The story of evolution-18: Missing links

About ten years ago, a group of engineering students came into my office. They were taking part in a scavenger hunt during Engineers Week and the one item that was very hard for them to find was a ‘slide rule’. They had little idea of what it was and no idea how it worked or what one even looked like but they knew it was old technology and they figured that I was old enough to possibly own one.

They were partly right. I had once owned a slide rule as a physics undergraduate in Sri Lanka but unfortunately did not have mine anymore.

For those not familiar with slide rules, the standard type looks like a ruler with another sliding ruler attached, and you use it to do complicated calculations. It was the precursor to the handheld calculator but with the arrival of cheap electronic versions of the latter, the slide rule went extinct. I actually owned a more unusual type of slide rule that was cylindrical rather than linear and was like a collapsible telescope. It had the advantage that it was small enough to carry around in your pocket, and being able to whip out a slide rule when the occasion demanded defined the nerds of that time.

The difficulty that the engineering students had in getting hold of a slide rule is due to the fact that when a new technology comes along, the old technology is superceded and devices built using it become extinct because no more units get produced and the old units get thrown away and end up in landfills. As another example of this phenomenon, at Case we have a state of the art Freedman Center where you can take information stored in any form (say phonograph records of any vintage, old 8mm home movies, etc.) and convert to digital formats. The one old format they cannot currently convert is videotapes made using the Betamax format and this is because they simply cannot get hold of any working Betamax players anywhere anymore. It has gone extinct. (If anyone has an unused but working Betamax player they would like to donate to the Freedman Center, they would be happy to take it off your hands.)

Like slide rules and Betamaxes, you would be hard pressed now to find many things that were mass-produced even just a decade or two ago. Apart from those in the collections of museums and idiosyncratic collectors, most other artifacts have disappeared forever.

Imagine an extraterrestrial archeologist visiting the Earth and seeing an electronic calculator. Even if he looks around fairly carefully, he would likely not find slide rules or indeed any earlier versions of such devices and conclude, erroneously, that Earthlings are brilliant designers who went straight from nothing to a fairly sophisticated calculator in one jump.

The analogy with missing links in evolution is obvious. This difficulty of finding well-preserved specimens of old things is even worse with the fossil record in evolution. As an organism evolves to a newer form, the old versions rapidly disappear and become extinct. As Steve Jones points out (Almost Like a Whale, 1999, p. 161), “When we see any structure highly perfected for any particular habit, as the wings and birds for flight, we should bear in mind that animals displaying early transitional grades of the structure will seldom continue to exist to the present day, for they will have been supplanted by the very process of natural selection.”

Even when it comes to fossils, since fossilization occurs only under very special conditions of organism and soil and climate, most of these dead organisms disappear forever and thus it is hard to find a continuous record of evolution. Even if a fossil is formed, the Earth itself is a dynamic system, with its crusts moving over each other, erosion, sedimentation, glacier movement, and even the rise and fall of mountains and oceans, all of which can destroy or bury or hide any fossils unfortunate enough to be in the way. As a result, “We continually overrate the perfection of the geological record and falsely infer, because certain genera or families have not been found beneath a certain stage, that they did not exist before that stage.” (Jones, p. 269) “The Cambrian Explosion [beginning about 545 million years ago], so called, is a failure of the geological record rather than of the Darwinian machine. Its radical new groups reflect not a set of exceptional events but something more banal: the first appearance of animals with parts capable of preservation. Before then, there were soft creatures that decayed as soon as they died. Why shells appeared all of a sudden is not certain.” (Jones, p. 274)

The rarity of fossilization can be seen by the fate of the passenger pigeon. Estimates put the number of them at over nine billion alive during the time of the Mayflower, more than the total of all the birds in the US today. They were still flourishing in the US as late as the times of the Civil War but the species went extinct in 1914 and not a single fossilized specimen has ever been found. If not for the existence of written records about this bird, we would not have known it even existed. (Jones, p. 266)

What gets preserved as fossils tend to be big and hard things like dinosaurs and mammoths, just like it is easier to find earlier versions of cars and ships than of slide rules. But thanks to the new techniques of DNA mapping, we do not have to depend exclusively on fossils to learn about how our ancestors evolved and diverged. DNA can interpolate the gaps in the record much better than even fossils can.

POST SCRIPT: Family Guy‘s Stewie and Brian go to Iraq


  1. shannon says

    I do not believe they have proven evolution to denounce the Genesis account of man. The Big Bang Theory is to simple. Timing is everything.

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