Jeff's Lunchbreak

This entry is part of a series. For a bit of an introduction and an index of all entries in the series, go here.

This installment covers Chapter 20, An Osborn Letter.

Perhaps this has something to do with McCann's seeming personal vendetta against Osborn.

Professor Osborn himself, in a letter to the editor of the New York Globe, June 1, 1921, gave a demonstration of his method of creating impressions at the expense of truth. He said: "The American Museum of Natural History and the Hall of the Age of Man, to which Alfred W. McCann refers, scrupulously avoid presenting theories and rest on the solid ground of well ascertained facts. This is why this Hall is sought not only by scientists from all parts of the world and by the rising generation of scientific men and women, but also by religious teachers who come here to see what Nature has thus far revealed concerning man's past history." (McCann 248-249)

Here McCann's still quoting Osborn's letter. The modern Clergy Letter Project (and its associated Evolution Weekend is definitely in this spirit.

"From time to time I see parties of clergymen of different denominations studying what this Hall exhibits of our past life. The spiritual value of the emergence of the Cro-Magnon race, many thousands of years ago, with its deep religious sentiments, is one of the greatest discoveries of modern times relating to the spiritual development of man. It is so regarded by all teachers and writers who are keeping up to date in the progress of discovery and human thought." (McCann 249 - quoting Osborn)

McCann made several mistakes here when discussing convergence.

Osborn's own evidence of convergence explains the "resemblance" of whales to fish, although whales are not fish at all, but true mammals. Changing their fore-limbs (arms) into fins (paddles) and their hind-limbs into nothingness the whales have converged ever more and more in external features toward true fishes with whom they are not at all related while they themselves have remained true mammals. Why does Professor Osborn withhold the suggestion that apes, despite their superficial convergence in externals toward a fantastic resemblance to man, remain nevertheless true apes? The writer frankly admits that convergence explains nothing, adds nothing and takes nothing away when any theory of evolution based on natural selection is under discussion. Why has the giraffe, for instance, not converged toward the elephant? If natural selection explains the long neck of the giraffe for high browsing purposes why would an extension of its nose, like the extension of the nose of the elephant, not have been better? Why has no other hoofed quadruped acquired a long neck and a lofty stature besides the giraffe? Why has the camel not acquired a proboscis like the elephant? Why is the elephant alone the beneficiary of a proboscis? Why has the elephant no neck at all? If natural selection is a freakish, whimsical, capricious handmaiden of evolution it ceases to be natural selection and becomes merely bizarrish selection. (McCann 253-254)

First of all, whales are only superficially similar to fish. A look at their anatomy, from mammary glands to lungs, shows them to be quite clearly mammals. Apes and humans, on the other hand, are not merely superficially similar. The similarities go right down to the bone. We can catch many of the same diseases that other types of mammals don't. Even Linnaeus, who was a creationist himself, classified humans as apes when he came up with his system.

McCann once again made the mistake of assuming teleology in evolution. There are no goals. A long neck may work for giraffes, but it doesn't mean that other animals will attempt to copy that strategy, or that evolution will strive towards long necks. The 'strategies' come about by chance, and are honed through natural selection.

There are many strategies that evolution can take, and some are 'easier' than others. For example, simply growing longer or shorter limbs is an easy adaptation. It only takes a few mutations. So, you'll see many animals with elongated necks, from giraffes, to llamas, to geese, to the now extinct baluchitherium. A prehensile nose is not a simple adapation. It's a fairly complex limb that takes many, many mutations to develop. So, you'd expect it to be a lot less common than long necks. And even though elephants may have the most developed prehensile nose, they aren't the only animals with one. Tapirs have a short prehensile nose, and there's evidence that some extinct animals also had one.

Organisms are also constrained by the laws of physics. The reason why cetaceans, fish, and ichtyosaurs look superficially similar, is because that's the shape it takes to be hydrodynamic. Physics explains why flying animals tend to have high aspect ratio wings. It's just what works.

Here, McCann discusses variation.

The vagueness and confusion provoked by the giraffe is set forth by Sir Charles Lyell, who so greatly influenced Darwin. He says ("Antiquity of Man," 1863, pp. 410-411): "Lamarck when speculating on the origin of the long neck of the giraffe imagined that quadruped to have stretched himself up in order to reach the boughs of lofty trees until by continued efforts and longing to reach higher he obtained an elongated neck. Darwin and Wallace simply supposed that, in a season of scarcity, a longer-necked variety survived the others and transmitted its peculiarity to its successors. Every naturalist admits that there is a general tendency in animals and plants to vary; but it is usually taken for granted that there are certain limits beyond which each species cannot pass under any circumstances or in any number of generations. (Here you have a law which is not bizarrish.) Darwin and Wallace say that the oppositive hypothesis, which assumes that every species is capable of varying indefinitely from its original type, is not a whit more arbitrary. We have no right, they say, to assume, should we find that a variable species can no longer be made to vary in a certain direction, that it has reached the utmost limits to which it might, if more time were allowed, be made to diverge from the parent type."

Perhaps in another million of years the giraffe will have twice as much neck as he now has and the elephant less neck than none at all, and a proboscis tremendously extended. Perhaps! (McCann 254-255)

Darwin and Wallace had it right. Why should it be 'taken for granted that there are certain limits beyond which each species cannot pass under any circumstances or in any number of generations'? Especially now that we understand genetics, we know there are no stop signs in our chromosomes. McCann's idea reeks of Platonic idealism.

McCann continued to harp on marsupials, which he discussed in the previous chapter.

Why, let us repeat, through these millions of years, have they remained marsupials, although Australia has presented opportunities for the most diverse modes of existence? Why, if not because the marsupials present a real type which varies in form but is not abandoned? There is an overwhelming body of proof that certain basal forms are firmly retained and that the whole theory of evolution from, a common ancestor must be completely abandoned. Certainly the marsupials have had time and opportunity for the full development of their maximum evolutional capacity. Why, then, through all these millions of years, have the limits to such evolutional capacity been so sharply defined? (McCann 256)

Once again, he thinks in teleological terms, or in the Ladder of Progress. There is no goal for evolution. There is no reason why marsupials should be expected to evolve into placental mammals.

The earliest mammals laid eggs, which isn't surprising, considering that it's the primitive form of reproduction for all tetrapods. Some mammals, the monotremes, still lay eggs. At some point, obviously, mammals began giving birth to live young. This also isn't a big deal, considering how many other animals also practice vivipary. It probably started simply by allowing the eggs to develop inside the mother without laying them. Now, the exact relationship between marsupials and placental mammals is a bit murky, but there are two probable scenarios. Either placental mammals evolved from marsupials, or they both evolved independently from that lineage of mammals where the mothers retained their eggs.

Recall from an earlier discussion in this series, where I said that some evolutionary strategies are more difficult to evolve than others. Simply retaining eggs to develop inside a mother is fairly simple, so it's seen in multiple lineages. A placenta, on the other hand, is not so easy to develop. For us mammals, in fact, it looks we owe the placenta to a viral infection. Endogenous retroviruses are those viruses that have managed to get their DNA incorporated into the genome of a population (by infecting germ cells). Many of the genes used that help protect a fetus from the mother's immune system are from endogenous retroviruses. Considering the circumstances involved, you would expect that this is a pretty rare way for animals to acquire genes, so it's not surprising that marsupials haven't independently evolved a placenta.

But just because marsupials haven't evolved a placenta, it doesn't mean that they've remained 'primitive'. In the hundred million years or so since our lineages have diverged, marsupials have gone on evolving, as well. Just look at the diversity of life forms in Australia. And, as should be expected, they've evolved some of their own unique characteristics that are absent from us placental mammals (for example, us humans haven't evolved the ability to glide like sugar gliders). Every animal can only build on the innovations that arose in its ancestors, not innovations that arose in its cousins. There is no single most evolved animal.

Proceed to Chapters 21 & 22