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Scientific American assesses naturalistic explanations for the origin of life

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From Scientific American. (H/T Letitia via Mary)

Excerpt:

As recently as the middle of the 20th century, many scientists thought that the first organisms were made of self-replicating proteins. After Francis Crick and James Watson showed that DNA is the basis for genetic transmission in the 1950s, many researchers began to favor nucleic acids over proteins as the ur-molecules. But there was a major hitch in this scenario. DNA can make neither proteins nor copies of itself without the help of catalytic proteins called enzymes. This fact turned the origin of life into a classic chicken-or-egg puzzle: Which came first, proteins or DNA?

RNA, DNA’s helpmate, remains the most popular answer to this conundrum, just as it was when I wrote “In the Beginning…” Certain forms of RNA can act as their own enzymes, snipping themselves in two and splicing themselves back together again. If RNA could act as an enzyme, then it might be able to replicate itself without help from proteins. RNA could serve as gene and catalyst, egg and chicken.

But the “RNA-world” hypothesis remains problematic. RNA and its components are difficult to synthesize under the best of circumstances, in a laboratory, let alone under plausible prebiotic conditions. Once RNA is synthesized, it can make new copies of itself only with a great deal of chemical coaxing from the scientist. Overbye notes that “even if RNA did appear naturally, the odds that it would happen in the right sequence to drive Darwinian evolution seem small.”

The RNA world is so dissatisfying that some frustrated scientists are resorting to much more far out—literally—speculation. The most startling revelation in Overbye’s article is that scientists have resuscitated a proposal once floated by Crick. Dissatisfied with conventional theories of life’s beginning, Crick conjectured that aliens came to Earth in a spaceship and planted the seeds of life here billions of years ago. This notion is called directed panspermia. In less dramatic versions of panspermia, microbes arrived on our planet via asteroids, comets or meteorites, or drifted down like confetti.

John Horgan is not a Christian, nor even a theist. This is the state of the art if you are a naturalist.

Basically, you have at most a couple hundred million years from the time the Earth cools to the appearance of first life. You are unlikely to get one measly protein without an intelligence arranging the amino acids. This is assuming we spot you a favorable environment for creating amino acids without intervention. And then there would still be the problem of sequencing the proteins.

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News

Doug Axe explains the chances of getting a functional protein by chance

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I’ve talked about Doug Axe before when I described how to calculate the odds of getting functional proteins by chance.

Let’s calculate the odds of building a protein composed of a functional chain of 100 amino acids, by chance. (Think of a meaningful English sentence built with 100 scrabble letters, held together with glue)

Sub-problems:

  • BONDING: You need 99 peptide bonds between the 100 amino acids. The odds of getting a peptide bond is 50%. The probability of building a chain of one hundred amino acids in which all linkages involve peptide bonds is roughly (1/2)^99 or 1 chance in 10^30.
  • CHIRALITY: You need 100 left-handed amino acids. The odds of getting a left-handed amino acid is 50%. The probability of attaining at random only L–amino acids in a hypothetical peptide chain one hundred amino acids long is (1/2)^100 or again roughly 1 chance in 10^30.
  • SEQUENCE: You need to choose the correct amino acid for each of the 100 links. The odds of getting the right one are 1 in 20. Even if you allow for some variation, the odds of getting a functional sequence is (1/20)^100 or 1 in 10^65.

The final probability of getting a functional protein composed of 100 amino acids is 1 in 10^125. Even if you fill the universe with pre-biotic soup, and react amino acids at Planck time (very fast!) for 14 billion years, you are probably not going to get even 1 such protein. And you need at least 100 of them for minimal life functions, plus DNA and RNA.

Research performed by Doug Axe at Cambridge University, and published in the peer-reviewed Journal of Molecular Biology, has shown that the number of functional amino acid sequences is tiny:

Doug Axe’s research likewise studies genes that it turns out show great evidence of design. Axe studied the sensitivities of protein function to mutations. In these “mutational sensitivity” tests, Dr. Axe mutated certain amino acids in various proteins, or studied the differences between similar proteins, to see how mutations or changes affected their ability to function properly. He found that protein function was highly sensitive to mutation, and that proteins are not very tolerant to changes in their amino acid sequences. In other words, when you mutate, tweak, or change these proteins slightly, they stopped working. In one of his papers, he thus concludes that “functional folds require highly extraordinary sequences,” and that functional protein folds “may be as low as 1 in 10^77.”

The problem of forming DNA by sequencing nucleotides faces similar difficulties. And remember, mutation and selection cannot explain the origin of the first sequence, because mutation and selection require replication, which does not exist until that first living cell is already in place.

But you can’t show that to your friends, you need to send them a video. And I have a video!

A video of Doug Axe explaining the calculation

Here’s a clip from Illustra Media’s new ID DVD “Darwin’s Dilemma”, which features Doug Axe and Stephen Meyer (both with Ph.Ds from Cambridge University).

I hope you all read Brian Auten’s review of Darwin’s Dilemma! It was awesome.

Related DVDs

Illustra also made two other great DVDs on intelligent design. The first two DVDs “Unlocking the Mystery of Life” and “The Privileged Planet” are must-buys, but you can watch them on youtube if you want, for free.

Here are the 2 playlists:

I also recommend Coldwater Media’s “Icons of Evolution”. All three of these are on sale from Amazon.com.

Related posts

Videos

New video takes you inside the cell to see how DNA is replicated

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Wow, this is pretty! (H/T Uncommon Descent via ECM)

If you need to understand how to explain this video in the context of intelligent design, see my previous posts on the building blocks of life and the origin of biological information. I find it useful to draw up the probability calculations for your friends. It’s all explained in the latter article. Fun!