Saltation
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[edit] Introduction
A saltation, if it ever happened, would be the sudden production of one species from another: for example, a sheep giving birth to a lion. This never happens.
Saltationism is the obsolete hypothesis that evolutionary changes happen by saltation. No biologist today believes that this is possible. It is nonetheless interesting to look back at saltationism: no-one really understands the theory of evolution unless they understand why saltationism is wrong.
[edit] Why is saltationism wrong?
As with other failed hypotheses about the mechanism of evolution, such as Lamarckism or Front-Loaded Evolution, the notion of saltation is not intrinsically silly. We can imagine a world in which evolution did work like that. As with the other failed hypotheses, saltationism can be seen to be wrong only in the context of our modern knowledge of genetics.
Consider what it would take in genetic terms to produce (for example) a well-adapted carnivore in one evolutionary leap from a well-adapted vegetarian. We could not, of course, deny that a set of mutations could achieve this, for it is plain that they could. The right combination of mutations could, in principle, change the genome of an sheep into the genome of a lion.
But there is a "but". In the first place, this would take millions upon millions of mutations happening all at once, rather than the hundred or so that typically occur between two generations of mammals. We must admit that this could happen, since the probability of any particular mutation occurring is independent of the probability of any other mutation happening.
So let's concede that at very long odds, this could happen. We would also require that of all the millions of mutations that happened, not one single one of them would be lethal. Again, we must concede that this could happen, but what are the odds?
However, let's admit that, at extraordinarily long odds, this could happen. But for this to be the genesis of a new species, we would need the new animal produced by saltation not just to be capable of mere life, but of pursuing its lifestyle successfully. We should need, all at once, this "hopeful monster" to be all at once endowed with carnivorous teeth, a gut suited for eating meat, instincts for chasing after prey animals rather than eating grass, and so forth: we would require that all these millions of mutations should turn out just right.
And even if all this happened, we may note that a lion cannot breed with a sheep: out new creature would certainly be reproductively isolated from its parent species. So in order for this saltation to be the genesis of a new species, it would have to happen twice, at about the same time, in about the same place. What are the odds?
Now, we may concede that all this is possible. The laws of probability tell us that a zillion-to-one chance will happen one time in a zillion. But the chances against this happening are so astronomically large that in practice we may disgregard it. In the same way, it is possible in principle for a man to roll a million dice, and for every single one of them to come up six. There is no actual law of nature that says that this can't happen. But the smart money is against it.
To summarize: a successful saltation is possible in principle, just like it is possible for a man to roll a million dice and for them all to come up six. But this will not actually happen.
[edit] Genetics and saltation
Consider the following fact: two people, both over six feet tall, can have sex and produce a child who is an achondroplasic dwarf. Is this not saltation?
It is and it isn't. Morphologically, it is a great big leap. But in genetic terms, we should say that it is the smallest change possible: it is a single nucleotide substitution.
So when we say that saltations don't happen, what we mean is not that a sudden morphological change can't happen; what we mean is that a whole lot of coordinated mutations won't all happen together.
We also know of mechanisms such as polyploid mutation and lateral gene transfer which can suddenly produce new genomes and new species from old. But both these mechanisms involve the production of new genomes by shuffling together pre-existing genes. These mechanisms do not involve the sudden coordinated simultaneous production of a whole lot of brand-new genes.
[edit] Saltation and punctuated equilibrium
Saltation should not be confused with the idea of punctuated equilibrium. Punctuated equilibrium is simply the proposition that the time in which a lineage undergoes evolutionary change is relatively short in comparison to the length of time that it spends in evolutionary stasis.
Now of course the proposition that the time spent evolving is short relative to the time spent not evolving is not the same as saying that all the evolution is done in a single jump --- a saltation. Yet there is a tendency amongst the biologically illiterate to confuse the two notions. This confusion, like every other misconception about evolution, has been actively promoted by creationists.
For more information on this topic, the reader may like to consult our main article on Punctuated Equilibrium.
[edit] Saltation and creationism
As we have remarked above, creationists like to muddle up saltation and punctuated equilibrium, as part of their perpetual campaign to confuse the public about evolution.
They also like to confuse saltation and the theory of evolution generally, by asserting or implying that the theory of evolution depends on saltation, or, as they sometimes call it, "macromutation". For example, they will sometimes demand "evidence for evolution" in the form of "a cat giving birth to a dog", or similar biological impossibilities.
As we have shown above, the actual theory of evoution says that such an event cannot happen. If such a thing happened, it would doubtless be an instance of evolution, but it would destroy the theory of evolution. By analogy, it would be an example of gravity if the Moon fell out of the sky, but it would flatly contradict the theory of gravity, which says that such an event cannot take place.
