Define population pressures which is a selective pressure.

Selective pressures are environmental factors or influences which may lessen reproduction in a species’ population and therefore contributes to evolutionary change or even extinction through natural selection.

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it is very expensive

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what do the different brain waves do?

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brainwaves are produced by synchronised electrical pulses from masses of neurons communicating with each other. brainwaves are detected using sensors placed on the scalp. brainwave speed is measured in hertz (cycles per second) and they are divided into bands delineating slow, moderate, and fast waves.