<span>All mammals have at least one X chromosome. Female mammals have two X chromosomes, so each of her eggs has a single X chromosome. Male mammals have XY chromosomes, meaning they can generate sperm containing the X chromosome, or sperm containing the Y. If the egg receives sperm containing the X chromosome, then the resulting individual forms ovaries, and is female.</span>
It is a perfect example of a natural selection.
(I'm not sure if this is the exact answer that you are looking for.)
This evidence supports the claim that some emotional reactions may occur without conscious thinking.
Thalamus is a small brain area located above the brain stem, with the main function of sending motor and sensory signals from the spinal cord and the mid-brain structures to the cerebral cortex.
Amygdala is a small brain region, which is part of the limbic system. It is considered the emotional control centre of the brain since it regulates emotions, survival instincts and some memory functions.
It has been proven that visual input is directly sent by the thalamus to the amygdala, which can trigger some emotional responses (such as fear) without any conscious processing.
Velocity is a vector quantity which means it has both magnitude and direction means in order to calculate it another vector quantity is used which is displacement on the other hand speed is a scalar quantity.