The mysteriousness of life's origin was brought home dramatically at a recent interdisciplinary workshop organized by UCLA. So was some of the scientists' faith, blind faith,not in the Divine Designer but in their own naturalistic assumptions.
The workshop focused on the origin of one particular characteristic of life's building blocks, the feature called "homochirality." [1] The "homo" part of the word means same. The "chiral" part refers to handedness. Obviously, molecules don't have hands, but they do have a configuration we refer to as being right- or left-handed. Amino acids and sugars are asymmetrical. Certain atoms stick out (like appendages) on either side of the molecule.
As it turns out, the amino acids in proteins all (but one that is symmetrical) have configurations skewed to the left, and sugars in DNA and RNA all have configurations skewed to the right, despite fairly even numbers of left- and right-handed amino acids and sugars occurring in nature. Researchers of course want to know why this is so, and how this homochirality in living systems came to be.
Inquiry began with experiments showing that without homochirality (left-handed amino acids and right-handed sugars mirroring each other), genetic material cannot copy itself. [2] The apparent necessity for homochirality has since fueled twenty-five years' research to discover chemical conditions and mechanisms that would transform random assortments of left- and right-handed molecules—called "racemic" (ray-see'-mick) mixtures—into mixtures that show at least some favoritism toward left- or right-handedness.
Alas, all experiments have failed to demonstrate any such favoritism. Rather, they have uncovered the reason for a lack of favoritism. The principle of entropy (the tendency for order and complexity to degrade through time as a consequence of the second law of thermodynamics) guarantees that even collections of molecules which begin with some favoritism will degrade to racemic mixtures.
Acknowledgment that entropy forces natural systems toward racemic mixtures has motivated some origin-of-life researchers to look for homochirality under the rare conditions of "coherent" physics. (Coherent refers to "ordered" or "congruous"—as opposed to randomized—conditions observed in such phenomena as masers, which are like lasers except that an m for microwave replaces the l for light, and neutron stars, which have no randomly moving protons and electrons, only neutrons stuck together in a massive crystalline structure.) One group of physicists went so far as to run experiments using electrons spinning in one direction only, but the results were negative. And since no one can imagine conditions on Earth ever generating anything like coherent physics, the investigators are stymied.
The world's leading homochiral researcher, Stanford University's organic chemist William Bonner, gave this summation to conferees: "Terrestrial explanations are impotent and nonviable." [2] So where do he and his peers suggest looking for answers? You may have guessed it: outer space. Their expressed hope is that in the environs of such astrophysical oddities as neutron stars, coherent conditions may be sufficient to overcome the normal consequences of entropy.
Some supernova remnants near neutron stars exhibit circularly polarized light (CPL). One Dutch experiment suggests that for one amino acid, tryptophan, CPL might induce a tendency toward homochirality. From this suggestion, a hypothesis has been developed that homochiral molecules were made in a comet while it passed through a supernova remnant near a neutron star. An unknown mechanism preserved in their journey from the supernova remnant to our solar system, where meteoritic pieces of the comet collided with the earth. These pieces supposedly salted primordial prebiotic soups on the earth's surface with homochiral molecules that became the seeds for the first life molecules.
Unfortunately for enthusiasts of the imaginative homochiral-molecules-carried-to-us-on-comets hypothesis, meteorites of cometary origin contain only racemic mixtures of amino acids. Astrophysically speaking, conditions are virtually the same today as they were in the past. As Scripps Institute chemist Jeffrey Bada observed, "If the earth were seeded with homochirals in the past, we should see it happening today." [3]
Undaunted, some researchers are suggesting that something is unique about Earth today that disturbs the homochiral conditions aboard outer space comets. To test their idea, NASA will send its Rosetta spacecraft to comet Wirtanen in 2003 to search for homochirality. Some researchers are also suggesting that a search for homochirality should be made on the Martian surface.
Many researchers are convinced, as I am, that the search for homochirality on Wirtanen will be a waste of effort and money. [4] However, the Martian research will eventually be successful and could prove deceptive. Homochirals must be present on Mars for the simple reason that the planet is being bombarded daily with life forms from Earth. [5, 6] But, not all researchers appreciate either the extent or the significance of this bombardment. Thus, the discovery of homochirals on Mars may lead them to publicize an incorrect conclusion—the conclusion that homochirality, and by implication, life itself, can and does originate under natural conditions.
I want my readers to be prepared for this eventuality, to guard the minds and hearts of those who don't know the whole story. Just as importantly, I want my readers to marvel at the results of the fervent and fruitless search for homochirality under natural, inorganic conditions. Here again we glimpse God's intricate and awesome work in creation.
1. Jon Cohen, "Getting All Turned Around Over The Origin of Life on Earth," Science, 267 (1994), pages 1265-1266.
2. Cohen, page 1265.
3. Cohen, page 1266.
4. Jeffrey L. Bada, "Origins of Homochirality," Nature, 374 (1995), pages 594-595.
5. Hugh Ross, "Life on Mars as Proof of Evolution?" Facts & Faith, volume 2, number 3 (1988), pages 1-2.
6. Hugh Ross, "Life on Mars Revisited," Facts & Faith, volume 3, number 2, (1989), page 2.
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