A population of organisms is represented by three black marbles and three gray marbles. The gray organisms have a beneficial genetic mutation. Draw a model that shows natural selection over three generations of these organisms.

true skin; another name for the dermis. lies directly beneath the epidermis and is often referred to as the true skin. outermost layer of epidermis, consisting of dead cells.

lichens that colonize bare rock secrete acids that break down the rock and start the soil-production process. so they expose rocks