this group have the same arrangement of parts.

One possible explanation is that these animals have independently acquired equivalent organs through a remarkable series of coincidences, but the most likely explanation is that these animals inherited similar organs through common ancestry. That is parsimony.

  • Octopus image courtesy of Gustav Pauley.

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Spanish translation of Understanding Evolution For Teachers from the Spanish Society of Evolutionary Biology.