Empty Headed

08 Apr

Koalas do not seem to lead very complicated lives. A dog, sure. Falcon? I could see that. What with the flying and everything. And I’d bet the day-to-day life of a whale is just as complex as our own. Perhaps they even take time to see a therapist once in a while. But koalas, no, I cannot picture them as being victims of questions unanswerable nor of being one of the great creative minds of the animal world. They seem content to sit in a eucalyptus tree and eat and sleep.

Perhaps, then, I shouldn’t be surprised to learn that koalas are not especially gifted in the brain department. In fact, their brain is so small that it only makes up about 0.2% of their body mass (A human brain takes up about 2.5%), and not only that, it doesn’t even fill the whole skull. About 40% of the space between their ears is full of cushioning cerebrospinal fluid.

Interestingly, this brings up some very complicated questions. For one thing, why is the skull full of fluid? Some scientists suggested that it was actually an adaptation to prevent brain trauma during falls, but this isn’t widely accepted. It’s much more likely that it simply fills the space left behind in the head. Brain matter is very expensive to maintain and having too much of it puts a strain on the animal’s energy supplies. Koalas would need to be especially careful since eucalyptus leaves give very little nutrients.

But this raises the further question of why even keep a head two sizes too big for the brain? The answer is that it probably doesn’t pose a real evolutionary disadvantage for the animal. If an overly large head reduced their fitness, we’d expect it to eventually be removed from the population, but for koalas, this size is probably the perfect balance of weight, mass, and volume. Neutral traits are often left untouched by evolution.

Finally, perhaps the most prominent question, does this make koalas dumb? Well, yes and no. The two scientists who discovered this thought that it might make the animals slow and clumsy. But while koalas do seem to spend most of their time lazing about, they have no problem moving quickly when they need to. Instead, it seems that this lack of gray matter affects their ability to learn and adapt more than anything else. They only eat one food and only do so in a certain manner. They won’t even touch eucalyptus leaves unless they’re still on the branch. Their lives are one of routine and adaptability simply isn’t a terrible concern for them.

This koala has nothing to say on the matter.

It would seem that the first impression is correct after all. The life of a koala is a simple one. And while other animals may need quick wits or clever plans in order to tackle the problems of everyday life, one could say that the only question a koala needs to answer is: Nap? Or no?

Sources: The Koala: Natural History, Conservation, and Management, The Animal FilesNational Geographic

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Posted by on April 8, 2012 in Natural History


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