The body design of giraffes has long fascinated researchers. Even Charles Darwin considered the evolutionary bodies of giraffes to represent a fascinating riddle. Previously, many researchers argued that giraffes only had slightly-longer necks, allowing them to reach leaves and other food only slightly-higher but still out of reach to other animals. Consequentially, giraffes had their own untouched food source, available only to them and extremely consequential in times of a food shortage or drought. The equation was 'neat and simple' writes Wired. "Short-necked giraffes+natural selection+time=long-necked giraffes," researchers concluded.
As illustrated by Elissa Cameron and Johan du Toit in a 2007 study of giraffe feeding ecology, it was found that lower-level herbivores deplete the abundance and quality of browse available to giraffes. By excluding browsers from feeding on certain Acaia trees, the scientists were able to measure just how much of a tree’s foliage competing herbivores scarf up, and it became apparent that giraffes would definitely get the most from each mouthful by browsing high when low- and mid-level browse had been cleared away. Giraffes can feed at a variety of levels, and this ability to reach high during times of tough competition certainly provides them with an advantage.
A competing theory evolved in a 1996 paper by Robert Simmons and Lue Scheepers entitled 'Winning by a Neck: Sexual Selection in the Evolution of Giraffe.' Stating their own observations that giraffes actually feed at a lower level in times of abundant food supply, the researchers postulated that the long necks of male giraffes were tied to sexual competition between males. In this controversial theory, female giraffes came along for the ride, as males continually pushed the limits of giraffe neck lengths.
One paper, published by G. Mitchell, S. J. van Sittert, and J. D. Skinner in the Journal of Zoology last year collected data suggesting that male giraffes do not energetically invest more in the growth in their necks than females do. In fact, not only did the necks of female giraffes continue growing through their lives, but they also added neck mass faster than males, and whatever differences there were between the necks of female and male giraffes appeared to be attributable to differences in overall body mass rather than the true sign of sexual selection. If the differences between living giraffes were so minimal, it seemed unlikely that males had truly driven the evolutionary change through sexual selection.
Until recently, researchers concluded that it might be decades before they understood how the giraffe got its long neck. This week we have new clues after researchers explain their sequencing of the DNA genome of giraffes, a scientific discovery revealing striking and unusual DNA eccentricities.
DNA Sequencing Reveals A Turbo-Charged Heart In Giraffes
In order to pump blood two meters up from the mid-section to the brain requires giraffes to have a turbo-charged heart.
"There are many theories about how the giraffe's neck lengthened but it does seem that the development of the cardiovascular system evolved in parallel with the development of the skeletal system," said Morris Agaba of the African Institute for Science and Technology in Tanzania.
Researchers are now focused on a small number of genes that have evolved over the last 11-12 million years in giraffes' legs as well as their hearts through changes in perhaps 70 genes, many of coding for proteins.
"The genes that we identified as likely determining giraffes' unique characteristics are, in fact, genes that were first discovered in other animals to be responsible for making key regulatory decisions about the body plan and function," says study co-author Douglas Cavener says.
The giraffe and its evolutionary relative the okapi share a common ancestor had an intermediate neck length, implying that when they split off about 11.5 millions years ago, the okapi evolved to have shorter necks, Dr. Cavener told the Christian Science Monitor. "As they evolved separately, the giraffe's key regulatory proteins genes underwent several modifications, promoting extended growth in the cervical vertebrae and the cardiovascular system, allowing the giraffe's heart to pump blood all the way up to its head. "
Traversing that six-and-a-half foot journey upward has "evolved a turbocharged heart" and a vascular system with twice the blood pressure as in other animals.
This evolutionary story is one of a modification of evolutionary modification of existing genes, rather than new ones, explains Dr. Cavener. "The message is that novelty is not created from scratch, but rather from building on solutions that have evolved over time. The giraffe's long neck and legs are kind of a good example."
Global Giraffe Population Down 40% in 15 Years
The research team in Tazania believes that the most important take-away from the four-year study is to highlight the critical importance of giraffe conservation. It's estimated that the global giraffe population has fallen 40 percent in just 15 years. Statistically giraffes are more endangered than elephants.
If elephants are threatened by an international demand for ivory, giraffes are threatened with extinction because of the local market for 'bush meat' and demand for skins in the luxury market. Not all species of giraffes are equally threatened.
A single Kordofan giraffe can produce up to 270 kilograms of meat, enough to feed an army of poachers for weeks, according to experts. Its unique and distinctive spotted skin is used for luxury goods and carries a high price in a country like the Congo where per capita income is less than $230.
Aimé Balimbaki, the head of research and monitoring at Garamba National Park, says that just 34 adult giraffes survive split between two herds, with four young calves between them. The current ratio is one male to 2.4 females, making it still sustainable with concentrated efforts. "If we have bad luck of if there is a serious menace -- even if we lose just five giraffes -- then the population may no longer be viable."
Garambia National Park covers about 5,5 sq miles and is a World Heritage Site since 1980. With the extraordinary violence in the Congo, giraffes but also animals, rhinos and other animals have been poached out by various armed groups, according to Erik Marary, the African-born Swede who manages Garamba for the non-profit organization, African Parks.
Elephants are also under assault in Garamba National Park, but for the moment our focus is giraffes.
Sadly, giraffe tails -- which caught Darwin's attention long before their necks -- are also highly prized in many African cultures. In a situation of sad irony, the desire for good-luck bracelets, fly whisks and thread for sewing or string beads, result in giraffes being killed for their tails alone. Note that smart poachers profit from the entire kill.
In another sad fact, with increased agricultural activities, expanding villages and municipalities, and road construction, the population of acacia trees is declining. These symbolic trees are the main source of food supply for giraffes.
World Giraffe Day is celebrated on June 21 and is a project of the Giraffe Conservation Foundation(GCF).