Part 6
You are going to read an article about about the evolution of hands. Six sentences have been removed from the article. Choose from the sentences A-G the one which fits each gap (37-42). There is one extra sentence which you do not need to use.
Our amazing hands
The hand is where the mind meets the world. We use our hands to build fires, to steer airplanes, to write. The human brain, with its open-ended creativity, may be the thing that makes our species unique. But without hands, all the grand ideas we think up would come to nothing.
The reason we can use our hands for so many things is their extraordinary anatomy. 37 . Some are connected to bones within the hand, while others snake their way to the arm. The wrist is a floating group of bones and ligaments threaded with blood vessels and nerves. The nerves send branches into each fingertip. The hand can generate fine forces or huge ones. A watchmaker can use his hands to set springs in place under a microscope. A sportsman can use the same anatomy to throw a ball at over 100 kilometres an hour.
Other species have hands too. 38 . In other cases we have to look closer. A bat’s wings may look like sheets of skin. But underneath, a bat has the same five fingers as a human, as well as a wrist connected to the same cluster of wrist bones connected to the same long bones of the arm.
In exploring how hands have evolved, researchers over the past 150 years have dug up fossils on every continent. They’ve compared the anatomy of hands in living animals. They’ve studied the genes that build hands. It appears that our hands began to evolve at least 380 million years ago from fins – not the flat, ridged fins of a goldfish but the muscular, stout fins of extinct relatives of today’s lungfish. Inside these were a few chunky bones corresponding to the bones in our arms. 39 . The digits later emerged and became separate, allowing the animals to grip underwater vegetation as they clambered through it.
40 . Some species had seven fingers. Others had eight. But by the time vertebrates were walking around on dry land 340 million years ago, the hand had been scaled back to only five fingers. It has retained that number of fingers ever since – for reasons scientists don’t yet know.
Nevertheless, there are still many different types of hands in living species, from dolphin flippers to eagle wings to the hanging hooks of sloths. 41 . They can also see that despite the outward differences, all hands start out in much the same way. There is a network of many genes that builds a hand, and all hands are built by variations on that same network. It takes only subtle changes in these genes to make fingers longer or to turn nails into claws.
The discovery of the molecular toolbox for hand building has given scientists a deeper understanding of evolution. 42 . It may just be a little more of one protein here, a little less of another there. In the past, scientists could recognise only the outward signs that hands had evolved from a common ancestor. Today scientists are uncovering the inward signs as well.
A Over time, smaller ones developed that would eventually become wrists and fingers.
B Although a vulture’s wing and a lion’s paw may appear to have nothing in common, the difference between them may come down to tiny variations.
C They also use them for a number of different purposes.
D No one would doubt that the five fingers at the end of an orangutan’s arm are part of anything else.
E By studying these, scientists are beginning to understand the molecular changes that led to such dramatic variations.
F The thumb alone is controlled by nine separate muscles.
G Early hands were more exotic than any hand today.
For this task: Answers with explanations :: Vocabulary