搶先看|SAT自然科學類解析

Let's read the passage together, and I'l walk you through each step of the way. 

(Highlighted notes and colored illustrations are provided hereby to faciliate your comprehension )

Here we go: SAT Natural Science 1

Context Background: This passage is adapted from Thor Hanson, Feathers. 2011 by Thor Hanson. Scientists have long debated how the ancestors of birds evolved the ability to fly. The ground-up theory assumes they were fleet-footed ground dwellers that captured prey by leaping and flapping their upper limbs. The tree-down theory assumes they were tree climbers that leapt and glided among branches. 

At field sits around the world, Ken Dial saw a pattern in how young pheasants, quail, tinamous, and other ground birds ran along behind their parents. “They jumped up like popcorn,” he said, describing how they would flap their half-formed wings and take short hops into the air. So when a group of graduate students challenged him to come up with new data on the age-old-ground-up-tree-down debate, he designed a project to see what clues might [lie in how baby game birds learned to fly. ]= the implication here is Ken Dial believes the acquisition of flight in baby game birds sheds light on the acquisition of flight in their evolutionary ancestors. 

Ken settled on the Chukar Partridge(is a ground dweller, who rarely flies +pic 1)as a model species but he might not have made his discovery without a key piece of advice from the local rancher in Montana who was supplying him with birds. When the cowboy stopped by to see how things were going, Ken showed him his nice, tidy laboratory setup andexplained how the birds’ first hops and flights would be measured. The rancher was incredulous(adj. doubtful). “He took one look and said, in pretty colourful language. What are those birds going on the ground? They hate to be on the ground! Give them something to climb on !” At first it seemed unnatural-ground birds don’t like the ground?(The line suggests that Chukar Patridge is a ground dweller.)But as he thought about it Ken realized that all the species, he’d watched in the wild preferred to rest on ledges, low branches, or other elevated perches where they were safe from predators. They really only used the ground for feeding and traveling. So he brought in some hay bales(pic 2) for the Chukars to perch on and then left his son in charge of feeding and data collection while he went away on a short work trip. 

Barely a teenager at the time, young Terry Dial was visibly upset when his father got back. “I asked him how it went,” Ken recalled, and he said ”Terrible! The birds are cheating!” Instead of flying up to their perches, the baby Chukars were using their legs. Time and again Terry had watched them run right up the side of a hay bale, flapping all the while. Ken dashed out to see for himself, and that was the“aha” moment. “The birds were using their wings and legs cooperatively,”(a big discovery: from the passage it can be inferred that the baby birds do not use wings and legs separately! )he told me, and that single observation (opens up a world of possibilities). like what?

Working tougher with Terry (who has since gone on to study animal locomotion), Ken came up with a series of ingenious experiments, filming the birds as they raced up textured ramps tilted at increasing angles. (pic 3) As the incline increased, the partridges began to flap, but they angled their wings differently from birds in flight. They aimed their flapping down and backward, using the force not for lift but to keep their feet firmly pressed against the ramp(pic 4). “It’s like the spoiler on the back of a race car,” he explained, which is a very apt analogy. In Formula One racing, spoilers are the big aerodynamic fins that push the cars downward as they speed along, increasing traction and handling (pic 5). The birds were doing the very same thing with their wing to help them scramble up otherwise impossible slopes. 

Summary: 

The author explains that Ken Dial created an experiment to study the evolution of flight by observing how baby Chukars learn to fly. During the experiment, Dial noticed the unusual way Chukars use their “wings and legs cooperatively” to scale hay bales, and he created a series of ingenious experiments to study this observation. After his additional experiments, Dial determined that these babies birds angle “their wings differently from birds in flight.”

Teaching notes:

This is the most confusing part of the whole passage. Starting from the last paragraph, the author leaves a hint”the aha moment opens up a world of possibilities.” But what does it refer to? Is there a third possibility that helps to explain how birds evolved the ability to fly?

As is noted in this paragraph, Ken worked with his son Terry and came up with various original experiments to verify this assumption. “They aimed their flapping down and backward, using the force not for lift but to keep their feet firmly pressed against the ramp.” Most students felt confused after reading it, just as the test maker expected. Therefore, comes the follow-up analogy, which helps to clear students’ minds.  Have you ever seen a Formula Once racing car before? That’s how it looks like. With the aid of spoiler, both traction and speed are increased and the cars move faster. That’s exactly how the baby birds are doing, in order to maintain balance on the tilting textured ramps. They 1) flap their half-formed wings (not the same as adult birds in flight=tree-down theory) in the meanwhile 2) their feet are pressing hard against the ramps (not the same as typical ground runners= ground-up theory). So, a third possibility is provided hereby to explain ancestor birds’  acquisition of flight. What is it called?  

Ken called the technique WAIR, for wing-assisted incline running, and went on to document it in a wide range of species. It not only allowed young birds to climb vertical surfaces within the first few weeks of life but also gave adults an energy-efficient alternative to flying. In the Chukar experiments, adults regularly used WAIR to ascend rams steeper than 90 degrees, essentially running up the wall and onto the ceiling. 

In an evolutionary context, WAIT takes on surprising explanatory powers. With one fell swoop, the Dials came up with a viable origin (WAIR)for the flapping flight stroke of birds (something gliding animals don’t do and thus a shortcoming of the tree-down theory) and an aerodynamic function for half-formed wings (one of the main drawbacks to the ground-up hypothesis).

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Did you get the gist? 

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