Season 1 Episode 12: Geographical Distribution: Chapter XII-XIII

In this episode we gather our liquid strength and courage to work our way through two chapters of Origin of Species, Chapter XII - Geographical Distribution and Chapter XIII - Geographical Distribution continued.  Although Sarah predicted the podcast would last 3 hours we luckily were able to restrain ourselves to 1 hour and 28 minutes.

We do have two corrections to make-
#1  Although Josh declared that Noah's Ark came to rest on the top of Mt. Sinai the general view is that it actually settled on Mt. Ararat.

#2 James mentioned the relationship between flightless birds (ratites) and the breakup of paleocontinent of Pangea when he should have said Gondwanaland instead.

Chapter XII-XII
These two chapters have been present in OoS since the first edition and it is in these chapters that Darwin defends his model against the prevailing view of the time - special creation. To make his argument Darwin uses modern distribution patterns of plants and animals on continents and islands, the success of introduced species to new habitats, experiments he conducted at Down House and data he collected from citizen scientists.

Geographical Distribution 

There is hardly a climate or condition in the Old World which cannot be paralleled in the New—at least as closely as the same species generally require....Notwithstanding this general parallelism in the conditions of the Old and New Worlds, how widely different are their living productions!

Sarah discussed the idea of the monkeys from Africa (Old World Monkeys) are quite different from the monkeys found in South America (New World). In Madagascar are found the prosimians "almost monkeys" like lemurs, aye-aye, and sifakas.

By Joseph Meyer - MKL online at Retro Bibliothek, work 149, 2009, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2598452

On the continent of Africa are a large diversity of primates that range from leaf-eating species like the colobus monkeys to the generalist species like the vervet monkeys and baboons.  In addition gorillas and chimps which are tail-less apes are also in Africa (we realize that these are not monkeys but they needed to be mentioned none-the-less).

www.discovery.com

The New World monkeys are quite different in form, long limbed with many species having a prehensile tail which they can use as a 5th limb.

http://www.wildernessclassroom.com/students/archives/2005/03/spider-monkey.html

Josh talked about the rich diversity of marsupial mammals found in Australia, the most striking is(was) the Tasmanian Wolf, a marsupial carnivore that looks like a dog but it is more closely related to a kangeroo! Here is a haunting silent 1936 film of the last known living Tasmanian wolf filmed in captivity.

 

James discussed Darwin's interest in the flightless birds like the ostrich, cassowary, rhea, emu, tinamou and kiwi and Josh reminded us of the extinct Moa. This picture shows the relative sizes of the kiwi, ostrich and moa with the eggs. Notice how large the egg of the Kiwi is relative to its body size. It is the largest egg per body size while the ostrich egg is one of the smallest relative to the body size!

Until recently the prevailing view of flightless bird evolution was that the early flightless bird evolved before the continent of Gondwana broke up into the separate continents and then each lineage of flightless bird evolved on their prospective continents - Rheas in South America, ostrich in Africa, Emu in Australia and Kiwi and Cassowary in New Zealand. Recent molecular evidence has challenged that view and actually argues that "flightlessness" evolved independently three times.

We discussed the various experiments Darwin conducted with seed dispersal in salt water or in the guts of birds and fish as well as insects and seeds being dispersed on the feet of duck, swans and other semi-aquatic birds. James was reminded of a childhood story in a Dr. Dolittle book, Doctor Dolittle's Garden in which a beetle recounts being brought to England on the foot of a duck.

http://gutenberg.net.au/ebooks06/0603431h.html#d5_THE_WATER_BEETLE

Sarah brought up the idea of endemics, and how unique species with limited geographic distributions are often found on islands or high elevation habitats which supports Darwin's model of isolation and speciation. Sarah used the Silversword as an example, a beautiful plant that is found only on the high elevations of Halaekala on the island of Maui in Hawaii. James exposed the beauty and elegance of the plant so here is a picture he took last May 2015.

Flowering silversword - photo by James Wagner

The opening and closing theme to Discovering Darwin is "May" by Jared C. Balogh. http://freemusicarchive.org/music/Balogh/Revitalized_Eyes/MAY

interlude music Octopussy by Juanitos. http://freemusicarchive.org/music/Juanitos/