Recently, while walking down a tree-lined street, we were startled by a sudden crash and scrambled to our feet. A squirrel had fallen from a tree! It quickly recovered and ran, back to the same log it came from. That never – or almost never – happens. Why not? Scientists at UC Berkeley have explored exactly that question.
The craving for a peanut is enough to make a squirrel give an Olympic performance. The scientists practically held up the “9” and “10” scoreboards as they watched their gas horns run through an obstacle course the researchers set up. The squirrels, who live in eucalyptus trees on campus, even made creative moves as the trail got tougher. This story shows that the good old empirical science still has the power to fascinate and build understanding, without the need for Darwinian stories.
How many movies show a protagonist running from danger and having to decide in a split second whether to jump over a hole? The scene out Raiders of the Lost Ark I think of Indiana Jones running off a rolling boulder, jumping over a chasm, and hanging by his fingernails. For squirrels jumping from branch to branch in the trees, this is the most natural thing in the world. Speaking of which, they also know parkour – the ability to bounce against a wall for extra spice in a dangerous jump. Parkour is a popular urban sport highlighted in many YouTube videos in which a runner attempts to jump from roof to roof without assistance through a quick series of daring jumps. It’s as dangerous as it looks, but some get really good at it, performing flips and twists in some of the riskier sequences.
UC Berkeley biologists Nathaniel Hunt and Robert Full, with the help of two colleagues from the psychology department, set up the outdoor experiments on campus. A short video shows the setup and some of the squirrel performances in slow motion.
The results made the cover story in Science on August 6 with the caption: “Acrobatic Squirrels Learn to Jump and Land on Tree Branches Without Falling.” It starts with enthusiasm:
Every day there are acrobatic extravaganzas going on above our heads. Navigating Squirrels remarkably complex and unpredictable environments as they jump from branch to branch, and mistakes can be fatal. These achievements require: a complex combination of evolved biomechanical adaptations and learned behavior. Hunt et al. characterized the integration of these features in a series of experiments with free-living fox squirrels (see the perspective of Adolph and Young). They found that the The Remarkable and Consistent Success of Squirrels was due to a combination of learned impulse generation when assessing the balance between distance and branch flexibility and the addition of innovative jumps and landings in the face of increasingly difficult challenges. [Emphasis added.]
Technical specifications of Parkour
A novice will not make a new parkour move on the first attempt. However, squirrels seem to be born with the ability to do it. A combination of qualities is needed: a flexible body, good senses, strength, agility, quick decision-making, instinct and learning ability. The UCB research team seems vague about the proportions of these specifications. Which traits are most critical to success? The lack of one of them could be fatal. It seems that an irreducibly complex set of specifications is required for parkour, no matter which animal does it. This is the case for monkeys, apes, lizards, flightless birds and the deer that bounce over the hood and trot away.
In their Perspective article on the study, “Learning to Move in the Real World,” Adolph and Young put forward another specification: the ability to quickly adapt to internal changes. Animals gain weight; females become pregnant. The body during growth and development constantly changes mass. This also happens to human babies, as every parent knows:
New possibilities arise during development as animals’ bodies, skills, and effective environments change. Human babies can grow up to 2 cm in one day. One week, babies are creepers; the next they are walkers — yesterday objects on the coffee table were out of sight and inaccessible; today they are accessible. So, learning takes place in the context of development, and the flow of body growth and the acquisition of motor skills causes: babies don’t learn fixed solutions. Static solutions would indeed be maladaptive in a continuously changing ecosystem. Instead, “teach babies to learn.” They learn to detect information for offers at any time to determine which actions are possible with their current body and skills in a given environment.
In the experiments, the team gave the squirrels challenges that required calculating risks and rewards. To get to the nut, a squirrel had to climb over a narrow flexible strip and then jump to a pole. Squirrels instinctively knew if the strip could support their weight and was stiff enough for launch. If the strip was stable enough, they would crawl and jump to the end. If not, they would start their jump further back with more energy. Sometimes they “parked” from the vertical wall to get to the pole. If they shot too much or too little, they had a backup plan: they knew their claws could save them. They would grab the bar, spin over it or under it, and land on top like a star gym. Usually they nailed the landing with all four legs to the provided taut platform. The scientists were amazed at their quick calculations.
“They won’t always be their best performance – they just have to be good enough,” he said. “They have redundancy. So if they miss they don’t hit their center of gravity exactly on the landing beard, they are great at grabbing. They swing below, they swing above. They just don’t fall.”
Well, almost never. And that adds another spec: an excellent kinesthetic feel. The animal must know the strengths and weaknesses of its body, its position and its current weight. If a mother squirrel jumps while carrying a baby, he must calculate his resources flawlessly every time.
A technical perspective
The “acrobatic extravaganzas” that take place all around us in the living world are easy to take for granted. A technical perspective helps unpack the requirements. What must be true for this phenomenon to take place? Evolutionists slander the achievements of squirrels and humans with their disdainful statements that phenomena have just evolved. The UCB scientists seem to recognize the requirements, but somehow attribute them to evolution:
The bridgeability of the gap depends on the complement of environmental characteristics with an animal’s locomotive capabilities. The synergy between biomechanical power management and learned information for launching and landing probably determines the jump into trees and eventually the path through the canopy. The role of fast and accurate jumping in driving the evolution of biomechanical capabilities, learning-based decision-making and innovation promises the mechanisms and origin of agility in trees
In that last sentence, they admit that they cannot explain the origin of these mechanisms. So how can they speak of “the evolution of biomechanical capabilities”? Their worldview forces them to imagine an unguided origin, because in their view animals did not have these biomechanical abilities in the past. How and when did they originate? What good is one specification if the others are not yet available?
It is the technical perspective that intelligent design offers that elucidates these questions. A complex skill, such as jumping a chasm to a reward, assumes a set of specifications. Every specification is measurable: for a squirrel mass m, needed to bridge a distance d, launching from a platform with resilience Xan engineer can calculate and test the force required with robotics. More variables can be specified for in-flight correction (parkour movements) and claw strength for gripping and swinging. The specifications are likely to become more complex when the requirements for detection and balance are considered. But this is science that is accurate, measurable and testable. It also has explanatory value: once the requirements are known, the set of causes necessary and sufficient to achieve them can be evaluated.
Lead author Nathaniel Hunt, who also works in the Department of Biomechanics at the University of Nebraska, should welcome mechanical engineers to his team. It’s not a big jump to a Biomechanical Engineering department. That, not evolution, is what would promise to “reveal the mechanisms and origins of agility in trees.”