Planets, Smells, Ice and Brains

The flurry of extraterrestrial planet discovery has led some to assume that habitable (by us) planets are common in the galaxy. To date, we've not observed a single exoplanet with the characteristics necessary for human survival, much less able to produce intelligent life as we know it. Simple estimates based on a "habitability zone" ignore a number of additional variables, ruling out all the planets in the Gliese 581 system, for example.

Optimism is dandy for some things. But uninformed optimism is distracting, drawing attention away from other wonderful but more realistic possibilities. It is like noticing that transistors are made of silicon, then presuming that the existence of silicate rock inevitably causes naturally occuring microprocessors.

The Drake equation is an estimate for the probability of intelligent life on other planets. It is a product of many probabilities, including the abundance of rocky planets at the right distance from the sun, chemical composition, and other items necessary to produce the only intelligent life we've observed so far ... us.

In Rare Earth, Peter Ward and Donald Brownlee add extra terms to the Drake equation, suggesting that Drake's small probabilities for intelligent life were extremely optimistic. A planet of the right mass at the right distance from the sun is not enough - to produce life like us, it must have many other attributes, including gas giants at the right distances, a large moon, plate tectonics, a sun aging at the right speed, and a number of other cosmic beneficences and statistical accidents. One accident is that enough supernovae have occured nearby to create the heavy elements needed to make rocky planets, but none have occured since the emergence of life on land.

Here, I propose adding even more terms than Ward and Brownlee. There may be many possible paths summed into the numerator of the "Drake Fraction", but the denominator grows very large indeed. It is possible that if we are stupid enough to wipe ourselves out, we will silence the only intelligence in our galaxy, and possibly in all of observable space. Intelligence may re-emerge in some distant galaxy, billions of years later, but if intelligence is indeed transitory on the billion year scale, then it is nearly impossible that two technological species will ever exchange information. The answer to the question posed by the Fermi Paradox, "where are they", could be "vaporized in the embers of a long dead star", or "awaiting the birth of the next suitable star and planetary system, and a very long string of luck". The optimistic answer may be "in a galaxy so far away that we will never receive a coherent pattern of photons from them, even if they use a solar-system-sized transmitter aimed at our solar-system-sized receiver".

Flowering plants, Chixulub, Noses, and Neocortexes

Ward and Brownlee present many fascinating prerequisites for intelligence, but they don't mention botany and neurology, thus missing a few additional Drake terms that make Rare Earths even rarer.

Michael Pollan's The Botany of Desire celebrates the co-evolution of domesticated plants and humans. Pollan's examples are four flowering plants: the potato, the apple, the tulip, and marijuana. Technology rests on civilization, which rests on agriculture, which is built around angiosperms, flowering plants including fruits, grains, and grasses. Angiosperms evolved 140 million years ago, and became dominant around 60 to 100 million years ago. The rise of the mammals closely tracks the angiosperms, and may be related.

Collections of neurons are not enough for intelligence - brains have been around for a very long time. In their book Big Brain Gary S. Lynch and Richard Granger suggest that mammalian neocortexes evolved out of the olfactory cortex to recognize complex patterns and sequences of odors. Perhaps the initial driver was the odors of angiosperms and the fruits they produce, originally created to attract pollinating insects, but later evolved to encourage mammals and birds to transport the seeds of those fruits far from the original trees.

The Chixulub impactor of 65 million years ago destroyed most of the dinosaurs and weakened the gymnosperms, vacating ecological niches for the mammals and angiosperms. Lynch and Granger hypothesize that learned pattern maps based on odors were essential to the survival of early mammals in the cold and dark after the impact. Brains work optimally over a very narrow set of environmental conditions, and it is arguable that a well tuned learning brain expends much mass and energy to create a coddled environment for the highly precise and rapidly-formed synapse structures storing memory patterns in the neocortex.

If the Earth had been turned slightly differently, the Chixulub impactor would have landed in Northern Africa (with little climatic effect) or in deep ocean (steamcleaning the land of life). A very precise cosmic alignment led to a mammal/angiosperm dominated planet, and us.

So - warm blooded mammals with neocortexes, and the grains and fruits that they eat. Perhaps a different class of animals could have evolved something that functioned like a neocortex, but they would have had to pass through a similar sequence of stresses to get there.

Ice Ages, Throwing, Grammars, Language, and Lying

The development of learning brains was a necessary but not sufficient step on the path to human intelligence. Intelligence requires a big brain, many levels of pattern recognition and response deep, and our large brains are incredibly costly, using lots of energy and requiring years to develop. What could possibly justify the development of such brains?

Big Brain comes close, but is marred by a mistaken reading of the paleontological record, citing a disputed large-brained hominid called Boskops. In The Throwing Madonna, neurophysiologist William Calvin proposes a more plausible hypothesis, based on the physics and neural circuitry of projectile hunting. Neural pathways are noisy, with accuracies on the order of 10 milliseconds. Throwing and releasing a stone aimed at distant running prey requires accuracies in the microseconds. Calvin proposes that this timing accuracy is achieved by signal averaging - 100 neurons averaged together have 10 times (square root) better timing accuracy than one neuron.

The decision and response system must be very fast and accurate, and the brain must somehow encode huge classes of many similar patterns to deal rapidly with many variations. The hunter must decide whether the prey is valuable and vulnerable, decide whether to expend the energy and a hoarded projectile, estimate where it will be when the projectile hits, not when it is seen, and make all these calculations, wind up, and throw, all possibly in less than a second. All these processes are open-loop - there is no time for propioceptive feedback to correct trajectories. Most of the throws will be misses. A more accurate and well trained brain will succeed more often. This provides a powerful and continuous driver for increased brain size, capable of storing and interrelating more intricate patterns. A longer adolescence provides more time to acquire more training, while a longer adulthood provides more time to use that training to feed more adolescent not-quite-survival-capable offspring. Given the seasonal nature of prey, and the rapidly varying landscape caused by the Ice Ages, a very large and adaptable brain, capable of storing decades of memories, had strong survival advantages. This strong evolutionary pressure exploded the size of the brain in a very brief time, evolutionarily speaking, while simultaneously evolving a robust yet flexible structure that could morph into many different forms, and did.

Calvin posits a 4th power law in brain size to accuracy - doubling the distance of a successful throw requires on average 16 times more neurons. His fourth power comes from curve fitting to simulations of a moving body carriage, turning with the throw. If propioception has time to operate, and modify the "calculation" of the eye to arm/hand/finger movement, he is right; but if there is not time to sense the exact angular position of legs and torso, the entire ensemble depends on a much larger signal averaging which goes as the 3rd power. Whichever way you slice it, though, a few more neurons can sometimes make the difference between success and starvation. That is all that evolution needs to work very quickly.

Calvin suggests that the "syntax" of throwing was coopted by processes for linguistics, socialization, music, and dance. The same signal averaging necessary for hunting turned out to be great for the precision movements and pattern recognition necessary for gesture and song, toolmaking and fighting for dominance. As soon as we learned to communicate, we learned to lie, and our social structures became increasingly complex to accomodate that.

The repeated winnowing of populations by climate change and geographic isolation brought on by glaciation periods increases the "genetic noise" and variation from which evolution selects new adaptions. With the development of speech, and the finely tuned cultural perception of fitness leading to "evidence-based" survival prediction by prospective mates, evolutionary forces become very highly tuned and incredibly rapid.

The Ice Ages themselves are a result of the north-south division of the Atlantic from the Pacific, the upthrust and weathering of the Himalayas, and the response of plants to CO2 and temperature, magnifying the 21,000 to 41,000 year precessions of the Milankovitch cycles, driving long term climatic changes.

The shape of the continents influenced the later spread of agriculture (there's those angiosperms again, along with grasses). Eurasia facilitated the same-latitude spread of cultivars and herd animals; the north-south axis of the Americas did not. A planet different tectonic plate distributions, and two north-south landmasses, would not develop civilization as rapidly, and might succumb to monocrop-driven land depletion and climatic failure faster than we have.

The rise of modern technology depended on coal geology - the coal seams that powered the beginnings of the industrial revolution came to the surface in England. England's climate and hydrology led to widespread combustion-fueled machinery. The culture and geopolitical ambitions of England fostered inventions like James Watt's double acting steam engine, and Henry Maudslay's precision screw and lathe, a direct ancestor of modern semiconductor technology.

Carboniferous era coal seams were the result of the evolution of woody lignin, which resisted decomposition until nature evolved termites, with their complex multistage gut chemistry and mutualistic bacteria. For millions of years. buried lignin turned into coal, sequestering CO2 and reducing temperatures, compensating for the steady aging and heating of the sun. This kept the Earth from turning into Venus.

These and many other conditions were prerequisites for human evolution and technological civilization. Few were inevitable - we could have been trapped in peasant labor economies like ancient China and India. We face many more traps in the near future, and our survival may depend on the selection of behaviors and social institutions that foster long term and practical thinking. It is unlikely that most cultures will survive the shocks of the next few centuries - it is possible that none will.

Other Paths, Only Paths

Perhaps there are other paths that would have led, sooner or later, to intelligence. But we have no evidence for those paths, while we have abundant evidence of side paths that easily could have failed to lead to intelligence, or land life, or even the survival of life itself. There is absolutely nothing inevitable about the evolution of intelligence - it is costly, and it may cause the end of all life on earth.

But if we do use our intelligence to survive, to spread into space, to modify our solar environment for billion year plus survival, observers in the distant future will observe that the well-documented steps that lead to them (will be / were ) absolutely essential. The history we are making today will be preserved by the same technologies that preserve life on earth. There will be ample documentation of specific (and abundant) wrong turns avoided. The chances of surviving long enough to detect other civilizations in distant parts of the galaxy may be slim, but for the first time in Earth's history a very few of us can think teleologically, and prepare for a long stay in this Solar System, and migrations to others. Those individuals, ideas, cultures and species that do not do this will disappear.