20 year old Nigerian. German major, Chemistry minor. Premed. Science lover and lover of language. German, virology, epidemiology, nuclear chemistry, orgo you name it!
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 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 larger lung
s 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:
Photo credit: Charles G. Summers, Jr.