Have you ever wondered why deer freeze when they are in the face of a car's headlights? The answer doesn't have to do with a deer's stubbornness but rather the biology of the deer.
Cone and Rod Cells:
Two different types of cells mostly make up the retina of an eye: cone cells and rod cells. Cone cells take in the wavelengths of light, allowing organisms to see in whichever type of light they need. For example, cone cells allow people to see in color. The job of rod cells is to take in light and is especially useful for nighttime vision since they are a thousand times more sensitive than cone cells.
Deer are usually crepuscular or nocturnal animals, which means they go out during twilight or nighttime. Because of their after-hours schedule, deers have evolved to have more rod cells than cone cells, making their eyes more sensitive to light. When the light from a car's headlight bombards a deer's sensitive eyes, the deer is blinded and does not know what to do, so it simply stands still. Because of the blinding light, deer also cannot judge the speed and mass of the object in front of them, so they often cannot move out of the way in time.
What Should You Do In This Situation?:
Swerving the car can cause it to lose balance and be extremely dangerous for anyone in the car. According to Geico, If you ever come across a deer that is not moving, it is safer to press hard on the car's breaks rather than swerve the car. There is a higher chance of survival for both parties involved if the driver hits the breaks instead of swerving the car.
Since the eyes of a deer are more sensitive to light, they can be easily blinded by a car's headlights. In their blindness and confusion, deer do not know what to do and stand frozen in front of the car. They can't judge the mass or speed of the car properly, so they do not know the danger that they are in properly until it is too late. If you are ever in a situation where a deer isn't moving, you should hit the breaks instead of swerving the car.