Shubin addresses that DNA extracting allows us to determine history of ANY part of the body, such as the inducing sense of smell. (140) Our ability to detect thousands of scents is advantageous as in attracting and repelling us towards different objectives. The tiniest molecules are detected as smells towards the brain through a lock-and-key model-type mechanism. However, odor genes vary in amount from animal to animal. Discuss genetic and evolutionary contributing factors of the potency of odor genes have in a a variety of species. For example, why is a human's sense of smell is much weaker than a dog's?
Kyle Kim (piece847@gmail.com)
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ReplyDeleteIn response to Jackie's comment about dogs depending on smell because they cannot see in color, dogs and other animals also depend heavily on smell in order to find prey (before they are domesticated). Nasal bones called conchae contain receptors that are stimulated by odor molecules, so an "odor is distinguished by how fast and where its molecules become attached to the receptor cells" (http://www.robinsonlibrary.com/science/physiology/senses/smell.htm). In this way, earlier species determine which prey is edible by the odors that are released from the individual.
ReplyDeleteLater species in evolutionary history have become more developed. As Jackie mentioned, humans have the ability to see in color, where dogs don't have this advantage. As time went on, vision began to take over as an evolutionary advantage over smell. While many more developed mammals like humans depend heavily on sight to survive during the day, earlier species used smell to navigate and survive. As eyesight increased however, receptors for odors diminished because they weren’t in use as much anymore. This pattern continued through evolution of different species until the later generations all depended more heavily on their other senses.
On the topic of pheromones, many animals also depend on odors picked up from pheromones in order to reproduce. In insects and certain mammals, “pheromones trigger specific courtship behavior” (Campbell 1125). To reproduce, many animals depend on the opposite sex releasing a pheromone so that the individual can find a mate. They rely on their sense of smell because the pheromones release odor molecules as well. However, because the human sense of smell is not as strong as other species, humans rely on visual factors to attract to the opposite sex. Pheromones don’t play an important part in reproduction for humans when they can’t smell the pheromones, but other species can only rely on pheromones to reproduce.
Claire Yao (claire.yao521@gmail.com)
Smell works by lock-and-key neuron receptors in the nasal cavity binding to particular molecules and transmitting resulting signals to the brain for processing (http://health.howstuffworks.com/human-body/systems/nose-throat/question139.htm). According to "The Molecular Biology of the Cell," "It is thought that there are hundreds of different olfactory receptors, each encoded by a different gene and each recognizing different odorants" (http://www.molbiolcell.org/).
ReplyDeleteThe potency of odor genes in different animals is a result of varying levels of environmental pressure on each animal's sense of smell. Dogs can detect chemical scents at 18ppm, whereas humans require 198ppm (MSU Department of Biology). This is because dogs evolved largely as scavengers, which needed to distinguish between different odors of food for survival with high precision, whereas humans were hunter-gatherers.
This pressure resulted in natural selection favoring dog-ancestors with a greater variety of olfactory receptors, as they could more efficiently determine where there was desirable food. Although this same pressure applied to humans, it was much less acute than that on dogs, so there has been less human evolution toward highly developed olfactory receptors (because, like every other evolutionary physiological development, it would take more energy to develop and maintain a highly developed sense of smell than a moderately developed one). As a result, dogs generally have around 220 million olfactory receptors in their noses, while humans have only about 5 million (http://www.aces.edu/pubs/docs/U/UNP-0066/UNP-0066.pdf).
- Vincent Fiorentini
(vincent@panatechcomputer.com)