Around 10 million years ago,  in the late Miocene epoch, an ancient moose-sized herbivore named Samotherium  roamed the grasslands of Eurasia and Africa.

It didn’t look quite like anything alive today, but it had two features that might help  you guess its closest living relatives.

On top of its head were two bony  structures, called ossicones, that it has in common with its modern  kin.

And perhaps the biggest giveaway of all is its meter-long neck.

This was an ancient giraffid, a close extinct cousin of giraffes and okapis.

And its neck length is about midway between those two living species, meaning Samotherium  occupies a fascinating evolutionary position.

It lets us glimpse an intermediate stage in the  elongation of the giraffid neck from shorter-necked ancestors.

A few million years after Samotherium, this process would produce the giraffe necks we’re used to today, which can measure over 2 meters long.

They’re basically the longest necks relative to body size that evolution has slapped on an animal since the sauropods.

But how and why this extraordinary trait  emerged in the first place has been a mystery that generations of biologists have argued over.

One that has made us reconsider our understanding of how evolution actually works over and over again.

And it’s taken both new ideas and  new fossil discoveries to show us that we may have been thinking about the  evolution of the giraffe’s neck all wrong.

We humans have been fascinated by giraffes for a  very long time, from depictions of them in rock  art that dates back thousands of years, to our  modern zoos where they’re often a fan favorite.

They’re such eye-catchingly weird  animals that we just can't help but be captivated by their unusual proportions.

And throughout history, as different thinkers tried to explain how things came to be the way they are today, they kept returning to the giraffe’s neck to test their ideas.

In the early 1800s, French naturalist Jean Baptiste Lamarck proposed that he had figured out how evolution worked, and he gave the giraffe's neck as an example of that process.

As earlier, shorter necked giraffe ancestors continually stretched and strained their necks  to reach higher food sources, their descendants inherited longer, stretched-out necks.

Traits acquired in an organism’s lifetime were transmitted to the next generation.

Lamarck believed that offspring were affected by how their parents used or didn’t use their various traits.

He thought this mechanism was how  all species changed over time, and how their adaptations came to be.

And he was wrong.

Traits that are acquired and flexed during an individual's  lifetime are not the basis of evolution.

Instead, we now know that evolution is based on  variation in inherited traits in a population, with some variants being favored, or ‘selected’  over time due to the advantages they offer.

When Charles Darwin challenged Lamarckism  by proposing his idea of natural selection, our understanding of basically all biological mysteries, including how the giraffe got its neck, changed completely.

Darwin saw the giraffe’s neck as a prime example of his idea instead.

Variation in a population automatically meant that   some giraffes had longer necks than others.

And competition to reach more food led to individuals with longer necks being more likely to survive and reproduce.

He was right - or at least more right than  Lamarck - but he was also kinda wrong, too?

Because while Darwin was able to explain  how the giraffe’s long neck evolved, the question of why has proved to be  much more complicated than we thought.

See, in 1996, two researchers argued that  Lamarck, Darwin, and generations of biologists since had totally overlooked the main driver  behind the elongation of the giraffe’s neck.

They said it wasn't a result of natural  selection to compete for food.

It was  sexual selection to compete for mates, instead.

Their hypothesis was literally ‘necks for sex.’ [laughs] Now, sexual selection can lead to exaggerated  traits that aren't always especially helpful in other aspects of the struggle for survival  - like a peacock's tail, for example.

This idea was another major  contribution of Charles Darwin to the field of evolutionary thought, though  he never applied it to the giraffe’s neck.

And the ‘necks-for-sex’ hypothesis was based on a few key observations.

For one, the researchers pointed  out that during the dry season, when competition for food should be at  the most intense, giraffes often browse low shrubs rather than tall trees.

Also, giraffes seemed to feed faster and more often with their necks  bent rather than stretched out.

And most importantly, male giraffes use their long  necks for a pretty dramatic behavior completely  unrelated to feeding: whacking other males.

The researchers argued that it was this competition for mates that, over  millions of years, had driven their ancestors towards ever-longer necks.

Now, sexual selection can be a very powerful evolutionary force, and despite  the fact that we’ve known how it works for almost as long as we’ve known about natural  selection, it tends to be an afterthought.

We’re just so used to searching for explanations that link directly to survival, like eating.

Those explanations are often the lowest hanging fruit.

So even though we’ve been pondering the giraffe’s  neck for hundreds of years, most people had just  accepted that it was competition for food rather  than competition for mates that was behind it.

This idea didn’t completely settle the  debate and not everyone was convinced by the necks for sex hypothesis.

But the very same year their paper was published, in 1996, paleontologists in China’s Gobi Desert found what turned out to be another piece of the puzzle, though they didn't know it at first.

They unearthed a fossilized braincase and  some vertebrae from a weird mammal dating back to about 17 million years  ago, to the early Miocene epoch.

The base of the skull and the neckbones that had  attached to it were strangely large and thick.

They couldn't immediately tell  what it was and gave it the name in Mandarin that translates to ‘strange beast’.

It wasn't until decades later, in 2022,  that a much more detailed description of  the ‘strange beast’ was published.

Scientists named it Discokeryx, and concluded that it was an early giraffoid  based on the shape of its inner ear.

But Discokeryx was unlike any  other member of the family… Its robust neck and head joints were the  most complicated ever seen in a mammal.

Plus it had a thick-boned  skull crowned with a large, disk-like headgear capped  with a bowler hat of keratin.

But while it may have looked like a distinguished  gentleman, it was anything but gentle.

Discokeryx was built for both dealing out  and withstanding massive blows to the head in competition between males.

In fact, the researchers’ models suggested that it may have had the most optimized adaptation for head-butting ever seen in vertebrate evolution.

Even more so than dinosaurs like Pachycephalosaurus, or modern head-butters like muskox and rams.

It looked to be another example of sexual  selection driving extreme head and neck traits in the giraffe family that  were totally unrelated to feeding.

And the researchers argued that it was this  fierce competition for mates that was behind   the evolution of so much headgear diversity, and  strange head and neck morphologies across the   20-or-so million year history of the group.

Varied and exaggerated traits seem to actually be a recurring theme of giraffoid evolution,  taking different forms in different species.

Including the elaborate headgear and thick  necks of ancient genera like Bramatherium and Sivatherium, for example.

So they saw Discokeryx as yet more evidence for the necks-for-sex hypothesis.

To them, the particular form of combat that giraffes engaged in was the primary driver behind the elongation of their neck, with the ability to browse on higher trees being a side-benefit.

Now, the debate is still far from settled.

Evolution can be convoluted, and we don't  know how much each type of selection pressure   contributed to the overall process.

For example, we don’t know if one was the driving force early on and then the neck  became co-opted for another role as time went on.

And so, hundreds of years after Lamarck  and Darwin thought they had solved the mystery of the giraffe’s neck, we’re  still working out the full story.

More than perhaps any other single  trait in the animal kingdom,