I would like to ask a question about evolution.?

Question

I want to take a common animal like the giraffe. The giraffe stands 19 feet tall, and has a heart 2 feet long in order to pump the blood up it's long neck, producing a blood pressure in excess of 200psi. The problem occurs when the giraffe has to lower it's head in order to take a drink. Without an elaborate series of valves in the giraffes neck, everytime the giraffe lowered it's neck, the pressure would be so great, the blood vessels would burst. Could anyone explain to me how these valves developed gradually over long periods of time using evolution.

Personally, I believe that God created the giraffe with fully functioning valves. But those of you who believe in evolution, how would you explain the evolutionary development of those valve. Like I said, if those valves aren't fully functioning, everytime the giraffe lowered it's head, it would die. And I want to point out one other fact: Dead giraffes can't evolve.

Any evolutionary theories out there?

Answer 1

One has to assume that the length of the giraffe's neck and the valves evolved together over time. I've never studied this particular case so I can't claim any specfic knowledge, but if you do a google search you will find some plausible explanations, like the one below.

I personally find very little satisfaction in any answer that amounts to "there is no other explanation, so it must be that God did it". Sure, there have been many times when the best thinkers of the era could not come up with another explanation, but eventually a natural explanation is discovered. The theory of Evolution has been remarkably successful in explaining a great deal that was mysterious about the diversity of life on this planet.

Answer 2

Since you probably didn't think of that question yourself I'm not going to take the time to reword this.

"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 and valve (common to mammals) that moderate appropriate pressure. 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.

This is a theoretical 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.

Answer 3

The valves, the neck, and the heart all evolve together. When the giraffe was first starting to evolve a long neck (lets say it was 10ft tall) it could still pump blood to its head and not pass out when it drank. But as it slowly started getting taller, the ones with larger hearts survived and the ones without didn't. Likewise, the ones that had the smallest of valves, or even just different shaped vessels, would survive. As the giraffe gets taller, the heart gets bigger, and the valves develop.

It actually makes perfect sense when you study evolution.

Answer 4

Darwin answered this claim in 1868 (206). The claim assumes that "gradually" must mean "one at a time." Not so. The different features could have (and almost certainly would have) evolved both simultaneously and gradually. Partial valves would have been useful for reducing blood pressure to a degree. An intermediate heart would have produced enough pressure for a shorter neck. A smaller net of blood vessels in the head could have handled the lesser pressure. As longer necks were selected for, all of the other components would have been modified bit by bit as well. In other words, for each inch that the neck grew, the giraffe's physiology would have evolved to support such growth before the next inch of neck growth.
http://www.talkorigins.org/indexcc/list.html

Answer 5

Giraffes started as a creature with a short neck (well, after millions of years of evolution to get to that point). The giraffes were competing for food with their neighbors. The ones with longer necks could reach the higher food. Thus, those giraffes lived longer and bred more. With each successive breeding, the gene was passed to more and more giraffes. Meanwhile, the giraffes with shorter necks died off because the longer necked ones beat them out for food.

Now, once these necks reached a certain length, they started to see the problem with leaning down. But there were a few with another odd gene that gave them a stop of sorts in their neck to alleviate the blood pressure. This probably started out as a simple flap of skin. Over millions of years, the neck continued to get longer in the above mentioned fashion and these flaps became more and more elaborate and tiny changes turned a random skin flap into a valve.

This really is not hard guys. We're talking MILLIONS of years for these tiny changes to take place. Really, this is not difficult to understand.

Answer 6

Easy. The giraffe's precursors had shorter necks. The selection pressure favors longer necks to reach leaves higher in the trees, so any gene modification which increases neck length will be favorable to survival -- if the valves are also in place, which is another evolutionary result. Humans also have such valves; important ones are in the legs, and a variety of griefs arise if they fail as they sometimes do. Evolution is now a proven fact.

Answer 7

If you're going to complain about evolution, at least get your complaints right.

I don't think a booster of evolution would say giraffes woke up one day with long necks and then had to come up the next day with valves.

Instead, you have a bunch of, say, horse thingies. Those guys can lean over just fine. Some have longer necks than others. And as ones with longer necks got more food and were more likely to survive shortages that killed the short-necked ones, they came to dominate the population. At no point does a creature who can't lean over show up.

It's not that hard. Read a book or something.

Answer 8

Over many years there were predecessors of the giraffe that had shorter necks. Those with slightly longer necks than their siblings were able to reach more vegetation and reproduced more. Next generation, those with the longer necks again survived until over the years their descendants had freakishly long necks. Out of this generation, some also had thicker arteries and veins than some of their siblings, making them less prone to problems associated with high blood pressure. They lived longer and reproduced more. That's a very simplified version and although I'm not too familiar with giraffe anatomy I think it will suffice.

Answer 9

Aren't you assuming here that the neck was fully formed in one generation? A lesser functioning valve could well serve a not-so long neck.

Also, there is an emergent theory that says that long necks were created for better participation in mating rituals.

“Fossil and modern skeletal evidence should reveal a disproportionate increase in the neck length over and above expected isometric increases associated with lengthening of other body proportions” (Simmons and Scheepers, 1996).When modern and extinct giraffids are compared this is just the case.The few fossil records suggest that fossil giraffids were stout in structure with shorter necks.

Answer 10

Yes there are. Would you like a simple, two paragraph answer like the explanations in the Bible.
Sorry, the epistemology of science, the way scientists know something, does not fit well with simple cliches, trite phrases and the llike.
Science explains things in laborious detail that anyone who reads the publication can verify by redoing the research. It is tedious work but exciting some times.
The results of science are wonderful things like hybrid plants and cars. IPods and DVDs, canned soup and televised Superbowls. Scientific discovery gains power and capability, religious beliefs are static and their Biblical foundations are becoming more and more silly as they are currently interpreted.
It is a shame that the religious do not confine themselves to matters of appropriate interpersonal conduct and helping others instead of meddling in the material world.