Common Descent

By Anthony | April 7th, 2006 | 12:33 am

A recent post at Dispatches from the Culture Wars contained a nice, concise outline of one of the lines of evidence for common descent – the idea that a few common ancestors, through descent with modification, gave rise to the wide variety of life that we see today. This line of evidence is the fossil record:

The theory of common descent not only helps us understand the fossil record, it’s the only explanation that makes any sense out of it at all.

The broad patterns of appearance that we see in the fossil record are clear. For the first 3+ billion years of life on earth, there was nothing but bacteria. Then simple multicellular life begins to appear and it steadily diversifies into a variety of forms of marine invertebrates. Then the first hemichordates and chordates appear, then the first true vertebrate fishes. Fish continue to diversify over a long period of time until the first amphibians begin to appear. Then later, reptiles. Finally, mammals and birds.

And within each of these types of animals, there is a similar pattern. The first amphibians to appear look the most fish-like and over time they diversify into many distinct types of amphibians, progressively less fish-like and more like extent species as they adapt to new environments. The first mammals to appear are the most reptile-like and they gradually diversify and become less reptile-like and more like extent species over time. The first birds to appear are the most dinosaur-like and over time they become less reptilian and more like extent species.

The only explanation that makes coherent sense of those patterns is common descent.

For more information, TalkOrigins has a more detailed look at common descent.

3 Responses to “Common Descent”

  1. Fecund Stench Says:

    Anecdotally, I find evidence of the truth of the notion in that I continue to strive mightily to “become less reptile-like.”

  2. PotatoStew Says:

    A worthy pursuit, to be sure.

  3. BrendaBowers Says:

    Fec Darlin’ I NEVER EVER thought you were a toad! Well, maybe you do have a few tiny warts that show up now and then (like JR’s blog).