Descendant Testes
From EvoWiki
In humans and related primates, males develop testes deep in the abdomen. The testes then descend to the scrotum. In order to accomplish this, a hole must form in the peritoneum (lining of the abdomen) through which the testes pass on their way. This hole is sealed, but not well. This faulty seal is unsuited for bearing the weight of the organs a human puts on it, and frequently tears in later life, resulting in the most common type of hernia. The challenge for creationism and evolution is to explain this situation.
The Evolutionary History of Descendent Testes
The formation of the testes in the abdomen is a common situation in vertebrates. In cold-blooded vertebrates, it makes sense. The testes work most efficiently if they can be kept at a constant temperature, and the closest thing to constant in a cold-blooded creature is towards the center of the body.
When warm-blooded traits began to evolve, the body temperature of mammals began to exceed the safe functional range of the testes. The testes had to be cooled. Different lines of descent in the mammals have solved this problem in different ways. Some species develop elaborate cooling systems around the testes. Others, such as ourselves and our primate ancestors, move the testes closer to the skin so that they may easily radiate excess heat.
Why form the testes in the abdomen and move them rather than just form them in the scrotum? Because evolutionary change is always easiest to accomplish by tacking steps onto the end of a process rather than modifying existing steps that work. It's just simpler to produce this kind of development. It's easy to see how each step closer to the surface was an incremental improvement in the situation, so this poses no challenge to evolution.
Why isn't the seal on the peritoneum better? Because for most of our evolutionary history, it didn't need to be. Our quadruped ancestors put no great weight on the seals, and so the seals had no tendency to rupture. When we started to walk upright, the weight of our internal organs was no longer borne by the front of our belly and by the supports hanging from our spines, but rather by the lower portion of our peritoneum. The seals that had been more than sufficient since we evolved into mammals suddenly became design flaws.
Since we have only been bipeds a short time, there has been insufficient time to produce a more effective arrangement. This is but one of several elements of our anatomy that shows insufficient adjustment from our quadruped ancestors. (Another being the aforementioned organ supports hanging from our spines, which are quite unsuited for life as a biped and are a major cause of lower back pain in later life.)
Creationism and Descendant Testes
Creationism has a much more difficult time explaining the descendant testes. In fact, the current author (MES) has not encountered a single attempt by creationists to explain this situation specifically.
In general terms, creationists react to such obvious examples of bad design in various ways, none of which adequately explains the descendant testes.
- Creationists frequently claim that apparent examples of bad design are, actually, good design, if looked at in the proper light. There seems little possibility of finding a "good purpose" for this formative arrangement, and until they come up with one, this is just blowing smoke. By all appearances, this is bad design for which a superior design is readily obvious. Claiming it is anything else requires some support.
- Creationists may lay the blame for bad design on "degeneration" caused by The Curse. It would certainly be possible to posit that the testes were moved from a better location to the abdomen as a result of degeneration, but how to account for them moving back? Isn't this a positive change that would have to occur after their initial misplacement, such that creationists deny is possible? Degeneration of the peritoneum to allow the testes through is probably acceptable to creationists, but the seals, as poorly designed as they are, are still an improvement over no seals, and thus the creationists deny they are possible to form. (That degeneration runs contrary to natural selection, which most creationists claim to accept, is another issue.)
In the end, creationists simply have no effective explanation for the process by which our testes descend. The clear poorly executed design of the system, along with an obvious history of improvements to it, denies the foundation of most creationist anti-evolution arguments and the descent of the testes must be seen as evidence against creationism.
