Yellow [YY] And Green [yy] would be [Yy] (Still yellow)
Endospore staining is used to stain the spore which reside inside the microorganisms, and unlike the exospores, are not present outside the microbial cells. The endospore stain penetrates the microbial cells, and then stain the endospore.
Answer: The literal reason would be because our ancestors did. The ancestors of all modern mammals had five digits on each limb up to 360 million years ago.
Explanation: