We have a clock in our brain that is based on circadian rhythms. The clock is connected to Earth’s rotation, and it provides daily periods of rest and recovery called sleep. Animals have it too, and for many animals, sleep is a dangerous time if there are predators around. Scientists have discovered that many animals, especially marine mammals, have a half-slumber system designed to keep them safe and yet allow them to sleep.
The half-slumber system allows half of the brain to sleep while the other half is awake and able to respond to danger or navigational needs. Studies in dolphins have shown that there are different regions of the brain that work together to allow one side of the brain to function while the other side sleeps. The hypothalamus contains ventrolateral preoptic nuclei that exchange messages between the left and the right sides of the brain. They determine which side sleeps and which side remains alert to danger. This also allows movement of the dolphin’s fins and tails to generate body heat in the coolness of the marine environment. It also allows the animal to surface, to breath, and to swim with its companions.
Northern fur seals have a similar system but highly modified. The fur seals come out on land and assume a posture that allows them to put one flipper in the water which they paddle with while keeping the other three flippers in the air to avoid heat loss. Their nostrils are out of the water, allowing breathing and one eye is open and looking for predators. The part of the seal’s brain that provides vision is not connected to the other functions of breathing or movement.
Birds also use the half-slumber design. Mallard ducks have a unique system where the ducks form a group. Ducks on the outside of the group have one eye open, and their brains function differently than ducks at the center of the group. Migrating birds that fly for very long times also use the half-slumber design with one eye and one side of the brain watching where the bird is going while the other side of the brain slumbers. Great frigate birds fly for ten days at a time using this system. Swainson’s thrush gets its sleep by taking micro naps when it is perched.
It seems that every creature using the half-slumber design to get its required sleep uses it differently. The changes are not small and are highly complex involving many organs. Intricate design differences in the brain primarily direct them. Studies of animal sleep are in an early stage, but the complexity of the system is undeniable. The Bible tells us that we can “know there is a God through the things He has made” (Romans 1:18-20). It is a very difficult challenge to understand just how complicated God’s design is. Even in our sleep, we demonstrate God’s plans and engineering.
— John N. Clayton © 2019