Homologous and analogous structures are two types of evolutionary evidence, taken together, provide strong evidence for when extinct species most likely diverged from common ancestors, relative to other events happening on Earth.
Several types of evidence support the theory of evolution: If two or more species share a unique physical feature, such as a complex bone structure or body plan, they can all inherit this property from the common ancestor. Physical traits shared through evolutionary history (common ancestor) they say they are homologous. Not all physical properties that look similar are signs of common ancestry. Some physical similarities instead are analogous: they evolved independently in different organisms because organisms lived in similar environments or experienced similar selective pressures.
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When our red-sensitive nerves in our eyes cannot respond to light properly this will result in color blindness - b.
When either of the three light-sensitive nerves in our nerve tracts; either green, red or blue, we become to color blind for a certain spectrum of light from nature.