The evolution of the eye has been a subject of significant study, as a distinctive example of a homologous organ present in a wide variety of taxa. Certain components of the eye, such as the visual pigments, appear to have a common ancestry: that is, they evolved once, before the animals radiated. However, complex, image-forming eyes evolved some 50 to 100 times – using many of the same proteins and genetic toolkits in their construction.
Complex eyes appear to have first evolved within a few million years, in the rapid burst of evolution known as the Cambrian explosion. There is no evidence of eyes before the Cambrian, but a wide range of diversity is evident in the Middle Cambrian Burgess shale, and the slightly older Emu Bay Shale. Eyes show a wide range of adaptations to meet the requirements of the organisms which bear them. Eyes vary in their visual acuity, the range of wavelengths they can detect, their sensitivity in low light levels, their ability to detect motion or resolve objects, and whether they can discriminate colours.
Read more about Evolution Of The Eye: History of Research, Rate of Evolution, One Origin or Many?, Stages of Eye Evolution, Evolutionary Baggage
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“The evolution of humans can not only be seen as the grand total of their wars, it is also defined by the evolution of the human mind and the development of the human consciousness.”
—Friedrich Dürrenmatt (1921–1990)
“The body was still resting on its legs, leaning against the end of the side of the bed, while one of the arms was close clasped round the bed-post. The mouth was rigidly closed, but the eyes were open as though staring at him.”
—Anthony Trollope (1815–1882)
“What we think of as our sensitivity is only the higher evolution of terror in a poor dumb beast. We suffer for nothing. Our own death wish is our only real tragedy.”
—Mario Puzo (b. 1920)
“The more specific idea of evolution now reached is—a change from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity, accompanying the dissipation of motion and integration of matter.”
—Herbert Spencer (1820–1903)
“For any eye is an evil eye
That looks in onto a mood apart.”
—Robert Frost (1874–1963)