How Giraffes Became Winners by a Neck

Giraffes have taught generations of students how evolution works. Not directly, of course. Communicating through nocturnal humming is a barrier to classroom instruction. But the modern giraffe – Giraffa camelopardalis – is often used as the textbook example of why Darwin and Wallace were right and Lamarck was wrong.

The setup goes something like this. Think of a little protogiraffe gazing hungrily at some tasty leaves high up on a tree. Someone from the Lamarckian school of evolution, the argument goes, might assume that the little giraffoid would stretch its neck to grab the lowest of those high leaves and, through exertion, develop a longer neck that it would then pass on to its offspring. Repeat for best results. A Darwinian, on the other hand, would expect the protogiraffes to vary in neck length and those that just happened to have slightly longer necks would be able to reach more food, survive longer, and mate often enough to pass on that variation to the next generation, who would play out the scenario over again.

While the scenario is a bit of a caricature of what Lamarck actually thought, it’s still useful in getting at the basic evolutionary equation that Darwin and Wallace independently distilled. Yet, despite the thought experiment’s popularity, we’ve known little of how the giraffe actually got its neck. Today’s tall browsers definitely evolved from shorter-necked ancestors, but how? A new study by New York Institute of Technology’s College of Osteopathic Medicine anatomist Melinda Danowitz and colleagues now provides an answer.

Giraffes aren’t the only animals to have evolved impressively-long necks. The sauropod dinosaurs and aquatic plesiosaurs, for example, stretched out to ludicrous lengths both by adding additional vertebrae to the column and elongating those individual bones. But giraffes have the standard number of neck vertebrae shared by most mammals – seven – with the first element in the thoracic part of the spine being modified as a possible eighth “neck” bone. But that’s it. Evolution, constrained by mammalian anatomy, molded giraffes in a different way than the long-necked saurians.

Danowitz and coauthors looked at anatomical landmarks on 71 giraffe vertebrae spanning 11 species from over 16 million years ago to the present, focusing on the second and third vertebrae in the neck. As it turns out, a proportionally-long neck isn’t new for these mammals.

The best candidate for a real protogiraffe, Prodremotherium, and an early giraffe named Canthumeryx already had neck bones that were long compared to their width. “[N]ot only did the giraffid lineage begin with a relatively elongated neck,” Danowitz and coauthors write, “but that this cervical lengthening precedes Giraffidae” – the giraffe subgroup typically thought of as encompassing all the long-necked forms.

The evolution of giraffe neck vertebrae. From Danowitz et al., 2015.
The evolution of giraffe neck vertebrae. From Danowitz et al., 2015.

But even though the earliest giraffes already had slightly-elongated neck bones, there was no “March of Progress” towards towering heights. At least one – and possibly more – giraffe lineages reverted to abbreviated necks hung around stout vertebrae. Giraffokeryx was among the earliest of the short-necked giraffes, browsing low-lying foliage around 12 million years ago, and within the last three million years Sivatherium, Bramatherium, and the okapi followed suit. The short-necks proliferated alongside their lankier relatives, which is why we still have both short- and long-necked giraffes today.

Truly long-necked giraffes didn’t evolve until about 7.5 million years ago. Samotherium, Palaeotragus, Bohlinia, the extinct Giraffa sivalensis and the living Giraffa camelopardalis preserve enough transitional features to let Danowitz and colleagues reconstruct how this stretching occurred. It wasn’t simply a matter of drawing out their vertebrae as if they were in some sort of anatomical taffy pull. The front half of the neck vertebrae became elongated in Samotherium and Palaeotragus, generating forms intermediate between today’s Giraffa and their foreshortened predecessors. Then, within the last two millions years or so, the lineage leading up to the modern Giraffa elongated the back half of their neck vertebrae, giving them even more reach and making them literally at the top of their class.

If you could assemble all these fossil bits and pieces into a short film replaying giraffe evolution, you wouldn’t end up with the smooth transformation of a small-statured herbivore into a towering, checkered browser. There’d be starts and stops and side stories, the ending not being a goal but a happenstance. In short, it’s time again to update those textbooks.

Reference:

Danowitz, M., Vasilyev, A., Kortlandt, V., Solounias, N. 2015. Fossil evidence and stages of elongation of the Giraffa camelopardalis neck. Royal Society Open Science. doi:

16 thoughts on “How Giraffes Became Winners by a Neck

  1. So how did the elaborate blood pressure management system that allows the head to go from low to high relative to the heart and not lose blood flow to the brain going up & not blow up with the increase in pressure as the head lowers “evolve”? Please feel free to attempt an explanation for this design to incrementally evolve and function at each of the intermediate steps.

  2. What I don’t understand is why the long neck evolved
    in the first place. True, a long neck gives access to a greater number of trees
    but it also means a larger body. A larger body requires more energy. Giraffes
    being warm blooded use even more energy and leaves are low energy food.
    How could the amount of leaves eaten offset the energy needed to sustain a larger
    warm blooded body?

  3. Once upon a time, giraffes had
    Hardly any size neck at all,
    Which made two giraffes very sad.
    Then from Noah they got the call.
    So he and she both went on board
    The ark, as all flooded like heck.
    Inside the ark they both got bored,
    So they both went up on the deck.
    A bolt of lightning grabbed both by
    Their heads and wow -necks did appear,
    Stretching so-o-o long into the sky.
    Later they told Noah, “All clear.”

    So if you want your neck to grow,
    Stand out in lightning – now you know.

  4. The giraffe is impressive creature, especially in person, but interestingly enough, the picture at the top shows a giraffe with 3 horns?

  5. So where are all the short neck giraffes with the same appearance except for the neck length? Where all the food sources all at very high levels? What would baby giraffes do until they could reach those heights? This is article and issue leaves too much open to be a logical and interesting article.

  6. In reality both Lamarck and Darwin were a little off track. Lamarck had the right idea but the mechanism is even more sophisticated than he thought. The physical stretching of the animal’s neck did not increase its length and such an occurrence would not affect the genetic code it passed to its offspring even if it had. What has to be recognized is that the genetic programming involved is a lot cleverer than we appreciate. The brain of the current generation (stretching for food) registers the issue and its subsequent genetic code is altered slightly such that is offspring will actually come into the world recoded for a better reach. This is also demonstrated by the fact that the animal’s legs are also a little longer and the overall skeleton is in fact given better high-reach capability (along with muscles and all other parts of the structure). “Inter-Generational Programmed Adaptation” (D. A. Ashton) is the process that leads to ALL evolutionary development, in all living things, not just skeletal, but all functioning aspects of the organism. Modern genome decoding research has managed to attribute responsibilities at the “feature” level to about 25% of the DNA structure. What will be shown is that a large part of the remaining DNA is dedicated to “Reacting to Environmental and Experiential” inputs in order to pass appropriately modified DNA to the following generation. So we must attribute “intelligence” to the evolutionary process, not “brute force” (Lamarck) or “chance mutation” (Darwin). Let the blowing of collective fuses and the academic meltdowns begin!

  7. What isn’t explained are the natural selection conditions that led to a long neck. Leaves have a low nutritional content. A huge amount per body weight of the herbivore is needed to sustain life. The larger the body the more energy needed to sustain it. For warm blooded mammals even more energy is needed. True a longer neck and bigger body gives more access to browsing for leaves but makes grazing for grass more difficult. Also would the amount of extra leaves accessible offset the increased metabolic demands of larger and warm bloodied body?

  8. Recent advances in the field suggest alternate routes and perhaps synergistic function. For example, inheritable DNA Methylation as a conveyance of expressed genome. 2. The 4-D structure of the Cell nucleus, so that Gene Folding becomes a player in gene expression. 3. Quantum Evolution: where it is more likely that say, another neck bone appears as the result of mutation, not quite truly “random”. In other words, close inspection is revealing very Lamarkian-like functions that seem to influence “pure” Darwinistic Evolution.

  9. So giraffe precursors are something like a deer, and then an extinct giraffe. There is zero evidence of anything in between but we know it ‘definitely’ happened. It’s a fairy tale, complete with made up drawings for brainwashing little kids to never question it. And to boot, it is portrayed as merely having a longer neck, completely ignoring (hiding) the myriad of anatomical and physiological functions and features in a giraffe that are different than an okapi type (horns, glands, muscles, overall size, heart and vascular system, trachea and respiration, skin, etc). Ignored because there is no explanation how they came to be either, and would have to evolve concurrently and slowly along with the longer neck completely by blind chance. (Although they appear abruptly in the fossil record) Please think about it. Don’t just accept blindly that given enough time, random and unguided errors will work any magic you want.

  10. At least one – and possibly more – giraffe lineages reverted to abbreviated necks hung around stout vertebrae. Giraffokeryx was among the earliest of the short-necked giraffes, browsing low-lying foliage around 12 million years ago, and within the last three million years Sivatherium, Bramatherium, and the okapi followed suit.

    I just want to be sure I’m understanding this correctly. Does that mean that the ancestor of okapis had a longer neck than okapis?

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