Rick Searle has a post up on Life: Inevitable or Accident? at his website Utopia or Dystopia. In it he discusses the somewhat contrasting ideas of Jeremy England and Henry Gee. I touched a little on Jeremy England in a post a few months ago.
England’s idea seems to be that the Second Law of Thermodynamics makes life inevitable. He has been quoted as saying that “You start with a random clump of atoms, and if you shine light on it for long enough, it should not be so surprising that you get a plant.” Really? Could we shine a light on rock and get life? Let’s me a little more generous with England’s comment. Perhaps it was taken out of context or was a bit of hyperbole. I happen to think the Second Law of Thermodynamics does have a lot to do with life and so have a great many others. The real trick is showing how injecting energy into a a group of atoms can create self-sustaining metabolism and reproduction. It may be with the right types of atoms at the right temperature, given time, life is inevitable, but showing exactly how is the difficult part. A group of scientists at Cambridge University have recently made real progress in this regard.
Gee’s ideas have more to do with the evolution of complexity. Rick Searle in his post writes: “His objective is to do away, once and for all, with what he feels is a common misconception that evolution is leading towards complexity and progress and that the highest peak of this complexity and progress is us- human beings.” I happen to think that evolution is leading towards complexity and that it might even have been leading towards something somewhat like us. My idea does not come from any belief in the supernatural but rather from how I think Nature plays the lottery.
Key to England’s argument is that life arises through the dissipation of energy. This primarily for Earth is the energy that comes from the Sun. The more likely outcomes of evolution are solutions that absorb and dissipate energy more energy through their evolutionary path. Reproduction is key to this since a species by copying itself can double the amount of energy the species as a whole absorbs and dissipates. With reproduction comes evolution primarily from slight modifications in the genetic code from generation to the next.
Genetic modifications (mutations) are tricky. Too much or too little could both lead to the extinction of the species. Too much mutation could lead to a species with fewer viable reproductive members or a species with numerous vulnerabilities that can be easily wiped out from simple threats. On the other hand, without an ongoing development of modifications in a species the genetic instructions of a species would become homogenized. This would make the species vulnerable to changes in its environment. Let’s say, example, the genetic pool of insect contained members that could only the leaves of one particular type of plant. If the ecosystem of the insect was invaded by invasive species that crowded out that plant, it could diminish the food supplies of the insect to the extent that the species would go extinct. On the other hand, if the population of the insect had a genetic pool that enabled it to eat many types of plants, the species would have a chance to survive. Diversity in the gene pool provides for flexibility and survivability.
There must have some self-tuning of the genetic modification rate early in the evolution of life. Many life forms went either too high or too low in their rate and vanished quickly but those that had approximately the right rate (and this could vary a bit based on the construction of the species and its ecosystem) would survive and evolve. Even with this it is sometimes said that 99% of species that ever existed have gone extinct. Did they all really go extinct or did some of them just evolve into a new species? Did Homo erectus who were normally say is extinct really just evolve into Homo sapiens?
So let’s imagine some primordial species – the first simple organisms on Earth about 3.5-4 billion years ago. These are the ones that came through the early tests and now have about the right rate of mutation. For the sake of argument let’s use “measure genetic complexity by the length of functional and non-redundant DNA sequence rather than by total DNA length” as Alexei A. Sharov and, Richard Gordon do in their Life Predates Earth paper.
In any given period, one of these species could:
- Stay mostly the same with modifications that do not change the essential character of the organism.
- Evolve into a new organism of similar complexity.
- Devolve into a new organism of lesser complexity.
- Evolve into an organism of greater complexity.
- Stay mostly the same and spin off a new separate species of less, same, or greater complexity.
- Go extinct.
We might imagine that the most likely of the options above would be 1 or 6. Options 2, 3, or 5 with the new species being of less or same complexity would probably be next in likelihood. Evolution to greater complexity by either species itself or by spinning off a new species would be the least likely and probably highly unlikely.
Here is where the lottery comes in. As long as we generating new species at a sufficiently high rate whether they be of the same or lesser complexity the evolution of more complex forms is inevitable.
Think of it like this. We are playing the lottery with 100 species/plays per draw. We go for a long time without winning anything in the lottery for greater complexity. Some of our plays die but some split so at the end of many plays we now have 1,000 species/plays. Another period of time passes and we end up with no winnings but we have 10,000 species/play. The next draw we hit on 1. More time passes and we get more hits but now we have 100,000 species/plays. Now we getting multiple hits every draw. In fact, now occasionally one of the species lines that moved above the primordial complexity has taken another step up the complexity tree.
The more we generate newness the more we expand our capability for generating more newness and more complexity. Evolution of complex forms becomes more and more likely or perhaps even inevitable as long we are generating new forms at a sufficiently high rate and the ecosystem is friendly enough that extinction rates are not too high.