Intelligent vs Stupid Design
As immaculately designed as Mike Seaver believes the banana is to lend itself to human consumption, there are plenty more examples of stupid design --instances in which a cosmic designer just plain done goofed.
There are some compelling and some less than impressive examples in the natural world to which proponents of Intelligent Design point to support their claim. In most cases aesthetics are their strongest arguments, things that please the human eye. It's of no circumstance that all these things were usually around before human beings were appeared to appreciate things like the lovely green grass that is comfortable to for or eyes to look upon, or the sublime beauty and intricacy of a bird's feather.
If I had to nominate the top examples of "intelligently designed" life forms on this planet, that is, critters that perfectly fit into their environment and at first glance give the appearance of having been built for a purpose, my selections wouldn't be quite as pretty as a beautiful piece of fruit or a butterfly's wing. No, if you want to get down to the nitty gritty, some of the best designed things aren't altogether pleasant.
Kirk Cameron cites the breath-taking banana as both beautiful and utilitarian, so I would counter by pointing to the Great White Shark: sleek, fast, and as Richard Dreyfus observed, an Eating Machine. Not only is the thing ideally "designed" to eat everything under the sea, sharks have an incredible immune system and aren't even susceptible to any type of cancer -- so successfully designed is the killing fish, that the only thing that's changed in millions of years is it's size, down from the 60' long gigantifish Megalodon, to a more modest 20 or so feet.
"All it does is swim and eat and make little sharks!"
And what of cancer itself? The blueprints for many types of cancer are contained in your genome from day one and through exposure to aggravating forces -- diet, pollution, smoking, playing under power-lines as a child -- either remain inactive, flare up into a devastating tumor, or something in between.
A perfectly designed organism
with no purpose but to destroy lives.
A symbiotic disease, we now have some hope through our understanding of the human genome that due to it's embedded position in your biology, there probably won't be just any cure for cancer, but instead it will take individually engineered cures for YOUR cancer to eradicate the bastard. The closest thing to the personification of evil in the natural world, seems exceptionally well designed, like many diseases, to rob you of life even if it means it's own demise.
And then there's Maude. Exceptionally well designed to make Archie Bunker's life a living hell, even getting her own spin-off before Golden Girls.
The more we've discover about the natural world in our very brief time on the cooling surface of this planet, the more we find that nature takes the more utilitarian approach of natural selection through random mutations.
That's not the same as chance, rolling the dice and waiting to see what comes up. If it were up to chance than we might very well have encountered Kirk Cameron's Croco-Duck. Far from chance, the random mutations are ongoing, field-tested and only stick around if they are of benefit to the organism's individual and communal success. Not all "designs" that work are pretty, not all that fail are ugly. It's a work in progress...