Tuesday, April 7, 2009

In the beginning of chapter 4, Carroll describes how colobus monkeys and chimpanzees use their sense of vision to find food and how the trichromatic vision of colobus monkeys allows them to select red leaves that are generally tender and young. What are other types of distinctions in the senses that give some organisms an advantage over others lacking this adaptation? Be sure to explain how this distinction within a sense has evolved and how it gives an organism a competitive advantage over another organism lacking this trait.

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  1. Amie KimApril 7, 2009 at 6:48 PM

    The specialized hunting behavior of cats led to their improved sense of hearing. While dogs possess a much keener acoustic range than human beings, cats surpass even dogs in their ability to hear high-pitched sounds. This is because humans and dogs rely most on tracking and snaring their prey, whereas cats choose to lie in wait in ambush and listen very carefully for the most diminutive sound. This hunting behavior made it crucial for cats to develop a high sense of hearing that could detect the most minute rustlings and screeches and pick out accurate direction and distance to pinpoint their prey.
    32 individual muscles in each ear allow for a manner of directional hearing, allowing for the cat to hear sounds from everywhere around it. The cat’s hearing range is 45 to 64,000 Hz compared to 64-23,000 in humans. They can hear both sounds of higher and lower frequency than humans are capable of hearing. Cats’ ears are uniquely designed to draw sound into the ear canal, and they are capable of hearing the sounds of a mouse rustling in the brush 30 feet away. Their ears are also more sensitive to higher amplitude of sound. Through its high sense of hearing, cats are able to locate the source of a sound, serving as a selective advantage when cats are hunting and need to locate the prey exactly. From a yard away, a cat can distinguish between sounds from sources only 3 inches apart.
    The development of cat’s high sense of hearing is the result of natural selection. The genes of the cat randomly mutated that allowed for a selective advantage in hunting resulted in the greater survival of the organisms with a selective advantage and the genetic inheritance of the advantageous genes to future generations. When there are random mutations that lower the cat’s keen sense of hearing, natural selection eliminates it with the power to “rigidly destroy injurious variations” (Carroll 83). The advantageous variations are preserved and passed on to future generations and further modified to today’s very keen sense of hearing.

    http://cats.about.com/od/healthfaqs/f/hearingsense.htm

    http://ezinearticles.com/?How-Keen-is-a-Cats-Hearing?&id=2062854

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  2. Mark LeeApril 7, 2009 at 7:05 PM

    A prime example of the differing evolution of senses due to environmental stresses can be seen by comparing the structure of the human eye to the structure of the feline eye. Many cats are highly active at night, and therefore require being able to see in darkness. As those cats that could see better in darkness have a better chance of feeding, and therefore reproducing, it was made a selective advantage to be able to see in the dark. Over the course of evolutionary history, several adaptations have arisen in the cat eye. The first is that cats have mussels surrounding their iris that can both narrow and widen their pupils depending on light conditions. This allows cats to expand their pupils as much as possible at night, to maximize the light entering the eye. Also a reflective layer behind the cat's retina called the tapetum can reflect light, allowing the rods and cones of the eye two opportunities to sense the light. Finally cats have evolved to have a higher proportion of rods to cones in their eyes than non nocturnal creatures. This is important as rods are highly light sensitive, allowing cats better night vision, however rods also are unable to discern wavelengths, therefore, cats are unable to see color as clearly as humans. These factors allow cats to see in one sixth the amount of light required for human vision.
    The eyes of humans, on the other hand, lack a tapetum, do not have as fine control over our pupil size as cats, and have higher proportions of cones in their eyes. This is because night vision was never a selective advantage for primates, because they were more active in the day than at night. Also, tying into Carroll’s example, we need the enhanced color vision granted to us by the relitivly high percentage of cones in our eyes (around 5%) to successfully differentiate between ripe and non ripe foods.

    http://cats.about.com/cs/eyesvision/a/cats_eyes.htm
    "Cats in the Womb"
    http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html
    http://www.ehow.com/about_4586813_are-cats-colorblind.html

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  3. Anirudh P.April 8, 2009 at 10:08 PM

    In the wild and in our world, it is the survival of the fittest. Only the strongest organisms and the ones that are most adaptive to change will survival. To survive a species has to be adaptive to the environment around them. Bats, for example, have developed keen distinctions in their senses to give them advantage over other organisms. Bats have a keen sense of hearing as they can hear frequencies between 3000 and 120000 Hz. This is a great advantage because they can be aware of predators which pose a threat to them. A noise from far away would alert the bat and it could take preparations in defense or fleeing the place they were stationed before. They can pick out the itty gritty noises or screeches which can help make them more alert. Another key point for their need for high frequencies is to navigate their way in the dark because they are nocturnal. The bats use echoes to carefully coordinate where they are and what is coming up. These frequencies are so much higher than many other organisms and this creates an advantage in that they can pick up different sounds at different frequencies that other organisms wouldn’t be able to pick up. Another key sense that gives a selective advantage towards these animals is that they can catch prey very easily with the supersonic hearing. As I have stated the bats use echolocation to navigate their way around. They can also use it for catching prey. They emit noises at very high frequencies which can only be picked up by them. The noise bounces off a prey and it returns to the bat. Their brain interprets the signals, allowing for accurate hunting. This is a selective advantage because other nocturnal animals can’t do this. This is a quite and sneaky way to hunt. Some bats have a fleshy structure called a "nose-leaf" surrounding the nose. These bats generally fly with their mouth closed and emit ultrasound through their nostrils. The nose-leaf is thought to act as a directional amplifier of this ultrasound, which is used to avoid obstacles and locate prey. The selective advantage and natural selection of these characteristics have made the bat very unique and this results to an advantage over other nocturnal organisms.

    http://faculty.washington.edu/chudler/amaze.html
    http://en.wikipedia.org/wiki/Bats
    http://en.wikipedia.org/wiki/Phyllostomidae

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