Fisking Ernst Mayr

A favorite strawman of intelligent designers is a calculation of the probability that a genome arose spontaneously from a mixture of the necessary chemical ingredients. As one might expect, it is infinitesimally small, and no one seriously believes that life on Earth arose in that fashion. Of course nobody does know how life on Earth did arise, but it seems plausible that some sequence of intermediate steps took place which made the transition to some kind of self-replication possible.

Oddly enough, those biologists who doubt the plausibility of intelligent life in the Cosmos like to make a very similar argument. Changcho recently linked to the debate between Ernst Mayr and Carl Sagan on just that topic. Mayr's contribution to that debate was the source of comments by PZ Myers, discussed in the comments to the previous post - and Sagan's contribution, rather egregiously quoted out of context, was the source of another of his comments.

The debate is about the the Drake Equation, and in particular, about one factor in that equation, the probability that, given life on a planet, intelligent technological life will evolve. Mayr, Myers, and some of my correspondents think small, but Sagan, and I, doubt it.

Let me skip over some irrelevancies and get down to what Mayr said:

What Percentage of Planets on Which Life Has Originated Will Produce Intelligent Life?
Physicists, on the whole, will give a different answer to this question than biologists. Physicists still tend to think more deterministically than biologists. They tend to say, if life has originated somewhere, it will also develop intelligence in due time. The biologist, on the other hand, is impressed by the improbability of such a development.

Life originated on Earth about 3.8 billion years ago, but high intelligence did not develop until about half a million years ago. If Earth had been temporarily cooled down or heated up too much during these 3.8 billion years, intelligence would have never originated.

This is Mayr's first invocation of the idea intelligence - we will see that he is not quite consistent in what he means by the term.

When answering this question, one must be aware of the fact that evolution never moves on a straight line toward an objective ("intelligence") as happens during a chemical process or as a result of a law of physics. Evolutionary pathways are highly complex and resemble more a tree with all of its branches and twigs.

No argument here from me or Carl Sagan.

After the origin of life, that is, 3.8 billion years ago, life on Earth consisted for 2 billion years only of simple prokaryotes, cells without an organized nucleus. These bacteria and their relatives developed surely 50 to 100 different (some perhaps very different) lineages, but, in this enormously long time, none of them led to intelligence . . .

Here we see the logical equivalent of the thought experiment with the soup of DNA ingredients. There are all sorts of reasons why bacteria couldn't be expected to evolve human level intelligence any more than atoms or molecules could be expected to spontaneously generate DNA - or a complete cell. The quasi-religious abhorrence of evolutionary theorists for the notion of "progress" in evolution leads them into absurdities. Continuing from the above:

Owing to an astonishing, unique event that is even today only partially explained, about 1,800 million years ago the first eukaryote originated, a creature with a well organized nucleus and the other characteristics of "higher" organisms. From the rich world of the protists (consisting of only a single cell) there eventually originated three groups of multicellular organisms: fungi, plants and animals. But none of the millions of species of fungi and plants was able to produce intelligence.

For the first two billion years of life, only bacteria like creatures existed, why? We don't know for sure, but a very plausible notion is that without enough oxygen, bigger creatures just don't work. Bacteria had to learn to transform the chemistry of the planetary atmosphere before the next steps could occur. Despite their chemical wizardry, bacteria have very simple methods for absorbing nutrients and other necessary substances. This fact limits their size and complexity.

Eukaryotes were apparently formed from the fusion of bacterial parts. That could occur because they had a new atmosphere to work with and because they had specialized tools for acquiring and processing nutrients. Their huge size compared to prokaryotes allowed them comparably increased complexity, and made possible the next big step, multicellularity.

Most cells react to their environment. Even bacteria can move up nutrient gradients with their clever little flagellar motors. Multicellular organisms, at least large ones, can't move effectively by those mechanisms. Consequently, many of them, like fungi and plants, are essentially sessile. Such creatures don't have or need specialized neural cells. Animals mostly have the capability of movement, and have neural and other cells specialized for movement or sensing - the beginning of multicellular smarts.

So far Mayr has been blowing smoke - merely noting that high IQs don't occur in organisms that couldn't possibly have intelligence.

The animals (Metazoa) branched out in the Precambrian and Cambrian time periods to about 60 to 80 lineages (phyla). Only a single one of them, that of the chordates, led eventually to genuine intelligence. The chordates are an old and well diversified group, but only one of its numerous lineages, that of the vertebrates, eventually produced intelligence. Among the vertebrates, a whole series of groups evolved--types of fishes, amphibians, reptiles, birds and mammals. Again only a single lineage, that of the mammals, led to high intelligence. The mammals had a long evolutionary history which began in the Triassic Period, more than 200 million years ago, but only in the latter part of the Tertiary Period-- that is, some 15 to 20 million years ago--did higher intelligence originate in one of the circa 24 orders of mammals.

Mayr has now given us two more implicit definitions of intelligence, both inconsistent with his first definition. Actually, though, there is clearly a fair amount of intelligence in at least two other phyla. Octupus are rather intelligent, and insects are quite amazing with their tiny brains. Ants, honeybees, and termites have even created technological civilizations, albeit ones without access to electronics or metallurgy. Arthropods are probably just too size limited by their exoskeletons to ever get much smarter than they already are. On the other hand, without competition from vertebrates, maybe the seas would be populated with giant and brainy arthropods.

What niches are open to a creature is very much a function of the competition, so it's not surprising that if one phylum goes in for the brainiac act, others find it convenient to get out of that line of work.

The elaboration of the brain of the hominids began less than 3 million years ago, and that of the cortex of Homo sapiens occurred only about 300,000 years ago. Nothing demonstrates the improbability of the origin of high intelligence better than the millions of phyletic lineages that failed to achieve it.

I would say that what is illustrated instead is that an awful lot of other things need to happen before high intelligence can arise. Only a large and big brained creature dependent on its wits is likely to evolve high intelligence. This required a lot of preconditions, and those preconditions took a long time to achieve, but given a few billion years of evolution, it seems likely that they would be achieved. Is it likely that lots of planets that evolved life got stuck at the bacterial stage? Well maybe, but it's also likely that that those bacteria eventually will learn enough metabolic tricks to evolve photosynthesis and transform their planetary atmospheres, making those planets safe for larger and more complex cell types capable of multicellularity.

How many species have existed since the origin of life? This figure is as much a matter of speculation as the number of planets in our galaxy. But if there are 30 million living species, and if the average life expectancy of a species is about 100,000 years, then one can postulate that there have been billions, perhaps as many as 50 billion species since the origin of life. Only one of these achieved the kind of intelligence needed to establish a civilization.

OK, I've been arguing that it doesn't make sense to act as if any species is equally likely to evolve intelligence, but forget that for a moment. Counting species for prokaryotes that reproduce asexually is a bit iffy - no doubt modern blue green algae are rather different from those that lived 2.5 billion years ago, but they are also pretty similar - where do you draw the species boundaries? Never mind that either.

Suppose we take Mayr's numbers at face value. What is our best estimate of the probability of a species being "highly intelligent" in the sense of creating a modern high tech civilization. It is 1/50,000,000,000. How many species are likely to arise on an Earth like planet that exists with life for 3.8 billion years? About 50,000,000,000. What is the probability that "highly intelligent" life would not arise in that circumstance? ((50,000,000,000 - 1)/50,000,000,000))^50,000,000,000. Calculus students might recall that the limit((n-1)/n)^n, n->infinity) is 1/e, where e is the base of the natural logarithms, so our probability is a number close to 1/e, and consequently the probability of intelligent life arising is approximately 1-1/e, which is between 1/2 and 2/3. (e is approximately 2.71828...).

To provide exact figures is difficult because the range of variation both in the origination of species and in their life expectancy is so enormous. The widespread, populous species of long geological duration (millions of years), usually encountered by the paleontologist, are probably exceptional rather than typical.

Why Is High Intelligence So Rare?
Adaptations that are favored by selection, such as eyes or bioluminescence, originate in evolution scores of times independently. High intelligence has originated only once, in human beings. I can think of only two possible reasons for this rarity. One is that high intelligence is not at all favored by natural selection, contrary to what we would expect. In fact, all the other kinds of living organisms, millions of species, get along fine without high intelligence.

I always get annoyed with biologists for repeating the old canard about eyes arising many times. Genetic experiments (inserting mouse eye generation turn on genes in a spider's knees produces spider eyes on the spider's knees) conclusively show that eyes all have a common ancestry, even though they have been elaborated in drastically different ways. Past time to discard that particular crock.

This is not irrelevant. Really good ideas in evolution are rare and tend to be preserved, though it may take a long time to come up with them.

The other possible reason for the rarity of intelligence is that it is extraordinarily difficult to acquire. Some grade of intelligence is found only among warm-blooded animals (birds and mammals), not surprisingly so because brains have extremely high energy requirements. But it is still a very big step from "some intelligence" to "high intelligence."

The hominid lineage separated from the chimpanzee lineage about 5 million years ago, but the big brain of modern man was acquired less than 300,000 years ago. As one scientist has suggested (Stanley 1992), it required complete emancipation from arboreal life to make the arms of the mothers available to carry the helpless babies during the final stages of brain growth. Thus, a large brain, permitting high intelligence, developed in less than the last 6 percent of the life on the hominid line. It seems that it requires a complex combination of rare, favorable circumstances to produce high intelligence (Mayr 1994).

I don't want to dispute that, but the missing point is that the most crucial ingredient is the starting point. Our close relatives the chimps have big brains, culture, and versatile hands. Horses don't have any of those things and so aren't in a position to evolve high intelligence. The largest factor in chimps not evolving into a human like plains ape is probably the fact that that niche was already occupied.

The rest of his argument, though interesting, is not really relevant to the topic of this post, but my rotten side can't resist reporting one misfire of his:

Would the Sense Organs of Extraterrestrial Beings Be Adapted To Receive Our Electronic Signals?

Has he not noticed that human's sense organs are not adapted to receive our electronic signals? A high technology civilization would undoubtedly develop transducers to allow it to observe otherwise invisible parts of the electromagnetic spectrum, just as we have.