Eons

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 didnt 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 were used to today, which can measure over 2 meters long.

Theyre basically the longest necks relative tobody size that evolution has slappedon 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 understandingof how evolution actuallyworks over and over again.

And its taken both new ideas and new fossil discoveries to show us that we may have been thinking about the evolution of the giraffes 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 theyre often a fan favorite.

Theyre such eye-catchingly weird animals that we just can't help butbe captivated by their unusual proportions.

And throughout history, as different thinkerstried to explain how things came to be theway they are today, they kept returning tothe giraffes neck to test their ideas.

In the early 1800s, French naturalist JeanBaptiste Lamarck proposed that he had figuredout how evolution worked, and he gave thegiraffe'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 organisms lifetime were transmitted to the next generation.

Lamarck believed that offspring were affected by how their parents usedor didnt 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 areacquired 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 biologicalmysteries, including how the giraffe got its neck,changed completely.

Darwin saw the giraffesneck 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 toindividuals with longer necks beingmore 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 giraffes 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 giraffes 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 giraffes 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 weve known how it works for almost as long as weve known about natural selection, it tends to be an afterthought.

Were 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 weve been pondering the giraffes 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 didnt completely settle the debate and not everyone was convinced by the necks for sex hypothesis.

But the very same year their paperwas published, in 1996, paleontologistsin Chinas Gobi Desert found what turnedout 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 mostoptimized adaptation for head-butting everseen in vertebrate evolution.

Even more so than dinosaurs like Pachycephalosaurus, or modernhead-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 behindthe elongation of their neck, with the ability tobrowse 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 dont 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 giraffes neck, were still working out the full story.

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