The Problem with Wookiees

Photo by Scott Ruether,
CC BY 2.0 

When making up alien creatures, imagination has no bounds. Alien characters in sci-fi stories are most commonly human-like, but with animal features. But be they scary, funny, or loyal comrades-in-arms, they exist purely for entertainment. We might laugh at the absurdity of a giant slug-like creature with a human face slithering around on a desert planet, but we don't care when engrossed in the story.

Nevertheless, the critique of aliens is a great exercise for biology students.  The fundamental rule is that evolution can only proceed through logical steps. Every feature of an alien needs to be explained in terms of adaptation to environmental conditions. In terms of this purely academic exercise, my favorite aliens, the Wookiees, raise a number of red flags.

I recently discovered a webpage purporting to describe the biology and evolution of Wookiees on their home world of Kashyyyk. Whether the facts stated therein were created by the writers of the Star Wars series or made up by imaginative fans, I don't know. But since they have been posted, they are fair game. As a botanist and biology teacher, I am obligated to respond! 

Wookiees qualify as human-like sentient beings. They are smart enough, and have the upright posture, flexible shoulder joints and grasping hands needed to manipulate weapons and fly spaceships. So their evolutionary history must account for both their body anatomy and the development of their large brains. We assume they acquired their human-like traits through an evolutionary history similar to ours. Indeed, they are described as tree-dwelling primates.

For our own species, however, the path to humanity required both an arboreal (tree-dwelling) phase and a hunting/gathering savanna phase. The arboreal phase evolved in tropical rainforests, which provided a rich diet of flowers, fruits, seeds, leafy shoots, and insects or other small animals. Accessing these food sources required efficient mobility to move around a tree canopy and from one tree to another. The interlaced system of slender branches and vines of the tropical rain forest fostered such mobility, resulting in grasping hands and flexible shoulder joints. 

The hands of our ancestors were uniquely claw-free. Claws as found in other animals, were replaced in our arboreal ancestors by flat fingernails and soft, sensitive undersides, allowed them to grasp relatively slender branches and vines firmly as they swung, ambled, and leapt about. They evolved uniquely twistable,  double-boned forearms that could turn the hands upward or downward, aiding in locomotion, as well as for reaching, picking, and manipulating food items.   

Shoulders could rotate, allowing us to reach in multiple directions for food items, or branches by which to "swing through the trees with the greatest of ease." Such anatomical features would later be essential for wielding sticks and stones, for playing baseball and ultimately assembling watches and cell phones. So among the denizens of the earth only primates have the dexterity to play baseball. Though it might be a nightmare to keep them focused on the game, a match between between the Chicago Chimps and the Green Bay Gorillas is at least technically possible, because primates have arms and hands capable of throwing things. I've seen annoyed gorillas in a zoo throw something much nastier than a baseball at heckling tourists. Non-arboreal animals are even more severely limited. Shoulder joints and paws (or hooves) are rigidly limited to their walking/running function. Though squirrels, cats, and raccoons can hold food items with their front paws, they cannot grasp, and cannot throw rocks. 

The second phase of human evolution came in the radically different, wide-open vegetation of the African savanna, where we had to make a leap in intelligence and brain size.  Water and food resources in the savanna were widely scattered and highly seasonal and we had to remember the places where they could be found. The fruits, vegetables, and occasional beetle grub so abundant in the rainforest were too scarce in the savanna to sustain us, and so we had turn to hunting small animals, who generally did their best to avoid becoming our dinner. We did not have the strength, speed, claws, or toothy jaws of our competitors, and so could only survive on our wits. We had to learn to use sticks and stones to catch and kill prey, as well as to defend ourselves against the bullies further up the food chain who considered us as slow-moving food items. 

Sticks and stones led to bows and arrows, houses, wheels, and ultimately space ships. Our brains grew to human proportions and capabilities as we adapted to the harsh realities of the savanna, but would not have been possible without the flexible anatomy we inherited from our arboreal ancestors.  

Koalas are arboreal animals with claws and some
grasping ability. As slow-moving leaf-eaters, 
there was less selective pressure for greater agility
and mobility, not to mention for intelligence. 
Photo from GreenLeft.org

Red flag #1: Though Wookiees appear to have grasping hands and rotatable arms, they are also said to have retractable claws for climbing up trees. Claws big enough to support the considerable weight of an average Wookiee adult could not be retracted enough for delicate work like pressing the triggers of weapons, operating the console of a space ship, or using tools to repair a space ship. In clawed animals, bone structure and musculature are focused on supporting the claws, which must bear the weight of the animal.  There are arboreal animals that climb with claws: squirrels, sloths, koalas, etc., but of these, only squirrels are really agile in trees. They, however, are small and light-weight, depending more leaping rather than grasping and swinging to move through a forest. The others are far more limited in mobility and depend on more limited diets. 

Red flag #2: The forests of Kashyyyk are said to be dominated by coniferous Wroshyr trees, sounding more like a boreal forest than a tropical rain forest, and would provide neither the variety of food sources nor the 3-dimensional jungle gym structure to move around in.  Also, Wookiee ancestors are said to have been carnivores. However, all known arboreal animals are vegetarian or omnivorous. It's too difficult to run down prey larger than insects, frogs or lizards in the forest canopy, unless you're a bird of prey, So it is unlikely that Wroshyr forests could have fostered the evolution of the flexible anatomy required for the later development of technology.  

Wroshyr trees are also said to be massive, supporting Wookiee communities within their trunks and large branches. Such trees are said to average 300-400 meters in height, with some varieties as tall as several kilometers. The tallest trees on Earth reach a little more than 120 meters, and are pushing the limit of the physical force of transpiration to lift water against the pull of gravity. If gravity were a little less on this planet, trees might be a bit taller, but if gravity were substantially weaker, the planet could no longer hold onto its liquid water or atmosphere. So  trees significantly larger than those on Earth are highly unlikely.

Red flag #3. It appears that Wookiees stayed in the forests. They did not face the challenges of the savanna or any other environment that could drive the evolution of upright posture and higher intelligence. Why is this important? If they indeed lived continuously in forests, they would have advanced little more than the great apes of Earth. The forests did not provide the necessary challenges.

Red flag #4: The dense hairy coat of the Wookiees, while fine for primates who never left the rain forest, would be a real liability in the savannas, in particular for developing greater intelligence, i.e. bigger brains. The brain is the most heat-generating organ of the body. As it increased in size, we required an improved cooling system. To provide cooling surface for all that brain heat, along with heat from the scorching savanna sun, we lost body fur and enriched our bare skin with fine sub-surface capillaries and  a high density of sweat glands. We retained hair on top of our heads to protect our brains from direct heating, but the rest of the body was freed up for cooling the blood. 

As a unique, omnivorous species in the savanna, we could not nap in the shade of trees after a big kill, because hunting and gathering had to continue all day long. So we became "naked apes." This is nicely explained in a 2010 article in Scientific American, by Nina G. Jablonski. Being naked therefore was also essential for breaking through to human-level intelligence. This also applies, incidentally, to our homegrown hairy aliens, Sasquatch and Yeti.

So we are left to ponder how the Wookiees became intelligent beings. If they did not follow the human game plan, what evolutionary history did they have? I keep coming back to my conviction that if we were to discover intelligent, technologically capable, alien life forms, they would have had to go through a similar evolutionary pathway as ours, and would look boringly like us (see my post on the inevitability of humans. Even with very human-like aliens like Vulcans, we have to explain pointy ears, green blood, and internal organs that are somehow different. If you are a teacher, try this with your students.  It's a topic that's guaranteed to wake up that guy in the third row who's been sleeping since the lecture on Cyanobacteria. Oh, and less you wonder if technological aliens could have evolved from sea creatures, have you ever tried to throw a baseball under water?