In a recent article over at reasons.org, Dr. Fazale Rana considers how the same buoyancy control mechanism could have evolved in two radically different species, sperm whales (with an average length of 52ft) and a copepods (with an average length of 1 – 2 millimeters). Both animals control their buoyancy by changing the state of fat in their bodies from liquid to solid. When fat is solidified, the animals generate a downward force allowing them to descend; when they want to ascend fat is converted to a liquid which is much less dense.
Macro evolution is based on the idea that a series of random, chance events, could cause life to evolve from single celled organisms into the vastness of life we witness today. However, it appears as if identical buoyancy control mechanisms have evolved independently in two radically different animals. If evolution rests on chance and randomness, it should be uncommon for us to find similiar systems in far removed species, yet we find it quite often.
From an intelligent design perspective this situation makes perfect sense. We would expect to see a designer reuse common design elements in much the same way that airplane designers reuse the concept of a wing or architects reuses the concept of a column. Convergent systems such as the buoyancy control mechanism strengthen the Chrisitian view of design and weaken the case for Evolution.