They are the tallest mammal on Earth reaching heights of up to 6 meters! Their necks can stretch up to 2 meters to reach their favourite food: The nutritious yet toxic pods and leaves of the Acacia tree. So how did Giraffes get their long necks?
Since the beginning of evolutionary science, giraffes have puzzled naturalists aiming to explain how evolution works. It is not surprising when you look at their ludicrous necks and overall proportions, they look as if they belonged to a different era.
Jean-Baptiste Lamarck, a naturalist of the XVIII century and a pioneer of evolution and extinction theories, thought that giraffes got their long necks after years and years of stretching to reach the leaves of the Acacia trees. Few years after, Darwin and Wallace’s envisioned a very different theory based on natural selection, where those giraffes that had slightly longer necks had better chances at reaching nutritious food, living longer and therefore, successfully passing on their genes to their offspring.
But the question about how they got the long necks still remained unanswered..
Different from birds and other long-necked animals, giraffes do not get their longs necks from extra vertebras. Their vertebras are simply longer. In fact, scientists recently found that the earlier ancestors of the giraffes had actually short necks, but their vertebras were longer compared to their width. [2]
The same study found that giraffes did not evolved their long necks in a linear way. Even though the earliest giraffes already had slightly-elongated neck bones, evolution went back and forth a few times creating different giraffe lineages. The short-necks proliferated alongside their taller relatives, which might explain why we still have long-necked giraffes and their close relative, the Okapi which looks more like a zebra with a long neck.
To answer the question of how they evolved their long necks, researchers from US and Tanzania turned to genetics. They compared the genetic material of giraffes, Okapi and other mammals including humans and found about 70 genes in the giraffe genome that showed adaptations not seen in other mammals.
The majority of these unique genes were responsible for regulating different aspects of development and physiology of the skeleton and the cardiovascular system. Scientists believe that more research into the unique mutations of the cardiovascular system that allows giraffes to have a blood pressure 2.5 times higher than humans, might provide guidance for future treatments of cardiovascular diseases in humans.
Finally, the study of the giraffe’s genome concluded that several genes functionally intersect metabolism, growth and cardiovascular functions, suggesting that giraffe’s unique features may have co-evolved to elevate its stature, adapt its metabolism for more toxic food sources (giraffes have a specific gene mutation that allows them to digest the highly nutritious yet toxic pods and leaves of their favorite Acacia tree) and adapt its cardiovascular and nervous system to the increased demands imposed by its unique morphology. [1]
We are just beginning to understand the uniqueness of this magnificent animal. Yet, we are losing giraffes at the speed of light. We have lost over 40% of the giraffes’ population in the last 30 years and there is still so much to be learned about them.
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[1] 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: 10.1098/rsos.150393
[2] Agaba, M., Ishengoma, E., Miller, W. et al. Giraffe genome sequence reveals clues to its unique morphology and physiology. Nat Commun 7, 11519 (2016). https://doi.org/10.1038/ncomms11519
So I totally thought it was from millions of years of stretching! It’s truly amazing how these animals adapt to survive.