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Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892

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BuyFindarrow_forward

Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

Discuss Concepts Humans have about 200 million photo- receptors in two eyes, and about 32,000 sensory hair cells in two ears. About 3% of the somatosensory cortex is devoted to hearing, whereas roughly 30% of it is devoted to visual processing. Suggest an explanation for these differences from the perspective of natural selection and adaptation.

Summary Introduction

To review:

The reason due to which only 3% of the somatosensory cortex is responsible for hearing while 30% of the sensory cortex is responsible for vision, based on natural selection.

Introduction:

The sense organs are not just present in vertebrates but are also present in different forms in invertebrates and single-celled organisms as well. The single-celled organisms are able to detect a chemical change in water. Invertebrates have very simple types of receptors that help them detect any change in their environment so that they could move to a safe harbor. The visual receptors and auditory receptors have evolved over the course of time. It has been speculated that eyes were the first sense organ that developed in living organisms.

Explanation

The eyes in vertebrate have photoreceptors that detect even a single photon and transduce the signals to the visual cortex of the brain. Studies have shown that there are about millions of photoreceptors, such as rods and cones that are located in the retina of a vertebrate’s eye. A simple organism like earthworm also has a few receptors that are not located in any specialized visual organs. The photoreceptors of earthworm are located in the skin and aid the organism in detecting light so that it can move away from it. Other organisms like planarian also sense light so that it can negatively respond to it by moving away from well-lit areas.

As the organisms became more complex, eye-like structures began to develop in them. The simplest types of eyes are compound eyes that are present in fruit flies. They have oomatidium which can detect even a small change in their environment...

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