In a desert, lizards that blend in with the sand survive more often. Over time, fewer bright green lizards are born.

Several genetic disorders (e.g., Tay-Sachs) are more common in Ashkenazi Jewish populations due to a small ancestral population and historical isolation.

In Nevada, isolated desert tortoise populations became genetically distinct simply because of distance and a lack of movement between regions—no environmental pressure, just separation.

On Pingelap, a small Pacific island, a typhoon reduced the population to about 20 people. One survivor carried a rare gene for color blindness, which is now unusually common in the population.

Elephant seals were hunted nearly to extinction in the 1800s. All current northern elephant seals descend from about 20 individuals, and now they have very little genetic variation.

On lava flows in the southwestern U.S., dark-colored rock pocket mice became more common than light-colored ones due to camouflage and predator pressure.

Five birds accidentally get trapped in a shipping container and are transported to a new continent. Their descendants look and behave differently than the original population.

A contagious cancer wiped out large portions of the Tasmanian devil population, leaving a few survivors with genetic resistance—those individuals have begun repopulating the area.

In certain areas of Costa Rica, hummingbirds have developed beak shapes that perfectly match the curvature of local Heliconia flowers. Birds with the best fit get the most nectar—and reproduce more.

Cheetahs today have incredibly low genetic diversity. Scientists believe this is due to a past event where only a few individuals survived, possibly due to climate change or overhunting.

In regions with high malaria, individuals with one sickle cell allele are more likely to survive malaria. Over time, this trait became more common in those populations.

In industrial England, dark-colored moths became more common due to pollution blackening tree bark, giving dark moths better camouflage.

In a lizard population, those with longer legs can run faster and escape predators. Over time, long-legged lizards become more common.