Thursday, March 26, 2009
Senses
On page 128 Carroll speaks of the relationship between sense of smell and sight, stating that there is a "striking correlation between the proportion of fossilized olfactory receptor genes and the evolution of full color vision" and that " the evolution of trichromatic vision has reduced their reliance on the sense of smell". My question is whether or not there are any other correlations between other senses and their intensity, perhaps a reason for the differences in hearing amongst species?
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Our sense of smell has weakened over time along with our sense of hearing. As a species humans have become smarter and rely on other things to get their information across to them. Humans do not face iminate threat from other predators. The evolution of the eye that produces color is important because it allowed humans before civilizations to spot potential prey and other animals that could possibly hurt and attack humans. Dogs on the other hand have a very keen sense of smell and a much wider range of hearing. This however is not as strong as the wolves sense of smell or hearing. This is because a wolf is not a domesticated animal and has to continuously look around for prey and watch for predators. They are able to smell something different and hear possible things that will need to protect themselves. Dogs evolved from wolves because they were domesticated by humans for their use and help. As they evolved from wolves they got smaller snouts and teeth; that lowered their need on the sense of smell and it become weaker as a result. They got their food and protection from humans and they did not have to worry about others going to hurt them. Dogs eyesight now needs a little more light than wolves do but still very functional in the night especially for hunting. A dogs hearing is also much better than humans but also worse than a wolves because over time they lost several muscles in their ear to help pinpoint a noise and to hear a wider spectrum. I think that as animals evolve and become more reliant on certain traits the others become weaker and then will weaken as in dogs coming from wolves they are not being hunted nor doing any hunting, but they are given things by their owners. This is just like the human reason because they use color in their eyes to detect most of the information they need, and are not needing as much of their other traits to be successful. Also humans brains have evolved to create many more thing to rely less on our senses so over time our sense will still get weaker.
ReplyDeleteIf we focus on primates alone, although true for all organisms, we see that the perfection in the evolution of certain senses correlates with the demands of the ecological niche for these organisms. The book focuses on the relationship between the senses of sight and sound. The evolution of the auditory sense also warrants evolutionary attention.
ReplyDeleteThe evolution of the auditory sense is fueled by the need to register those phenomena which can not be seen. For example, hearing is necessary for those who are nocturnal or live in dense tropical rain forest environments, both of which characterize primates and probably the first qualify for. While there is no doubt that prey localization is facilitated by the auditory system, this by no means precludes selection for increased visual field overlap to improve image brightness and break crypsis. There is a direct relation between the width of the field of best vision and the degree of auditory acuity. For example, animals that devote a very narrow portion of the visual field to high visual acuity also have a well-developed ability to localize a sound source in space. Thus, the function of sound localization ability is to inform the visual system where to look- a sort of coupling of the senses facilitated by natural selection. This suggests that selection for increased visual field overlap in early primates would have been associated with increased sound localization ability as well. Some argue that small mammals augment high-frequency hearing to facilitate use of spectral cues in localization of sound sources in the environment and that large animals such as humans and elephants do not retain good high-frequency sensitivity because they do not need it for sound localization.
The evolution of the sense of touch also is adapted to make-up for faults in the other senses. The mammalian somatosensory system (a diverse sensory system comprising the receptors and processing centers to produce the sensory modalities) permits inferences about the physical properties of the outside world, using information from receptors that respond to touch and vibration, body movement, temperature, and painful stimuli. Interestingly, anthropoid primates have several unique specializations, first in the density of digital mechanoreceptors, where there is an unusual emphasis on the hand as tactile organ, and then in the thalamus and cortex, where more subdivisions of the brain are devoted to somatosensory perception. Such elaborations and specializations appear to relate largely to the recognition and identification of objects and surfaces by touch. The process of object identification is aided by fine motor control of the hand and fingers and modifications in the motor cortex. Some receptors in the skin have evolved to have two functions: frictional and tactile. Although an enhanced tactile sensitivity on slender locomotors substrates probably conferred strong selective pressures to primate ancestors, the dispersion of these receptors in anthropoid fingers raises the possibility of a more specialized co-opted function (a structure that evolved because of the demands of fruit selection). Softening texture is a salient sensory cue during fruit development and perceiving the textural properties of fruits may provide a rapid means of discerning edibility. Primates have thus evolved the behavior to palpate fruits during foraging. Therefore a major drive for the coupling of the hearing, touching, and already explained olfactory and vision senses is the drive for food.
Sources:
http://people.ucsc.edu/~njdominy/publications/pdf/Anat_Rec_Intro.pdf
Our sense of smell has weakened over time along with our sense of hearing. As a species humans have become smarter and rely on other things to get their information across to them. Many believe this is because of our hyper evolution of the brain. It is thought that because the brain is so powerful it can take little/weak amounts of information, and make very good conclusions from it. Humans do not face imminent threat from other predators. The evolution of the eye that produces the full color is important because it allowed humans before civilizations to spot potential prey and other animals that could possibly hurt and attack humans. This evolution of the eye gave it a stepping stone above all other hunters and gathers because it enables for quicker differentiation through similar things but one might be poisonous and the other is just mimicking it. This is an example of Batesian mimicry. Dogs on the other hand have a very keen sense of smell and a much wider range of hearing. This is done because their eye is not as advanced as the human eye making it need to excel in other areas to succeed. Also, the dog brain is not an advanced as the human brain, so it will need more refined methods of getting their information processed in a quick responsive matter. This is simple physiology because the dog brain is smaller; but the more muscles in a larger ear let the dog hear more as well as position it to hear well in every direction, and the nasal cavity is larger as well letting it able to process much larger amounts of odor in comparison to the human. This however is not as strong as the wolf’s sense of smell or hearing. This is evidence is different dog breeds who are more adapted to hunting have stronger smelling and hearing senses compared to smaller dogs who are not as well structured for hunting. This is because a wolf is not a domesticated animal and has to continuously look around for prey and watch for predators. They are able to smell something different and hear possible things that will need to protect themselves. Dogs evolved from wolves because they were domesticated by humans for their use and help. As dogs evolved from wolves they got smaller snouts and teeth; that lowered their need on the sense of smell and it become weaker as a result. They got their food and protection from humans and they did not have to worry about others going to hurt them. Dog’s eyesight now needs a little more light than wolves do but still very functional in the night especially for hunting. A dogs hearing is also much better than humans but also worse than a wolves because over time they lost several muscles in their ear to help pinpoint a noise and to hear a wider spectrum. I think that as animals evolve and become more reliant on certain traits the others become weaker and then will weaken as in dogs coming from wolves they are not being hunted nor doing any hunting, but they are given things by their owners. This is just like the human reason because they use color in their eyes to detect most of the information they need, and do not need as much of their other traits to be successful.
ReplyDeleteI think as the power of the eye has evolved, it has made the need for other important senses to be less relied on. As seen in dog’s evolution from wolves, they still posses’ strong abilities to help them survive, but come closer to a human eye because they need more light to function and their eyesight has a little more variation of color. When comparing humans to monkey especially chimps it is obvious to see that the full color eye is very important evolutionary step. Physically the chimp’s nasal cavity is a little bit larger than the humans giving it a better sense of smell. Then their ears are much larger so it has a much better hearing than humans. It is obvious that the chimps and humans gave up their keen sense of smell for full color eye sight, and it is shown that chimps do not have a full three color eye sight, but are color blind to some colors and can learn to differentiate them. This is also shows the reason their olfactory genes are still larger than humans. These examples show that full color eye sight is sought after by many animals and once it has devolved it; it weakens other senses because of the vast knowledge and ability is posses itself.
http://www.deepmarket.com/uncategorized/degraded-sense-evolution-of-human-scent/
http://genome.wellcome.ac.uk/doc_WTD020881.html
http://www.aces.edu/pubs/docs/U/UNP-0066/UNP-0066.pdf