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Discovering Darwin

Updated 5 days ago

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A website dedicated to the podcast Discovering Darwin.

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A website dedicated to the podcast Discovering Darwin.

iTunes Ratings

3 Ratings
Average Ratings

iTunes Ratings

3 Ratings
Average Ratings
Cover image of Discovering Darwin

Discovering Darwin

Updated 5 days ago

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A website dedicated to the podcast Discovering Darwin.

Rank #1: Season 1 Episode 7: Difficulties with the Theory

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In this episode we decided to break from the standard form of the podcast and discuss two chapters at once instead of the traditional single chapter per episode. Episode 7 covers Chapter VI - Difficulties with the Theory and Chapter VII - Miscellaneous Objections to the Theory of Natural Selection. We note that Chapter VII is really more of a vanity press project where Darwin dedicates a whole chapter to personally rebuke the concerns and critiques of Mr. St. George Mivart, a fellow biologist who published criticisms against Origin of Species.
St. George Mivart, as Charles Darwin saw him Transitions. 
"First, why, if species have descended from other species by fine gradations, do we not everywhere see innumerable transitional forms? Why is not all nature in confusion, instead of the species being, as we see them, well defined?” pg 212

James used the imagery of a rainbow to argue that we often ignore the transitions or force transitional forms into the more distinct categories.

The biggest challenge of a transitional form is that it is a challenge that increases exponentially with each attempt to address the lack of transitions. We discussed that if you see Species A and Species C and believe they are closely related then the criticism of lack of transition can be leveled at the evolutionist. If the transitional form Species B is found in the fossil record then the challenge for transitional forms doubles because now you must find the transition between A & B and B & C. Each new transitional form increases the demands for more transitional forms. Sarah made the argument that the transitional challenge is often the case of moving the goal posts.
The other challenge of transitional forms is that speciation can occur in two major patterns - anagenesis and cladogenesis. This figure represents the two forms of speciation.
figure from
In anagenesis the species goes through transformation such that the original form is replaced by the new form and both are recognized as unique species. This shift in form can often occur quickly so that there is little opportunity for fossil evidence of the forms or the transitional forms are quickly replaced by the new forms.

Old photographs of common dog breeds show how quickly we have modified the breeds in just 100 years. A summary of this can be found at Science and Dogs website where we collected this intriguing comparison of how the bull terrier has changed over the past 100 years. Of course these are not true species but the premise is the same, shifting from one form to another can occur quickly and no transitional forms remain for comparison. This is where my rainbow metaphor comes to play.

The other form of speciation is called cladogenesis which involves a subset of the species that diverge from the ancestral form. Josh spoke about bat bugs and bed bugs and how they share an ancestry but it would be difficult to find the specific transitional individual between bat and bed bugs.
image from
"It has been asked by the opponents of such views as I hold, how, for instance, could a land carnivorous animal have been converted into one with aquatic habits; for how could the animal in its transitional state have subsisted? [220]"

The evolution of whales, at one time a challenge to Darwin, have now become one of the best examples of evolution. The fossil record for whale evolution is robust because the ancestors of whales were semi-aquatic or aquatic mammals and their remains would often sink to the silty bottom of the ocean or bay where they lived. Buried in the mud the remains would quickly become entombed so their skeletons remained intact. Our current understanding of whale evolution is beautifully represented by this graphic from Berkeley website.
A nice video animation summarizes the proposed process of whale evolution and it can be watched here. As Darwin argues, the large differences in forms that we see today developed over long periods of time with successive accumulated changes in form. The scale involved in the process, millions of years with many millions of individuals is often difficult for humans to appreciate or comprehend.

James talked about the flying squirrel and how cute it is. Here is his photographic proof of its cuteness.

flying squirrel in Kentucky, cutest animal on earth?
Complex Structures 

The eye to this day gives me a cold shudder, but when I think of the fine known gradations, my reason tells me I ought to conquer the cold shudder. - Charles Darwin in a letter to Asa Gray (February 1860).

The complexity of the eye with all of its intricate interconnecting parts seem, at first blush, to be too complex to have been formed by natural selection. This has historically been a difficult problem to solve because the eyeball does not fossilize so we are left to look for examples of eye evolution by looking at extant species. However, modern biology using molecular techniques and studying the genes involved in the production of the eye have beautifully reconstructed how a camera-like eye of vertebrates could have evolved from a simple light sensing structure seen in primitive chordates like the hagfish.
hagfish with slime - photo from ecouterre
There a nice TED talk with awesome graphics that summarizes our current state of knowledge  of how the eye evolved.
The opening and closing theme to Discovering Darwin is "May" by Jared C. Balogh.
Copyright: Attribution-NonCommercial-ShareAlike:
Sep 26 2015

Rank #2: Season 2 Episode 1: Hot Coffee

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This is the first episode for Season 2 of Discovering Darwin. We have titled this season Darwin the Adventurer because we plan to explore in detail the Voyage of the Beagle, Darwin's five year around-the-world survey in which he collected the specimens and made the observations that ultimately led him to develop his theory of evolution and write On the Origin of Species.

In this episode we introduce the three major characters involved in the famous voyage- Captain Robert Fitzroy, Charles Darwin and the ship the HMS Beagle.
HMS Beagle in the Galapagos (painted by John Chancellor)
Josh introduced us to Pringle Stokes, the original captain of the Beagle during its maiden voyage (1826-1830) to South America on a survey voyage to map the Straits of Magellan at the tip of South America. However the HSM Beagle, a Cherokee class brig-sloop which were often derogatorily referred to as "coffin brigs", was a difficult ship to control in the severe winds, strong currents, high seas, and rogue icebergs that were typically encountered around Cape Horn. Josh explained how Pringle Stokes commits suicide on the ship in 1828 and Robert Fitzroy is assigned to captain the ship after Stokes demise.
Robert Fitzroy - photo by Hemus, Charles 1849?-1925
[Public domain], via Wikimedia Commons

We talked about the contingencies of history and how some tierra del fuegian children became the nexus for Fitzroy, Darwin and the HMS Beagle.  We will dedicate a later episode to the depressing tale of Jemmy Buttons, York Minister and Fuegia Basket, kidnapped tierra del fuegians who rejected their roles as Christian missionaries for England and forever haunted Robert Fitzroy and many others back in England.
Drawings by Robert Fitzroy
Because of Robert Fitzroy's short temper and willingness to lash out to those crew members he felt were wanting he was given the nickname "Hot Coffee" by the crew.  A meticulous man and data collector, Fitzroy would often retrace his sailing path to confirm his charts and maps, a level of meticulousness that would exasperate his crew and Darwin.Fitzroy's iterative approach to sailing. Map from caption
The opening and closing theme to Discovering Darwin is "May" by Jared C. Balogh. 
Interlude music is Rite of Passage by Kevin MacLeod
Mar 15 2017

Rank #3: Chapter XIV Embryology

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This episode discusses Chapter XIV where Darwin applies his ideas of evolution and descent with modification to explain the developing "natural system" of classification, the unity of embryos and why organisms have rudimentary or vestigial organs.  

From the most remote period in the history of the world organic beings have been found to resemble each other in descending degrees, so that they can be classed in groups under groups. This classification is not arbitrary like the grouping of the stars in constellations. The existence of groups would have been of simple significance, if one group had been exclusively fitted to inhabit the land, and another the water; one to feed on flesh, another on vegetable matter, and so on; but the case is widely different, for it is notorious how commonly members of even the same sub-group have different habits.

Cuvier in 1817 proposed a system of classification that recognized animals as belonging to one of four forms  - Vertebrata, Mollusca, Articulata (arthropods) and radially shaped animals (Radiata).
image from argues that the hierarchical system of classification mirrors his idea that new species formation mirrors the pattern of inheritance and genealogy we see in family tree. 
 A nice example is the phylogeny of placental mammals, those are mammals different from marsupial mammals (kangaroos, opossums, etc.) and monotremes (egg laying mammals like platypus)  in that they retain the embryo internally in a placental sac where they feed and protect the developing embryo. Placental mammals represent the majority of extant species of mammals today and seem to have evolved from three major geographical locations - Africa, Laurasia and South America. This is a a beautiful artistic representation of the placental mammal phylogenetic tree.
A comparison of early development of placental mammals from the Afrotheria clade (left most branch) shows similarities and divergences in the different types of mammals.

 [A.. Tenrec [tenrecoidea], B. Golden mole [Chrysochloridae] C. Elephant shrew [Macroscelididae] D. aardvark [Tubulidentata] E. Bush elephant [Proboscidae] F. dugong [Sirenia] G. hyrax [Hyracoidea] Image from Hautier, Lionel, et al. "Patterns of ossification in southern versus northern placental mammals." Evolution 67.7 (2013): 1994-2010.

Modern phylogeny and classification is based on Darwin's ideas of descent with modification and we now use DNA, RNA, and protein sequences to expand and improve our understanding of the relatedness of organisms


We have seen that the members of the same class, independently of their habits of life, resemble each other in the general plan of their organisation. This resemblance is often expressed by the term "unity of type;" or by saying that the several parts and organs in the different species of the class are homologous. The whole subject is included under the general term of Morphology. This is one of the most interesting departments of natural history, and may almost be said to be its very soul. What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include similar bones, in the same relative positions?

Homologous bone structure of tetrapod limbs

James attempted to differentiate homologous structures from analogous structures but showed how complicated it can be when discussing flying adaptations in mammals. As you can see in the figure above, the limbs of birds, bats, humans, seals and turtles contain the same bones in the same configuration making them homologous in morphology. What changes in the relative size to each other not their relative position. In vertebrates, the evolution of powered flight occurred independently three times - in Pterosaurs (reptiles), bats (mammals), and birds (again reptiles) so their wings are functionally analogoussince they are wings constructed of different specific materials. James erroneously said that the pterodactyl wing was from a super elongated index finger but in fact it is the 4th digit what we associate with the pinky finger.  We colored the figure below of a pterodactyl wing to conform to the color legend in the figure above.


Earnst Haeckel was a famous scientist in Darwin's time who applied Darwin's idea of the evolution of organisms in his studies of the embryonic stages of chordates

As Sarah mentioned this set of illustrations were updated but the overall conclusion does not differ. Follow this link to read a wonderful summary of the Haeckel embryo controversy with modern drawings and interpretation. Overall embryo development does show that chordates exhibit very similar and distinct stages of development whereas the adult forms can be quite different in form.

Rudimentary Organs
 Humans exhibit a number of traits, that we see in other mammals, but are degraded or rudimentary in their form. Some classic examples we discussed were the coccyx (tail bone), wisdom teeth and appendix but failed to mention the degrading nictating membrane in the corner of our eyes. In other chordates it is semitransparent film that can over the eye to clean and protect it. Ours is reduced to a little nubbin in the corner of our eye.
The opening and closing theme to Discovering Darwin is "May" by Jared C. Balogh.

interlude music is Otrov by Black Bear Combo
Jun 28 2016

Rank #4: Chapter XV - Recapitulation and Conclusion

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In this episode we discussed Chapter XV - Recapitulation & Conclusion from Darwin's Origin of Species. It is our final podcast of this season and we chose not to recapitulate as much as discuss how Darwin's book was received at the time and how Darwin handled the release of his book.

Although only 1250 copies of Origin of Species was published in the first edition, Darwin purchased 80 or so copies himself and Mudie's Circulating Library purchased 500 copies for use in their subscription service library, a service widely used by many middle class British folk.

It was through the subscription library that allowed Darwin's ideas to be widely distributed to the general public while fevered debates occurred in churches and academic halls.

The original 1859 publisher of Origin of Species was the Murray Publishing House book and the publisher was very generous in allowing Darwin to make corrections after the first printing run which is why the 2nd edition of OoS has a 1860 publication date.

We discussed how Darwin was often portrayed as an ape in cartoons published at the time. When we discussed the infamous images of monkey-like Darwin James erroneously associated those images with the famous Punch magazine but it turns out the ones he was thinking of came from other magazines of the time.
Charles Darwin considering the fashion of the time - the bustle (Fun magazine 1872)

 from The Hornet magazine, 1871
We really appreciate you listening to our podcast and we hope you return later this fall when we return with Season Two - Darwin the Adventurer.

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

Interlude music is bensound retro soul
Aug 15 2016

Rank #5: Season 1 Episode 8: Chapter VIII Instinct

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MANY instincts are so wonderful that their development will probably appear to the reader a difficulty sufficient to overthrow my whole theory. [page 317]
In this episode of Discovering Darwin we covered Darwin's chapter on Instinct and how Chuck attempted to explain how animals exhibit complex behaviors that are not learned. More importantly Darwin was trying to outline how behaviors could evolve in the same way he explained the evolution of physical traits.

It is not too difficult to study the evolution of physical traits because we often have fossil evidence of their transformation. Last episode we discussed the evolution of whales and the plethora of fossil evidence that has allowed researchers to reconstruct the evolution of the terrestrial ancestor of whales to the streamlined marine mammals we see today. 

Behaviors are harder to imagine through the lens of natural selection because we can only see those behaviors that are exhibited by extant (living) organisms and behaviors can evolve much faster than physical traits. Cultural evolution can allow individuals within their lifetime to adopt a new behavior that they learn from others. One of the wonderful examples of this is dolphins using a sponge to protect their rostrum (beak) as they hunt for prey in coral structures. They can pass this idea on to other dolphins and you can track the rapid transmission of this behavior through a population.
Picture from
Darwin was not interested in learned behaviors in this chapter but he was interested in behaviors that are known at birth or at specific developmental times in the organism's lifespan. Darwin called these behaviors instinct. In exploring this idea Darwin focused on three major examples of innate/instinctual behaviors:

1. Cuckoos and their behavior to dump their eggs in other birds nests.
2. "Slave making" ants species which capturing of other ant species to become sources of forced labor in their own colonies.
3. Honey bees and their complex, mathematically efficient, honeycomb making behavior.
Cuckoos exhibit a behavior known as "brood parasitism" where they lay their eggs in the nest of a host species and leave the eggs to be incubated and hatched by the host. The host also raises the cuckoo baby as their own until it is strong enough to fledge from the nest. Below is a dramatic photo showing the poor host Reed Warbler dutifully feeding the ginormous common cuckoo (Cuculus canorus) nestling.
"Reed warbler cuckoo" by Per Harald Olsen - Own work. Licensed under CC BY-SA 3.0 via Commons -
You may wonder why the Reed warbler does not recognize the cuckoo offspring is not their own offspring? What you are really asking is why has the Reed warbler not evolve the ability to recognize its own offspring from another species? If you were switched at birth in the hospital, do you think your mother would know? What ways do we know our offspring are actually ours? Only through hospital tagging or non-interrupted contact are we to "know" the offspring we have are the ones we gave birth to. 

Why have we not evolved an ability to recognize our own offspring? Probably because there has not been a selective advantage to recognize our offspring because over evolutionary time it has been rare for humans to be in a situation where we must recognize our newborn from other unrelated newborns. Since that ability is rarely useful, selection has not favored it in our species. In the same manner, birds that nest individually associate those eggs in their nest as being their own. Recognition has not evolved because there is little selective advantage for that ability. However there are birds that do exhibit an amazing ability to discern their own specific offspring among a throng of others. Colonial nesting birds like albatross and penguins have an unerring ability to discern their own chick from maddening crowds because selection has favored that ability.
baby penguins awaiting the return of their parents to feed them. Image from Mike Johnson
In nesting birds like the Reed warbler it would normally be rare for it to be stuck raising an unrelated offspring so they have not developed the ability to recognize that the over-sized baby is not really their own offspring. Instead the poor Reed warbler probably thinks she has the largest and healthiest reed warbler baby in the world. Feed it some more!

Because nesting birds are less discerning in recognizing their young, brood parasitism has the opportunity to evolve and based upon phylogenetic analysis it seems it has. Brood parasitism has evolved independently seven times in the evolution birds resulting in 75 species out of the 8600 known species of birds exhibiting forms of brood parasitism from occasional indiscretions to those species which never raise their own offspring, instead relying totally on other species to incubate and raise their young. 

This extreme form of brood parasitism intrigued Charles Darwin in that a cuckoo could be born in a Reed warbler nest, be raised by Reed warblers, fledged from the nest and go off to grow up and retain its identity as a cuckoo bird and not a reed warbler or whomever was its host species. The identity of the cuckoo was innate, instinctual and expressed itself in the adult females when they reached reproductive age.
Image from

Darwin predicted the cuckoo species we see this complex behavior in various stages of complexity, transitions if you will. There are some cuckoos which specialize in parasitizing a single species of birds while other cuckoo species are generalist and parasitize a wide variety of host species. The research suggests it is difficult to discern if the evolution of cuckoo behavior went from specialist (single host species used) to generalist (many potential host species used), or vice versa.  In addition, within the common cuckoo (Cuculus canorus there are families (gentes) who specialize on parasitizing a single host species and the cuckoo egg color has evolved to better mimic their hosts eggs. In the picture below see the cuckoo egg indicated by the arrow in a variety of host nests while showing the great variation in egg coloration within the single species of cuckoo.

By what steps the instinct of F. sanguinea originated I will not pretend to conjecture. But as ants, which are not slave-makers will, as I have seen, carry off the pupæ of other species, if scattered near their nests, it is possible that such pupæ originally stored as food might become developed; and the foreign ants thus unintentionally reared would then follow their proper instincts, and do what work they could. If their presence proved useful to the species which had seized them—if it were more advantageous to this species to capture workers than to procreate them—the habit of collecting pupæ, originally for food, might by natural selection be strengthened and rendered permanent for the very different purpose of raising slaves.[page 338]

Polyergus mexicanus workers return from a successful raid with captured pupae of the host species, Formica subsericea. Urbana, Illinois, USA Photo from
Sarah discussed the intriguing behavior of slave making ants and how Darwin thought it evolved and how modern science has supported, somewhat, his original view. The biggest hurdle for slave making to evolve is that each ant species relies on species-specific and colon-specific pheromones for individuals within a colony to recognize each other. Individuals from other colonies, and even more so, individuals from other species will smell distinctively different from the slave making ants so how do they suppress aggression towards their newly captured indentured pupae?  It was proposed that ants should raid closely related species so that their pheromones are more likely to be similar to reduce aggression between raiders and potential slaves. This is known as the Emery Rule.

Interestingly, scientists since Darwin have been studying the evolution of slave making behavior and much is still to be figured out. The closing remarks on a wonderful review paper about the evolution of social parasitism and slave making behavior in ants makes the following observation:
"Though slave-making ant species have been studied for more than 150 years, many problems are still open, the most prominent obviously being the evolution of slave  raiding itself. Recent investigations have given contradictory results concerning, for example, the mechanisms of  chemical integration of slave makers and their hosts in a  mixed society, the pattern of sex allocation in slave makers, and coevolution between social parasite and host….Considering that almost all  slave-making ant species are listed as threatened by the  World Conservation Union (IUCN), investigations on  their behavior, population structure, and genetic variability may help us learn more about how endangered they  really are and if and how they can better be protected." (D'Ettorre & Heinze 2001)  
 Josh ended the program with a discussion of the perfection of honeycombs and how is that bees make such perfect hexagon shapes?
stockphoto from
Josh explained that cell shapes within the colony can range from a circular shape to the beautifully distinct hexagon shape we associate with honey bees. Two major hypothesis, which are not mutually exclusive, have been proposed to explain the hexagon shape. The first is the efficiency hypothesis which argues that wax is expensive to produce so bees would evolve to be the most efficient in building their combs and hexagon shape requires the least amount of material and produces the least amount wasted space. 
Notice this circular form above has many gaps between the cells in contrast the compact arrangement in the hexagon com.  

The second hypothesis Josh brought up was the idea that in the bee hive, the bees body heat melts the wax and the wax then forms a shape that requires less energy to maintain so the straight edges between the cells forms as an outcome of soft wax reaching a low energy resting state.  In this model the bees are not intentionally creating a hexagon shape but it emerges from their constant activity and body heat. 

It is interesting that the questions that Darwin outlined as interesting issues for evolution are still be investigated and we are beginning to understand these instinctual behaviors better because of the evolutionary framework that Darwin gave us over 150 years ago.
The opening theme to Discovering Darwin is "May" by Jared C. Balogh.
Interlude music is Rhapsody In Blue Part 1 by Paul Whiteman and George Gershwin Published 1924
Nov 12 2015

Rank #6: Season 2 Episode 2 - and he the end.

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In this episode we discuss the extensive library on the HMS Beagle that was created by Charles Darwin and Robert Fitzroy.  Over 400 books were in the ship's library and the catalog had a heavy emphasis on travel accounts (travelogues), natural history and geology.  We discussed Humboldt and his influence on Darwin and Jeremy told the story about the dragon tree and Darwin's wish to travel the lands of Humboldt to see the same sights as Humboldt.
Dragon trees in the canary islands (picture from is Humboldt's description of the dragon tree-
Although we were acquainted, from the narratives of so many travellers, with the dragon-tree of the garden of Mr. Franqui, we were not the less struck with it's enormous magnitude. We were told, that the trunk of this tree, which is mentioned in several very ancient documents as marking the boundaries of a field, was as gigantic in the fifteenth century, as it is at the present moment. It's height appeared to us to be about 50 or 60 feet; it's circumference near the roots is 45 feet. We could not measure higher, but Sir George Staunton found, that, 10 feet from the ground, the diameter of the trunk is still 12 English feet; which corresponds perfectly with the assertion of Borda, who found it's mean circumference 33 feet 8 inches, French measure. The trunk is divided into a great number of branches, which rise in the form of a candelabrum, and are terminated by tufts of leaves, like the yucca which adorns the valley of Mexico. It is this division, which gives it a very different appearance from that of the palm-tree*. [Humboldt, Alexander von. 1814-1829. Personal narrative of travels to the equinoctial regions of the New Continent, during the years 1799-1804. pgs 144-145]
Since 36% of the books in the Beagle library were travelogues, and Darwin's own Voyage of the Beagle is a travelogue, we invited Dr. Jeremy Paden, professor of Spanish Literature at Transylvania University, to discuss with us the role of travelogues in the 16th-19th century as a literature form.

During our discussion Jeremy highlighted Thomas Falkner as an influential travelogue writer who wrote  A description of Patagonia, and the adjoining parts of South America (1774).  Falkner described the region of Patagonia, a rugged area at the tip of of South America that also encompassed the Streights of Magellan.

Straits of MagellanUnlike the map above which show the Straits of Magellan as a simple channel, the real Straits of Magellan are quite complex and convoluted as seen in the Google map below. Notice the large number of cul-de-sac inlets and waterways that can easy lead you astray.

We noted that the tip of South America looks more like a spongiform brain that has mad cow disease as shown in the image below, left image is a brain with Creutzfeldt-Jakob disease and brain on the right is normal brain.

James highlighted an unusual book in the collection - Werner's Colours, a small book that includes colour swatches that Darwin used as reference when he was taking notes of specimens.
Excerpt from Werner's Colours
You can peruse the entire Beagle library at the Darwin Online website.

At the end of the podcast we spoke with Dr. Paden about his own research and interest in poetry. James mentioned his appreciation of Jeremy's poem on the liver fluke parasite and we reprint it here-

Falling from the masticating jaws of ungulatesthat clip the tips of grass blades, the black antescapes this evening’s immolationand the circuitous route of cud-balls,from stomach to teeth, stomach to teeth.
Ignorant of why it leaves the sweet feastof slime balls secreted by common land snails,come dusk, the ant climbs again the broad greenleaf to spend the night in sirshasana​,​pinschers clamped ​to the end of a grass blade.
Larval lancet liver flukes, encystedin snail-trail droppings, once eaten,​ move to​the ganglion below the gullet,​ and force ​​Formica fusca to climb​ the blade​ andwait for the grazing cattle to come home.
If you are interested in reading more of Jeremy Paden's poems you can find his published book of poems concerning mining in Chile here or here.

The opening and closing theme to Discovering Darwin is "May" by Jared C. Balogh. 
Interlude music was Procreation by Little Glass Men
Apr 30 2017

Rank #7: Season 2 Episode 3 - Court of Neptune

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In this episode Sarah, Josh and James discuss the opening chapters of Voyage of the Beagle where Darwin recounts the initial months of his voyage that includes an aborted stop at the Canary Islands, a visit to Cape Verde and then his first overland trip in Brazil. James discussed how Darwin spent as much time off the Beagle traveling overland than he did sailing in the Beagle.

By Jules de Caudin - Relation complète du naufrage de la frégate La Méduse faisant partie de l'expédition du Sénégal en 1816, by A. Correard, H. Savigny, D'Anglas de Praviel and Paul C.L. Alexandre Rand des Adrets (dit Sander Rang). Reprint 1968 by Jean de Bonnot éditeur., Public Domain, talked about the work of the scholar John van Wyhe who scoured through Darwin and Fitzroy’s diaries and journals to reconstruct the day-to-day itinerary for the HMS Beagle during the 5 year voyage and lists location, latitude/longitude coordinates and where Darwin was located – either on ship or on land. When you break down of the 1,740 day voyage you realize Darwin made great efforts to spend time away from the ship. From Darwin’s perspective he almost equally split his time between being at sea, at anchor or traveling on land. Based on the itinerary of the Beagle Darwin spent 580 days at Sea, 566 days at anchor and 594 days away from the Beagle on overland excursions. 
Interesting, even when anchored or exploring on land, Darwin would return to sleep on the Beagle which he found to be very comforting.  Darwin spent 1,144 nights on the beagle (65.8% of the trip) whereas he spent 596 nights off ship which is only 34.2% of the trip. Over half (55%) of that time was spent in South America alone. 
James discussed how Darwin's diary and notebooks in the first 2 months of the journey included interesting details that were absent in the Voyage. In particular, Josh talked about the ritualized hazing that sailors would inflict on the new crew members when they crossed the equator, a ritual called the line-crossing ceremony.

Josh referenced this nice article from the Atlas Obscura website that discusses the odd ritual of hazing as one crosses an imaginary line on the earth's surface. Sarah also talked about the Tropic of Cancer and the Tropic of Capricorn and how the wind patterns associated with those imaginary lines on the earth drove trans-Atlantic slave trade and the conquest of the New World.

We focused on the first overland trip that Darwin took when he landed in Brazil. This was the first of many trips that Darwin took while Captain Fitzroy fastidiously checked his charts and maps by reiterately sailing up and down the coast of South America.
As Darwin traveled overland he mentioed many interesting animals and plants he encountered in the jungles of Brazil. One group of animals Darwin became enamored with was planaria (Plathyhelminthes). Interesting, even to this day new species of flatworms are being discovered in Brazil.

James pointed out that this group of animals also exhibit great species diversity in the marine habitat where they show a beautiful diversity in colors. Here are just few examples of the amazing color diversity of marine flatworms one can find with a simple google image search.

Sarah became obsessed, like Darwin, with bioluminescence. Sarah discussed the amazing evolution of bioluminescence and how it has evolved independently across a number of disparate phyla and kingdoms. Darwin was particularly enamored by a large click beetle that incorporates bioluminescence in mating display. One of our students took a wonderful picture of the same beetle during our Tropical Ecology class to Belize.
photo by Kali Mattingly
The opening and closing theme to Discovering Darwin is "May" by Jared C. Balogh. 
Interlude music
Apr 30 2017

Rank #8: Episode 5: Chapter IV - Natural Selection; or Survival of the Fittest.

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As we thought, this became the longest episode we have recorded yet but then again, we had a lot to cover. Chapter IV is the part of Origin of Species where Darwin outlines how he believes natural selection, over long periods of time, can generate new species. It is a rich and complex chapter and our wide-ranging conversation explored a large number of the issues Darwin brings forth in the chapter.

We discussed at great length the variety of ideas that Darwin encapsulates within the only figure in the book. James mentioned how Darwin first sketched the figure in his notebook B - Transmutation of Species with the understated "I think" title followed with "Case must be that one generation then should be as many living as now. To do this & to have many species in same genus (as is) requires extinction. Thus between A & B immense gap of relation. C & B the finest gradation, B & D rather greater distinction."

  Image from Original Notebook at Darwin Online.

 Ultimately this image became refined for Origin of Species to look like this -

In our discussion we noted that this image represents ideas like: a large number of extinction events, the lack of predictable direction in evolutionary change, no change (E & F), increase in species numbers, differential rates of evolution as indicated by the slope of the lines radiating out at a specified time era (e.g., era IV, z4), and that species can converge in character traits (e.g., how f lineage shifts to look like extinct d lineage). A larger version of the figure can be found here.

 Sarah noted how human evolution phylogenetic tree can show the same sort of pruned bushiness that Darwin represented in his figure.
This figure is from the Smithsonian and is an interactive figure at their site that is worth checking out.

Interestingly there has been recent researchers who reject the evolutionary tree model for human evolution. Instead of the classic tree structure they note that the mitochondrial DNA (mtDNA) analysis suggests all modern humans can be traced back to African ancestors who dispersed out of Africa only 100,000 years ago. However, those various subspecies of humans interbred and migrated back into Africa thereby creating a more reticulated, "trellis" evolutionary relationship than the classic branching independent lineages as represented in a tree. Follow this link to read a nice summary of the alternative view with a figure to illustrate the trellis view of human evolution.

Sarah mentioned how quickly other scientists adopted Darwin's tree model to represent relatedness and she noted how the embryologist Ernst Haeckel drew up a phenomenal evolutionary tree. To truly appreciate this tree  you should see it in a larger format.
We also discussed the rapid evolution of the Hawthorn maggot fly and its shift to feeding on introduced Apples and how that resulted in two populations with little genetic exchange between them. It is a beautiful house fly sized insect with painted wings which they flick to mimic the movement of jumping spiders. Photo Copyright © 2013 Harvey Schmidt
Do you see the jumping spider in its wings?

At the end of the podcast we attempted to read the epic opening sentence in Darwin's summary in a way that brings the words to life. Here it is for you to try.

If under changing conditions of life organic beings present individual differences in almost every part of their structure, and this cannot be disputed; if there be, owing to their geometrical rate of increase, a severe struggle for life at some age, season, or year, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of life, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, it would be a most extraordinary fact if no variations had ever occurred useful to each being's own welfare, in the same manner as so many variations have occurred useful to man.
Jul 21 2015

Rank #9: Episode 9: Chapter IX - Hybridism

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We dedicate this episode of the podcast to Chapter 9 - Hybridism in Darwin's Origin of Species (OoS). We all agree that this chapter is one of the most challenging chapters to read in OoS. In this chapter Darwin force marches the reader through example after example of hybrids while simultaneously admitting his ignorance on why these creatures should exist.

It is not inherently obvious to the reader why they are being subjected to this catalog of biological anomaly and minutiae concerning pollination of orchids and other flowers but Darwin is adamant to share his knowledge, like a proud new parent inflicting others to look at numerous photos of their newborn. Darwin , early in Chapter I of OoS, argued against the notion that new species are formed through hybridization of existing species and we expected him to make that point in this chapter, but he never really does.

It seems that by the end of the chapter we are exhausted from Darwin's recounting various animal and plant hybrids and admitting his ignorance of sterility in hybrids but that does not dissuade Darwin from concluding he was right all along - “…the facts given in this chapter do not seem to me opposed to the belief that species aboriginally [emphasis added] existed as varieties”. Darwin stays on point.

We started off our discussion identifying our favorite hybrids. Josh first suggested mermaids as his favorite hybrid but James required he offer up a "real" hybrid.
Mermaids James grew up with in FloridaJosh introduced us to the Liger, a hybrid between a male lion and female tiger both species have 38 chromosomes which also allows for reciprocal mating. Male tigers and female lions create tigons. The hybrid nomenclature is a portmanteau word derived from using the male species as the prefix and the female as the ending of the name hence a liger and tigon being separate types of hybrids.
900 lb Hercules

Sarah mentioned the Zedonk, a hybrid between a zebra and a donkey. This is another one of the hybrids that are created artificially in captivity. Few people realize that there are actually three different species of zebras - Grevy's, Plains and Mountain zebras - and each species has their own number of chromosomes. Grevy's zebras zebras have 46 chromosomes, Plains zebras have 44 and the Mountain zebra has 32 chromosomes whereas the donkey has 62.
Image from Carole Coleman James suggested the Grolar, a hybrid between a grizzly and polar bear, was his favorite hybrid.

A grizzly bear with her grolar cubsUnlike the liger and zedonk, the grolar occur in nature when the two species of bears interact. Historically grolar bears were less common since Grizzly bear distribution was further south than Polar bears but the warming of the climate has caused both bears to extend their range, polar bears southward and grolar bears northward, such they now more commonly overlap during the breeding season. Research suggests Polar bears "recently" diverged from brown bear ancestors with the speciation event occurring only 343,000-479,000 years ago. A mere blink of time in terms of the geological record.

We discussed the most famous of all hybrids, the mule and how it is formed from the male donkey breeding with a female horse. Pictured below is a horse (left) and a mule (right) showing how the mule is often much larger than either of its parents, an example of Hybrid Vigor.
picture by Merle

We noted that the mule hybrid can only be formed from male donkeys and female horses and rarely rarely formed from a male horse and female donkey. Sarah suggested that the reason the mule can only be formed from a male donkey and female horse has to do with the constraints of difference in gestation times between horses and donkeys. It turns out that horse gestation is 11-12 months whereas donkey gestation period is 11-14 months. There is a lot of overlap in gestation time between the two animals but it is an intriguing idea to consider it may influence non-reciprocal successful mating. 

We introduced the idea of prezygotic isolating mechanisms and how they would evolve to prevent hybrids from being formed. Behavioral isolation is frequently seen in the complex displays and calls given by a variety of birds species and James mentioned the beautiful flashing patterns exhibited by the different species of fireflies. The image below shows the species-specific color and flash pattern of lightning bugs in Florida.

Go here to learn more about fireflies
Josh introduced us to the sordid and dark world of duck mating behavior and male duck genital morphology. Here is just one example of the size and complexity of the male duck penis which has evolved in response to female duck vaginas. Female ducks have evolved elaborate shaped vaginas to avoid fertilization from other species of ducks.This interesting topic is covered nicely in this short article here.

Sarah spent some time explaining the intricacies of pollination and how pollen is actually greatly reduced multicellular structure that produces sperm - pollen is actually plant testicles. Plants evolve complex pollen grains, much like the extreme duck penis, to create reproductive barriers between species. The forms of inter-specific (between-species) barriers to reproduction would evolve because those individuals who are more discerning in their choice of mates would waste less time/energy fertilizing and producing those hybrid offspring which are often, at best, viable but infertile but more likely enviable. Often it is the female of the species that is the one who evolves the reproductive challenge for the male because she produces fewer, and often more metabolically expensive, gametes (eggs/ova) than her male (sperm) counterpart and therefore has more to lose if she errs on who she mates with than he. 
Public domain image (created by the Dartmouth Electron Microscope Facility)
Ultimately we conclude that hybrids exist because Darwin was correct in his model of speciation, that is new species derive from varieties of preexisting species (see Chapter 4 blog post) so they share many of the common genetic traits with their ancestral or closely related species. Surprisingly Darwin did not recognize that hybrids are his best argument against the special creation model of immutable species since one should not expect hybridism to occur between two immutably formed species that were specially created.
"That's a Wrap" & "Aces High" Kevin MacLeod ( Licensed under Creative Commons: By Attribution 3.0
Jan 05 2016

Rank #10: Geographical Distribution: Chapter XII-XIII

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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,
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.comThe 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.
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.
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.

interlude music Octopussy by Juanitos.
Jun 16 2016

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