Endothermic or Ectothermic – What’s the Difference?

You are an endothermic mammal. That means your body’s metabolic rate controls your internal body temperature. We describe that condition by saying you are “warm-blooded.” Many life forms on our planet are “cold-blooded” (ectothermic) because the environment controls their internal body temperature. The limitation of being cold-blooded is that it requires warm environmental temperatures. Ectothermic life forms can’t survive in polar areas. Endothermic life can survive almost anywhere.

During the time of the dinosaurs, the planet was very hot. That means biological systems, including plants, grew quickly. Those conditions were part of God’s preparation of resources that humans would need, including oil, coal, topsoil, and oxygen. However, the geologic record shows a point in Earth’s history when the climate radically changed. 

As the entire planet cooled, areas at or near the poles became too cold for cold-blooded life to exist. Studies of bone growth rates and oxygen isotopes in ancient bones indicate a rapid change. This change would not be a problem for warm-blooded animals but would reduce the number, size, and activity of cold-blooded life forms.

The challenge would be to design living creatures that can translate food into enough internal heat to survive in a cold environment. Science News reported on studies of the inner ears of reptiles and mammals. In warm-blooded animals, the inner ear fluid is less viscous, requiring that the ear canals become smaller. As a result, fossils show a sharp change in inner ear morphology at the time when Earth’s climate became colder. 

Many other changes were required for life to go from ectothermic to endothermic. However, the inner ear structure is preserved in the fossils, making it useful for scientists to study the history of life on Earth. The complexity of endothermy reminds us again of the words of Psalms 139:14, “I will praise you, for I am fearfully and wonderfully made: marvelous are your works.” In our time of changing climate, the design of life continues to show the wisdom involved in life’s creation. 

— John N. Clayton © 2022

Reference: Science News August 27, 2022, page 9, and Nature.com