Evolution

By | September 9, 2016

Fossils of prehistoric animals show us that life on Earth is always changing. Over time, old species disappear and new ones develop from them, like new relatives appearing in a family tree. These new species appear thanks to a process of gradual change we call evolution.

NATURAL SELECTION

frogs-laying-eggs

Breeding frogs lay many hundreds of eggs, but only a tiny number will survive to become adults themselves.

Evolution is driven by a process called natural selection. Animals and plants produce more offspring than survive to adulthood, all of them slightly different. Nature selects those with the best characteristics, which then pass on these characteristics to the next generation.

The giraffe’s neck

giraffe-neck

Giraffes feeding from a tall tree

 

The giraffe’s long neck evolved because natural selection weeded out individuals that couldn’t reach food high in the trees. With each generation, the tallest giraffes got the most food and had the most babies. Over time, the species changed as its neck grew longer.

TAKE A LOOK—A STORY OF FINCHES

darwin-finches

This picture is a result of Darwin’s researches

The most famous person to collect evidence for the idea of evolution was the English naturalist Charles Darwin. He visited the Galápagos Islands in the 1830s, where he found a range of similar finch species, each with a beak suited to its particular diet. He realized they’d all evolved from a common ancestor that had settled on the islands long ago.

An unpopular theory

darwin-chimpanzee-1871

Charles Darwin’s satirical portrait from 1871

People made fun of Darwin for his ideas; he was drawn with the body of a chimpanzee in 1871 when he proposed that humans were related to apes.

FOSSIL EVIDENCE

 Archaeopteryx had feathers but also teeth, claws and a tail like those of dinosaurs (above); Fossil remains of Archaeopteryx (below);

Archaeopteryx had feathers but also teeth, claws and a tail like those of dinosaurs (above); Fossil remains of Archaeopteryx (below);

One reason Darwin was ridiculed is that the fossil record is much too sparse to show a process of gradual change. However, some key fossils show clear links between related animal groups. One example is Archaeopteryx—a missing link between dinosaurs and birds.

EVOLUTION OF THE ELEPHANT

evolution-of-elephant-1

In a few rare examples, we can see gradual evolution in fossils. The elephant belongs to a group of animals called proboscideans. Over time, proboscideans became larger and developed larger tusks and trunks. But the ancient animals shown here may not be direct ancestors of the elephant—they are merely glimpses of parts of the elephant’s large and hidden family tree.

Artificial selection

evolution-of-wolf

All domestic dogs today around the world have a common ancestor in the wolf

Darwin realized that animal breeders change their breeds using a process very similar to natural selection. Instead of letting nature choose which animals will breed, breeders make the choice themselves.

Darwin called this artificial selection. All dog breeds were created this way from their wild ancestor, the wolf.

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