A Brief Look at…. Giraffes!
At one time, giraffes came in a variety of neck lengths. Some giraffes had very short necks,
and others were quite long like the ones we see today. The short-necked giraffes died, and
only the long-necked giraffes survived. Why do you think this happened?
Well, the giraffes with shorter necks couldn’t compete with long-necked giraffes. Food
supplies were limited and all species were constantly in competition with one another!
Unlike the giraffes with long necks, short-necked giraffes couldn’t reach leaves and twigs up
high as well as the ones closer to the ground.
Over time, only the giraffes with long necks survived. In
the 18th and 19th centuries, there were two competing
theories about why exactly this occurred. These were from
a French scientist named Jean-Baptiste Lamarck, and an
English naturalist named Charles Darwin.
More evidence supported Darwin’s theory: because many
other animals could eat the low-lying vegetation, fewer
short-necked giraffes got enough to eat. Over generations,
giraffes with longer necks grew stronger and healthier. The
long-necked giraffes had more and more babies that, like
their parents, inherited long necks and were better able to
survive when food was scarce; no other animal could
reach the high leaves as well as they could. Over time,
more and more short-necked giraffes died before they
could reproduce more short-necked babies. Eventually,
only long-necked giraffes were born. This process of
change, called natural selection, happens in all species.
NOTE: The giraffe’s long neck is called an adaptation, which is a trait that helps an organism
fit in and survive in its environment. We will learn more about adaptations later.
Darwin’s theory
Charles Darwin was an English naturalist who studied variation in
plants and animals during a five-year voyage around the world. He
explained his ideas on evolution in a book called On the Origin of
Species, published in 1859.
The main features in his theory are that:
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individuals compete for limited resources
individuals in a population show natural variation
individuals with characteristics best suited to their environment are more likely to survive
to reproduce
'successful' characteristics are inherited
Species unable to compete successfully eventually become extinct.
Darwin's ideas caused a lot of controversy, and this continues today. They can be seen as
conflicting with religious views about the creation of the world and the creatures in it.
Lamarck's theory
Darwin was not the only person to develop a theory of evolution.
Jean-Baptiste Lamarck was a French scientist who developed an
alternative theory at the beginning of the 19th century. His theory
centered on two ideas:
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the law of use and disuse
the law of inheritance of acquired characteristics
His theory said that a characteristic which is used more and more by
an organism becomes bigger and stronger. One that is not used
disappears eventually. Any characteristic of an organism that is
improved through use is passed to its offspring.
These lists summarize the two different explanations for long necks in giraffe.
Darwin
1. a giraffe with a longer neck can reach food high up
2. a giraffe is more likely to get enough food to survive to reproduce
3. a giraffe's offspring inherit its long neck
Lamarck
1. a giraffe stretches its neck to reach food high up
2. the giraffe's neck gets longer because it's used a lot
3. the giraffe's offspring inherit its long neck
Lamarck's theory was eventually discredited because acquired characteristics do not have a
genetic basis.