A tall story – how the giraffe got its neck
A tall story – how the giraffe got its neck
The giraffe (Giraffa camelopardalis) is the tallest land-living animal, with long legs and a neck which distinguish it from all other living animals - it is the sole member of its genus, or family, and has no close living relatives. But how did the giraffe get its long neck? Understandably, many a tall tale has been told attempting to explain such a unique feature.
It certainly puzzled eminent scientists in the early 1800s who, fuelled by the frenzy of worldwide exploration and collecting of biological samples, attempted to describe and understand the world around them.
In the early 1800s Chevalier de Lamarck was one of the first to propose a concept of organic evolution. Lamarck and his contemporaries were becoming increasingly aware that life forms were not fixed, and that when environments changed, organisms had to also adapt to survive.
Lamarck thought that valuable new characteristics acquired during an individual’s lifetime were somehow passed on to the next generation. In the case of the giraffe, Lamarck proposed that stretching to reach higher leaves resulted in the neck growing longer during an individual’s lifespan, and that offspring would inherit this characteristic.
The inheritance of acquired characters, known as ‘Lamarckian’ inheritance, would however soon lose favour to another theory. It would be Alfred Wallace, a contemporary of Charles Darwin, who in 1858 (a year before Darwin published his famed On the Origin of Species) first proposed a form of natural selection which exerted its influence over generations. For Wallace, competition for food was the selective factor that drove the evolution of the neck.
Wallace wrote that the giraffe did not “acquire its long neck by desiring to reach the foliage of the more lofty shrubs, and constantly stretching its neck for the purpose, but because any varieties… with a longer neck than usual at once secured a fresh range of pasture over the same ground as their shorter-necked companions, and on the first scarcity of food were thereby enabled to outlive them.”
In his groundbreaking publication on evolution Darwin himself used the example of the giraffe’s vertebrae to illustrate unity of type across organisms, which he suggested reveals a common ancestry between organisms, writing: “The framework of bones being the same in the hand of a man, wing of a bat, fin of the porpoise, and leg of the horse - the same number of vertebrae forming the neck of the giraffe and of the elephant - and innumerable other such facts, at once explain themselves on the theory of descent with slow and slight successive modifications.”
But both Wallace’s and Darwin’s theories lacked a mechanism for the transfer of evolved characteristics – something which would only be answered with the identification of DNA and the study of genetics in the 1950s, nearly one hundred years after they proposed their revolutionary theories.
The evolution of the giraffe’s neck is widely considered a classic example of evolutionary biology. However its explanation is not as obvious as may first appear.
Fossil evidence shows that the ancestor of the modern giraffe, known as Paleotragus, existed during the African Pliocene, 12 million years ago. When the okapi (Okapia johnstoni) was discovered in the mountainous rainforests of the Congo Basin early in the twentieth century (Henry Morgan Stanley was one of the first to report rumours its existence) it was as if an ancestral form of the giraffe had been rediscovered - a ‘living fossil’ or missing link in the evolution of the modern giraffe.
However even today there is a lack of scientific consensus on the exact evolutionary processes which drove the development of the giraffe's long neck. The theory which is still most widely accepted is that longer necks confer a feeding advantage, and that over generations selection pressure favoured the survival of longer necked individuals.
An alternate hypothesis is that the giraffe evolved longer legs to run away from predators and needed an equally long neck to reach the ground to drink. Others have suggested that the neck evolved through a process of sexual selection, with females selecting males with longer necks as a sign of fitness. Indeed the neck plays an important part in male competition for dominance, with males using their necks and heads as clubs with which they attempt to knock each other literally senseless.
And there are, of course, those who believe that the giraffe is as the giraffe has always been – perfectly designed by a divine creator and never changing.
Which all goes to show you don’t need a neck as long as a giraffe’s to gain a good perspective on the world around you, even though it can be dizzying trying to make sense of it all.
More from this issue:
Zambezi Traveller (December 2013)
More from the Zambezi Traveller:
Luangwa Destination Profile