Those Incredible Dolphins!
Those Incredible Dolphins!
“By all rights, life in the sea should leave a dolphin baked, crushed, and sterile. This graceful mammal avoids such a fate only by slipping through loopholes in the laws of physiology.” With such a come-on, who could resist reading “The Dolphin Strategy,” in the March, 1997, issue of Discover? The discoveries revealed in the article proved to be fascinating and exciting.
One puzzle for scientists was the problem of oxygen consumption on a deep dive. Research showed that “it was simply physiologically impossible for dolphins to do what they do.” Despite various oxygen-saving “tricks,” calculations showed that “a dolphin should run out of oxygen and drown in mid-ascent.” Obviously that doesn’t happen, so investigation continued. Further research revealed that at 70 meters the pressure of the surrounding water becomes so great that dolphins’ lungs collapse and the great creatures just “fall” like a rock. They are able to survive several minutes at depths up to 200 meters. Then, upon ascent, the heart races for a few seconds until the 70-meter mark where the lungs open, the body again becomes buoyant, and they glide to the surface.
Think of the problems this involves, though. When the lungs collapse, so does the rib cage, squeezing the heart and forcing blood out of it with so much pressure that it would “literally blow the dolphin’s brains out” if it had a normal carotid artery. “Instead, the blood flows from the aorta into a mesh of capillaries called a rete mirabile – Latin for ‘miraculous net.’ The effect is like water from a faucet pouring into a sponge; as the blood surges into the fine vessels, it slows down. Only then does it gently flow into an artery that dives into the spinal canal and up to the brain.” The author calls this a “remarkable piece of cetacean anatomy.” Wouldn’t you agree? (By the way, a similar system is found at the base of the skull in the giraffe. Did dolphins evolve from giraffes or is this another example of remarkable design?!)
One “trick” used by dolphins to help conserve oxygen during long dives is to restrict circulation to the skin and extremities. While helping with the oxygen problem, though, this creates another problem. Dolphins, like other mammals, must finely regulate internal heat. A thick layer of blubber protects from cold, but how then does the dolphin get rid of excess heat produced during heavy muscular activity? Research has shown that blood vessels in the dorsal fin and tail fluke are involved in cooling. If these vessels are closed during long dives, though, how is the excess heat dissipated? The article states, “the dolphin’s remarkable physiology had devised an elegant solution to the conflicting problems of oxygen conservation and heat buildup.” The excess heat is stored until surfacing; then the blood vessels in the extremities open and release it very rapidly.
So far so good, but now another problem arises. Dolphins are mammals which bear live young, but here again we run into heat problems in both the males and females. Sperm require temperatures slightly lower than normal body temperature. In most mammals, this need is solved by the location of the testes in a sac outside the body cavity. Obviously this solution would not work in a swimming animal with a hydrodynamic shape. So, the testes of dolphins are contained within the body cavity, but now they are surrounded by massive muscles generating enormous amounts of heat. What, then, is the answer to the heat problem? It turns out to be another “elegant solution.” The testes are surrounded by a thick layer of special vascular tissue. Veins carry cooled blood from the dorsal fin and tail directly to this region. These veins then divide into smaller and smaller vessels, which lie directly adjacent to tiny arteries carrying hot blood. The whole system works as a countercurrent heat exchanger, warming blood in the veins, cooling blood in the arteries, and cooling the testes at the same time.
In females, the problem is the excess heat produced by the high metabolic rate of the fetus in the womb. The cooling system works in a manner similar to the male. Blood from the tail and dorsal fin flows directly to a heat-exchanger arrangement near the womb, removing excess heat and protecting the fetus from heat damage.
Though the author of this fascinating article apparently accepts the standard evolutionary scenario, he could not help using words and phrases like “design,” “architecture,” and “elegant solution” in describing these amazing creatures. We, too, recognize design, but do not believe that chance and accidents would ever produce such remarkable systems. The only adequate cause is our great Creator God. We praise Him for His awesome power and ingenuity expressed through His creation!
By Dave Nutting
This was published as an article in the July/August 1997 Think and Believe.
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