A modern cell, even of a simple organism like a bacterium, is intensely complicated. The cell membrane is studded with receptors like keyholes that allow sophisticated communication among cells. The cytoplasm, the fluid making up the interior of the cell, hosts elaborate biochemical pathways that process and propagate biological signals. Complex structures called ribosomes are like sliding clamps with integrated information readers; they produce new proteins in assembly-line fashion.
Proponents of the pseudo-scientific theory "Intelligent Design" (ID) use the above examples as evidence to suggest that no natural process could have resulted in a cell. In ID, cells are purported to be "irreducibly complex," meaning they cannot function in the simpler forms that would be expected according to the theory of evolution.
One cannot prove a negative; a single example to the contrary falsifies a negative statement. Inconveniently for ID proponents, recent research is working steadily to falsify this particular negative statement.
While modern cells possess the array of machinery described above and more, no researcher has ever shown that all of it is absolutely necessary for life to exist. According to one astrobiologist, Peter Ward, the bare minimum for a cell to live, metabolize, and reproduce may be no more than a membrane to separate cell contents from its surroundings and a bit of genetic material.* And Scientific American recently reported that Harvard Medical School researchers have caused this type of structure to arise spontaneously in a test tube. They mixed certain organic molecules (ones thought to have been around in earth's early pre-life days) in a test tube of water.
The result seems like wildly optimistic science fiction: some of the molecules (lipids, which are the building blocks of oil and fat and which don't mix with water) spontaneously formed a "pouch" with another molecule (DNA) inside, then more molecules (nucleic acids, building blocks of DNA) spontaneously crossed the barrier, and the DNA spontaneously replicated.
Did I mention that all this took place spontaneously, with no tinkering from an intelligence? Not only that, it required no more than 24 hours. Chalk up a blow to the argument that the cell is irreducibly complex.
|*Actually, Ward suggests the minimum definition of life may be considerably less even than that. I am currently reading, and must recommend, his book Life As We Do Not Know It: The NASA Search for (and Synthesis of) Alien Life.|
|Read the whole Aliens and Origins series here. Make sure you don't miss upcoming posts by subscribing.|