Giraffes are known for their long necks that allow them to feed on tall trees. But their necks may have evolved due to sexual combat, not the need to feed.
"Necking" in the savannah: Scientists think today's giraffes (two in the background) evolved from an ancient predecessor, Discokeryx xiezhi (here in the foreground)Image: WANG Yu and GUO Xiaocong
Advertisement
Throughout history, we have tried to explain how giraffes evolved — not least because of their long, beautiful necks.
Fantastical theories in the middle ages suggested that giraffes were a crossbreed of panthers and camels. Other theories proposed that giraffes were a type of gentle chimera or a version of a mythical Chinese creature known as a qilin.
The British naturalist Charles Darwin used the giraffe's neck as an example of evolution and natural selection. Darwin said the animal's neck had grown in length over millions of years, allowing it to reach for higher tree branches as sources of food.
But more recently scientists have proposed a different theory that suggests the giraffe's neck grew through intensive sexual combat.
The "necks-for-sex" theory argues that "necking" combat was a form of sexual competition between males.
Now, a new study published in Science suggests there is more compelling evidence that those fierce battles among early giraffes may have created a selection pressure to develop more extreme types of neck.
Advertisement
How did the giraffe get its neck?
Scientists found this new evidence while studying fossils of an ancient creature called Discokeryx xiezhi. The species is considered to be an early version of the giraffe that lived about 16.9 million years ago in open savannah, much like giraffes do today.
The scientists found the D. xiezhi had an unusual head-neck morphology, or shape, with a thick-boned helmet on top of the cranium and extremely thickened cervical vertebrae.
D. xiezhi is also known as a giraffoid. It is said to have the most complicated head-neck joints in mammals known to date.
A giraffe's long, strong neck: For feeding and breedingImage: DW
Its bone structure was highly specialized for high-speed, head-to-head butting, a possible form of sexual competition between males.
Males with stronger, longer necks beat weaker rivals and were able to mate with females, thereby passing on their genes to drive a selection process.
Over thousands of generations of breeding, spanning about 11 million years, giraffe necks gradually elongated, according to the science.
Head-butting through the generations
Head butting is still a common type of aggressive behavior among animals, particularly mammals such as deer, sheep, stags and bison. It is used in mating contests and to fight off predators.
All those head collisions can lead to severe injuries over time — as they would in humans.
But that wasn't the case for D. xiezhi. The researchers suggest that the species had a uniquely sturdy head and neck anatomy for withstanding necking.
They estimate that D. xiezhi's head could withstand huge collision forces in a fraction of a second with almost no strain on the brain. The strength of the skull may have reduced the risk of concussions and other brain injuries.
And the researchers suggest that despite their overt, gentle beauty, modern-day giraffes engage in fierce necking battles, like their apparent predecessor, D. xiezhi.
Edited by: Zulfikar Abbany
Giraffes: Earth's threatened giants
Long overshadowed by poaching crises hitting elephants and rhinos, the perils facing giraffes are slowly gaining attention. But for the world's tallest land animal, whose numbers are dwindling, it may not be fast enough.
Image: Getty Images/J.Martinson
A 'silent extinction'
Giraffe numbers have plummeted in recent years, with conservationists warning of the "silent extinction" of the world’s tallest land animal. Just 97,500 now exist in sub-Saharan Africa, falling almost 40 percent since 1985, says the International Union for the Conservation of Nature. Check out this week's eco@africa show to see how giraffes are coming back from the brink of extinction in Niger.
Image: DW/Inga Sieg
'Trophy' animals
These majestic creatures have suffered from disease, habitat loss and illegal hunting for bushmeat, as well as collisions with vehicles and power lines - there are now fewer giraffes than elephants in Africa. Campaigners say giraffes now face additional pressure from "trophy" hunters traveling to Africa to shoot their big-game quarry - these hunters mostly come from the US.
Image: Getty Images/M.Ralston
Not one species – but four?
In 2016, researchers found that there are not just one but four distinct species of giraffe. The research, published in the journal Current Biology, is now being reviewed, but if formally recognised as four separate species, three of those four would suddenly be deemed more seriously threatened on the IUCN's list of endangered animals, hopefully prompting greater conservation efforts.
Image: Getty Images/K.van Weel
How the giraffe got its long neck
Giraffes' necks can be as long as six feet – despite only containing seven vertebrae, the same number as a human's, although a giraffe's are elongated. For blood to reach the brain, the heart must pump it to a height of two meters. Scientists are still trying to solve the mystery of how the giraffe got its neck.
Image: Getty Images/C.De Souza
Arriving with a bump
Pregnancies are long, lasting up to 15 months, and end with the giraffe giving birth standing up – that means their offspring have rather a bumpy welcome into the world, having to endure falling more than five feet to the ground at birth. But baby giraffes are fast learners: they can stand within just 30 minutes of the birth and can run with their mothers only 10 hours after being born.
Image: Getty Images/M.Cardy
Eating around the clock
Giraffes eat most of the time, chewing through hundreds of pounds of leaves each week and must travel miles to find enough food. But its height can make drinking difficult and dangerous. To do so, they must spread their legs and bend down, making them vulnerable to predators. Thankfully, giraffes only need to drink once every several days, as they get most of their water from the plants they eat.
Image: Getty Images/J.Thys
Dining with a view
A giraffe's 21-inch tongue is crucial in helping them pluck leaves from branches–and also helps in the birth process. Giraffes graze on leaves and buds in treetops that few other animals can reach, with acacias a particular favorite.
