Appliance of Science: Why do giraffes have such long necks?

This week’s question was sent in by seven-year-old Sábha, from Bray, Co Wicklow. Sábha would like to know… why do giraffes have such long necks? 

Giraffes are the tallest land mammals on Earth. Their necks make up nearly half their height; they can be almost 2.5m long in a fully grown adult male. With such long necks you would expect their bones to be very different to ours but they have the same number of vertebrae in their necks as we do. All land mammals, except sloths, have seven vertebrae in their necks; it is just that the giraffes’ are a lot bigger (a giraffe’s vertebra is 15 to 20 times larger than a human’s).

Exactly how giraffes ended up with such long necks is still unclear. There are a number of theories.

THE THEORIES

Many scientists believe that giraffes have longer necks to give them an advantage when it comes to getting food. They live in areas where food can be scarce; the land is prone to draught. Giraffes eat grasses and leaves. When food supply is limited and lots of animals are competing for it, there can be a big advantage to having a supply of food that only you can reach.

There are many scientists who oppose this theory and propose their own. Maybe giraffes have evolved their long necks to use as weapons. Male giraffes often fight each other in a process called necking

. Using their long necks like whips they butt each other with their hard heads. Usually the biggest male (with the longest, strongest neck) wins the fight. So the longer-necked giraffes get to pass on their genes to the next generation.

Those that oppose this theory say female giraffes have very long necks too, almost as long as their male counterparts, but they do not use them for fighting. Others suggest that giraffes’ long necks give them an advantage when spotting prey. Their only predators (apart from humans) are lions and crocodiles. Their tall necks would not help them to spot the crocs though, unless they hold them low to the ground.

Can you take one more theory? Perhaps the giraffes’ long neck gives them a larger surface area of skin to help them regulate their body temperature.

It may be that the reason for the giraffe’s long neck is actually a combination of some, or all of these theories. Each one suggests an advantage to the giraffe’s long neck. But are there any disadvantages?

WHAT DOES THE GIRAFFE SAY?

We all know the sound of a dog , but what noise does a giraffe make? Until recently it was thought that they ‘said’ very little. Although they have all the equipment to make sounds, (like a voicebox) it was thought their relative silence was due to their extra-long neck. Now scientists have recorded some low-frequency humming sounds they make, but only, it seems at night.

DIZZY SPELLS

With such a long neck the giraffe has had to evolve some other changes to their body to stop them from fainting every time they lift their head. They have very big hearts and they have a muscle in their jugular vein (which is very unusual) and both of these help pump blood all the way to the head and maintain their blood pressure, despite the lofty heights.

Naomi is a science communicator and mother to three inquisitive children. She can be found at sciencewows.ie

Feel free to email your questions to drhowsciencewows@gmail.com


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