Saturday, May 11, 2013


Evolution and Asteroid Strikes


Where would we be without asteroid strikes? 
We might still be here, but we would look entirely different.  Bombardment with asteroids and other space debris was much more common a billion years ago.  At that time life in our ancestral line had reached a worm-like stage that also gave rise to some other forms less like our egocentric selves.  The bombardment had an enormous impact on the course of evolution.

When God created the universe it began as a speck over twelve billion years ago as we measure time.  That speck was endowed with the properties that would spawn several generations of stars and the galaxies we see today.  It had all the potential for the formation of elements and star systems with associated planets as well as the evolution of life as we know it.  Darwin realized this as the work of the Creator before events sped his drift into agnosticism.

I know, from the things science has discovered, some major things that answer a few major evolutionary questions.  It is not because of personal brilliance or planning that I know them.  It is not because of some revelation that I know them.  It is the result of an unusual set of circumstances which I, have blundered into and, now view as God’s direction of the chance events that made it possible for me to put the bits of the puzzle together.

In 1987 two paleontologists (Raup and Sepkoski) published a study of extinction rates that showed high peaks associated with major asteroid impacts.  A regression line, which I calculated from their data, projected back over half a billion years to the beginning of the Cambrian where it reached a 100% extinction rate.  That obviously did not occur because there are Pre-Cambrian fossils, some of which had remains looking much like tubes of pogonophorans, which still live in the abyssal regions of the ocean bottom.

Pogonophorans were able to survive the Precambrian bombardment because they had evolved by natural selection to survive by absorbing nutrients from sediment and lost many of the typical annelid worm features of their ancestors.  They even lost the mouth and rigid early embryological features of their ancestral annelids.  Some changes now evident in their descendants led to, among other things- our systems being upside down as compared to most worms, our fertilized egg’s ability to have each of the early cells survive as twins or multiple births instead of dying when separated, and our pituitary to have its peculiar blend of hormones (the endodermal and ectodermal tissues that form the pituitary couldn't have joined if the pogonophoran pharyngeal region had not been suppressed during the period the former circumesophageal nerves were fusing).

Biologists think ancestral forms are replaced by new forms and cannot be found unchanged today.  But pogonophorans, because of the peculiar features of the deep sea have extremely long lives as individuals and thus those that stayed there evolved very slowly.

Many astronomers have come to believe the moon (Wikipedia, moon formation) started as a result of a collision of the earth with another heavenly body.  They believe the probability is very minuscule, but why bother when it is obvious that the following is much more likely.  The asteroid belt consists of orbiting fragments from a collision of two or more planets, or a planet and another major object, in that region between the orbits of Mars and Jupiter.  The scars on the moon, other planets, and large asteroids show the evidence of past impacts.  This immense accumulation of space debris was sufficient to slow the moon’s rotation so gravity’s effect could bring it to zero rotation with respect to the earth.  The earth’s greater mass was sufficient to keep it rotating even though we probably received more mass from space than did the moon, slowing us from 400 plus rotations per year to 365.  Tidal friction is used to explain the slowing of rotation for both the moon and the earth; but, shouldn't it have been more dramatically slowed for the earth with its oceans if that were true?

So we have cleaned out most of the fragments in earth’s orbital path and have a much reduced probability of an earth shattering strike from outer space than in prehistoric times.  The relative peace with the reduction or cessation of celestial bombardment, the last really major event being the strike that helped end the dinosaurs at the end of the Mesozoic about sixty-five million years ago, left a partial void that was repopulated in part by survivors from the deep sea.  The process of re-population from the deep-sea was much more important as the Cambrian began.

Incidentally, the idea of annelid worms being in our ancestral line was much more popular a hundred years ago.  Our annelid ancestry was rejected because of the great differences in embryology of annelids as compared to the vertebrates and invertebrates sharing our ancestral line starting with the pogonophorans.  When genetic information helped us see that the embryological differences were not the complete answer, the old annelid origin theory was not restored.  DNA/RNA studies are excellent for determining the relationships of closely related organisms.  Nucleic acid studies, as currently performed, have not yet been refined enough to project distant relationships. We know more about distant relationships from other data for widely different groups.

Almost anybody can write a book.  I've written a manuscript for one explaining some of the above.  But it runs counter to popular opinion of most students of evolution.  Why?  Probably because few biologists today have time for the range of course work common in my generation.  I had to dig into the literature on pogonophorans to revise an invertebrate zoology text for a second edition that was published in 1968.  I found that they must live for several thousand or more years, thanks, in part, to my knowledge of marine biology.  I might not have realized that if I hadn't developed an interest in causes of longevity during my doctoral studies (at MSU) comparing Michigan and Tasmanian isopod crustaceans (thanks to a 1956 Fulbright Grant for study at the University of Tasmania).

So the obscure pogonophorans that weren't even known about a hundred years ago provide important clues.  They show up in odd places in molecular studies of evolution because they have changed only slightly genetically while more recent groups have changed greatly.  Thus the great differences between the extremes of more recent groups are greater than the difference between either of the extremes and the pogonophorans.  I know it is due to the ancestral position of the pogonophorans and their extreme length of life.  My evolutionary colleagues think it can be explained away as an anomaly called “long-branch attraction”.

If my argument that major asteroid strikes are remarkably less likely in the future than in the past does not comfort you, consider the following.  If strikes are random, the likelihood of a strike is directly proportional to the area considered.  The mid-February one exploded above Chelyabinsk, Russia. On average, for every 63 that hit Russia, the largest country in the world, only 36 would hit the United States; about 100 would hit Russia while 1 is hitting Michigan; Liechtenstein would get about one strike for every 100,000 to hit Russia.  Kalamazoo is smaller than Liechtenstein, so sleep well tonight.  If you are still worried, remember that the one hitting Russia is only about the second big one to hit in the past one hundred and five years, the other knocked down trees over a large area in Siberia.

Oh, by the way, the regression line that I calculated hit 100% extinction rate at the beginning of the Cambrian, if I remember correctly, projecting forward, it did not hit zero anytime soon.  But with strikes in our area likely to be about once every twenty million years there doesn't seem to be much to worry about if the injuries are no worse than in Chelyabinsk.

Joseph G. Engemann, Kalamazoo, Michigan, Emeritus Professor of Biological Science, Western Michigan University. 

This was written for, but not sent, to the Kalamazoo Gazette letters editor in late February. Edited 5/11/13.

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