Thursday, January 26, 2012

Homologous Structures and their Evolution

So for my first post, I originally wanted to post about the earliest signs of appendages and found that that post may be a bit long. (Appendages exist at the cellular level and even though I love cellular biology I didn't feel like reading papers today. ha) So I decided to do it another time.

I remembered that in class we looked at the figure of the different forelimb structures in mammals, and saw that they were homologous. Now for those of you reading this blog that are not from my class, homologous is defined by Mariam-Webster Dictionary as "having the same relative structure." A link to the dictionary entry can be found at the bottom of this post.

So from this we can derive that the homologous limbs in mammals are those that have similar bone structure.

So the question I had was how did these changes in function occur? We know that all mammals had a common ancestor? But what did that ancestor look like. The Canadian MUSEUM of nature states that "one of the earliest mammals was the shrew like animal shrew-like Morganucodon." The have a really cool video that shows the diversification of limbs over the centuries as mammals evolved, but also hows they maintained the same general structure. The video takes the mammal phylogeny and follows the the tree from the Morganucodon to modern day humans, bats, and whale, and shows some of the forms limbs took along the journey of evolution.

The interactive video can be found at:


  1. To answer one of your questions:

    The easiest and the simplest assumption as to why these "changes in function" occurred is perhaps the environment itself: whales develop fins because they need to swim; bats develop wings to avoid ground-level predators. Of course, there is more to this, but perhaps by studying the "intermediate missing links" that show the midpoint of these limbic developments, we can learn more about what environmental pressure they were put in.

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