Imperfect evolution (Introduction)

by David Turell , Monday, January 19, 2015, 15:27 (3596 days ago)

Heart rhythm disturbances in aquatic diving mammals:-http://www.sciencedaily.com/releases/2015/01/150116085554.htm-"Instead of a single level of reduced heart rate during dives, the researchers found that heart rates of diving animals varied with both depth and exercise intensity, sometimes alternating rapidly between periods of bradycardia and tachycardia. Cardiac arrhythmias occurred in more than 70 percent of deep dives.-"We tend to think of marine mammals as completely adapted to life in the water. However, in terms of the dive response and heart rate, it's not a perfect system," Williams said. "Even 50 million years of evolution hasn't been able to make that basic mammalian response impervious to problems."-"The conflict between dive-induced bradycardia and exercise-induced tachycardia involves two different neural circuits that regulate heart rate, she said. The sympathetic nervous system stimulates the heart during exercise, whereas the parasympathetic nervous system controls the slowing of the heart rate during the dive response."