Pollinators

Above is a bee of the genus Andrena (looks like Andrena dunningi) visiting an ornamental flower in Oak Park, IL.

Pollinators

The vast majority of terrestrial biomes rely on animal pollinators. Angiosperms dominate most terrestrial plant assemblages, and 70-90% of angiosperm species rely on animal pollinators. Although some agricultural species, such as wine grapes and peas, self-fertilize, most domesticated angiosperms benefit from pollination and some require it to set seed. For instance, apples must be pollinated by insects (bees and flies, generally) to set seed and develop fruit, same with cocoa (small rainforest bees and midges), coffee, almonds, and other crops too numerous to mention.

Recently, because of a decline in the abundance of feral and domestic honeybees (Apis mellifera, an exotic species imported to the US from Europe) in the United States and in Europe, a great deal of attention has focused on native pollinators. It is very sad that we have only started caring about these creatures now, because a great deal of the damage has been done, and it will take years for populations of native pollinators to recover, even if we were to act immediately. Native pollinator assemblages have been hit hard by pesticide use, habitat destruction, and changes in farming practices, but still provide many of the pollination services we associate with honeybees, for free, every year. If a figure were set on these services, it would amount to 6-8 billion dollars a year, for the US alone, perhaps more. Native pollinators include, roughly in order of importance, bees, moths and butterflies, flies, hummingbirds, beetles, thrips, and bats. Different ecosystems have different pollinators. Some pollinator-plant relationships are tightly coevolved (an obligate mutualism, or at least an oligolectic pollinator that can only visit one plant), or loosely associated (a facultative mutualism, usually because the pollinator is polylectic, and can visit multiple plants). Most ecosystems have both types, and fortunately, there is often a great deal of redundancy.Above is the halictid bee, Agapostemon virescens, pollinating an ornamental flower in Oak Park, IL.

Bees

There are about 20,000 species of been in the world, including approximately 3500 that inhabit the United States (Goulet and Huber, 1993). The bee fauna of North America encompasses a large number of ecological generalists, as well as many species whose ecologies are specialized to some degree. For example, bees can be polylectic; feeding from, or gathering pollen from a variety of flowers, or be oligolectic; specializing on a limited number of flowers, most likely close relatives. Some bees gather nectar from a wide variety of flowers, but gather pollen from a much narrower subset of the available flora (for an excellent discussion, see Cane and Sipes, 2006). Bees can be univoltine; having one generation a year, or multivoltine; having several. Likewise, bee species differ in their vagility, some being more prone to migrate than others. Some are habitat specialists as well, requiring a particular plant assemblage to be present at a particular time of the year with a particular type of soil for nesting. Nest site requirements vary among bee species. Different taxa of bees may utilize twigs, beetle burrows, sandy soil, packed sand, grassy tussocks, abandoned rodent burrows, the abandoned burrows of other bees, or other nesting substrates. This is an important aspect of bee ecology that is often neglected by agriculturalists. A typical almond orchard is often so systematically flat and homogeneous that ground nesting bees lack opportunities to nest, and even the piles of broken brush and beetle-infested trees that provide nest sites for leafcutter bees, such as orchard bees of the genus Osmia, are absent because orchard managers groom away these features of the landscape. In England, a shift from traditional modes of agriculture to the more Ameicanized, "efficient" modes of agriculture, has been hard on the local Bumblebee species, with many declining severely, because tussocks of grass and rodent burrows have been removed, plowed, and variously "cleaned up" to make room for useful farmland.

Bees are very vagile, and have probably always been prone to what evolutionary biologists call "metapopulation dynamics". A population goes extinct one year, bringing all of its various parasites and hangers-on with it, only to be recolonized by migrants from other populations the next year. Every stretch of habitat is probably being colonized by migrants from outside populations of some species, even as other species go extinct from within. Some of this may be due to the weather, some of it might be pure, random chance. A a mud riverbank that formerly hosted hundreds of bee nests slides into a stream and carries a population of bees with it, a Bombus queen arrives and builds a nest under an overturned flower pot. This temporal variability has always made bees difficult to monitor (Williams et al., 2001). The good news from this is that, if you build it, they will come. An area that has the appropriate resources for bees to survive and prosper will inevitably accumulate species, the same way Mc Arthur and Wilson predicted that oceanic islands, such as Krakatoa, accumulate species from the mainland. The bad news is that an isolated patch of nice-looking wetland or praire will inevitably loose much of its original pollinators over time, with subsequent replacement by an assemblage of pollinators dictated by dispersal, chance, and whatever biotic changes have occurred in the region.

Lepidoptera

To the left is a moth, probably Haematopis gratiara, the chickweed geometer.

Unlike bees, Lepidoptera lay eggs on a host plant (usually, some are decomposers, parasites, or social cleptoparasites), and the larva needs a host plant to grow. Once grown to adulthood, adults rely on nectar for energy. Unlike bees, moths and butterflies do not gather pollen for their own needs-it sticks to them.

Butterflies are wonderful, and they get great press. Probably, every species of butterfly in the world is known, is in a museum somewhere with a pin through it, and has enough enthusiasts that when it begins to decline in numbers, people take notice and start to save it. In the Bay Area, for instance, the endemic San Bruno elfin has enough enthusiasts that the decline of this odd little lycaenid, and its subsequent reappearance, all made news and had the potential to affect public policy. Butterflies, in essence, are just glorified moths, however, and moths don't always get the same press.

Flies

Many groups of flies, including the syrphidae and the bombiliidae are important pollinators. These species feed on both nectar and pollen as adults, and lay their eggs on host plants (syrphidae), or in the nests of their host victims, usually bees, (bombyliidae). Flies almost never get the credit they deserve as pollinators, which is unfortunate, because they are probably more important than anyone guesses. In early spring especially, flies are ubiquitous on flowers.

Others

Beetles, thrips (insect order thysanoptera), hummingbirds (and ecological analogs, such as the unrelated honeycreepers), and bats are also important pollinators.

There are probably three things that people can do to encourage pollinator conservation. One is to buy organic produce whenever it is possible, and to buy produce that was grown via sustainable agricultural practices. The countryside was formerly teeming with habitats for pollinators that simply no longer exist because massive, industrial agriculture and the widespread use of pesticides have simplified the ecosystems to the point that pollinators can no longer find an ecological niche to exist. A second thing is to create friendly situations in their gardens, farms, and parks for pollinators to use as habitats, and habitat corridors, to allow dispersal, and the third, of course, is to support local conservation efforts. Barbara Kremen's work in California has demonstrated that conserved areas serve as source populations of bees, that disperse into agricultural habitats and provide services to humans. Besides beauty, conserved areas provide economic benefits that go beyond the original intentions of the conservationists, and are ultimately important for our survival.

Passage below quoted from: Pollinators Need our Help and Chocolate's Sweet Little Secret (North American Pollinator Protection Campaign)

"The work of pollinators ensures full harvests and seed production from many agricultural crops and provides for healthy plants grown in backyards, community gardens, and other urban areas.

Worldwide, of the estimated 1,330 crop plants grown for food, beverages, fibers, condiments, spices, and medicines, approximately 1,000 (75 percent) are pollinated by animals. It has been calculated that one out of every three mouthfuls of food we eat, and beverages we drink, is delivered to us by pollinators.

More than half the world's diet of fats and oils comes from oilseed crops. Many of these, including cotton, oil palm, canola, and sunflowers, are pollinated by animals.

In the U.S., pollination by insects produces $40 billion worth of products annually.

Pollinators are essential components of the habitats and ecosystems that many wild animals rely on for food and shelter.

Approximately 25 percent of birds include fruit or seeds as a major part of their diet.

Plants provide egg laying and nesting sites for many insects, such as butterflies.

Berries and other fruit form a significant part of the late-summer diet of animals, such as grizzly bears, which fatten themselves in preparation for winter hibernation."

The photos in this post are by Marcus Thomasson, my original field assistant, thank you Marcus....

Genesis Falsified

A Critique of the Account of Creation Posited by the Book of Genesis

There are a great many people who take the biblical book of Genesis as a literal document, detailing the events responsible for the origin of the universe, our planet, and  our species.  In fact, this belief is quite common, held by millions of Americans to this day.  In some circles, it has become fashionable.  The various schools of creationism fall along a continuum between these two positions.  Young earth creationists take genesis quite literally, to the extent of postulating that nearly every geological event has an explanation in the so called “Noachian” flood.  These are religious views, however, and not shared by the scientific community.  The vast majority of the scientific community do not see the biblical account of creation described in the book of Genesis as a meaningful source of scientific hypotheses.

From a the perspective of a contemporary scientist, to take the Book of Genesis as a scientific document, as creationists have done, is misguided for a variety of reasons.  

One reason is that the book details supernatural events.  Contemporary science seeks to explain phenomena based upon reproducible, repeatable, and potentially comprehensible patterns.  Supernatural explanations, very common in ancient and medieval cosmology, are no longer considered to be valid science.  We no longer consider it fruitful to explain a phenomenon in terms of forces that are inherently beyond our understanding.  Supernatural thinking gets us nowhere.  

Another reason is that, in order to be a good scientific hypothesis, it should be possible, at least in theory, to demonstrate that the notion is wrong.  This notion of falisifiability is central to contemporary science, because it allows us to put our notions of reality up to the test and see which ones hold up.  The book of Genesis, being a religious doctrine, is also unfalsifiable.  It is central to a great many divergent religious doctrines, and as such, will not be abandoned by its adherents.  Any potential test of validity by such an adherent will be explained not as a failure of the supernatural, but as a failure of the investigator or the investigation.  The rules must be rewritten because the belief cannot be abandoned.  Unfalsifiable notions, “Truths” that must be accepted regardless of the facts, violate the fundamental tenets of contemporary science. 

Objectivity, and the lack of it among its proponents, is another reason for rejecting Genesis as a scientific document, or at least rejecting any hypothesis test conducted by believers.  The religious doctrines surrounding the biblical book of Genesis police its validity.  To deny the reality of the events described therein is believed by some to carry the potential for terrible supernatural punishment in the afterlife.  That, in and of itself, virtually guarantees that the document cannot be taken as any kind of scientific evidence.  By its very nature, it motivates any believer to create hypothesis tests that appear to confirm its validity.  The scientist cannot be objective, or even skeptical, without a substantial threat to their view in the eyes of the creator.  

I think it quite possible that this fear of supernatural punishment is the motivation behind earnest attempts by those few scientists with creationist beliefs to demonstrate the validity of the biblical account of creation, and to persist in such attempts despite an almost complete disconnect between the events detailed in the book of Genesis and any modern scientific understanding of our solar system and our universe 

Would it be a useful exercise to consider the book of Genesis to be a scientific document, generated several thousand years ago by the mind of god acting through the oral and literary traditions of humans, full of potentially testable hypotheses, each potentially confirmed by astronomical, biological, physical, and anthropological discoveries made since then?  Are there testable hypotheses in Genesis, waiting for the right observation?

Perhaps we should take the Book of Genesis as a scientific hypothesis, formulated approximately four thousand years ago, and see how well it holds up to the scientific observations we have conducted since then.  If there is a strong correspondence between its predictions, and later observations, we can conclude that it has some validity.  Maybe we have found scientific proof for the existence of god.  If there is little or no correspondence, we must be reasonable and toss Genesis into the scientific trash heap.   

From the onset, the Book of Genesis gives the clear impression that the Hebrew conception of the universe was thoroughly thoroughly anthropocentric, quite small, and subject to laws and mechanisms that were quaint even by the standards of the more literate societies of the time.  I take these lines from a New American Bible, St. Joseph Edition, but the more famous King James Edition translates the same passages somewhat differently.  This issue, translation from ancient Hebrew, presents its own difficulties, which I will discuss later.

Though variously translated into English, the oft-quoted first line of Genesis reads as follows:

“In the beginning, God created the heavens and the earth, the earth was a formless wasteland, and darkness covered the abyss, while a mighty wind covered the waters.”

This line reveals the ancient Hebrew conception of the ocean as a wasteland.  Being landlocked, mostly nomadic, pastoralists, they knew of no life that could exist under the ocean, and viewed a dark world filled with ocean as a hostile, primordial, place.  From an anthropological point of view, it would be sensible to hypothesize that he Hebrews borrowed and adapted their model of cosmology, and their origin myth, from their neighbors.  In fact, many elements are held in common between Genesis and the Babylonian story of Earth’s origins.  This is exactly the sort of thinking I am trying to avoid here, however.  We are to take the book of Genesis literally, an accurate account of God’s creation transmitted to the minds of the ancient Hebrews, perhaps about 3000 BCE.  

From the first line, we can draw two of predictions;

PREDICTION  ONE: At its origin, the earth was totally and permanently dark.  It harbored an ocean and an atmosphere.  

PREDICTION FALSIFIED:  Nobody was there at the origin of the earth, but the current scientific model for the formation of the solar system is well-supported by several lines of astronomical and geological evidence.  Solar systems, including our own, form from the collapse of interstellar clouds of gas and dust.  Stars are forming today, and telescopic observations of some of them, such as Vega, have indicated that rotating disks of dust, laced with debris, are condensing into planets as I write this.  The best evidence we have indicates that earth aggregated together from millions of tiny grains of dust, which formed larger objects called “planetesimals”.  The aggregation of these particles released an enormous amount of heat, through the radioactive decay of elements, and the initial surface of the earth was molten for a period of time sufficient to allow the heavier elements to sink the bottom.  As large objects formed from these smaller dust grains, the Earth was bombarded by objects, ranging in size from grains of sand to mountains, more or less constantly.  Early in the process, the earth must have developed a hydrogen atmosphere, which was blown off by radiation from the sun, and replaced a few million years or more later with a new atmosphere, and ocean, resulting from outgassing of volcanic gasses.  The vulcanism, and to a lesser extent, bombardment by meteors, continues to this day.

     

This sounds like the stuff of a great creation myth, but curiously, genesis says nothing about this.  On one hand, it is very likely that early in its history, after the crust cooled, the earth developed a very impressive ocean.  It is possible that large continents did not form until hundreds of millions of years later, and the extensive vulcanism must have given rise to irregular and unstable weather patterns.  However, a young sun shown in the sky, and there was never a time when the earth existed without a sun.  From the perspective of current science, an ocean, or an atmosphere, without a sun, is completely impossible.  Without a sun, the atmosphere would freeze.  So would the oceans.  The earth would go careening into space, and there is no chance that it would be part of a solar system with other planets, in regular coplanar orbits, as we observe them today.  If you take this passage literally, you have to count this as a falisfication of the Genesis model, which fails to mention dust clouds, planitesimals, outgassing, radioactive elements, or anything exciting like collisions with asteroids and protoplanets.  Even if we are to discard these events, since they have not been directly observed, Genesis is completely wrong in its postulation of an earth without a sun.

PREDICTION TWO: The earth was here at the beginning of the cosmos.

PREDICTION FALSIFIED:  Many diverse lines of evidence suggest that the Earth and the solar system are approximately 4.5 billion years old.  Other lines of evidence, too numerous to mention, suggest that the universe is older, approximately 12 billion years old.  The big bang model of the origin of the universe is supported by several lines of evidence, including a pervasive, universal red shift in the spectra of distant galaxies, indicating that the universe is expanding and has been continuing to expand for a very long time.  The oldest stars, and galaxies, we can see, are 10-11 billion years old, something we can infer from their red shift.  Astronomers have dated globular clusters in our galaxy at close to that age.  Generations of stars came and went before the origin of the sun, these generations seeding the universe with the heavier elements from which our planet is built.  Contemporary astrophysics has determined, quite conclusively, that all of the atoms in the universe heavier than hydrogen and helium, come from the centers of exploding stars.  The bible says nothing about the big bang, the origin of subatomic particles from more exotic high-energy states that existed early in the universe’s history, its progression from a hot place full of exotic radiation and strange particles to a cooler place full of the types of matter and energy we experience today.  Genesis says nothing about other solar systems, or how the galaxy coalesced from clouds of early gas and protostars.  Yet, these events are well supported by contemporary astrophysics.  We can measure the microwave background resulting from the big bang.  We observe a shift in the spectrum of distant galaxies because the universe continues to expand, billions of years after its origin.  Even if it turns out that the dominant paradigm in astrophysics, the big bang theory of the origin of the universe, is subverted, we must conclude that genesis is falsified simply because the bible states something that is flatly wrong.  The universe did not begin with the earth, it was here before.

The next line is even more famous than the first:

“And God said ‘Let there be light’ and there was light.  God saw how good the light was.  God then separated the light from the darkness.  God called the light ‘day’ and the darkness he called ‘night’.  Thus, the evening came, and the morning followed-the first day”

PREDICTION:  Day and night, as we experience them on Earth, are a fundamental attribute of the cosmos.

PREDICTION FALSIFIED:  Day and night are a subjective phenomenon.  The ancient Hebrews were unaware that the Earth was a sphere, and that when night occurs, light from the sun is effectively blocked by the mass of earth underfoot, and that when day returns, it is the rotation of the earth, bringing the viewer into sunlight, that causes this.  As I type this, during the day, it is night in Bangalore.  I can email friends in Moscow and verify this firsthand.

Next Line.

“Then God Said, ‘Let there be a dome in the middle of the waters, to separate one body of water from the other.”  And so it happened.  God made the dome, and it separated the water above the dome from the water below it.  God called the dome ‘the sky”.  Evening came, and morning followed-the second day.

PREDICTION:  The Earth has a dome over it, a physical object that makes up the sky.  Above this dome is water, somehow held back by this dome.  The major bodies of water on earth have somehow been separated from it.  

PREDICTION FALSIFIED.  The sky is not a physical piece of architecture.  It is a gaseous envelope.  There is no vast ocean of water just beyond the sky.  In fact, the clouds of water vapor we can easily observe from earth make up a very small proportion of the water on the earth, much less than the ocean.

It is quite clear at this point that, to take the book of Genesis seriously as a scientific document, one has to reject nearly every aspect of our understanding of the Earth, its shape and size, the nature of its atmosphere, and its age.  Genesis predicts an essentially flat earth, with a dome over it, and an ocean of water above a physical dome.  Many aspects of our everyday lives contradict this.  Anyone who has seen a satelite weather forecast has had an everyday experience that contradicts Genesis.  Even as this account was being passed from one generation of Hebrews to the next, the Greek scientist, Animaxander, was demonstrating that the Earth was indeed spherical.  From a scientific perspective, Genesis has been falsified for nearly three thousand years.

The next line reads:

“‘Let the water under the sky be gathered into a single basin, so that dry land may appear.’ and so it happened:  The water under the sky was gathered into its basin, and dry land appeared.  God called the dry land ‘The Earth’ and the basin of water he called ‘The Sea” and he saw how good it was.”

PREDICTION:  The continents of the earth result from the spontaneous formation of an ocean basin.  The oceans receded from the continental land masses.  

PREDICTION FALSIFIED:  There is no geological evidence for this, in fact, available evidence suggests that the contemporary continents, as we see them, are composed of lighter crustal material that effectively floats upon the Earth’s mantle.  The ocean basis could not have been excavated from them.  Geologically, they are composed of different minerals, and are recycled by tectonic activity as new ocean basin is pushed up from the Earth’s mantle and older basis in subducted beneath the continents.  There is no excavation activity we can observe, nor is there any evidence that such events ocurred in the past.  What evidence we have suggests that the continents originated as patches of crustal material called “cratons”, which have gradually accumulated area as smaller expanses of continent, island chains and the like, have been brought into contact with them by tectonic activity.  Mountains can be pushed up by tectonic activity, this process continues to this day, and new continental material can take shape as sedimentation erodes these structures and forms new sedimentary rock, but no process excavates the ocean basins so that dry land can form.  It is becoming apparent, at this point, that the originators of this document had a very limited knowledge of geography.  There is no single basin called “the sea”, in fact, there are many ocean basis on the earth, and many lesser bodies of water.  Not all bodies of salt water occupy deep basins, for instance, the Red Sea and Persian Gulf are quite shallow, relatively speaking.  Huge bodies of fresh water exist, with no apparent origin so far.

Next line.

“Then God said, ‘Let the earth bring forth vegetation: every kind of plant that bears seed and every kind of fruit tree on earth that bears fruit with its seed with its seed in it.’ And so it happened:  the earth brought forth every kind of plant that bears seed and every kind of fruit tree on earth that bears fruit with its seed in it.  God saw how good it was.  Evening came, and morning followed-the third day.

PREDICTION: Angiosperms, and most likely gymnosperms as well, were created by a supernatural power, after the origin  of land, but before the later appearance of the sun.  

PREDICTION FALISFIED:  There is no evidence of a sudden appearance of gymnosperms, worldwide, before the origin of other life forms.  The fossil record contradicts this in the most unequivocal way.  Life existed for millions of years before the first terrestrial plants, and the first plants did not bear seed or fruit, they produced spores.  Various aquatic forms of vegetation existed before these plants, for hundreds of millions of years, and before that, photosynthetic prokaryotes.  Curiously, the biblical book of Genesis does not provide an account of the origin of life.  The first living organisms mentioned are sophisticated photosynthetic life forms, interdependent with fungi, bacteria, and insects for their survival.  It is not clear when insects originate, and it seems obvious to any reader versed in ecology that the originiators of the document lack any understanding that vascular plants, in order to produce fruit, generally require insect pollinators.

How much farther do I need to go?  There is a second, contradictory creation myth coming up soon.  A good theory does not contradict itself.

It has always been my belief that to take the biblical account of creation as literal truth is laughable from a scientific perspective, but unfortunate from a religious perspective as well.  Genesis was written by a variety of authors, entirely unknown to history, many from nonliterate societies, spanning a considerable amount of time.  It is a nuanced and complicated document, originally written in an ancient language very different from the english of the King James Version of the Bible, and conceived by authors with the limited and idiosyncratic perspective of ancient nomadic and agricultural peoples.  

Though it has been evolutionary biologists who have taken the brunt of the attacks by creationists, it is easy to demonstrate that a literal interpretation of the biblical story of creation runs contrary to our contemporary understanding of astronomy, physics, mathematics, chemistry, history, anthropology, and just about every other science.  It should also be obvious that to take genesis as literally true is to assume that the majority of human beings who occupy the planet, as well as nearly all of those who have come before, are simply wrong in their own religious or scientific beliefs.  If Geneis is literally true, the Hindu account of creation clearly must be wrong, as must be every Native American, Polynesian, or African account of creation.  God is a male entity, an we live in a universe in which one small group of tribal peoples, living in a narrow window of time, has been favored over all the humans who have lived before or since.

From a theological perspective, it is nonsensical to imagine that a document of such subtlety, containing loaded passages and mysterious contradictions, was intended by a supernatural power as a literal account of anything.  I have read the bible a few times, but I do not pretend to be a theologian.  It is clear, however, that  the various authors, both those that transcribed ancient oral traditions, and those late authors that collected written material into a single account, rejecting books and passages that did not fit established doctrine, were not literal thinkers, and intended their document to be strange and full of interesting allegories.  Religious books must maintain a sense of mystery to them.

No Zombies

Today I woke up in a world without zombies. No machete under my pillow. A baby slept next to me, foot shoved under my chin. She was not breakfast, some desperate attempt to stay alive. She was to live in a world without the terror of the undead, smashing their skulls against the too-fragile doors of our house, a world without deadly rays from space animating the dead. There was coffee, that wonderful tropical seed, roasted and shipped thousands of miles, something impossible in a world where rotting corpses stalk the jungles and hide buried in the soil to devour the passerby. Running water, electricity, even a working automobile outside. I decided to be grateful for all of it.

Life

I stole this text from a paper I wrote nearly ten years ago. It is fun though, and worth reprinting as a blog. The paper itself is permanently unpublishable, because thought it was actually ACCEPTED FOR PUBLICATION in a very prestigious planetary science journal, the editors wanted me to do stuff with the model I wrote that are just plain impossible, given our current state of knowledge.

The Drake equation predicts the approximate number of intelligent, technological, civilizations in the galaxy at any particular time (Shklovski and Sagan, 1966);

(1) N=R_f f_g f_p n_e f_l f_i f_civ L_civ

when N=the number of technological civilizations, R_f =the rate of star formation, f_g =the fraction of stars able to sustain habitable planets, f_p =the fraction of such stars with planets, n_e =the number of habitable planets per solar system, f_l =the fraction of these planets that support life, f_i =the fraction of these planets on which intelligent species evolve, f_civ =the fraction of these species which create technological civilizations, and L_civ =the average lifetime of such a civilization.

These parameters touch upon diverse areas of human knowledge such as astronomy, biochemistry, evolutionary biology, and anthropology. A few are known to an order of magnitude. Others are outright guesses. Although of limited predictive value, the Drake equation it is an interesting heuristic tool. It allows us to organize ideas about how each factor might influence our likelihood of someday encountering another intelligent civilization.

Advances in astronomy, planetary science, and biochemistry have shed light on some parameters, including R, f_p, n_p, and perhaps even f_l. Some analyses are sobering, such as a computer modeling study by Michael Hart suggesting a star’s so called “habitable zone” may be very narrow (Hart, 1979; but also see Kasting et al., 1993), and Shiv Kumar’s theoretical study suggesting stable planetary systems may be uncommon (Kumar, 1974). Orbital eccentricities of recently discovered planetary systems seem to support Kumar’s prediction (Resio and Ford, 1996; Glanz, 1997).

Other areas of research have provoked a resurgence of optimism, such as the discovery of planetary systems around a growing number of nearby stars (i.e., Mayor and Queloz, 1995; also see Schilling, 1999). Discovery of complex communities of organisms associated with deep-sea hydrothermal vents, deep under the Earth’s crust, and in a growing variety of exotic microenvironments, has provoked speculation that suitable environments for life may be more abundant in the galaxy than once thought (Vogel, 1999). Additionally, there is growing geological evidence the Earth underwent at least two periods of global glaciation (Hoffman et al., 1998; see also Warwick and Howard-Williams, 2000). The survival of life on Earth through such an event suggests Hart’s definition of the habitable zone may be unduly narrow, and supports Kasting’s et al.’s less restrictive model for the habitable zone of a terrestrial planet (Kasting et al., 1993).

SETI searches are designed to detect intelligent life, and these findings naturally beg the question of what fraction of life-bearing planets might ultimately be expected to produce an intelligent species.

F_i, the fraction of life-bearing worlds that should ultimately be expected to develop intelligent species, remains one of the most nebulous parameters of the Drake equation. Values cited by various authors range from approximately 1 (Baugher 1985, Mentzel 1965), to .1 (Sagan 1973), to essentially zero (Simpson 1964, Mayr 1985).

Diversity of opinion is inevitable, considering that an intelligent species has evolved exactly once (of which we are aware), on the one planet that we know sustains life. The prevailing view among astronomers and physicists has been that f_i should equal approximately 1, since greater intelligence is (supposedly) unconditionally adaptive and confers greater possibilities to the organism. By contrast, evolutionary biologists have been pessimistic about the probability of intelligent species evolving on other earthlike planets (see Mayr, 1985). This view is based upon the notion that, given a replay of the Earth's history for the last few hundred million years, the odds against the evolution of anything like a human being are virtually nil.

While the first view is ill founded from a biological perspective, the latter view might prove to be unduly pessimistic.

Natural selection does not inevitably favor increasing intelligence. For any given organism, greater intelligence is usually maladaptive, since it carries a high cost in terms of energy and increased developmental time. This is one case of a widespread phenomenon is known as stabilizing selection ( ). Since the benefits of increased intelligence are balanced against the disadvantages of higher energy cost and slower development, intelligence remains stable over long periods of time. As an example, the human brain uses up to one sixth of the resting body’s energy budget (Smith, 1984), a fraction that would be unacceptable to organisms with different life histories. Large, warm-blooded animals with relatively high intelligence have slower developmental times than simpler organisms and are often more vulnerable to extinction.

Two influential evolutionary biologists, George Gaylord Simpson and Ernst Mayr, have argued that extraterrestrial intelligence is unlikely because the odds against the evolution of anything like a human being are virtually nil. This argument does not preclude the existence of intelligent species on extrasolar planets, since we do not expect an intelligent extraterrestrial to resemble a human being. There is no need to recapitulate the evolution of our own species to produce intelligence. Even on a planet identical to Earth such an event would be inconceivably improbable. It is more appropriate to ask; given a planet like Earth, how probable is the eventual evolution of at least one species with the human grade of intellect?

Studies of animal cognition suggest that the human mind differs from those of other animals largely in matters of degree (Wilson, 1975; Budianski, 1998, Butterworth, 1999). In the macro-evolutionary sense, human intelligence can be viewed as the endpoint of a long random walk that ultimately produced one species with an exceedingly complex nervous system. With the increasing diversity of species on Earth, the most complex animals on Earth have become more complex for the last 540 million years This does not imply that evolution is an inevitable march to complexity, and most terrestrial life forms exhibit simple behavior.

The evolution of increasingly intelligent forms is not unique to our own lineage of animals. The most recent common ancestor of humans and cephalopods (octopi, squids, and their relatives) was comparable to a flatworm, yet cephalopod nervous systems share much in common with our own, including image-forming eyes and reliance upon learned behavior. There may, in fact, be an infinite number of evolutionary pathways that ultimately produce intelligent organisms.

Periods of rapid speciation foster the diversification many different lineages of organisms. Within each lineage, species spread along axes of behavioral and morphological complexity determined by their development and body plan. (see Valentine and Campbell, 1975; Valentine, 1992). These adaptive radiations depend upon novel adaptations, or "evolutionary innovations". Evolutionary innovations enable the temporary escape from interspecific competition, and allow many new species to proliferate and replace existing ones.

For example, the evolution of a chitinous exoskeleton and jointed appendages allowed one (or perhaps several) marine annelid-like organism to diversify into the vast array of arthropod forms, each with a different ecological niche. This, in turn, facilitated the invasion of land by arthropods, and the spectacular adaptive radiations of the insects. Each novel adaptation is built upon previous ones, however, and they constrain the future evolution of a lineage as well as facilitate it. Returning to insects as an example, the geometry of the chitinous exoskeleton and the design of the insect respiratory system are excellent means by which to supply a small organism with mechanical support and oxygen. While fostering their enormous success, both adaptations constrain insects to a relatively small body size. This and certain other features of insect development constrain insect nervous systems to simple but efficient structures that make due with a limited number of cells. Social bees have existed on Earth for perhaps 40 million years, since the Miocene. In this time, they have evolved a wide range of problem-solving behaviors, interesting architecture, and complex societies. It is doubtful, however, that any of them will ever build a radio telescope (but not impossible, as I will discuss later). This because insect nervous systems are constrained to a mere 7000 neurons or so, compared to the fifteen billion neurons of the human nervous system.

Evolutionary constraint is critical to the evolution of intellect, which is the product of multiple sequential adaptive radiations. Each radiation is built upon an evolutionary innovation. Some facilitate greater neurological integration and behavioral complexity (i.e., the vertebrate neural crest, a tissue that gives rise to our brains and a wide range of other specialized tissues). Others may be only peripherally related to intelligence (i.e., the tetrapod limb). Each novel adaptation has the potential to stymie the evolution of greater intellect much as the arthropod exoskeleton ultimately stymied the evolution of intelligent insects.

On Earth, there are a limited number of independent lineages, which compete for ecological niches in the biosphere. Each lineage has a different body plan. By number, and possibly by numbers of species, most terrestrial organisms are prokaryotes such as bacteria, cyanobacteria, and archaeans. Our own lineage, the eukaryotes, is one branch in the early adaptive radiation of terrestrial life. Since there are no truly multicellular prokaryotes, we can guess that eukaryogenesis carries with it features necessary for the later evolution of multicellular life. Had another group of organisms displaced the eukaryotes early in their evolution, multicellular life might never have evolved on Earth.

Among multicellular lineages, there are many protists, the fungi, plants, and animals. Fungi and plants have adaptations that, although tremendously useful, prohibit their eventual evolution of intelligence (in both cases, their cell walls obviate the need for a central nervous system, since they restrict them to an immobile lifestyle). There may have been as many as 100 animal phyla in the past, of which approximately 25 remain. Most of these major phyla arose at a certain critical period approximately .7 billlion years ago to .4billion years ago, and subsequent diversifications of animal life have been built upon these plans. Likewise, the evolution of classes within phyla and families within classes has slowed considerably, so that new species almost inevitably arise from existing body plans that arose 540 million years ago.

Given these major body plans, the biosphere cycles through an enormous number of species. Conservatively, there are perhaps 10 million species on the planet right now. This number represents a small fraction of the total species that have ever existed. Although speciation and extinction rates vary considerably among taxa, species tend to last between 1 and 10 million years before going extinct.

In 2000, I came up with an intentionally oversimplified model to produce a guess as to this figure. I basically used taxonomic trees from biology textbooks as my data, and based my guess on the negative binomial distribution. This is the same distribution that tells you how many times you are likely to be able to flip a coin till it lands on tails. I basically assumed that each branching event was like flipping a coin for a while, trying to get a string of ten or fifteen heads, and no tails (not a fair coin, the odds of a lineage loosing the ability to evolve intelligence were higher than a bump in that direction, but there was a neutral state as well-it was a three headed coin-where landing on tails meant that a whole branch on the tree of life had to stop flipping), each flip, however, led to a branchpoint, so that there were multiple chains of coins flipping at any given time, but the descendants of a lineage that came up tails were always there, competing with the others, but fated to never evolve intelligence. I used a lot of C++.

I plugged a lot of data from guesswork biology into the thing, and my figure was .01. Just my guess. It is interesting to note that, although just under one percent of planets actually produce an intelligent species some time in their histories, we should not expect one percent of planets to actually harbor them. The proportion of habitable worlds sustaining an intelligent species at any given time should be much smaller. This is because any given species survives only a small fraction of the planet’s history. The average lifespan for a terrestrial mammal species is 1.5 million years (Savage 1988). Once established, however, intelligent species would tend to give rise to other intelligent species, increasing the duration a planet harbors intelligent life. If successful, a single intelligent species might give rise to an entire family of intelligent forms. The lifespan of a typical terrestrial vertebrate species is approximately 23 million years (Savage 1988). This is still a very short time compared to the lifespan of an entire planet, but long enough to suggest intelligent species from different solar systems might have time to come into contact by some means (perhaps with biological descendants of the species that initiated the communication).

Even if intelligence is short lived, the proliferation of intelligent species might have major implications for the evolution of technological civilization. Although the first intelligent species on a planet may have limited aptitude for technology due to behavioral and ecological traits inherited from its ancestors, subsequent species might overcome these obstacles. This is exactly the process that produced our own species. Although we are the lone intelligent species (of which we are aware) on Earth at present, our species is the product of an intense but short-lived radiation of African Homonids. This radiation quickly (in geological time) gave rise to Homo sapiens, a species which has subsequently developed sophisticated technology and transformed the biosphere.

Our species may be unusual in this regard. Once intelligence has originated in one species, the proliferation of intelligent species may continue for a long time before a technological civilization arises. Technological species that originate from established families of intelligent life forms would share the world with tens or hundreds of fellow thinking beings.

August

Summer and late summer again.  Sunflower season ebbing, and I find myself waiting for goldenrod.  That is the end of it, the goldenrod, setting fluffy seed when halloween decorations go up.  This is the time when my ancient ancestors took in the harvest.  Survival for now no matter what, even the leanest harvests would keep a person alive till frost comes.  Tomatoes now.  A fan buzzes quietly, like the agnostic pencil-chipper at my grandmother's house.  No symbol of late summer is as resonant to me.

I wonder about old Tethys, about goldenrods blooming on the shore of that dying ocean as it finally closed up in Cimeria.  I also wonder, every moment, what strange attributes will materialize in the mind of the tiny being who sleeps in my lap as I write this.  Today, she blindly grabs for gouramis through the glass of a pet store tank, desires to stay awake forever, plays with shoes.  Tomorrow? She is just as actual as I am now.

An array of forces are massed against me

it is true, and my allies may prove to be unreliable. the dinosaurs we ride are hungry and unpredictable. our axes are rusty. there are too many orcs. it will be a matter of surviving onslaught after onslaught, and waiting for them to loose interest in their campaign of conquest. what brought me here. poor bookkeeping or encroaching mental illness, or perhaps the collective mania that brought all of us to this? this citadel will stand.

on other news...Chicago lacks a volcano, still, because the geothermal hotspot for this great continent still selfishly lurks under yellowstone. to see a volcano in Lake Michigan would brighten my day, perhaps by inking out the sky in magnetic ash.

the nugget grows into a fun little companion, crawling in a fresh diaper and an avocado-stained t-shirt across the living room floor. she is bright enough to loose patience at an empty bottle of formula, or a full one not put to good use. she likes the garden. she hates the vacuum.

dream.

oh, nugget

oh nugget.  you are a person of such strong feelings, especially about rolling around on blankets between mom and dad, popping off little smiles like a baby discovering clever super powers manifest in a world of cherry and rambutan baby food and bouts of horror strapped into a baby car seat.  such bleak loneliness, all that, with no means of judging how long squirm time must stop.  your first brain freeze, a notion of temperance, that too much of a good thing can somehow be bad, i confess i mostly understand that particular paradox in terms of photosytnthesis and cell division.  so many uses for bbrain cells, and the most stark realization ever, that things like ice cream get used up and somehow come to an end.  cry about that one, it never stops.  this six months, an eyeblink in a world of bills and semesters, an eternity for you, in nugget time, measured in smiles and objects chewed.  a tooth.  soon more.   a little friend to me now.