Season 4 Episode 2: Absolutely useless faculty

 

In this episode we discuss Chapter 1 of Descent of Man and are joined by a special guest - Evolutionary developmental (EvoDevo) biologist Dr. Belinda Sly. Darwin spends the chapter documenting how human bodies show the scars from evolution past. Darwin takes two approaches in convincing the reader that humans are modified from "lower forms". In one approach he discusses how humans share ailments, diseases, and parasites with other animals. The argument of homology. The second argument Darwin uses is cataloging the various rudimentary, vestigial, and nascent structures humans have and how they are present and useful in other animals.

Sarah highlighted the homology argument that Darwin used - the fact that humans share diseases and parasites with other animals, showing the similarity of our bodies with other animals - by discussing the diversity of human lice - head, body, and pubic lice. After explaining the differences between each, Sarah helped us understand how they are used to identify important points in our evolutionary past, when we became hairless and when we adopted clothes. 

The strongest homology argument that Darwin presented was the similarity in form of vertebrate embryos and how the new technology of the time - microscopes - was increasing that dataset.  Dr. Belinda Sly discussed the different scientists of the time that were documenting embryo development - Karl Ernst von Baer and Ernst Haeckel. There is great similarity in embryo forms for various vertebrate animals, although Haeckel seems to have exaggerated those similarities in his illustrations. Belinda discussed the power of the comparison of embryos, and how they do give the best evidence of evolution via descent with modification but fall short of the old adage "ontogeny recapitulates phylogeny".

The second line of argument Darwin discussed was the various rudimentary or vestigial structures we have that are of "absolutely useless faculty".  In particular he spent some time highlighting our restricted ability to use our panniculus carnosus muscles to move our skin as illustrated in this GIF of a horse twitching its skin to dislodge flies. In humans the ability is mostly restricted to our ability to move our eyebrows, but Darwin discussed some families ability to move their scalp and Sarah shared her "lamest super power ever" ability to slightly move her ears. 

The opening and closing theme to Discovering Darwin is "May" by Jared C. Balogh.

1st interlude music is Head Lice song https://www.youtube.com/watch?v=7us3ucQmrIE

2nd interlude music is Black Bear Combo - Black Bear Kolo http://blackbearcombo.com/