Posted on 01/20/2003 7:01:47 AM PST by forsnax5
That enduring metaphor for the randomness of evolution, a blind watchmaker that works to no pattern or design, is being challenged by two European chemists. They say that the watchmaker may have been blind, but was guided and constrained by the changing chemistry of the environment, with many inevitable results.
The metaphor of the blind watchmaker has been famously championed by Richard Dawkins of the University of Oxford. But Robert Williams, also at Oxford, and Joäo José R. Fraústo da Silva of the Technical University of Lisbon in Portugal say that evolution is not strictly random. They claim Earth's chemistry has forced life to evolve along a predictable progression from single-celled organisms to plants and animals.
Williams and da Silva take as their starting point the earliest life forms that consisted of a single compartment, or vesicle, enclosing the cytoplasm that produced polymers such as RNA, DNA and proteins. That cytoplasm was partly dominated by the reducing chemistry of the primitive oceans and atmosphere from which it formed, and has changed little since, says Williams.
As these primitive cells, or prokaryotes, extracted hydrogen from water they released oxygen, making the environment more oxidising. Ammonia became nitrogen gas, metals were released from their sulphides, and non-metal sulphides became sulphates.
These changes forced the prokaryotes to adapt to use the oxidised elements, and they evolved to harness energy by fixing nitrogen, using oxygen, and developing photosynthesis. But these oxidising elements could also damage the reducing chemistry in the cytoplasm.
For protection, there was just one option: isolate the elements within internal compartments, says Williams. And that gave rise to eukaryotes - single-celled organisms with a nucleus and other organelles.
Harold Morowitz, an expert on the thermodynamics of living systems at George Mason University in Fairfax, Virginia, says these ideas are very exciting. "It's part of a quiet paradigm revolution going on in biology, in which the radical randomness of Darwinism is being replaced by a much more scientific law-regulated emergence of life."
According to Williams and da Silva, eukaryotes also had to evolve a way to communicate between their various organelles. The surrounding raw materials dictated how this could be done. Calcium ions would have routinely leaked into cells, precipitating DNA by binding to it. So cells responded by pumping the ions out again.
Eukaryotes evolved to use this calcium flow to send messages across internal and external membranes. Similarly, sodium ions formerly expelled as poisonous became the basis of communication in nerve cells.
Life continued to react to Earth's oxidised environment. Hydrogen peroxide gave rise to lignin - an oxygen-rich polymer that is the chief constituent of wood. And eukaryotes used copper oxidised from copper sulphides to cross-link proteins such as collagen and chitin, which help hold nerve and muscle cells in place. Such evolution of materials suitable for multicellular structures paved the way for plants and animals.
Not everyone is convinced. Evolutionary biologist David Deamer of the University of California, Santa Cruz, says the claim that evolution followed an inevitable progression should be qualified: "The inevitability depends on the origin of life and oxygenic photosynthesis."
He agrees that life arose in vesicles, but says that oxidative chemistry cannot explain everything from prokaryotes to humans.
Williams admits their theory has limitations. For instance, he agrees that Dawkins's argument is correct in that chance events drive the development of species. But he does not believe random events drive evolution overall. "Whatever life throws away will become the thing that forces the next step in its development."
However, David Krakauer, an evolutionary theorist at the Santa Fe Institute in New Mexico, says Williams and da Silva have simply listed the chemical processes that coincided with each evolutionary transition, which does not prove that the chemistry caused the transitions. But Williams says that the environmental changes had to come first, because they occur faster than changes in biological systems.
It doesn't happen often, but sometimes a newbie will show up in one of these threads, pop his big killer question, and then -- when the question is almost immediately answered -- the newbie just vanishes, never to be heard from again. I don't know if they suffer a crisis of faith, or a revulsion that there really are satanic eee-vooo-luuu-shunists on the website, or what.
When it happens to me, there are too many people making jokes about it, so I just have to join in. Like the time when I spent days saying that Uranus was the 8th planet ...
There is a science called population genetics, and it has mathematical formulae for how quickly favorable genetic changes can spread throughout a population of sexually reproducing creatures. From these formulae, Nilsson and Pelger concluded that the 1829 steps could happen in about 350,000 generations.
In real life, an eye could evolve a little more quickly than that, or more slowly. It would depend on how much the specific creatures were being pressured to change, and on whether vision was relevant to their lifestyle.
If one year equals one generation, then a fairly good eye could evolve in maybe a third of a million years. It is thought that animal life has been on earth for at least 600 million years. That is certainly enough time for eyes to have evolved many times over.
In fact, taxonomists say that eyes have evolved at least 40 different times, and and possibly as many as 65 times. There are 9 different optical principles that have been used in the design of eyes and all 9 are represented more than once in the animal kingdom. Why so many? Well, because there was time.
This is for all those creos who claim there is not enough time for evolution to have occurred.
I still say Romania would be utterly landlocked if the Black Sea did not exist.
Well, 6000 years really isn't a lot of time.
Not everyone is convinced.
That says it all.
If I could just point out one tiny, itsy bitsy problem here: the geologic evidence does not document a reducing atmosphere in the primitive earth - there is plenty of oxygen as evidenced by the presence of ferric iron in the rocks from these time periods.
These guys are apparently making the same erroneous assumptions Stanley Miller did in 1953. The presence of oxygen in any significant quantities is anathema to these reactions.
Indeed it does! Thank you for looking it over and for your post!
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