Intermediate Forms

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[edit] Definition

If an organism B is intermediate in form between organisms A and C, then it is said to be an intermediate form between A and C.

[edit] The theory of evolution predicts intermediate forms

Intermediate forms are one of the key predictions of the theory of evolution, which stipulates that species evolved through a gradual process of natural selection acting on small variations. It follows that if a kind of animal C is evolved from a different kind of animal A, there will have been intermediate forms B1, B2, B3 etc between A and C.

This leads to the question: where are all the intermediate forms? In some cases, they are still with us; ring species[1] provide a startling example.

Or we might consider the sharks and the rays; we have no problem identifying the sharkiest sharks and most rayish rays, but if you lined them all up in order from most sharky to most rayish, you would find an area in the middle where only arbitrary lines may be drawn.

However, in many cases, we find gaps in the set of living creatures; for example in the order Carnivora, there is no chain of living intermediates from some generalized carnivore to the felids, and from the same generalized carnivore to the canids.

The reason for this, of course, is that not all species are living, as we know from the fossil record: to a good approximation, 99% of species are dead. Now this leads to a prediction. We know that some animals are fossilized: only a tiny proportion of them, to be sure, but that's a tiny proportion of a lot of animals. Hence from the theory of evolution we can derive the following prediction:

The theory of evolution predicts that intermediate forms, consistent with our knowledge about evolution from other data (morphological, genetic, et cetera) will be found in the fossil record.

This prediction has been triumphantly confirmed; we now know of many thousands of sets of fossils which can be lined up in a chain showing clear morphological intermediates. [2]

Note that when we describe this as a prediction of the theory of evolution, we mean that it was not only a prediction in the scientific sense of the word, that is, a logical consequence of the theory, but also a prediction in the ordinary usage of the word; for when Darwin wrote the Origin of Species, no-one knew of any such fossils.

[edit] How to falsify the theory of evolution based on intermediate forms

If a theory genuinely has predictive power, then there must be some observations which, if they were made, would prove the theory false. It has sometimes been claimed by creationists that the theory of evolution is not in principle falsifiable in this way. It is interesting to look at this in the light of intermediate forms.

The theory of evolution would be falsified if there were no intermediate forms in the fossil record. Creationists must know this well, for you can often hear them claiming that there are in fact no intermediate forms and that this proves false the theory they describe as unfalsifiable.

The theory of evolution cannot be falsified by the absence of any particular fossil from amongst those discovered: any given intermediate form might not have been found yet, or might not have been preserved (see the discussion below of "gaps in the fossil record"). However, the theory of evolution could be falsified by the presence of the wrong intermediate forms.

The theory does not merely say that there will be intermediate forms, it also predicts which intermediate forms can be found: they must be consistent with our knowledge about evolution from other data (morphological, genetic, et cetera). So the theory of evolution allows us to find intermediate forms between land mammals and whales, for example, because genetics and morphology shows that whales are descended from land mammals. On the other hand, the theory does not allow an intermediate form between a shark and a whale, despite their superficial similarities.

To take another example, genetics and morphology link birds to saurians: so the theory of evolution permits us to find something intermediate between dinosaurs and birds, but not between bats and birds. The only intermediate forms allowed by the theory of evolution are those which fit into the history of evolution as reconstructed from other data, and the discovery of exceptions would overturn the theory.

[edit] Examples of intermediate forms

  • One interesting recent example is the discovery of Tiktaalik. The discoverers knew that there was a gap in the record of fish-to-amphibian evolution; they knew from dating the rocks before and after the gap that this missing link should be found in the Late Devonian, probably between 380 and 363 million years ago; they looked at a geological atlas to see where they could find exposed rocks of the right age; they picked Ellesmere Island, Canada, went there, and found Tiktaalik fossils. [3]

[edit] Misconceptions corrected

There are a number of common misconceptions concerning intermediate forms, and thanks to the activities of creationists these errors have been widely propagated.

[edit] "Intermediate form" is a morphological term

It seems difficult to misunderstand a phrase which is as self-defining as "intermediate form". To say that B is an intermediate form between A and C means in itself no more than that the form is intermediate. Deciding whether this is so does not depend on any of the imaginary "evolutionist assumptions" that creationists love to talk about. It is purely a question of animal morphology: it can be checked given three animals, or fossils, or morphological descriptions, and it can in principle be carried out by someone ignorant of the theory of evolution or opposed to it. There is certainly historical precedent for this: when Linnaeus, a creationist, used comparative morphology to order living creatures into a taxonomic tree, he had no conception of evolution and no idea that he was sketching out a family tree of life: he was merely observing what comparative morphology had to tell him.

[edit] Taxonomy is not based on shared-acquired characteristics

Creationists are fond of pretending that taxonomic classification is based on the "assumption" that common form means common ancestry rather than common function, as shown in this little gem from Answers in Genesis:

"If one were to consider the evidence seriously, one must conclude that this argument really does not prove evolution at all. What it proves is common need calls for common structures. Morphological homology is not a proof for or against evolution, yet it is the major proof for this belief system." [4]

Whether through dishonesty or stupidity, this canard turns the science of taxonomy on its head. Scientists are well aware that common habits of life lead to similar structures, because:

The theory of evolution predicts convergent evolution.

In fact taxonomists concentrate on those features which cannot be explained by "common needs": for example at the homology between the hand of a man, the wing of a bat, and the flipper of a whale; or at the fact that the forelimbs of dromaeosaurs, the wings of archaic birds, and the limbs of no other species contain the structure known as the semilunar carpal. We should like to see a creationist try to explain what "common need" applied to the arms of dromaeosaurs (but no other dinosaurs) and to the wings of extinct birds (but no living birds); and to no other species.

Of course, in giving these brief examples, we do not mean to suggest that claims of affinity are based on any single homology, but rather on inspection of all the fine details of the organisms being compared.

[edit] Common ancestors are not necessarily intermediate forms

A common ancestor is not necessarily the same thing as an intermediate form. The common ancestor of men and all living monkeys, for example, was not a half-man, half-monkey creature; anatomically it might best be described as a primitive monkey, and the only human characteristics it showed were the characteristics which humans share with monkeys. A "half-man, half-monkey" (to use a very unscientific phrase) would be found between this common ancestor and men.

If we looked at the other branch of this family tree, we should see ancient monkey-like species becoming more like modern monkey species. Hence we would have two sets of intermediate forms leading from the same starting place.

This point was stressed by Darwin in the Origin of Species; the full quotation, which is lengthy, appears in appendix at the end of this article.

[edit] Intermediate forms need not be intermediate in time

One of the commonest creationist misconceptions is often stated in the form "If we evolved from monkeys, why are there still monkeys?" It is based on ignorance of the concept of adaptive radiation. In the specific case of men and monkeys, for example, the answer is simple: we do not compete with monkeys in their environmental niche of living in the tops of jungle trees.

In general, then, it is the case that a species C may evolve from a species A, via an intermediate B, and that any two or all three of these kinds will continue to flourish and develop, so long as they are suited to different habits and habitats. We have given the sharks and rays as a case where there is a wide variety of coexisting intermediate forms.

It is also possible for a species to become separated geographically. For example, if a species is carried from the mainland to an island, there is no pressure on the mainland for to develop, and certainly no reason for it to go extinct. Hence, in general:

The theory of evolution does not predict that if fossils A, B, and C form a morphological sequence, then they must be found in that order in the fossil record.

However, it is possible to derive a real prediction on this subject. If the animals really did evolve in some order (let's say A, B, C for convenience) then if we had a sufficiently detailed fossil record, we would find that in the earlier rocks there was A but no B, in later rocks we'd find B and possibly A, and in later rocks still, C and possibly B and/or A.

The theory of evolution predicts that as the number of known sites bearing relevant fossils grows large, such a temporal sequence will become apparent.

So, for example, in horses, where the fossils are very abundant, we can see a clear temporal sequence: first there are only four-toed types, then there are only three-toed types, then there are three-toed and one-toed types, and finally there are only the one-toed types. In birds, by contrast, where fossil evidence is scanty, it is possible to construct a beautiful morphological sequence, but so far as we know it is not possible to illustrate the whole sequence using fossils in their temporal order in the fossil record. This would become a challenge to evolution only if this develops as a pattern when the number of known sites for proto-bird and dromaeosaur fossils becomes large.

[edit] Intermediate forms need not represent a line of direct descent

This follows from the previous proposition.

We may add that there is nothing in the theory of evolution that tells us that we should know a direct line of descent if we saw one. For example, there are thousands of fossils documenting the reptile to mammal transition, and for that very reason it would be a brave paleontologist who would declare that he knew for certain which was the ancestor of living mammals. In short:

The theory of evolution does not predict that by looking at fossils we should be able to determine whether one was the direct ancestor of the other.

Nor, of course, could any other theory offer us such knowledge: the thing could only be done in the case of a creature like the mythical phoenix, of which it was said that only one could live at a time; in the real world, the similarity of individuals, and of species, would prevent us from claiming that we knew we had a clear line of descent, even in those cases in which such a claim happened to be true.

However, the claim that something is an intermediate form, is, as we have said, purely morphological; it is not necessary to know that there is a direct line of descent in order to know that one form is intermediate between another two.

[edit] "Gaps in the fossil record"

We may note that although the theory of evolution says that we should be able to find intermediate forms if we look, it does not put a timescale on this; it depends partly on luck, partly on the effort put in, and partly on the chances of any given creature being fossilized. Hence:

The theory of evolution does not predict that we will have found a complete set of intermediate forms by the year 2010.

On the contrary, the fact that scientists are turning up more and more intermediate forms (at an increasing rate, since there are now more scientists in more places) suggests that there is plenty more to find. The existence of gaps in our present knowledge of the fossil record in no way invalidates the theory of evolution: the fact that these gaps keep being filled with the requisite forms tends to confirm it. To quote Francis Collins, Director of the Human Genome Project:

"Elephants, turtles, whales, birds often have been cited as species where transitional species have not been identified. This is no longer true. We have gained more in the fossil record in the last ten years than in almost the entire previous history of science".[5]

Meanwhile, here is what a creationist has to say on the same subject:

"The links are missing. Nearly all the fossils are just our present animals, and the links between them are just not there. Few scientists today are still looking for fossil links between the major vertebrate or invertebrate groups. They have given up! The links just do not exist and have never existed." [6]

It is not clear from those two very different statements that the distinguished scientist and the undistinguished creationist are living on the same planet.

The same man also complains loudly, with much underlining and colored ink, that scientists find it hard to find intermediate forms even though they know exactly what they should look like. But this is, of course, no help in finding such fossils. Geologists also know what gold looks like. The trick is knowing where to look for it. There is, of course, a reason why paeleontologists can't just go to the right place to find a desired hypothetical fossil and find one:

The theory of evolution does not predict exactly where to find intermediate fossils.

It is some guide, of course. For example, before any intermediate forms were known for whales, we would on evolutionary grounds have said that since they are ungulates, they evolved after ungulates appear as a group, they must have done so on the continents to which ungulates were confined (so not in Australia, for example) and that this must have happened by some large body of water. This leaves an awful lot of rocks to look at.

A particular evolutionary event happens in a particular place. The evolution of whales from land animals took place in coastal regions of Pakistan and North India, and anyone looking anywhere else would not have seen it. Consider, instead, what people looking elsewhere did see. In other locations in the world, you would see a fossil record empty of whales, and then a fossil record with lots of whales, just as though someone had waved a magic wand and made whales, with no transition visible from anything to anything. To take another example, we know from fossils that the evolutionary events that gave us the third canid radiation (modern wolves, foxes, etc) took place in Europe. Anyone looking at American fossils would see the second wave of canids displaced by the third without seeing any intermediate forms between the two. This point, again, was made by Darwin in the Origin of Species; the quotation is in the appendix to this article.

There is something deeply dishonest about the way in which creationists state their claim. To point to a particular case where we know of no intermediate form, and to describe this ignorance as a "gap in the fossil record" is to speak of what one does not know. There may be no gap at all in the fossil record, merely a gap in our present knowledge of the fossil record; which is hardly the same thing. In general, we may note that a gap in factual knowledge can never condemn a theory; only a discovery which runs counter to that theory can do that. The fact that Galileo didn't know what the far side of the moon looked like could not legitimately be used by the Pope as an objection to his heliocentric theory; and we believe that in those days, the Biblical literalists were smart enough not to argue from ignorance. The theory of evolution might conceivably be overturned by better knowledge of the fossil record; but not by our ignorance of the fossil record.

[edit] Real gaps in the fossil record

There is also a certain ambiguity in the phrase "gap in the fossil record" which creationists love to exploit. It would be quite in order to have a "gap in the fossil record" in the sense of a time and a place from which there are no surviving fossils. In such a case there would be an excellent reason why transitional fossils in particular would not be found from that time and place. Now given that each evolutionary event does happen in some place at some time, there is always a possibility that the fossil evidence for it will be swept away, leaving us only such considerations as morphology, genetics, and biogeography to fall back on.

The theory of evolution does not predict that Nature will have kindly preserved any particular form that scientists might want to study.

In order to demonstrate a gap in the fossil record of any significance, it is necessary for there to be a fossil record. If, for example, we found that the fossil record worldwide had a layer with abundant dinosaur and mammal fossils, and then a layer with abundant mammal fossils, and then a layer where the dinosaurs were represented again, then we should have a serious anomaly: for the fact that the mammals were well preserved would show that a fossil record of terrestrial life was being laid down, and so we would have to say that the gap in the record of dinosaurs represented a gap in the history of dinosaurs; and evolution would be in big trouble.

But if we see dinosaurs, an absence of fossils, and then more dinosaurs, it seems more parsimonious to assume that the absence of dinosaur fossils is a consequence of the general absence of fossils, rather than as a consequence of a temporary shortage of dinosaurs; again, this will be found in the Origin of Species (see appendix).

[edit] "In Their Own Words"

One creationist tactic to confuse this issue was pioneered, so far as we know, by Henry Morris in his pamphlet In Their Own Words. It seems to be based on three observations.

  • There was a time at which scientists knew of no intermediate forms at all; so for any particular intermediate form, there will be a period of time during which scientists were ignorant of it.
  • Scientists are candid and open about the things they don't know, so if you look at statements made before the discovery of any particular intermediate form, you'll find reputable scientists, rather than creationist kooks, saying that they can't find such-and-such an intermediate form.
  • If you presented such a list to someone who was entirely ignorant of the discoveries made in the last century and a half, you might convince him that these intermediate forms are still missing.

Such lists usually use the latest quotation possible. So, for example, to get a quotation saying that there are no intermediate forms in the fossil record, it is necessary to go back to the early editions of the Origin of Species; and only the early editions will do. But for quotations saying no intermediate land animal-whale forms have been found, it is only necessary to go back ten years or so. This feature of these lists of quotations suggests a degree of dishonesty in their compilers: for it is hard to see how one identifies the latest possible quotation saying that some intermediate form is missing without also finding out when that form was in fact discovered.

[edit] Stephen Jay Gould and transitional fossils

The creationist spiel is well represented by this sample from CreationWiki:

"Stephen Jay Gould in an often quoted statement calls the lack of transitional forms the "trade secret" in paleontology." [7]

We shall quote a little Stephen Jay Gould ourselves, and give a reference so that the quotation can be seen in its full context:

"[T]ransitions are often found in the fossil record ... Faced with these facts of evolution and the philosophical bankruptcy of their own position, creationists rely upon distortion and innuendo to buttress their rhetorical claim. If I sound sharp or bitter, indeed I am —- for I have become a major target of these practices ... it is infuriating to be quoted again and again by creationists -- whether through design or stupidity, I do not know -- as admitting that the fossil record includes no transitional forms. Transitional forms are generally lacking at the species level, but they are abundant between larger groups." (Stephen Jay Gould, Evolution Is A Fact And A Theory [8])

He wrote this in 1981, and 25 years later "by design or stupidity" the lie continues to be spread.

[edit] "Mosaics"

Another creationist blunder concerns what they like to call "mosaics". Here's a sample of the genre:

Of course, evolutionists have long cited Archaeopteryx as a transitional form between dinosaurian/reptilian ancestors and birds, citing its mix of avian and "reptilian" (non-avian) characteristics. Creationists have rightly responded by pointing out that Archaeopteryx is a mosaic of fully-formed reptilian features and fully-formed avian features, not a half- reptile/half-bird. Whether such odd mosaics are genuine transitional forms is doubtful.[9]

This seems to be based on misreading a single passage from Steven Jay Gould and Niles Eldredge, which reads as follows:

Smooth intermediates between Bauplane are almost impossible to construct, even in thought experiments: there is certainly no evidence for them in the fossil record (curious mosaics like Archaeopteryx do not count).

Obviously Gould is not saying that Archaeopteryx is not an intermediate form, nor that mosaics are not intermediate forms, but that they are not smooth intermediate forms. This is exactly what we would expect: as he points out, it is barely possible to imagine an evolutionary transition which would involve every anatomical feature at exactly the same rate in perfect synchrony. Certainly there is nothing whatsoever in the theory of evolution which predicts that this is how transitions take place as a general rule.

We repeat Gould's plea for a little honesty among creationists:

"[T]ransitions are often found in the fossil record ... If I sound sharp or bitter, indeed I am —- for I have become a major target of these practices ... it is infuriating to be quoted again and again by creationists -- whether through design or stupidity, I do not know -- as admitting that the fossil record includes no transitional forms. [10]

We fear that it will fall on deaf ears.

[edit] Intermediate forms are not the only evidence for evolution

The theory of evolution was, as we have pointed out, discovered by Darwin before a single intermediate form had been found, and he felt confident enough in it to lay it before the scientific world on the basis of biogeography, morphology, and the sheer logic of natural selection. To this we have added modern sciences such as behavioral ecology and genetics. The fossil record alone, we suppose, would be proof enough of evolution; but so would morphology and biogeography.

In particular, we have observed creationists producing a quotation (usually out of date) from some scientist bemoaning the lack of a certain intermediate form, and then attempting to paraphrase this by saying "So in other words [a favorite creationist phrase] he admits that there is no evidence that such-and-such an animal evolved." This is simply not the same thing in other words: the same scientist would be able to give abundant morphological and genetic evidence that the creature in question was the product of evolution.

Moreover, there can be few species for which we know of no evolutionary history in the fossil record: for example, if a creature is a mammal then we can at least illustrate the history of how its ancestors evolved from reptiles to mammals with abundant fossils, even if subsequent details are, for now, obscure.

[edit] Creationists in retreat?

Some creationists have firmly attached themselves to the doctrine of "no intermediate forms", Duane Gish for example:

"If creation is true, we'd expect each one of the created kinds ... to appear abruptly and fully formed, with no indication that they had evolved from a common ancestor" (Duane Gish; Saladin - Gish debate, 1988)

However, more sensible creationists realize that this proposition, taken in conjuction with the plethora of intermediate forms, means that creation isn't true. It is evidently time for a bit of backing and filling. The well-known creationist ministry Answers In Genesis have added it to their ever-popular list of "arguments we think Creationists should NOT use"[11] although the author goes on to say:

"While Darwin predicted that the fossil record would show numerous transitional fossils, even 140 years later, all we have are a handful of disputable examples."

While we would concede that anything is "disputable", given an opinionated crank and a soapbox, the word "handful" is mere fantasy.

Kurt Wise, on the other hand, is a creationist who believes that "creation theory" can be modified to allow the existence of intermediate forms without exciting the wrath of God. As he believes he can get round the existence of intermediate forms, he does not have the usual creationist obligation to deny the obvious. The following is an excerpt from a paper written for a creationist journal:

"Darwin's second expectation -- of stratomorphic intermediate species -- has been confirmed by such species as Baragwanathia (between rhyniophytes and lycopods),Pikaia (between echinoderms and chordates), Purgatorius (between the tree shrews and the primates), and Proconsul (between the non-hominoid primates and the hominoids). Darwin's third expectation -- of higher taxon stratomorphic intermediates -- has been nicely confirmed by the mammal-like reptile groups between the reptiles and the mammals and the phenacodontids between the horses and their presumed ancestors. Darwin's fourth expectation -- of stratomorphic series --- has been beautifully confirmed by such examples as the early bird series, the tetrapod series, the whale series, the various mammal series of the Cenozoic (e.g. the horse series, the camel series, the elephant series, the pig series, the titanothere series, etc.), the Cantius and Plesiadapus primate series, and the hominid series. The existence of stratomorphic intermediates of the general type expected a priori by macroevolutionary theory (above the level of species) should be acknowledged by creationists for what it is: very good evidence for macroevolutionary theory. It certainly CANNOT be said that the traditional creation theory expected (predicted) any of these fossil finds." (Kurt Wise, Towards a Creationist Understanding of 'Transitional Forms CEN Technical Journal 9 (1995) p. 218-219)

[edit] Links

[edit] Appendix: Darwin on intermediate forms

The following quotations are taken from the sixth edition of Darwin's Origin of Species. [12]

Darwin makes it clear that a common ancestor is not necessarily an intermediate form:

"In the first place, it should always be borne in mind what sort of intermediate forms must, on the theory, have formerly existed. I have found it difficult, when looking at any two species, to avoid picturing to myself forms DIRECTLY intermediate between them. But this is a wholly false view; we should always look for forms intermediate between each species and a common but unknown progenitor; and the progenitor will generally have differed in some respects from all its modified descendants. To give a simple illustration: the fantail and pouter pigeons are both descended from the rock-pigeon; if we possessed all the intermediate varieties which have ever existed, we should have an extremely close series between both and the rock-pigeon; but we should have no varieties directly intermediate between the fantail and pouter; none, for instance, combining a tail somewhat expanded with a crop somewhat enlarged, the characteristic features of these two breeds. These two breeds, moreover, have become so much modified, that, if we had no historical or indirect evidence regarding their origin, it would not have been possible to have determined from a mere comparison of their structure with that of the rock-pigeon, C. livia, whether they had descended from this species or from some other allied species, such as C. oenas.
So with natural species, if we look to forms very distinct, for instance to the horse and tapir, we have no reason to suppose that links directly intermediate between them ever existed, but between each and an unknown common parent. The common parent will have had in its whole organisation much general resemblance to the tapir and to the horse; but in some points of structure may have differed considerably from both, even perhaps more than they differ from each other. Hence, in all such cases, we should be unable to recognise the parent-form of any two or more species, even if we closely compared the structure of the parent with that of its modified descendants, unless at the same time we had a nearly perfect chain of the intermediate links."

Darwin points out that the origin of a new type does not necessarily mean the disappearance of the old:

"We have no reason to believe that forms successively produced necessarily endure for corresponding lengths of time. A very ancient form may occasionally have lasted much longer than a form elsewhere subsequently produced, especially in the case of terrestrial productions inhabiting separated districts. To compare small things with great; if the principal living and extinct races of the domestic pigeon were arranged in serial affinity, this arrangement would not closely accord with the order in time of their production, and even less with the order of their disappearance; for the parent rock-pigeon still lives; and many varieties between the rock-pigeon and the carrier have become extinct; and carriers which are extreme in the important character of length of beak originated earlier than short-beaked tumblers, which are at the opposite end of the series in this respect."

Darwin makes it clear that we have no "right to expect" that all intermediate varieties will be preserved:

"Closely connected with the statement, that the organic remains from an intermediate formation are in some degree intermediate in character, is the fact, insisted on by all palaeontologists, that fossils from two consecutive formations are far more closely related to each other, than are the fossils from two remote formations. Pictet gives as a well-known instance, the general resemblance of the organic remains from the several stages of the Chalk formation, though the species are distinct in each stage. This fact alone, from its generality, seems to have shaken Professor Pictet in his belief in the immutability of species...
On the theory of descent, the full meaning of the fossil remains from closely consecutive formations, being closely related, though ranked as distinct species, is obvious. As the accumulation of each formation has often been interrupted, and as long blank intervals have intervened between successive formations, we ought not to expect to find, as I attempted to show in the last chapter, in any one or in any two formations, all the intermediate varieties between the species which appeared at the commencement and close of these periods: but we ought to find after intervals, very long as measured by years, but only moderately long as measured geologically, closely allied forms, or, as they have been called by some authors, representative species; and these assuredly we do find. We find, in short, such evidence of the slow and scarcely sensible mutations of specific forms, as we have the right to expect."

Darwin explains that transitions will be seen only at the locus of evolution:

"Local varieties will not spread into other and distant regions until they are considerably modified and improved; and when they have spread, and are discovered in a geological formation, they appear as if suddenly created there, and will be simply classed as new species."

Darwin on the argument from ignorance:

"I have felt these difficulties far too heavily during many years to doubt their weight. But it deserves especial notice that the more important objections relate to questions on which we are confessedly ignorant; nor do we know how ignorant we are. We do not know all the possible transitional gradations between the simplest and the most perfect organs; it cannot be pretended that we know all the varied means of Distribution during the long lapse of years, or that we know how imperfect is the Geological Record. Serious as these several objections are, in my judgment they are by no means sufficient to overthrow the theory of descent with subsequent modification."

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