A Journey Into the 3.5 billion-year History of the Human Body
by Neil Shubin
For excellent summary discussion
of Tiktaalik, with updates,
Updates (2009 and 2010) to the original posting (May 2006):
Classroom discussion question, to which you could add:
by Larry Flammer
# You may already know that the genes for making our limbs
are nearly identical to those for making fish fins.
These many practical questions about how our ancestral past connects to our modern human condition make it so obvious how useful a knowledge of evolution can be. Paleontologist and anatomist Neil Shubin brings a fascinating account of how we came to be the way we are, tying together and making sense out of many seemingly unrelated observations.
Early in this little book, Shubin describes how he applied his fascination with fossils to predict a likely region in Northern Canada, in rocks of a particular age, where he would most likely find fossil evidence of a transition between fishes and land vertebrates, from the fins of fish to the limbs of tetrapods. In 2006, he announced his discovery of a fish fossil with a pair of fins in the rear, and typical leg bones in its forelimbs - Tiktaalik - a fish with wrists! It fills a short but important evolutionary gap for a time when that transition must have happened, from all the fossil evidence previously found. This was an example of a "Fair Test" - where results could have weakened the previous understanding that such a transition must have happened, but they didn't, so the understanding becomes even stronger. Be sure to check the discussion (with updates and teaching ideas) of Tiktaalik at the Understanding Evolution site (outlined at top of this page).
Weaving his experience with anatomy and fossils, he adds the growing wealth of knowledge about evo-devo, how genes control the development of limbs and other structures. In the process, Shubin sprinkles brief accounts of how scientists gradually discovered the process and began to explain its mechanism. In like manner, he extends our understanding of genetic tools that control the development of tissues and organs, taking what seems to be a very complex process, and showing how the modifications and timing for just a few basic types of tissue can produce the great diversity that we find.
In the process, Shubin reveals how body plans unfold, how organs of vision, hearing and other senses can be traced to their places and functions in other animals. Again and again, he points to the clear evidence where current anatomical structures can be seen as old structures (found in other creatures) that have been "repurposed," clear examples of "descent with modification."
Great summer reading for all biology teachers. Be prepared
to take a few notes. I know you will want to include a number
of Shubin's illuminating examples throughout your course, as
well as in your unit on evolution. If you develop any clever
interactive activities built around those examples, please share
with us at ENSIweb. At the very least, be sure to encourage your
students to read the book. Many eyes will be opened.