Discovering Darwin

In this episode of Discovering Darwin we discussed the fifth chapter of Origin of Species titled Laws of Variation. Ironically there are no laws actually discussed in the chapter but Darwin does outline a variety of phenomenon and patterns of inheritance and variation that puzzled and intrigued him. When we consider the great variation in forms that we see in nature it is often difficult to tease apart the cause of that difference in form. For example, variation in form may be genetically determined as described by Mendel and his experiments with pea plants. Of course Darwin did not have a sense of genes and how multicellular plants (excluding mosses) and animals get two copies of each gene, one form their mother and one from their father, that codes for traits. Those two copies of the genes determine the expression of physical traits. Looking at the chart below of Mendel's pea plant traits you can see how variable the sweet pea plant could be. Imagine Darwin's confusion if he saw pea plants with yellow or green seeds, purple or white flowers and variation on where the flowers are located on the plant. Even more intriguing is the notion that yellow seeded pea plants with purple flowers could be crossed and produce offspring with green colored pea seeds and white flowers! Today, with our knowledge of genetics, we understand the concept of recessive and dominant traits and how recessive traits can be hidden in the parents but expressed in the offspring when they inherit only the recessive versions of the gene. We discussed if Darwin actually was aware of Mendel's work and Josh mentioned an interesting paper by Bizzo and El-Hani that argued Darwin was aware of Mendel's work. That paper can be found here. Acclimation versus Adaptation Sarah discussed how Darwin seemed to use the terms acclimation and adaptation interchangeably as he worked through his understanding of how organisms can exhibit variation in form. Today biologists see these two concepts as separate and unique characteristics. Some of the best examples of acclimation can be seen in arctic animals, like this arctic fox, that can dramatically change their coats from winter to summer. Acclimation is when the organism alters its form, physiology or behavior in response to local environmental conditions. Often these changes are induced by hormonal changes in the organism which themselves are triggered by environmental stimuli.  These changes are typically not permanent. In contrast, if you look at a population of a species you may see variation in forms but these are adaptations to local conditions. An interesting example of local adaptations is seen in the north American rock pocket mouse (Chaetodipus intermedius) that lives in the southwest desert areas of US and Mexico. This small, bite sized rodent, lives in a variety of rocky habitats which differ in color depending upon the geological history. The brown sandy colored rocks are in contrast to the black balsaltic rock that formed from geologically recent lava flow events. The mice have strong local selection to avoid being seen by their natural predators so selection favors coat colors that blend with the background. The top two images are showing the local mouse in its native local condition, the bottom two panels are swapping mice from their native locations. All of these mice are the same species but their coat color variation is genetically determined by expression of Mc1r gene for black pigmentation and that gene has undergone local mutations and selection. http://uanews.org/story/coats-different-color-desert-mice-offer-new-lessons-survival-fittest   We also discussed how creatures locally adapt to caves by losing the ability to see and often become pale colored or completely lose their coloration.  Josh read a wonderful quote by Darwin where he described blind cave crabs possessing components of the eye but it was incomplete in form. Image from http://imgarcade.com/1/blind-cave-crabWe also d

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 http://bugguide.net/node/view/817659 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

In this episode of the podcast we explore Chapter II- Variation Under Nature from the 6th edition of Charles Darwin’s Origin of Species. One of the big themes Darwin explores in this chapter is the arbitrariness in defining a species and how to differentiate species from a variety or subspecies.  Sarah brought up the example of ring species, in particular we talked about the herring gull species complex that circumnavigates the northern hemisphere. The ring species model (also called rassenkreis) of speciation was first developed in 1942 by Ernst Mayr (yes, the same Ernst Mayer mentioned by Josh) and it proposes that as a population disperses around a large scale geographical barrier (e.g., ocean, mountain ranges, etc) the sub-populations diverge genetically with distance from the ancestral original population. Ultimately when these sub-populations meet again on the other side of the barrier they have diverged so much as to become reproductively isolated. In our conversation we discussed the herring gull species complex and mentioned the salamander species complex from the California central valley as examples of ring species. More recent research has questioned if these two are actually examples of Mayr’s ring species model but instead are products of the standard allopatric speciation model which requires the populations to become reproductively isolated from the parental population and speciation occurs as the sub-population become adapted to their local environmental conditions.  Regardless of the speciation model that is occurring, the herring gull complex exhibits a great array of interbreeding subpopulations that blurs the line between species and subspecies and it illustrates intermediate forms in the speciation process. The figure below is from a 2004 paper that challenges the view that the herring gulls are an example of a true rassenkreis.   Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Figure on the left represents the classic view, as described in our podcast, of how the herring gull species complex came about. The new alternative mode, figure on the right, reveals multiple origins, allopatric speciation events, and more complex dispersal patterns. Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} We also discussed Carl Linne’ (Linnaeus) and the organization scheme he proposed in 1735 that involves nested hierarchies: Kingdom > Phyla > Class > Order > Family > Genus > Species which we still use today.  James noted how Linnaeus looked like Ed Asner with a wig and questioned Linnaeus’ decision to use himself as the type specimen for all Homo sapiens.   Modern Carl Linnaeus as portrayed by Ed Asner Typ

  This is episode 2 of the series and we read and discuss Chapter One from Origin of Species entitled Variation Under Domestication. We talked about the great diversity of pigeon breeds that Darwin was impressed with and used as a model to explain how selective breeding can create new varieties and forms. Scroll down on this website to see a nice slide show of Pigeon Breeds. James made the claim that giraffe's necks are actually short compared to other herbivores in Africa and this photo shows a giraffe having to kneel to drink water where the zebras have no problem reaching the water with their long necks. Giraffe and group of Burchell's zebras drinking at a waterhole in Kruger NP by Holger Karius on Dreamstime.com The scientific paper that Sarah referenced concerning a current view of dog evolution can be found here.   Wired magazine wrote a nice summary of the cattle evolution story and it can be found here. Interlude music within the podcast is "Vadodora Chill Mix" Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 http://creativecommons.org/licenses/by/3.0/

In this first episode of Discovering Darwin, Sarah, Josh and James introduce you to Charles Darwin - the man and the myth. We explore who Darwin was in his time and how he came to develop one of the most influential idea of the 19th Century.   One of the great online resources about Darwin and his life is the Darwin Online website maintained by the UK Arts & Humanities Research Council. This amazing website has all of Darwin's works online as TEXT files, PDFs and, most excitingly, as IMAGES of the original books. You can peruse the digital pages of actual books and see random annotations from readers of the past. It has all of Darwin's published works, notebooks, letters, journal entries and random interesting documents like student bills, marriage note and diaries. It also has other relevant books from other authors that were in Darwin's personal library.  During the discussion James referenced a wonderful book by Rebecca Stott called Darwin's Ghost but, unfortunately, he forgot the author's name at the time.  Darwin's Ghosts explores in detail a number of the people Darwin acknowledges in his short introduction chapter called An Historical Sketch.  The opening theme to Discovering Darwin is "May" by Jared C. Balogh. http://freemusicarchive.org/music/Balogh/Revitalized_Eyes/MAY  Copyright: Attribution-NonCommercial-ShareAlike:  http://creativecommons.org/licenses/by-nc-sa/3.0/