Discovering Darwin

 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 https://www.britannica.com/topic/Beagle-shipAdd caption The opening and closing theme to Discovering Darwin is "May" by Jared C. Balogh.  Interlude music is Rite of Passage by Kevin MacLeod

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.   Classification 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 http://www.buffalolib.org/content/milestones-science/georges-cuvierDarwin 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. http://eurwentala.deviantart.com/art/Eutheria-345487389 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 Embryology 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

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.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. 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

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.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. 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

Let us now see whether the several facts and laws relating to the geological succession of organic beings accord best with the common view of the immutability of species, or with that of their slow and gradual modification, through variation and natural selection. In this episode we explore Chapter XI that deals with the fossil record and how patterns in the fossil record fit with Darwin's model of descent with modification. We begin the discussion with Darwin's views on extinction and how this phenomenon is part of his model of evolution. Sarah introduced the idea that extinction occurs at two different rates - normal background rate of extinction where species themselves have a measured lifespan based on how long they exist in the fossil record. Current analysis of the fossil record indicates that many species persist for a period of time and then go extinct. From this  data scientists calculate an average lifespan for a species - That is, how long in the geological record does a species typically persist? Many authors have written about this idea and many of their findings have been summarized in Extinction Rates, a book edited by J. Lawton, and R. May (1995). Generally species lifespans are varied and biased by the size of the organisms. Small unicellular marine dinoflagellates have species "lifespans" in the 10's million years whereas large multicellular Cenozoic animals had a species 'lifespan" of 1-2 million years. These normal background rates of extinctions in the fossil record are punctuated by five massive extinction events where 75%-96% of all species went extinct. Sarah mentioned the dramatic "soot' line that demarcated the mass extinction event called the K-Pg (formally called the K-T) extinction event that occurred 66 million years ago. This extinction event was correlated with a thin layer of metal iridium that is visually and chemically distinct from rock material layers above and below the line. This layer was now thought to be have been created when a small asteroid impacted the earth near the Yucatan peninsula contributing to massive habitat destruction and climate change. These massive changes in climate are thought to have contributed to the extinction of all non-avian dinosaurs. image from http://waynesword.palomar.edu/images2/KT1c.jpg Sarah recommended a book on extinctions by Peter Ward called Under a Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future (Harper 2008). Affinities of past to current organisms Let us now look to the mutual affinities of extinct and living species. All fall into a few grand classes; and this fact is at once explained on the principle of descent. We discussed how many of the organisms in the fossil record can be directly related to species we see today - the wide array of extinct elephants themselves are a dramatic example of extinct forms being related to extant forms today. image from http://img13.deviantart.net/1309/i/2015/120/9/7/elephants_by_fotostomias-d34pdf2.jpg James spent some time explaining the background story of the archeopteryx fossil that was found in 1861 in Germany just after Darwin published Origin of Species. Photograph: Jason Edwards/Getty Images On the photo above notice the fingers on the wing and the long bony tail that extends off of the pelvis region. Museums are now creating displays that highlight the feathered dinosaurs that have been found in the past 10 years.  In 2016 the American Museum of Natural History opened a display that highlighted many new feathered dinosaurs. http://www.nytimes.com/2016/03/18/arts/design/fine-feathered-fiends-dinosaurs-among-us-at-the-american-museum-of-natural-history.html The relationship between organisms we see today to extinct versions in the fossil record is one of the stronger pieces of evidence that supports Darwin's model of descent with modification. In the next episode we will discuss how this relationship between extinct and extant organi

...so must the number of intermediate varieties, which have formerly existed, be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely-graduated organic chain; and this, perhaps, is the most obvious and serious objection which can be urged against the theory. The explanation lies, as I believe, in the extreme imperfection of the geological record.  [406] This episode focused on Darwin discussing the state of the fossil record, why he felt transitions may be rare and why he does not think the imperfection in the geological record was fatal to his theory. We discussed three of his major issues with the fossil record and then discussed the age of the earth and the sudden appearance of diversity in the fossil record. A phenomenon often referred to as the Cambrian Explosion. How to make a fossil?  One of the challenges of creating a fossil is avoiding the rapid decay and destruction of the organic material by bacteria, fungi and other decomposers.  The majority of the decomposers require oxygen to live so a successful fossilization event requires the remains to settle in an area that is anaerobic (anoxic for aquatic systems) (without oxygen). Anaerobic conditions occur in deeper waters where oxygen is slow to replenish from the surface, or it can occur in wet terrestrial systems like bogs or river banks where wet saturated soils can become anaerobic. We didn't mention in the podcast the amazingly preserved 1,000-2,000 year old humans discovered in peat bogs in Europe. These acidic and anoxic environments deter the growth of most bacteria and fungi. image from: http://ngm.nationalgeographic.com/2007/09/bog-bodies/clark-photography This is a picture of a sheep that fell into a ditch that was then frozen over, although it is not technically a bog, it does show the difference between access and lack of access of decomposers to a body. image from: https://i.imgur.com/S6Hn8i6.jpgUltimately the conditions that favor fossilization result in a bias in who gets fossilized which greatly biases and restricts the fossil record. In general you can say that to become a fossil you should be: Small and abundant. The more abundant you are in the environment the more likely you could experience the rare opportunity to become fossilized. Live in or near an aquatic environment.Have hard body parts than can resist decay. Scales, shells, bones, exoskeletons and woody material often resist decay whereas flesh, hair and soft tissue not so much.If you are small, blind, sessile and attached to the sea floor you are more likely to become a fossil or fossil imprint than if you are large, active and run across the Serengeti or swim in the shallow, wave disturbed seas.Although the fossil record is biased towards small, aquatic organisms there are museums full of large and dramatic fossils that contradict the rules above. So when you consider the improbability of a creature becoming a fossil the fossil record is actually quite impressive! photo of Sue by James Wagner Is evolution predictable? James mentioned that evolution tinkered with different materials or metabolic pathways but ultimately settled on a few systems that are widely utilized across the diversity of life. In particular we discussed how evolution utilized many different chemical mixtures to create a hard support system (endoskeletal, shell, or exoskeleton) with an interesting alternative seen today in the "glass" sponges. Glass sponges utilize silica to create their hard spicules, the support material utilized by sponges to give strength and support to the jumbled array of barely specialized cells that constitute a sponge. Unlike most sponges which create individual spicules which they assemble with the organization that resembles a game of pick up sticks, spicules by http://www.jeolusa.com/Portals/2/ModuleDNNGridGallery/ncaor_india_sponge-spicules.jpg the glass sponge sili

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 in

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 http://www.livescience.com/21989-dolphin-sponge-tools-culture.html 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. Cuckoo 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 - https://commons.wikimedia.org/wiki/File:Reed_warbler_cuckoo.jpg#/media/File:Reed_warbler_cuckoo.jpg 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 abilit

In this episode we take a side trip with Dr. Mark Jackson, our colleague from the psychology department, to explore the historical view of instinct behaviors in humans. The next chapter of Darwin's Origin of Species deals specifically with instinct behavior in non-human animals and it stimulated us to question what the thought of the time was considering human instinct behavior. Dr. Jackson brings his sly wit to the conversation and tells us how the early field of psychology dealt with or explained innate behaviors in humans. Mark introduced us to noted historical psychologist William James who is known as offering the first psychology class in the United States and considered the "father of American Psychology". Dr. "Will.i.am" James One of the interesting ideas that we discussed concerning instinctual behaviors in humans is how many of our emotions are frequently intertwined with physical aspects of our bodies. Mark recounted the example of you seeing a bear and how your body may initiate the flight response before your mind can consciously evaluate the situation and determine you are afraid. Unknown man having his legs decide how to deal with the situation before his rationale thought process begins.

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 http://krupp.wcc.hawaii.edu/ 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 http://ohioline.osu.edu/hyg-fact/2000/2105a.html Saltations "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