Abiogenesis
From SkepticWiki
Contents |
[edit] Definition
Abiogenesis is the process by which life originates from unliving manner, as presumably happened at some point in the past on Earth. As of 2005 (and in all probability, for quite some time in the future) it remains an important open question of science about how, exactly, it occurred.
Abiogenesis is separate from the question of Theory of Evolution, although many creationists do not properly make the distinction. However, the Theory of Evolution properly only addresses the question of how life changes over time once it has already arisen, leaving questions of the origin of life alone.
[edit] Discussion
[edit] Creationist Strawmen about Abiogenesis
The failure of creationists to distinguish these concepts can be clearly seen in quotes such as the following:
- "Ignoring the obvious Intelligent Design that permeates life, scientists have developed the theory of evolution in an effort to explain the origin of life via spontaneous generation."[1]
- "Evolution teaches that life arose and evolved into its present complex forms by mindless, random, chance processes." [2]
- "Every scientific theory has assumptions that cannot be proven. If any of these assumptions prove to be invalid, then the theory is false. The Theory of Evolution also has unproven assumptions. These are as follows: 1. Life arose from non-living matter (Spontaneous Generation)." [3]
- "According to the Theory of evolution, life begins in the early seas also know as the primordial broth. This spontaneous appearance of complex living cells is also know as Abiogenesis." [4]
Unfortunately, this is a simple but pernicious misunderstanding about the relationship between abiogenesis and evolutionary theory. It is, for example, possible that a supernatural entity (God) created "life" in the form of a single cell or something even more primitive, and that all life on Earth has evolved via descent with mutation since that foundational event to create the diversity of life today. Nobel laureate Francis Crick, in particular, is somewhat infamous for his suggestion of "panspermia," the idea that life on earth was seeded by alien microorganisms. Although neither of these ideas receieves much serious scientific attention, they do show that evolution is not wedded to the idea of "the spontaneous appearance of complex living cells."
Furthermore, arguments against evolution via abiogenesis tend to misstate the actual scientific hypotheses about abiogenesis. In particular, "this spontaneous appearance of complex living cells" is a complete non-starter because modern living cells are organisms of such complexity. But for precisely this reason, scientists have developed a number of different accounts that present potential pathways by which complex cells could have developed via replication and evolution from earlier, simpler, components.
[edit] Scientific Hypotheses of Abiogenesis
Despite the theoretical separability of "evolution" and "abiogenesis," scientists are of course interested in the questions of the origins of life. Unfortunately, there is little data available and much of the scientific argument in this area is little more than speculation and hypotheses. Two major candidates are the "Warm Soup" hypothesis and the clay crystal hypotheses.
The "warm soup" hypothesis suggests that life arose as a collection of organic molecules in the primordial oceans. In a famous experiment in 1953, biologists Miller and Urey prepared a version of what was believed to be Earth's early atmosphere (mostly methane and ammonia) and passed electrical current through this mixture. After some time had passed, he analyzed the resulting muck and found that much of the carbon had become organic compounds, including amino acids (from which proteins and enzymes are made). In theory these amino acids could assemble into self-replicating compounds that would mine the soup for constituent molecules, forming a replication basis from which evolution can begin.
Similarly, the work of Sol Spiegelman and Manfred Eigen suggest that RNA can form and self-replicate from a suitable collection of random organic molecules. This leads to the so-called "RNA World" hypothesis, where naked strands of RNA act both as enzyme catalysts and self-replicating genetic carriers.
Alternatively, another hypothesis (Cairns-Smith) suggests that the origins of life started from crystal irregularities, for example in successive deposits of layers of clay. Richard Dawkins presents this admittedly controversial hypothesis in detail in his book The Blind Watchmaker.
Unfortunately, the evidence for any of these specific ideas is quite scant. Further research work is continuing, and no doubt will continue for the foreseeable future. None of this in any way detracts from the intellectual edifice that is evolution itself.
[edit] References
- Crick, F. H. C., and Orgel, L. E. "Directed Panspermia," Icarus, 19, 341 (1973).
- Wikipedia's article on the origins of life
