Observers, Anthropic Reasoning and Biology

The observer plays an explicit role in the formulation of relativity theory and quantum theory, and even more so, in the concepts of anthropic reasoning.

Steven Weinberg recently suggested, that to determine a physical constant, "Anthropic reasoning makes sense for a given constant if the range over which the constant varies in the landscape is large compared with the anthropically allowed range of values of the constant, for then it is reasonable to assume that the a priori probability distribution is flat in the anthropically allowed range. We need to know what constants actually "scan" in this sense. Physicists would like to be able to calculate as much as possible, so we hope that not too many constants scan...We would expect the anthropically conditioned probability distribution for a given value of any constant that scans to be proportional to the number of scientific civilizations that observe that value. In the calculations described above, Martel, Shapiro, and I took this number to be proportional to the fraction of baryons that find themselves in galaxies..." See Weinberg, S. (Nov. 2005).

The priniciple of mediocrity (Copernican Principle or Cosmological Principle) suggests that throughout the universe, the most fundamental (among correct) physical laws should lead to similar predictions; there should be no privileged frames of reference from which observation of physical reality would provide unique answers. One possible consequence is that on average, and over the entire universe, any event that happens in one place and time should have a finite probability of being able to occur elsewhere, from scratch; an ergodic principle. By itself, this might seem to imply that the development of living organisms, as on earth, and their ability to evolve into sentient creatures like ourselves, (over the last 2 billion years of the 20 billion 'available'), ought not be an uncommon occurrence. But is that conclusion reasonable? "Able to occur," although meaning finite, can mean an infinitesimal probability. If a probability is small enough, 20 billion years and 10⁸⁰ baryons (the approximate number in the observable universe) may simply not provide enough time and stuff. This would not contradict the principle of mediocrity.

The combinatorial space available, for the evolution of an organism with a 10^-12 gm. of DNA per cell that codes for sequences of 20 kinds of amino acids, contains a maximum of roughly 10^130,000,000 possible genetically different organisms (messages). Even with 10⁸⁰ baryons and many billions of years, the separate independent (accidental) origin of any two identical (or even quite similar) messages, from scratch, within the universe is so vanishingly small as to best be considered as virtually impossible, [see my Science (1964) page]. So there may be a serious problem with anthropic reasoning:

The question: "What's the expected frequency of observers within the observable universe?" first received serious attention by Frank Drake. He formulatied an infamous equation that he developed to show why a search for extra terrestrial inteligence (SETI) was a 'scientifically reasonable' project for radio astronomy. The equation is a product of 6 'probabilities', including physical estimates; like the probability of other earth-like planets. And it includes biological estimates; like the probability that life would evolve on other earth-like planets and the probability that intelligence would then also evolve on such planets. Since he ended up assigning probabilities of about 1.0 to all the entries, he was quite optimistic that the universe is filled with other intelligent observers...and that our best bet of proving that, is to 'listen' for radio (or perhaps laser) signals from them.

Since Drake's equation contains a few biological probabilities, you might think that he might have given some careful attention to an analysis of the biological data that might be used to try to support such estimates. He didn't.

The same question must be asked to try to estimate the order of magnitude of a physical constant, using anthropic reasoning. And in support, a similar wildly optimistic assumption is made, by physicists such as Weinberg et al., who "took this number to be proportional to the fraction of baryons that find themselves in galaxies" !

What's a fair method for estimating the frequency of "scientific civilizations"?

On Earth, there appear to have been a number of unique, consecutive evolutionary events, each of which was necessary to permit the ultimate evolution of brainy, model-making observers and communicators: humans. A conservative analysis leads to the conclusion that each of the following occurred only once: the origin of life on earth; the origin of the universal genetic code that's used by all organisms; the origin of the precursor of the ubiquitous light sensors used by all animals and plants [derived from the amazingly-complex (9 + 2 microtubular) cilium/flagellum sub-cellular structure, perfectly conserved throughout the eucaryote kingdom]; the origin of the animal nerve cell, the unit of all later information processing networks; and probably the origin of the camera eye (and the PAX gene which guides its development). These are almost certainly not the only evolutionary bottlenecks to consider. But the chance of reproducing even as few as five, consecutive, one-time, evolutionary bottlenecks is vanishingly small. (The confidence interval for a probability based on a single occurence, is indeterminate.) In 1982 in Physics Today, I tried to show that careful examination of the evolutionary record, and what it must mean, makes Drake-type estimates quite outlandish; and this must similarly apply to much anthropic reasoning. Also see my VitalDust page.

Such a conclusion is supported by a number of different kinds of data and arguments:

If some kind of non-trivial biological determinism is a natural consequence of physical law, then many biological 'inventions' should have had evolved from different beginings, more than once, in the hundreds of millions to billions of years that organisms are known to have inhabited earth. But it's important to distinguish non-trivial from trivial, and cases of independent invention from inheritance from a common ancestor. So one must look carefully at the record.

For solving the very simplest problems, human tools, composed of various substances, can often serve similar purposes. A number of metalic elements, and their alloys, are hard enough and maleable enough to be shaped into similar tools; likewise, different kinds of rocks, can be used as tools to hammer or crush. A few inventions of such tools have almost certainly been examples of convergence. It's so 'easy', if you have hands and a brain; it must have happened a number of times, independently of awareness of earlier similar inventions; it's trivial. Chimpanzees and Sea Otters each have independently invented the use of stone hammers; without learning from us or from the other species.

Biological evolution also has found ways, again and again, to use different substrates as tools to solve important survival problems. For example some four-footed mammals lost limbs (dolphins, manatees, whales) and developed streamlined shapes, skins and musculatures to become efficient swimmers, similar to fish, (although that depended on reuse of some machinery inherited from their distant, fish-like ancestors). Insects, birds and mammals also refashioned limbs of their ancestors into wings, proportioned to body weight, in order to swim in the very low viscosity atmosphere. Most of these evolutionary lines were unique, independent inventions of 'similar' solutions from rather different beginnings. These are clear examples of 'some degree of biological determinism'. The paleontological fossil record makes it clear that there was no direct path from some single, primitive, flying, common ancestor of insects, birds and mammals to all the later flyers. Flight was reinvented quite a few times, almost from scratch; and this is a clear example of not-so-trivial convergent evolution. But the paleontological record is...and will always be quite incomplete. Lots of probable (as well as improbable) intermediate "missing links" so far have not been found (and may never be found) in the fossil record.

Until recently, it appeared, to many biologists, that some 20 different kinds of camera eyes had evolved independently, by multiple, routes of convergent evolution. Since camera eyes involve much greater complexity than the tool-box for flight, such a rich record of convergence of such complexity seemed to strongly support non-trivial biologic determinism. And since it can be argued that some of the functions of the eye (sensing environmental structure and primitive analysis of scenes with built-in neural networks) are precursors for what the human brain does on a much grander scale, this seems especially relevant to the question of the probable independent origins of intelligent observers.

This appearance, however may be decieving. It largely depends on the fact that what are considered to be some of the most primitive living members of each of the 20 evolutionary lines, lack camera eyes (for example; Amphioxus, a primitive Chordate; Planaria, a primitive Platyhelminth; both have only very primitive, eye-spots). These species, however, might represent descendents of animals who had more complex camera eyes, but these were later lost on the way to Amphioxus and Planaria...just as whales have lost their feet. Fossils of the whale's recent ancestors have been discovered, and these clearly had feet! But fossil evidence to make such paleontological judgements about the eyes of ancestors leading to Amphioxus (and finally man), is denied to us. Eyes, are free of hard mineral substances and simply fail to leave a fossil record...so paleontology can't help us unravel their evolutionary history. However, there are numerous examples of species, isolated for thousands of years in lightless environments, (e.g., caves), that have lost their eyes. Loss of function through loss of genes is one of the most common, evolutionary strategies for adapting to special niches, (such loss usually puts a species on a one-way street to ultimate extinction when the niche is destroyed or invaded). [For more discussion, again see my SETI paper from Physics Today (1982)]

Fortunately the recently developed ability to sequence long stretches of DNA, opens up new doors. It has been clearly demonstrated, that the more closely two species are related, the fewer differences they exhibit in the sequences of most of their genes. We now know that the nucleotide sequences of many genes, that are essential to survival, exhibit very few changes over long evolutionary periods; the sequence is largely conserved; useful inventions are reused, only slightly changed as they're passed down through millions of generations. And the sequences of particular genes that play important roles in the development and functioning of particular mechanisms (like a camera eye) often show very strong conservation of sequence similarities across even distantly related organisms and evolutionary epochs.

The probability of the independent evolutionary convergence of long nucleotide sequences from very different starting sequences, or from scratch, is extremely remote, as discussed in the fourth paragraph (above). Therefore, the apparent independent convergence of 20 different kinds of camera eyes was deceiving. It now looks like they all probably descended from one primitive common ancestor that had already developed a prototype camera eye, near the root of the animal evolutionary tree. [See footnotes on my Science (1964) page.]

Based on the biological implausibility of an anthropic landscape, awash with intelligent observers, does an argument like that of Weinberg, Martel and Shapiro, still " makes sense"? Also see: Starkman, Trotta, R. "Anthropic Reasoning Cannot Predict L" Phys Rev Lett 201301: 1-4 Nov. (2006).