Don't tell Geoffrey Simmons — he's been on a credulity junket lately, crowing about every functional adaptation, including the egg, as proof of purposeful design. I don't know about you, but a system that muddles excretion with reproduction and that allows random lizards to crawl up your butt and squat in your oviduct doesn't sound like great engineering to me.
Another reason to wear underwear at all times
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I've expounded before about what constitutes good design. For a more thorough discussion of the subject, I'd suggest Henry Petroski's The Evolution of Useful Things: How Everyday Artifacts-From Forks and Pins to Paper Clips and Zippers-Came to be as They are, a wonderful book on engineering and design. Note the word "evolution" in the title. The truth is that good functional designs never spring full grown from the mind of an engineer. They take refinement and adaptation to the realities of the environment in which they'll be used. This is how biological evolution works, as well.
I'm not familiar with all the authors of Creationist books out there, but I'd be surprised if any of them ever actually created a functional design. Most clearly don't understand how engineering works.