One hypothesis David Shenk discusses regarding the superior running ability of the Kenyan Kalenjin tribe relates to an economic incentive. Kenyans may have obtained their running ability after generations of cattle raiding—the more cattle a man had, the more wives he could pay for (103). Similarly, evolutionary adaptations are prevalent in the history of animal diversity. For example, Cephalopods, as a result of requiring high energy, have developed closed circulatory systems whereas the majority in their phylum, Mollusca, still has open circulatory systems. Now, discuss some evolutionary adaptations developed throughout time that distinguishes phylum from phylum, class from class, etc. Hint: think about tissues (diploblastic, triploblastic, or none); body cavity (acoelomates, pseulomates, or coelomate); open or closed circulatory systems; cephalization; segmented bodies; etc. Refer back to Unit 13 (Invertebrate and Vertebrate) as needed. Relate your answer to the theme of evolution.
~Linda Xu (lindaxu22@hotmail.com)
-The Argument
ReplyDeleteI can definitely see the importance of cattle raiding in relation to the running ability of the Kenyan Kalenjin tribe considering cattle raiding requires greater active duty of these Kenyans in addition to the economic incentive you had discussed. We can also relate the running ability of the Kenyan tribe to Shenk’s GxE interaction in which “genes powerfully influence the formation of traits” as well as “a wide range of external and internal stimuli” (Shenk 19-20). In the case of Kenyans, we don’t see genes dominating the traits that Kenyan gain, but rather the active duty and economic incentive brought about by the environment.
In a majority of animal diversity unit, we were introduced to many different animals that all diverged from a single common ancestor, yet differ in body structure, energy use, and most importantly, the environment. When we look at the formation of a body cavity from the animals of Phylum Porifera and Cnidaria that lack a coelom or pseudocoelom, the body structures of acoelomates lack the specific organs that coelomates and pseudocoelomates have in order to survive in demanding environment and maintain energy use. In terms of cephalization and the introduction of closed circulatory systems, the animals from Class Cephalopoda of Phylum Mollusca show how environmental stress has triggered change in the bodily systems of Cephalopods. Unlike other classes of Phylum Mollusca, Cephalopods are cephalized (they have a head and foot) and have closed circulatory systems due to their demand for energy for their carnivorous diet as well as quick, directional movement through water to avoid the cephalopods’ predators (Campbell 680). The fact that many vertebrates have developed closed circulatory systems as well is due to the internal stimuli of expending a large amount of energy while accounting movement because of the environmental stresses of predators and climate, especially terrestrial animals that lack continuously, available moisture.
In Nico Eisenhauer’s journal article, “Impact of above- and below-ground invertebrates on temporal and spatial stability of grassland of different diversity,” Einerhauer talks about moisture and light can affect biological clocks and energy expenditure of earthworms, below-ground insects, and above-ground insects. We can relate Eisenhauer’s article back to the idea that through environmental stress, insects above ground rely on light in order to determine when to expend their energy for food whereas earthworms and below-ground insects have to rely on the temperature and moisture of their environment to determine the amount of energy spent for food.
Due to the inherent role of environment on animal diversity, the theory of evolution can incorporate how animals from different environments share similar genes, but have changed the function of certain body systems to survive under the stress of internal and external stimuli. Evolution is no longer based on the passing of genes from parent to offspring, but on the environment as well because “the environment demands development” (Shenk 41).
-Trish Chari (trishtennis@gmail.com)
In response to Trish’s comment, I definitely agree with the role cattle raiding plays on the epigenome of Kenyans, making them fast runners. However, I also believe that personal mental motivation other than cattle raiding is a big factor in the determination of Kenyan epigenomes. For example, David Shenk states that “the brain drives the brawn… [and an] increase in specific task knowledge … [and] elaborate self-monitering mechanisms that allow for constant adjustments in real time” account for much of any “genius’” success in his or her field. I just want to mention that the individual runner has a mental as well as reproductive advantage over lesser runners because they’ve developed intuitive thinking that is “saving time and energy” for themselves, making themselves incredibly efficient.
DeleteIn response to Linda’s post, I can relate the evolutionary adaptations of Kenyan runners to the adaptations of (invertebrate) sea wasps, from the Cnidarian phylum. Whereas the Kenyans’ environment of cattle herding demanded long distance running from the ranchers and created a selective advantage for the better runners, the sea wasp’s environment similarly creates a selective advantage of having poison that can “subdue fish and other large prey, [and] is more potent than cobra venom” (672). I would imagine that super-potent venom on the tentacles of sea-wasps will make it easier for the sea-wasp to capture prey in an environment where this are a lot of other animals competing for the same food;the Pelagic zone is the sea wasp’s habitat. (Courtesy of http://www.ucopenaccess.org/mod/resource/view.php?inpopup=true&id=25115). Relating back to our ecology unit, the reason that the Pelagic zone is filled with so many tertiary consumers (such as the sea wasp) who feed on the abundant amount of secondary and primary consumers, which is caused by the huge amounts of phytoplankton that live in a photic zone. Examples of primary and secondary consumers in a marine food chain include zooplankton (primary) and fish (secondary).
Another challenge the environment puts on the sea wasp that has caused the species to evolve so that their venom is so deadly is the loss of net production as each link of the food chain progresses. As a tertiary consumer, a sea wasp jelly would probably only get around one-thousandth of the available energy available to the primary producers (like algae and phytoplankton) (1229). (Courtesy of our Campbell textbook). Over time, only the box jellies that captured the largest prey or the most prey with the most potent venom would out-survive other box jellies and reproduce. Therefore, the amount of energy available for net production as the trophic level increases plays a large role in the evolutionary adaptations of a sea wasp.
(Tina Ding: yuning.tina.ding@gmail.com)