Ancient Bones by Madelaine Böhme

Author:Madelaine Böhme
Language: eng
Format: epub
Tags: SOC002020, SCI054000, HIS051000, SOC002010, SCI027000, HIS002000
Publisher: Scribe Publications Pty Ltd
Published: 2020-09-29T00:00:00+00:00

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THE GREAT

BARRIER

A Gigantic Desert Becomes an Insurmountable Obstacle

THE RECONSTRUCTION OF the world in which Graecopithecus lived proves that the story of the Sahara goes much further back than we have long supposed. But how did this enormous desert influence the evolutionary story of life so many millions of years ago? To get closer to an answer, it is worth taking a look at the Sahara and the people who live there today. This is the only way we can understand why deserts have always been hostile barriers of sand, dust, and rock that have left their mark on the distribution of plant and animal species far beyond their borders.

The Sahara is a tropical-subtropical hot desert where the sun is close to its highest point in the sky year-round. The intense sunlight heats the ground so much that in some places, temperatures near the ground can reach 140 degrees Fahrenheit (60 degrees Centigrade) or more. There is barely any precipitation. The central area of the desert has less than 0.4 inches (10 liters per square meter) of rain per year—one-hundredth the amount of rain that falls every year in New York City on average. The few plants that can survive under such extreme conditions get by on tiny amounts of water, such as the dew that collects overnight when the cool night air condenses. Every drop of water is valuable in this extremely dry region. It is hardly surprising that the only appreciable plant communities in the Sahara grow in oases or in the somewhat moister margins of the desert. Many areas in the heart of this desert are essentially bare of vegetation.

Of the relatively few animals in the Sahara, most are insects, spiders, scorpions, snakes, and lizards. Many species are crepuscular or nocturnal—that is to say, they are active at dusk and dawn or at night. To protect themselves from the heat of the day, they withdraw into underground hiding places or bury themselves in the sand. Mammals rarely live in deserts.27 Those that do are usually small, like the other desert dwellers, and do not leave their hiding places until the sun sets. There is, however, an exception—an animal to which the rules of the desert seem not to apply and that is unique in the history of evolution: the camel.28 This desert dweller is barely affected by hot and dry conditions because it has evolved to be perfectly adapted to this extreme habitat. No other animal even comes close. Camels are ungulates, hoofed mammals, but they have lost their hooves, because hooves would be useless in the desert. Instead, they have two extremely powerful toes padded on the undersides with large, round calluses, ideal for walking without sinking deep into the sand.

Camels have developed fascinating strategies to deal with the lack of water. They get most of the water they require from their food, so they do not need to drink much to supplement their intake. In addition, they have physiological adaptations to severely restrict the amount of water they lose in the hot desert climate.

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