Step in Speciation


 Speciation & Maroevolution

An Interactive Activity by Joe Walsh

Ring Species: sub-species separated in space. Compare human-chimp lines, separated from LCA (Last Common ancestor) in time, in similar fashion. Biology teacher Joe Walsh describes a kinesthetic activity relating ring species (speciation in space) to phylogenies (speciation in time) in his article in the Dec. 2007 issue of The Science Teacher (Idea Bank, pp. 62-64) The activity should take about 20 minutes. You may need to be a member of NSTA to get this from their archives. If you can't find it, contact the ENSI Webmaster

Joe derived his idea while reading Chapter 1.3 in Richard Dawkins' A Devil's Chaplain (2003). In that chapter, Dawkins uses the well-known example of a ring species of the circumpolar Herring Gull / Lesser Black-backed Gull ring. Instead, Joe Walsh used the Ensatina salamander in California for the ring species example in his article.

In response to a discussion topic, Joe posted the following on the NSTA listserve:
Ask your students to visualize the following as you read it: 1) a human chain formed by joining your left hand to your mother's right hand, and your mother links her left hand to her mother's right hand, and so on through your maternal ancestors in a straight line; 2) a chimpanzee faces you and does the same thing with his or her mother, grandmother and ancestors in a line paralleling your ancestral line, forming a chimpanzee chain; 3) the two lines will form a common line after about 448 km (280 miles, allowing one meter per person, each representing a 20-year generation); it may help them envision this by showing a map from say, Boston to Syracuse, or similar familiar distance in your area. The only visible manifestations of this common ancestry will be you and the chimp's immediate 2 or 3 ancestral generations, but the ancestry and common descent is clearly shown, and also the fact that humans are not "descended from chimps."
Joe Walsh .

After posting this description, Joe received a couple questions about it, so he added these details:
Asked about what materials he uses with the activity, he said "I use no props except a picture (from the textbook) of the ring of Ensatina variants around the Central Valley of California and the paint chip cards that you can get at Home Depot. Try to get 7-9 tones that form a continuum in one color, and likewise for a similar color that grades from the same extreme shade (for the common ancestor) of the other set. " [See another source for Ensatina below, at the end of this article].

Have the students line up exactly as the Ensatina diagram shows (the separate species towards the bottom in Southern California and the two most different colors toward the back of the room), with one student toward the front of the class, and two lines from that student to either side of a row of desks [There are 10 subspecies used in the ENSI lesson linked to below, with most ringing the Great Central Valley of California.]. The student towards the front holds the paint chip that is in the middle range of all the paint chips as far as color, and two lineages of color changes going off to either side of the desks. They can see that that there is a gradual continuum and that the phrase "incipient speciation" might be applied to the variants on either side close to the front of the room, but the two "variants" furthest from the front of the room might be different enough to be considered two species. It may be hard to tell the subtle differences between adjacent color chips, but the difference between the color chips of the two students furthest from the front is obvious. This basically forms a phylogenetic tree in space. It just so happens that all the intermediates in the ring are still alive, and the continuum is still evident.

Once this is done, the phylogenetic tree in time is drawn on the board with exactly the same format, with the hominid line on one side and the chimp line on the other. [Probably best to show this with the LCA (last common ancestor) at the bottom of the "V" shape - in its relative geological time position.] The student who is towards the front of the room is now the LCA of humans and chimps, and the desks represent separation by time. This is the phylogeny in time. All the members of the continuum are NOT seen in the present. We can dig up some fossil hominid members of the lineage to modern humans, but even these are probably not on the line [unlikely to be exact lineal descendents - more likely to be side branches, but sharing features similar to the actual lineal ancestors]. And there are no fossil members found on the chimp line [forest habitat of chimps is acidic, so bones don't survive long enough to fossilize]. So the connection between humans and chimps is harder to visualize (than those in the ring species examples) since there are gaps in the lineages, but this phylogeny in time is just as real as the phylogeny in space.

Ring species are used as the bridging concept for those who are willing to accept microspeciation but have a harder time with macrospeciation (those who "believe in inches but not miles"). Creationists will create a strawman by asking at what point a human/ chimp ancestor gave rise to one chimp lineage and one sibling human lineage. The ring species demonstrate incipient speciation, possible early interbreeding and hybridiization, and the continuity of life. The dichotomies and labels that scientists create are operational tools of convenience more than reality. [Studies have actually shown evidence of interbreeding and hybridization with early chimps in the early years of our lineage. In addition, the human lineage clearly shows many examples of a mosaic of traits - a patchwork mix of both human and chimp features - with a clear and gradual shift to an increasing balance of human traits with a decreasing proportion of chimpanzee traits over time. For first hand experience with this, do the Skulls Lab on the ENSI site - especially by using the materials developed by Larry Flammer - item #7 - in the Extensions & Variations section.]

Chapter 1.3 in Dawkins' book A Devil's Chaplain deals succinctly with this whole concept and is a great read, as is the whole book, for any biologist. I realize that Dawkins has now become famous as much for his atheism as for his biology, but books like The Selfish Gene, The Blind Watchmaker, and The Ancestor's Tale are incredibly rich and provocative just from the scientific viewpoint.

Coincidentally, I was listening to a podcast yesterday that had an interview with Peter Singer, the author of The Great Ape Project referenced in Dawkins essay in A Devil's Chaplain. Singer believes that all sentient beings, whether human or non-human animal, deserve respect, and therefore we should all abstain from carnivory. Dawkins has long held the view that at least the great apes deserve some protection. When Dawkins was asked if he eats beef or chicken, he replied that he did, and he admitted that he was hypocritical to some extent. However, in my view, the exercise with the students of forming a human chain back to the chimp/human LCA just shows that all of us, vegans included, are always eating our relatives. We are obviously more closely related to chimps, then gorillas, then Asian apes, then other primates, then mammals, etc. But we are still related by common ancestry to those tomatoes in our salads, just more distantly. Dawkins didn't bring that up in his reply.
Joe Walsh .

See ENSI lesson: A Step in Speciation for full color illustrations of the 10 sub-species of Ensatina salamanders, and a map of California where students can plot their locations.

Article in the Dec 2007 issue of The Science Teacher (Idea Bank, pp. 62-64) by Joe Walsh.