
Synopsis
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Of course, this one piece of evidence does not �prove� something as complex and far ranging as the evolution of life on Earth.
Behe is wrong because there is no such thing as �devolution.� Evolution is simply heritable change, any change, and that change can create more complexity or more simplicity. Further, altering a protein does not �degrade� it � that notion is based on the false premise that there is a �correct� sequence of amino acids in any particular protein. Evolution just makes proteins different. Proteins perform �better� or �worse� only in so much that they contribute to the survival and reproduction of the individual. If it is better for the survival of the organism for an enzyme to be slower, then the slower enzyme is better for that organism.
The first is basically the lottery fallacy � considering the odds of John Smith winning the lottery by chance alone and concluding it could not have happened by chance. Rather, you should consider the odds that anyone would win the lottery. This is actually pretty good. Behe looks at life on Earth and asks � what are the odds that this specific pathway or protein or whatever evolved by chance alone. He is failing to consider that there may have been billions of possible solutions or pathways down which that creature�s ancestors could have evolved. Species that failed to adapt either migrated to an environment in which they could survive, or they went extinct. In other words, Behe should not be asking what the odds are that this bit of complexity evolved, but rather what are the odds that any complexity evolved. It is difficult to know the number of potential complexities that never evolved � that number may dwarf the odds of any one bit evolving. Right there Behe�s entire premise is demolished �
Biologically and chemically, there is no reason why this particular genetic code, rather than any of millions or billions of others, should exist, scientists assert. Yet every species on Earth carries a genetic code that is, for all intents and purposes, identical and universal. The only scientific explanation for this situation is that the genetic code was the result of a single historic accident. That is, this code was the one carried by the single ancestor of life and all of its descendants, including us.
Much as Lamarck suggested, changes in the environment literally alter our biology. And even in the absence of continued exposure, the altered biology, expressed as traits or in the form of disease, is transmitted from one generation to the next.
the rate of random DNA sequence mutation turns out to be too slow to explain many of the changes observed. Scientists, well-aware of the issue, have proposed a variety of genetic mechanisms to compensate: genetic drift, in which small groups of individuals undergo dramatic genetic change; or epistasis, in which one set of genes suppress another, to name just two. Yet even with such mechanisms in play, genetic mutation rates for complex organisms such as humans are dramatically lower than the frequency of change for a host of traits, from adjustments in metabolism to resistance to disease.
The unifying theme for much of modern biology is based on Charles Darwin�s theory of evolution, the process of natural selection by which nature selects the fittest, best-adapted organisms to reproduce, multiply and survive.
We suggest that read-through is due to PTC recognition by a near-cognate tRNA that allows insertion of an amino acid instead of translation termination.
Pseudogenes are generally considered to be non-functional DNA sequences that arise through nonsense or frame-shift mutations of protein-coding genes. � We identify functional PTC-containing loci within different olfactory receptor repertoires and species, suggesting that such �pseudo-pseudogenes� could represent a widespread phenomenon.
By comparing how many genes organisms share, we can figure out how they are related. For instance, humans share more genes with apes like chimps and gorillas than other animals, as much as 96%. That suggests they are our closest relatives.
"Try to explain that in any other way than the fact that those relationships are based on a sequence of changes through time," says Chris Stringer of the Natural History Museum in London. "We have a common ancestor with chimpanzees, and we and they have diverged since then from that common ancestor."
Over the last century scientists have catalogued the genes from different species. It turns out that all living things store information in their DNA in the same way: they all use the same "genetic code".
What's more, organisms also share many genes. Thousands of genes found in human DNA may also be found in the DNA of other creatures, including plants and even bacteria.
These two facts imply that all modern life has descended from a single common ancestor, the "last universal ancestor", which lived billions of years ago.
P1: All living things store information in their DNA in the same way.
P2: Organisms also share many genes.
C1: All modern life has descended from a single common ancestor.
For scientists, evolution is a fact. We know that life evolved with the same certainty that we know the Earth is roughly spherical, that gravity keeps us on it, and that wasps at a picnic are annoying.
Descent with modification, which is caused by random mutations in genes, ultimately leads to gradual changes and the formation of new species � much of it driven by natural selection, which weeds out those organisms that are less suited to their environments.
Given enough time, these changes mount up and lead to the appearance of new species and new types of organism, one small change at a time. Step by step, worms became fish, fish came onto land and developed four legs, those four-legged animals grew hair and � eventually � some of them started walking around on two legs, called themselves "humans" and discovered evolution.
But then with me the horrid doubt always arises whether the convictions of man's mind, which has been developed from the mind of the lower animals, are of any value or at all trustworthy. Would any one trust in the convictions of a monkey's mind, if there are any convictions in such a mind?
The fossil record is only so much help here, because it is incomplete. "If you look at most fossil records, what you actually see is one form that lasts quite a long time and then the next bunch of fossils that you've got is quite different from what you had before," says Jones.
While that�s a lot faster than 15 years, it�s still much longer than typical �direct selections� used by microbiologists where a readily accessible mutation might confer, for example, resistance to an antibiotic after a day or two.
"It really shows the process of evolution," says Moran. "It's not all just adaptation and things getting better, there's also this big potential for things to get worse."
"That's what evolution is," says Steve Jones of University College London in the UK. "It's a series of mistakes that build up."
As you explain in your textbook, describing the pathways to modern species contributes to the FACT of evolution and the FACT of descent with modification but how those genetic changes actually occur and become fixed is part of evolutionary theory. Do you distinguish between evolutionary theory and the actual history of life?
I would say that it needs replacing. Yes. � The reasons I think we�re talking about replacement rather than extension are several. The first is that the exclusion of any form of acquired characteristics being inherited was a central feature of the modern synthesis. In other words, to exclude any form of inheritance that was non-Mendelian, that was Lamarckian-like, was an essential part of the modern synthesis. What we are now discovering is that there are mechanisms by which some acquired characteristics can be inherited, and inherited robustly. So it�s a bit odd to describe adding something like that to the synthesis ( i.e., extending the synthesis). A more honest statement is that the synthesis needs to be replaced. � By �replacement� I don�t mean to say that the mechanism of random change followed by selection does not exist as a possible mechanism. But it becomes one mechanism amongst many others, and those mechanisms must interact. So my argument for saying this is a matter of replacement rather than extension is simply that it was a direct intention of those who formulated the modern synthesis to exclude the inheritance of acquired characteristics. That would be my first and perhaps the main reason for saying we�re talking about replacement rather than extension.