P.S
A little light googling reveals this:
The Creationist argument combines errors in understanding the theory of evolution, and errors in simple biological facts.
Their theoretical failure involves overlooking the fact that evolution occurs in small stages, each selected for the benefit of the organism.
It is perfectly true that the neck of the giraffe would be fatal if the giraffe had a small heart, or that the blood pressure produced by the heart of the giraffe would be fatal if the giraffe had thin arteries. However, evolutionary theory does not say that evolution does its work first on one feature of an animal, and then on another: it says the very opposite. Obviously random mutations do not form an orderly queue, with those extending the length of the neck going first, those increasing the blood pressure going second, and so forth. Instead, a slightly longer neck gives a selective advantage to a slightly stronger heart, which gives a selective advantage to slightly thicker arteries. So long as there is environmental pressure for slightly longer necks, there is also a selective pressure for these coadaptations, and mutations for them will be favored. It is rather depressing to think that nearly 150 years ago, Darwin gave the same answer to the same grotesque misunderstanding of his theory concerning the same animal, and that it is necessary to repeat it:
With animals such as the giraffe, of which the whole structure is admirably co-ordinated for certain purposes, it has been supposed that all the parts must have been simultaneously modified; and it has been argued that, on the principle of natural selection, this is scarcely possible. But in thus arguing, it has been tacitly assumed that the variations must have been abrupt and great.
With this theoretical error, the Creationists compound a crass factual error: supposing that the particular features named are unique to the giraffe. Not one of them is.
* The giraffe has elasticated arteries? So do you, I trust. Hardening of the arteries is an undesirable medical condition: all arteries are by nature elastic.
* The giraffe's cerebrospinal fluid produces a counter-pressure to prevent rupture or capillary leakage? This again is true of all mammals, and is a matter not of design nor of evolution, but basic physics.
* The giraffe has valves in the veins of its neck? So do all mammals. You too have a jugular valve.
* Giraffes have pressure sensors in their neck arteries? Again, so do all mammals.
* The giraffe has a rete mirable? So do most of its relatives:
The function of the rete mirabile is to regulate the flow of arterial blood towards the cerebrum as well as the thermal regulation of the brain preventing it from overheating; the arterial system of the cerebrum in ruminants is equipped with a safety system.
* The giraffe has a shunt between the carotid and vertebral arteries? So do many of its relatives, including its closest relative, the okapi, which has a short neck.
In summary, the mechanisms which the giraffe uses to control its blood pressure are all either common to mammals in general, or common to the species most closely related to the giraffe.
Fossil record:
Holocene Giraffa camelopardalis (the modern giraffe), Okapia johnstoni (the modern okapi)
Pleistocene Giraffa camelopardalis, Giraffa jumae, Giraffa gracilis, Giraffa sivalensis, Okapia stillei, Sivatherium giganteum, Sivatherium maurusium
Pliocene Giraffa attica, Giraffa punjabiensis, Giraffa priscilla, Samotherium boissieri, Samotherium sp. , Honanotherium sp. , Samotherium mongoliensis, Helladotherium sp. , Bramatherium perimense
Upper Miocene Samotherium africanum, Samotherium sp., Palaeotragus germaini, Honanotherium sp. , Honanotherium schlosseri, Honanotherium sivalense, Birgerbohlina schaubi, Giraffokeryx punjabiensis, Bramatherium megacephalum, Shansitherium fuguensis, Shansitherium tateli, Palaeotragus primaevus, Progiraffa exigua
Middle Miocene Palaeotragus primaevus, Giraffokeryx sp., Giraffokeryx tungurensis, Giraffokeryx punjabiensis
Lower Miocene Prolibytherium magnieri, Climacoceras africanus, Climacoceras gentryi, Canthumeryx sertensis
Oligocene Eumeryx sp.
