Tête-à-Tête-Tête

I have stated before on this blog and in other contexts that universal common ancestry is “proven” by multiple lines of very strong evidence. I sometimes take it for granted that most people are at least dimly aware of this, even if they haven’t looked into the question personally in any depth. That is a patently absurd assumption, as a majority of Americans doubt evolution. This is a sad artifact of a program of deliberate deception, carried out largely as a project of fundamentalist Christian churches, dating back to Darwin’s own day. The end result is that many people have been more exposed to people whom they are inclined to trust repeating or casting aspersions on this science than have been to the science itself.

It’s not a very simple issue. It’s difficult for anyone to spend enough time on the subject to get a clear picture of what the hard evidence conveys, despite the fact that the evidence is enormous, and the picture it conveys is strikingly clear and incontrovertible.

I’ve been asked by a skeptic to lay out some sources for the evidence that will back up my claim that anyone aware of the evidence will find that, rather than a leap of faith being required to accept evolution - a giant leap of faith is required to reject evolution.

It is no simple task, but I feel confident that anyone who reads this post and subsequent posts fairly, and checks the claims that seem dubious to them against trustworthy sources until they are satisfied of each claim’s overall accuracy, will find themselves in the same position I am in. That is to say, they will consider universal common descent (UCD) proven beyond a reasonable doubt. Or put more eloquently, they will find it ‘confirmed to such a degree that it would be perverse to withhold provisional assent.’ (-Stephen Jay Gould)

This first post in the UCD series is about the fossil record, discussed very broadly. We learn in grammar school that the fossil record is one of the most important sets of evidence for evolution.

We live in a life-rich world, full of diversity, populated with more varmits, literally, than we can count the species of. In this world, we have an abundance of rocks, whose ages we can estimate. And in many of those rocks, we find the fossil remains of a grand diversity of life that lived here in eras long past. Many of these remains are familiar - or at least similar to organisms that still live today. Others are unfamiliar to modern eyes. But there is a curious point that must bookend the discussion of present life and ancient life. That is the point that the oldest rocks we find show no trace of life. Rocks only slightly younger than those oldest show unicellular life and unicellular life only.

Scientists don’t know how that unicellular life got here. But they know that for hundreds of millions of years, that is the only life that left us remains in the rocks. And, they know, in general terms, how life changed over time so that the unicellular life of 3 billion years ago gave way to the diversity we see today.

I’ve created a chart of now-living organisms, broadly speaking. The chart shows estimations of how old are the fossils that can be found that would be categorized in these groups. I must stress that these oldest fossils were *not* the same types of organisms as exist today. They were different species - different genera - different families. These oldest fossils referred to are only those that carry the signature that makes these groupings unique. Whether it’s mouse, man, or pachyderm we know a mammal when we see one. The oldest mammals on the chart probably resembled mice more than anything else living today, but they were not mice by any useful scientific definition. The point of the chart is to show that before that time, there were no mammals of any sort in the fossil record. And, though there may have been mammals alive prior to that time - perhaps by a few million years - it is very unlikely that there mammals were alive from 300 million years ago to 195 million years ago (a space of over 100 million years) without leaving a single fossil trace. In other words, there was a very long time when there were no mammals on the earth.

If evolution is true mammals could not be here before the reptiles from which they evolved. If we stretch our imaginations, we could think that they could preexist reptiles if they evolved from amphibians or from fish. There are reasons, independent of the fossil record to show us that they could not have evolved from amphibians or fish, but even if we ignore these, we cannot stretch so far as to see how mammals could have evolved from an invertebrate.

If most anything other than evolution is true (one can contrive exeptions - and this has been done) then we could find mammals three billion years ago, find them extinct two billion years ago, and find the wide array of them we see today only in the rocks a million years old or younger. In fact, we could find almost any arrangement of mammals in the fossil record. Instead we find them continuously from a time only about 100 million years after the oldest reptile fossils to the present.

According to evolution, humans must appear at some point after the oldest great ape, since it is the apes from which we evolved (or, cladistically speaking, we are apes). If evolution were not true, there is no reason we should expect not to find humans older than the apes, or even older than the other primates. Humans could be the among the oldest mammals - assuming that they did not have to evolve from reptiles that resembled rodents as much as they did any other non-reptilian creature.

The following chart is not 100% accurate. New fossils are found every day, and occasionally, the “oldest” specimen moves the date back a few million years. The figures behind the chart were gathered in haste, and may not reflect the best scientific values. However, the figures used for this chart are at least close approximations to the most ancient ranges for fossils of each category represented.

The chart is not a very good representation of the various forms of life on Earth. Only a few broad categories are presented, representing the most familiar of our moden flora and fauna. To make a more comprehensive chart would be onerous work for someone who has so little time, and would make following the genesis of individual groupings in the fossil record a difficult task for the reader. I’ve left out all the invertebrate animals, many interesting varieties of vertebrate animals, many interesting varieties of plants, and several other major groups like fungi and protists. Nevertheless, what I have preserved in the chart makes a striking picture about how the set of organisms living on earth has changed over time. Each group makes an appearance before which it is entirely absent from the fossil record for millions or billions of years. Each group appears only after its evolutionary predecessors have appeared - predecessors which, by multiple independent sets of evidence, must be their evolutionary ancestors. There is not a single mammal fossil that is found older than the oldest reptiles. Not a single flowering plant as old as the oldest algae (neither unicellular nor multicellular algaes are included on this chart, but both are much older than anything that appears on it!). Not a single reptile as old as the fishes:

The horizontal axis is scaled as “mya” or million years ago.

Had there been room, I might have included the dinosaurs. Had I, you would have found that the oldest dinosaurs were younger than the oldest reptiles, and the oldestest birds were younger than the oldest dinosaurs. As it is, you can see that birds are much younger than the reptiles (specifically dinosaurs) from which they evolved. If nothing else, let your eyes find the “fish” line, and read upward from there until you reach “modern humans”.

My chart may be a tad sparse, but this same thing can be done ad infinitum with any set of organisms, those still living or those extinct. Each time, the same thing will be found. A vacuum over millions or billions of years, then an appearance some time after the appearance of their evolutionary predecessors.

As I hinted earlier, if we had no other evidence to guide us, we would be able to explain this arrangement in other ways, if very contrived ones. “Young Earth” Creationists, who reject the various means of testing the ages of our rocks, nevertheless must acknowledge that “older” fossils appear in “deeper” strata of rock. They propose that these strata represent depths at which the fossilized organisms were buried during the great flood, and that humans and birds were best at finding the “high ground”. Their model doesn’t speak very well of itself, since fishes should have done at least as well for themselves as aquatic mammals, rather than being among the first buried. And, of course, multiple lines of extremely strong evidence - attested to by all but the most backward of Creationists - prove that our methods of estimating the ages of these fossil rocks may be flawed, but not nearly so flawed as to consistently produce results millions of years off and fitting so perfect a pattern of evolution.

Others - including some “Old Earth” creationists and their more reticent cousins in “Intelligent Design” suggest that God created (or designed) the species in exactly the order that evolution would predict, but without making use of its mechanism, for His own inscrutable reasons. If this possibility seems hopeful now, it should begin to appear less hopeful as we get into some of the other pieces of evidence that come to bear on this question.

For now, this has been a primer on the broadest strokes of evolution as it applies to a few major groupings of living organisms.