Evolution
While
it has some flaws that demonstrate its origin, the neck of a giraffe is
nonetheless a great example of evolution. Humans and giraffes each have
seven cervical vertebrae, but the giraffe has ball-and-socket joints
between them that allow for far greater mobility than we have. They have
extremely powerful hearts (which can weigh more than 11kg), a higher
concentration of red blood cells and la
rger
lungs than an animal of their size usually does to compensate for the
trachea's large length. When they bend down to drink, a complex of
arteries and veins - known as the rete mirabile, or "wonderful net" -
prevents a lethal headrush from the change in blood pressure.
Two evolutionary hypotheses have been put forward to explain the
giraffe's neck. The first, suggested by Darwin himself, is that the
giraffe's height allows it to eat leaves other animals can't reach. The
taller ancestors could pass on their genes because shorter
giraffe-ancestors often died out, forming the modern giraffe's
astonishing neck. The second, the "necks-for-sex" hypothesis suggests
that those with longer necks were more successful reproductively because
of sexual selection. Giraffes fight by "necking", where their necks and
heads are used in combat for females. Those with longer necks had an
advantage and so left more descendants.
There are some problems
with both hypotheses. If the neck lengthened to feed, then why is the
giraffe approximately 2 metres taller than its nearest competitor? And
if they evolved by sexual selection, why do female giraffes - who do not
engage in necking - have similarly long necks? The most likely
explanation is probably a mix of the two. Some have suggested that
natural selection originally lengthened their necks, and then sexual
selection took over. At any rate, the mystery isn't completely solved
yet.
A video of giraffes necking:
http://www.youtube.com/
Photo credit: Charles G. Summers, Jr.
http://
http://www.newscientist.com/
http://
While
it has some flaws that demonstrate its origin, the neck of a giraffe is
nonetheless a great example of evolution. Humans and giraffes each have
seven cervical vertebrae, but the giraffe has ball-and-socket joints
between them that allow for far greater mobility than we have. They have
extremely powerful hearts (which can weigh more than 11kg), a higher
concentration of red blood cells and la
rger
lungs than an animal of their size usually does to compensate for the
trachea's large length. When they bend down to drink, a complex of
arteries and veins - known as the rete mirabile, or "wonderful net" -
prevents a lethal headrush from the change in blood pressure.
Two evolutionary hypotheses have been put forward to explain the giraffe's neck. The first, suggested by Darwin himself, is that the giraffe's height allows it to eat leaves other animals can't reach. The taller ancestors could pass on their genes because shorter giraffe-ancestors often died out, forming the modern giraffe's astonishing neck. The second, the "necks-for-sex" hypothesis suggests that those with longer necks were more successful reproductively because of sexual selection. Giraffes fight by "necking", where their necks and heads are used in combat for females. Those with longer necks had an advantage and so left more descendants.
There are some problems with both hypotheses. If the neck lengthened to feed, then why is the giraffe approximately 2 metres taller than its nearest competitor? And if they evolved by sexual selection, why do female giraffes - who do not engage in necking - have similarly long necks? The most likely explanation is probably a mix of the two. Some have suggested that natural selection originally lengthened their necks, and then sexual selection took over. At any rate, the mystery isn't completely solved yet.
A video of giraffes necking:
http://www.youtube.com/
Photo credit: Charles G. Summers, Jr.
http://
http://www.newscientist.com/
http://
Two evolutionary hypotheses have been put forward to explain the giraffe's neck. The first, suggested by Darwin himself, is that the giraffe's height allows it to eat leaves other animals can't reach. The taller ancestors could pass on their genes because shorter giraffe-ancestors often died out, forming the modern giraffe's astonishing neck. The second, the "necks-for-sex" hypothesis suggests that those with longer necks were more successful reproductively because of sexual selection. Giraffes fight by "necking", where their necks and heads are used in combat for females. Those with longer necks had an advantage and so left more descendants.
There are some problems with both hypotheses. If the neck lengthened to feed, then why is the giraffe approximately 2 metres taller than its nearest competitor? And if they evolved by sexual selection, why do female giraffes - who do not engage in necking - have similarly long necks? The most likely explanation is probably a mix of the two. Some have suggested that natural selection originally lengthened their necks, and then sexual selection took over. At any rate, the mystery isn't completely solved yet.
A video of giraffes necking:
http://www.youtube.com/
Photo credit: Charles G. Summers, Jr.
http://
http://www.newscientist.com/
http://
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