Reading 1

Unit 10 - Reading 1

Page 146

Giving Nature a Hand

For most of human history, humans have had to live with the body that nature gave them. They lacked the knowledge to improve eyes that couldn’t see clearly, or help ears that couldn’t hear. Such disabilities were more than an inconvenience for early humans; they were a threat to their existence.

A person with impaired vision might not be able to hunt or work with tools, for example. Over time, the incentive to survive led people to develop devices that would fix these impaired conditions.

EARLY WAYS TO IMPROVE VISION

During his 12th-century travels through China, Marco Polo supposedly saw people using eyeglasses. Soon, eyeglasses came into common use in Italy The objective of the earliest lenses was to help people see things that were a close up so they could do tasks like carving or sewing. Soon after, lenses to help people see distant objects became common.

In the 18th century, the two types of lenses were combined in one pair of bifocal lenses so individuals who were both farsighted and nearsighted needed just one pair of eyeglasses. Early glasses were held in the hand or clipped on the nose, held there by the tension of the stiff wire they were made from. Modern framed glasses, suspended from the ears by earpieces, were uncommon until the 19th century.

IMPROVING VISION TODAY

Nowadays, other options are available. For example, about 2 percent of the people in the world opt for contact lenses, which lie on the surface of the eye. Fortunately, corneal implants and laser surgery may one day eliminate the need for corrective devices altogether.

WAYS TO IMPROVE HEARING

No evidence exists of an early device to enhance hearing, but it probably did exist. It was likely a hollow, cone- shaped animal horn with the point cut off. Held with the tip by the ear, the horn could be directed toward a voice, for example, so sound waves from the voice could be focused into the ear.

In the 20th century, battery-operated hearing aids became common. The components included a case that contained a battery and a sound-amplification device. A wire attached the device to a disc that was inserted into the ear. Today, thanks to electronics, tiny devices that fit behind the ear contain both energy cells and an amplifier.

They provide not only better amplification, but also better discrimination between various sounds. There is now a surgical alternative to improve hearing without an external device. A medical evaluation can determine whether this alternative-a cochlear implant—might be right for someone with a hearing loss.

REPLACING TEETH

Tooth loss was common among our early ancestors due to accidents, infection, and disease. Being toothless affected people’s ability to eat and speak clearly. It also made them physically unattractive. The earliest known false teeth, or dentures, date from the 15th century, when rich people were willing to spend a large sum of money for uncomfortable false teeth carved from ivory, animal I so teeth, or wood.

When the process of making rubber was perfected in 1851, dentists immediately advocated its use as a base material for dentures. It was soft, so it would be comfortable. It could be molded to fit individual mouths, and it could securely hold artificial teeth.

It was also cheap, making dentures affordable to everyone. Today, dental implantation is available for people who need to replace one or several teeth. Fixed into the jawbone with a titanium screw, an implanted tooth becomes a permanent replacement rather than a removable dental device. The exploration of an ancient Mayan burial site in Honduras uncovered the tomb of a young woman, confined there for 1,400 years.

Her jawbone contained three tooth-shaped pieces of seashell embedded into the bone in spots where three of her natural teeth were missing. Was the dental implant a punishment imposed on her, or was it a voluntary procedure? Were the Mayans the first humans to give nature a hand with dental implants?