My friend Ted asked me recently for my thoughts on some basic questions in astrobiology. I thought you might be interested, so here they are.
How much respect do you hold for the Miller/Urey experiment?
I think that the Miller/Urey experiment was a wonderful demonstration of the abiological formation of complex organics. This is not my area, but I believe our ideas of early Earth environments have changed, meaning this no longer represents a great model for early formation of organics on Earth.
As to the bigger question, I think the mechanical philosophy forces us to assume (while doing science) that life came from non-life at some point. I’m happy for science to pursue this path and, as my theology leans toward God acting primarily through laws (rather than around them), I think scientists will find good answers – eventually. It remains a very difficult problem.
Do you think we could add the origin of life on the front end of evolution, or do you think it requires a completely different theory?
Currently evolutionary biology (post modern-synthesis, commonly but problematically called “Darwinian” evolution) gets you from one organism to two, from one species to two. It cannot get you one from none. It only applies once you have good, but imperfect replicators – think “RNA world.” How you get those replicators remains a mystery. We are very interested in where Earth water came from and, within that water, how do you generate high enough concentrations of organic molecules to do any interesting chemistry. It’s easy to form nucleotides and amino acids, what’s hard is getting enough of them in solution in one place to do metabolism (the chemistry of life). I don’t know of anything in this area other than bold theory. It may pan out, but it has not yet.
Once you have a replicator, you have selection and probabilistic forces can move you toward biological complexity surprisingly quickly. Before that, though, you are stuck with more limited physical systems – what the general public thinks of as “random forces.” I think Daniel Dennett (building on Mayr and Monod among others) has said some interesting things about proto-Darwinian selection algorithms and how the process of repetitive geological processes may do some of the heavy lifting. Heating/cooling or drying/wetting cycles may have given you useful concentrations. Again, though, we’re living in a very abstract realm until someone can make a simple replicator in the lab.
So currently, I would separate evolution by natural selection from abiogenesis (life from non-life). The former is a great explanatory theory supported by billions of observations, consistent with all the data (variation, inheritance, and differential survival occur) and logically necessary given what we know about biology (natural selection and speciation will occur given the three factors). The latter is basically disproven (under the head of spontaneous generation), but required by our philosophical framework. Abiogenesis is still a research program, rather than a body of data.
Do you think life is plentiful in the universe?
I suspect it is. I believe the data is so scarce as to justify practically no confidence either for or against the idea of “life out there.” We haven’t even left the solar system with our robots, meaning that the probability of achieving inter-stellar communication is somewhere between 0 and 1. The lifetime of that communication is complete unknown. The absence of detected radio signals gives us a very small line of evidence against radio signal producing intelligences in the near stellar neighborhood, but I would be uncomfortable generalizing from that.
There is life here, so the probability of life is non-zero. No advanced civilizations have contacted us, so the probability of life just about everywhere is zero. Still, it could easily arise once in every solar system without our noticing it at current levels of technology. So I don’t speculate (as a scientist) on the probability of life out there. We just don’t have the data.