In chapters 8 and 9, Schubin discusses how, over time, a strong sense of smell has been replaced with advanced vision. Why did this change occur? What does this tell us about the changes happening to the earth during this time? What does this tell us about the lifestyles of these animals? How does this show the theme of evolution?
Marissa Lobl marissa.lobl@gmail.com
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ReplyDeleteOver time, primates developed advanced vision, and though their sense of smell has been compromised, it still exists in a less extreme form. Smell is the body’s response from molecules inhaled through the nose, stimulating nerve cell receptors. This ability has allowed organisms to detect pheromones in the air and sense when other animals, such as a possible predator or prey are near based off their scent. Many animals depend heavily on this sense such as the silkworm moth that detects the moth sex pheromone for mating, but most animals do have receptors for other specific molecules such as carbon dioxide, glucose, oxygen, etc. (Cambell 1090).
ReplyDeleteHowever, some organisms adapted the ability to detect light waves, which move much faster than air and therefore are a much more reliable source of information(http://people.ucsc.edu/~njdominy/publications/pdf/Anat_Rec_Intro.pdf). This adaptation of sight as well as the neurological advances that allowed animals to recognize shapes and objects became much more favorable than the ability to smell (Campbell 1074). And as the theme of evolution suggests, an organism with a more favorable adaptation is more likely to survive and reproduce to carry on that trait to its offspring.
Gilad et al. concluded this idea in their study of primate genes in an attempt to show that as sight developed in primates, their smelling ability began to decrease. In their experiments, they found that full trichromatic vision such as that found in many old world monkeys as well as the howler monkeys did lead to deterioration of the olfactory repertoire(http://naturalsystems.uchicago.edu/evolgenome/Gilad_Olfactory-Receptors.pdf). In conclusion, although many animals do still rely on the sense of smell for identifying other organisms or avoiding dangers, primates have developed an ability to identify objects and organisms through the much more efficient and quick approach of sight.
(Alex Sapozhnikov marijio@gmail.com)
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ReplyDeleteFurther elaborating on this idea, humans and their close ancestors began to lose their strong sense of smell just as whales and dolphins lost theirs. Dolphins and whales no longer used their nasal passages to smell,rather, they used them as blowholes. As in humans, this was important because they still contained all of the odor genes but not one was functional.(Shubin 146) Since the genes are still present in the DNA, they remain as silent records of evolution.
ReplyDeleteAs described above by Alex, the purpose for the transition from a strong sense of smell to sight was because of the effectivness of sight. The Max Planck Institute for Evolutionary Anthropology founnd that a decrease in the size of the intact olfactory repertoire, this gives sense of smell, occurred independently in two evolutionary lineages: in the ancestor of Old World monkeys and apes, and in the New World howler monkey.(PLOS Biology) It offered a better means for close ancestors of humans to hunt and perform daily routines. Thus, humans still have hundreds of usless olfactory genes remaining from mammalian ancestors(Shubin 147).
The eye evolved from simple eye spots that were sensitive to light.As specific animals were using these sensitive areas for different purposes, some developed no more than black and white or blurry vision while others can see ten times farther and clearer than humans.(Dermo) Overall, as animals began to develop strong sight, survival favored animals which could see farther, thus starting the transition from strong smell to vision; nowadays we see the evolutionary history of olfactory genes as they are present in most mammals but are in an "inactive" form.
Eryk Fundakowski- arthur2446@comcast.net
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC314465/?tool=pmcentrez
http://test.abovetopsecret.com/forum/thread542777/pg1