Physically and behaviourally well-suited to their environment, giraffes are an extraordinary example of adaptation in the animal world. Inhabiting grasslands and open woodlands throughout sub-Saharan Africa and towering up to 5.8 metres (19 feet), giraffes are the world's tallest mammals, weighing an average of 1,270 kg (2,800 lbs). Their specialised anatomies facilitate feeding, social hierarchy and defence. With hearts beating at double normal pressure and lungs vastly larger than those of humans, but breathing at a much slower rate, giraffes are a marvel of survival and design.
The giraffe's 2.5 metre (8 feet) neck allows it to reach feeding places that other herbivores can't. However, giraffes spend half their time grazing below shoulder level. Giraffes' long necks are a result of sexual selection because bulls use them extensively in "necking," or battling over females. This might explain why males' necks continue to grow after maturity while females' necks do not.
Towering over predators and striking out with their forefeet delivering savage blows, giraffes are well-equipped to combat danger. Their forelegs are only one-tenth longer than their hind legs, making them a formidable defence. Despite the much lengthier appearance of the forelegs, this is all the additional protection they need. When their 35 mph speed is insufficient to out-run attackers, giraffes' legs afford them added defence in the form of extremely tough skin and inner fibrous connective tissue that prevents wounds from excessively bleeding.
Mouth and tongue
With specialised mouths, tongues and upper palates, giraffes are undeterred by thorns, devouring up to 64 kg (140 lbs) of fresh vegetation daily. The animals easily process thorny foods because of their leathery mouths, thick gluey saliva and long prehensile muscular tongues, the strongest in mammals. Giraffes are ruminants -- animals that rechew partially processed food sent back up from the stomach -- and their stomachs have four chambers. They graze 16 to 20 hours per day. They're well-adapted to drought and can go a month without water, relying on the water content of their food and morning dew.
Remarkably adapted to their physiology and lifestyle, the giraffe's heart and circulatory system are the most powerful in the animal kingdom. The 60 cm (2 feet) heart requires at least double the normal pressure to pump blood the long way up into the brain. The blood-carrying carotid artery balloons, absorbing increased pressure when giraffes lower their heads. With heads raised, check valves in the jugular prevent sudden dangerous backflows from the head, avoiding unconsciousness and even death.
Although giraffes' lungs are eight times the size of those in humans, their respiratory rate is only one-third the rate of human respiration. This lower rate allows them to avoid windburn to their 3.6 metre (12 feet) tracheas while inhaling their required massive volume of air. As giraffes breathe, previous oxygen-depleted breath can't be totally expelled. Consequently, there must be enough lung volume to make "bad air" a small percentage. Without extra air-pumping capacity of over-sized lungs, giraffes would breathe the same used air over and over again.
Giraffes' colouration blends well with their habitat, affording them some camouflage from predators. Their extreme long-range visual acuity helps them keep track of predators and enables communication with other giraffes over several miles.