For convincing proof that atheists must be correct, look no further than the panda. A glamorous icon for the WWF and cuddly toy of countless pre-pubescent girls it may be, but it's also clearly the worst designed animal ever.
Consider: the average male panda weighs 100kg, that's bigger than me and nearly half the size of my flatmate. Its padded paws (the panda, not my flatmate) hide fearsome claws and vicious incisors line its mouth. It is, in short, plenty capable of killing and eating tasty mammals and reptiles (the panda, not my flatmate, although he probably could do). Yet, a few million years back, pandas decided to give up eating meat and focus instead on bamboo. Whatever prompted their decision to become vegetarians - a dodgy madras, a flyer from Greenpeace - dietary efficiency was not a consideration; they can only extract about 20% of the nutritional value of the green shoots they cram into their mouth. They shit nearly pure bamboo. They have to spend almost their entire day eating. True, there are days I'd like to spend doing nothing but eat, but I'd rather the smorgasbord contained more than a selection of fibrous shoots.
Consider also: not only are they famously rubbish at getting jiggy-wid-it, they are also utterly stunned by the only occasionally resulting act of childbirth. In the video they show at the Chengdu panda research centre a birthing mother is so stunned at the child that is launched metres out of her that she jumps two feet in the air and then starts knocking the mewling pink infant around the floor with her huge paws and an inquisitive look. The staff rush in to pick the baby up before the mother damages it.
And consider: pandas have opposable thumbs. Well, sort of, they've adapted their wristbones so they can clutch as if they had thumbs. We developed opposable thumbs and a few million years later we've managed to create Timmy Mallett and the Nokia 6230. They develop opposable thumbs and a few million years later they're still sitting on their backside eating bamboo.
So the panda. Proof that either God does not exist, or he takes a very hands-off attitude to animal design.