10 Worst Adaptations in the Animal Kingdom

Like a lot of the so-called "worst adaptations," the appendix gets a bad rap. Sure, it can kill you by bursting and there's basically little consequence for taking it out like yesterday's trash. And in Charles Darwin's day -- when finding evolutionary reasons for adaptations was pretty important to further his survival-of-the-fittest theory -- Mr. Darwin himself was stymied by the appendix. He thought maybe it was a vestigial part of the cecum, a section of the gut full of bacteria that was used to break down leaves. As we chomped less greenery, the cecum shrunk and our appendix became just a sad, shriveled reminder of our big-cecum days.

Scientists now see that the appendix could possibly have a function after all, although they're not entirely sure what it is. They think it still might have something to do with gut bacteria: It's possible that good bacteria can migrate to the appendix when an infection occurs, keeping them safe from the bad bacteria, thus allowing a healthy repopulation after the infection is over [source: Barras]. But not every mammalian species has an appendix, which might make the "worst adaptation" not for those with the appendix – but for those without.

Humans do not need their pinky toes.

Without your pinky toes, you could walk. You could run. You could be the prima ballerina at the Bolshoi Ballet. (That's unconfirmed, but we can dream.) Basically, whatever you as a modern human need and want to do, you're set even without the little guys. According to a 1990 study published in The Journal of Bone and Joint Surgery, 160 subjects put the least amount of pressure on their pinky toes while walking and standing [source: Hughes et al.]. Big toes withstood three times as much pressure [source: Hughes et al.]. But if you go way, way back to our primate ancestors, you'd be hard-pressed to live happily without your smallest piggy.

Those ancestors needed far more functional toes and feet; they had to grab limbs to swing from, and scramble quickly up or around inhospitable terrain. So having a pinky toe that -- at one time, at least -- functioned dexterously was pretty important. Now, of course, our toes just help us stand around when we're waiting in line for Starbucks. But while we don't need the pinky toe per se, if we didn't have the metatarsal bone that connects that pinky toe to our ankle, we'd be extremely unbalanced as the middle and inside of our foot couldn't properly distribute our weight [source: Zhang].

Most of us operate under a couple of misconceptions when it comes to the Adam's apple. One is that only men have the bump on the throat, which enlarges with puberty. The other misconception somewhat logically follows: If men only have one and women manage to have a full and healthy life without one, then it doesn't serve any function.

Wrong on both counts. Both men and women have Adam's apples, and -- just like any part of our anatomy -- they're bigger for some, and smaller for others. Adam's apples are just cartilage plates around the larynx that swell as growth takes place. And yes, there's certainly a tendency for men's larynxes to grow bigger, but they also look bigger simply because male Adam's apples tend to protrude from the neck at a different angle.

So all of us have so-called Adam's apples, and they're in place to shield our vocal cords [source: Pikul]. While it's clear that having an Adam's apple is a good deal, we could argue that it's a pretty terrible adaptation for men, who get all the protection that women get, plus a larger bump on their neck to boot.

Wisdom teeth are what we call a vestigial organ, or a part of our anatomy that's a remnant of an earlier time in human evolution. They served a purpose then, but now these organs are basically taking up space. So these vestigial organs are not so much an example of adaptations gone wrong, but a lack of adaptation. And that lack of adaptation means a lot of us have stories of swollen, bruised jaws and stomach-churning cases of dry socket after our "successful" wisdom teeth removal.

The problem is, our mouths used to be a lot bigger. And when our grins were wider, that meant we could fit more teeth in -- and we needed some big ol' molars to spring up. These teeth would help us crack and eat nuts, grind our leafy greens into a mushy pulp, and chew the gristle of the wild mastodon (never happened, but you get the idea).

But as our human brains evolved and invented Greek yogurt, we gradually didn't have much use for third molars. (Not to mention the fact our bodies literally couldn't fit them in our mouths anymore.) Our wisdom teeth -- so-called because they come in our late teens and early 20s when everyone is a real genius -- were causing more problems than they were worth by crowding our mouth and causing infection.

So far we've had some pretty staid adaptations (or lack thereof) that are either slightly inconvenient, possibly unnecessary or just in the way. Now we enter the world of nonhuman animals, which have adaptations so troublesome that they must burn with jealousy at the streamlined, well-designed human body -- wisdom teeth and all.

We begin with our sticky friends, the banana slugs. Number one, slugs are all hermaphrodites. No biggie, right? In some ways, that's an adaptation that's super easy -- everyone can mate with everyone, with no pesky civil union/marriage question! But in this case, it can get a little tricky.

When banana slugs mate, they both insert their penises into each other. But at the end of the deed, occasionally a slug -- or both slugs, simultaneously -- will chew each other's penis off. Why? Some researchers think they need to in order to separate. And no, the penis doesn't grow back [source: Miller]. But good news! Now they just use the female reproductive organs and carry on.

Although our banana slug compatriots get to switch sex on a whim, most females in the animal species are pretty much left to gestate and birth their offspring. Most of them -- humans included -- at least get to find a fairly comfortable position to push a living being out of their birth canal.

But giraffes give birth standing up.* Yes, not only does it sound unnecessarily uncomfortable (which it probably isn't, if they all do it, right?), but remember what animal we're talking about here: The giraffe's birth canal is 5 feet (1.5 meters) above the ground [source: National Geographic]. So yup, baby giraffes suffer a pretty decent smack on their first landing. Perhaps worse for the giraffe mom, their little ones start running about 10 hours after birth [source: National Geographic]. These kids go from zero to hell-raising toddler in no time.

*We should note that some humans prefer to give birth standing up, too.

As far as quality of life goes, you'd think a sloth has it made. About 10 hours of sleep (more in captivity), a diet of healthy greenery, a side of bark and a life in the trees [source: Briggs]. What could be so bad?

Unfortunately, the sloth's low-key existence also leads to some complications. One is that a sloth's diet isn't that nutritious, so they need a big stomach with several chambers to hold a lot of food at once. Sloths can take an entire month to digest one meal, and they have to live a seemingly lazy lifestyle so they don't divert any energy needed to live [source: National Aviary].

Sloths also have a really low body temperature, but it can't get too low. If it does, the bacteria in the sloth's gut that digest food will stop working. That means that even if the sloth had just eaten enough food to fill its belly for a month, it can starve to death because the food will just sit there, undigested [source: National Aviary]. It's gotta be one of the worst -- and the most ironic -- of all the animal adaptations around.

Anyone who's caught a good portion of "Jurassic Park" knows that Tyrannosaurus rex isn't to be trifled with. Up to 45 feet (14 meters) long (for its usual posture was horizontal), its 4-foot- (1.2-meter-) long jaw could crush your head once it got a hold of you [source: Padian]. Once you were firmly in its jaws, the dinosaur's serrated teeth could gnaw your face off.

But wait a second. Our despotic dinosaur had an adaptation that isn't just a cosmetic embarrassment, but an actual impediment. It's those tiny arms that were so wildly ineffective that poor T. couldn't even use them to grab prey or put said prey in their mouth [source: Barrett]. In fact, Mr. or Ms. Rex couldn't use their little arms to push themself off the ground [source: Barrett]. (It's worth remembering that a lack of arms has never kept some snakes from being formidable predators.)

Even stranger, T. rex only had two fingers on each hand, unlike most dinosaurs with three -- which makes grabbing a lot easier. Apparently, evolution might've slowly been phasing out the arms of the T. rex, instead relying on the strong jaw of the animal to pick up and devour prey. Some even propose that if the dinosaur had stuck around much longer -- a million years or so -- those arms would've adapted right into oblivion [source: Barrett].

You might notice that pandas get no qualifier for what adaptation is especially bad. I do not in any way want to goad the panda lobby (Big Panda): Pandas are painfully cute. And just when you think pandas can't get more adorable, you are confronted with a baby panda and you die from unbearable (HA!) delight.

But here's the thing.

Pandas are the worst. You think turkeys are dumb? Pandas don't understand mating. And not like humans, who are just perplexed by who should pay for dinner. A panda male at Smithsonian's National Zoo, for instance, tried to mate with his partner's foot, wrist and -- getting closer? -- ear [source: Buchen]. That was better than the second try during which the next male attempted to maul the same female.

OK, that's not entirely fair. For one, those are examples of pandas in captivity. But even in the wild, pandas have trouble. They have to eat a fourth of their weight every day, and that's largely because their all-vegetarian diet isn't actually all that good for their digestive system. Which also might be why they poop 40 times a day: That's one adaptation that isn't going to do the panda any favors [source: Buchen].

So this probably isn't one we're as familiar with as, say, our appendix or the panda's insatiable appetite for foods that aren't really that good for them. But the hyena's sexual organs should get their due for just how cruel an adaptation can be.

First off, the female hyena has an enlarged clitoris that's difficult to distinguish from the penis of the male. That's fine and good; we don't judge organs for superficial reasons here. And, in a twist that might seem downright convenient, the clitoris is used for urination, mating and giving birth [source: Michigan State University]. A pretty useful structure for multitasking.

Unfortunately, it has a nasty side effect. The clitoris -- which is about 6 to 7 inches (15-18 centimeters) long -- is not ideal as a birth canal [source: Michigan State University]. And we should say that the cubs do travel through a vaginal canal before being delivered eventually through the clitoris. The penis-like structure is only about an inch in diameter, and cubs can suffocate during birth [source: Michigan State University]. Females giving birth can be injured, too. Which would cause one to assume that evolution would bring an easier, more lenient system to hyena procreation.