googlef87758e9b6df9bec.html A Sure Word: Most Mammals Have 7 Cervical Vertebrae – Not Quite Enough to be Evidence for Evolution

Sunday, November 1, 2015

Most Mammals Have 7 Cervical Vertebrae – Not Quite Enough to be Evidence for Evolution

Giraffes have seven cervical vertebrae (neck bones), the same number as humans. Given that the giraffe's neck is so much longer than ours, some people are surprised we have the same number of neck bones. The fact of the matter is that nearly every mammal has seven neck bones – mice, dogs, and even whales. I've heard it proposed that this is because all mammals are descended from a common ancestor which also had seven neck bones and so the nearly universal number of seven vertebrae is strong evidence for evolution.

A similar argument is often made concerning the bone structure of the forelimbs in tetrapods. Mammals, reptiles, amphibians, and birds all have representative species that have the homologous structure of humerus, radius, and ulna. The case is made that these limbs are similar because all these creatures have descended from a common ancestor which had the same structure.

I heard this argument – the one about giraffes having seven neck bones – online again the other day. The whole story sounds kind of contrived to me. I got to thinking about how I might be able to test that theory. Like any scientific theory, it should be able to make predictions. So, if different species which are descended from a common ancestor have the same number of cervical vertebrae, what else might I expect to be true?

The first prediction I might make is that if giraffes and humans have the same number of neck vertebrae due to common descent, then all mammals should have the same number of cervical vertebrae. Is this what we find? In short, no. Most mammals do indeed have seven neck bones but not all of them do. The two-toed sloth has 5-7 vertebrae, the three-toed sloth has 8-10, and manatee have only 6. So this prediction fails.

I might also predict that mammals should also have similar numbers of vertebrae in other parts of their spines. A quick look at Wiki shows this isn't the case. In the thoracic vertebrae, numbers vary between 12-15 in different species of mammals; in the lumbar region there are usually 6-7 but some species have 20; the number in the sacral region can vary between 3-10. Any similarity in the number of vertebrae exists only in the cervical area of the spine and even that isn't universal. Another failed prediction for the theory.

I would also think that if descent with modification were true, then there should be a discernible pattern in the number of ribs among mammals. There isn't any. Mammals have varying numbers of ribs between 6 and 15 pairs. Even in the famous horse evolution sequence, there are reversals in the numbers of ribs between oldest alleged ancestor and the “transitions” to the modern horse. Still another fail.

Now, since there is supposedly homology in the forelimbs of, say, mammals and birds, then could we also predict 7 cervical vertebrae among birds? We might, but birds have far more cervical vertebrae than mammals. So similar forelimbs in mammals and birds is supposedly the product of evolution and a different number of neck bones is also the product of evolution?  Fail.

Think about this too: all mammals (well, we've already seen it's not all mammals) have the same number of cervical vertebrae. Then could we expect something similar to occur among the members of other classes? Do all birds, for example, have the same number of cervical vertebrae? No. Do all reptiles? No. Do all amphibians? No. Why does common descent “explain” this common feature among mammals when we don't see a similar thing occur among the other classes of animals? Fail.

Finally, birds are alleged to have evolved from dinosaurs. If descent with modification is true, then wouldn't there be some correlation in the number of cervical vertebrae between birds and dinosaurs? Well, there isn't any. Long-necked sauropods had up to 19 cervical vertebrae. Most bipedal dinosaurs had less. Birds have up to 25. Fail.  Fail.  Fail.

Time after time, we see that things we might predict if evolution were true aren't found. Any claim that the common number of neck bones among mammals is evidence of descent from a common ancestor is nothing more than special pleading. If the same number of vertebrae is evidence for evolution, than differing numbers should be evidence against the theory. Of course, evolutionists don't see it that way. They're perfectly content with a theory that could explain the same number of neck bones in different species but doesn't require it. In other words, they have a scientific theory that doesn't really explain or predict anything.

Not a very good “theory,” is it?


Steven J. said...

Cornelius Hunter has argued on his blog that evolutionists routinely argue for evolution on the grounds that "a Designer wouldn't have done it that way." He stopped allowing comments after too many evolutionists pointed out that properly, the argument is that "common design doesn't explain this feature, but common descent does." Granted, the widespread seven cervical vertebrae is not the most obvious feature to be used this way, because common descent doesn't have a detailed or compelling explanation for this, beyond vague handwaving about "developmental constraints in mammals not found in other classes." Now, if you enter "why do almost all mammals have seven cervical vertebrae," you will find an article by Frietsen Galis of the University of Leiden, in the Netherlands, with exactly that title. He notes that mammals are more prone to cancer than birds and reptiles, and argues in the paper that the constraint on variation in neck vertebrae number is because mutations that alter the number of neck vertebrae also make cancer more likely -- and mammals can't (for the most part) handle the increased risk. Other articles called up by the same search note that mutations for different numbers of neck vertebrae in mammals are often accompanied by other problems (e.g. "misplaced or crushed nerves, muscles, or blood vessels"). All this raises the question, of course, of why mammals, of all vertebrate classes, should have such developmental constraints. But it does seem to me that this is an even bigger problem for creation, since a Creator would not be constrained, as evolution is, by past evolutionary history. Evolution can paint itself into a corner in some lineages; creation can always magic up a new door.

I should note that, having observed that, e.g. snakes have more vertebrae than lizards, or in general that not all vertebrate species have the same number of vertebrae, I would on evolutionary grounds infer that cervical vertebrae number should not be constant even within species. As Richard Dawkins notes in one of his books, no matter how dramatic the difference between two species, those species trace back to a single ancestral species, and to two individuals no more different than brothers. Indeed, Galis, in the aforementioned paper, notes that in many species of birds and reptiles, healthy individuals in the same species can have different numbers of vertebrae. He does not note another fact, which is that rib number varies the same way: not only do different mammal species often have different numbers of ribs, but many species, including humans, are known to vary in rib number among individuals. Bone number is surprisingly variable in many species (as are a host of other details), which is why the seven-cervical-vertebrae figure is interesting: that rarity of disparity between (or within) species calls for explanation, which evolutionary biologists are working on.

Steven J. said...

A couple of additional notes:

Again, basically, evolutionary theory demands that large-scale adaptions (e.g. a wing from a front leg) is simply the accumulation of small-scale adaptions (e.g. a taller or wider, flatter tail for swimming). An observed trait of small-scale evolution is that change in a trait can change direction (e.g. the size of a finch's bill in the Galapagos might increase in dry weather and shrink again as the climate grows wetter). There is no obvious reason why this should not be true also of large-scale evolution, and over the course of horse evolution lineages grew and shrank in overall size, teeth changed shape to adapt to browsing or grazing and back again, and, yes, average rib number changed. Again, the reversals among a line of genera is no greater than the variation in rib numbers in modern horses.

You mention but don't otherwise address homologies among forelimbs of different vertebrate groups. The chart you post illustrates an argument raised by Charles Darwin: we would expect common design for common function from intelligent design or special creation, but we would not expect what we in fact see: similar designs for dissimilar functions (e.g. bat wings and whale flippers), yet dissimilar designs (or at least dissimilar modifications of underlying similarities) for similar functions (e.g. the wings of small insect-eating bats and small insect-eating birds). This, again, is more easily explained by common descent with opportunistic modification: evolution must "re-invent the wheel" (or the wing, anyway) every time a lineage acquires the ability for flight, and the closest homologies to that wing will be found among the closely related non-flying groups (e.g. terrestrial theropod dinosaurs for birds and, um, probably primates for bats).

RKBentley said...

Steven J,

You said, “I should note that, having observed that, e.g. snakes have more vertebrae than lizards, or in general that not all vertebrate species have the same number of vertebrae, I would on evolutionary grounds infer that cervical vertebrae number should not be constant even within species.”

Thanks for your comments. They're interesting, as usual but your single statement here highlights my problem with your theory. Scientific theories should be explanatory and predictive. Right? I mean, that's not my rule – it belongs to the scientific community at large. I also routinely hear that creationism isn't “scientific” because it cannot be used to make predictions.

What you have in evolution is a theory that could explain why all mammals have the same number of cervical vertebrae but also “explains” why other classes don't have the same number of cervical vertebrae. Surely you've heard it said that a theory that explains anything really explains nothing. That's exactly what is going on here. The number of cervical vertebrae among all vertebrate species seems random and evolutionists invent ad hoc theories to explain why it's one way here and another way over there. There's nothing explanatory or predictive about it.

So now you say that, based on your theory, you don't even believe members of the same species should necessarily have the same number of neck bones? OK. Then why do people on your side keep pointing out the seven neck bones in most mammals as though it's evidence of anything? That was sort of the whole point of my post, wasn't it? If common descent doesn't even require members of the same species to have the same number of neck bones then the constant appearance of 7 cervical vertebrae among mammals is as easily explained by coincidence as evolution. It could even be said to be evidence of design.

Thanks again for your comments. God bless!!


Steven J. said...

OK. Then why do people on your side keep pointing out the seven neck bones in most mammals as though it's evidence of anything?

I thought I explained that. However tentative and incomplete evolutionary explanations are (for why mammalian cervical vertebrae are constrained, in most cases, to seven in number), it is entirely inexplicable on creationist grounds. If God creates separate "kinds" separately, He cannot be constrained by their (nonexistent) past evolutionary history -- there should be no reason why extra vertebrae in most mammals causes problems when it doesn't in birds or reptiles). "Coincidence" (mere happenstance with no special reason for it) is not really an explanation consistent with a single Creator (though we could invoke multiple creators who just happened to settle on similar designs by accident).

Surely you've heard it said that a theory that explains anything really explains nothing.

On the other hand, any account of vertebrate origins has to be able to account for the actual differences in vertebrates -- why male lions are larger than female, but male eagles are smaller than female, or why bone number increases with neck length in birds but not in mammals. There are, on the other hand, possible observations that evolution could not explain -- if, e.g. Duane Gish had been right when he said, in debates, that human albumin is more similar in amino acid sequence to frog albumin than to chimpanzee albumin, but which would be as consistent with special creation as the pattern which we in fact observe (i.e. human and chimp albumin are identical, and much different from frog albumin). If we shared endogenous retroviruses with dogs and cats that we didn't share with monkeys, that, again, would be consistent with "God just arbitrarily decided to make it that way" but not notably consistent with "homologous ERVs in homologous loci are inherited from a common ancestor with that ERV in that locus."

RKBentley said...

Steven J,

I'm not sure what more to say except to once again ask what value is the theory if it isn't predictive? You say mammals have 7 neck bones because of common descent but common descent doesn't require animals to have any specific number of neck bones. So if the same number of neck bones and varying number of neck bones both fit your theory, then your theory doesn't really explain anything.

You may recall a while back I talked about similarities in creatures that are not supposed by evolutionists to be closely related. Chimps and humans are said to be similar because they are closely related – but placental moles and marsupial moles are very similar even though they can't be as closely related. In one case, they're said to be similar because they share a common ancestor; in the other case, they're said to be similar because they've adapted to similar environments. So if similarities in animals is not necessarily the result of a recent common ancestor (even according to your own theory) then how can you ever say similarity is evidence of a common ancestor?

By the way, you never addressed the extreme disparity in cervical vertebrate between dinosaurs and birds. If birds are related to dinos, I would predict some correlation between the number of neck bones between the descendent birds and their dino ancestors. There isn't any. Similar anatomical features have been used as evidence that birds are related to dinosaurs but birds have far more neck bones than dinos did. If similarities are evidence for your theory, then why aren't differences evidence against your theory?

So your theory “explains”...

Why some animals have similar number of neck bones
Why other animals have varying numbers of neck bones
That some animals look alike because they have a common ancestor
That other animals look alike though they don't have a common ancestor
That some animals are related based on their similarities
That some animals are related in spite of their differences
Why some birds have bright feathers
Why some birds have drab feathers
Why humans are altruistic
Why humans are aggressive
Why humans are monogamous
Why humans are promiscuous

Evolution explains nothing. It predicts nothing. All of evolution's explanations are ad hoc and not useful for anything. It's junk science. Evolution has zero impact on conducting science, inventing life improving technologies, or just living our lives in general. Common descent hasn't happened anyway. How can something that's not even true ever be useful?

Thanks for your comments. God bless!!