you're reading...
evolution, Religion, science

Gaps in the Fossil Record

Thanks again to my reader, Russ, for inspiring a blog entry.  In a recent thread, Russ pointed me to a propoganda piece by the Institute for Creation Research.  I say propaganda because actual research has not been forthcoming from the institute since its inception.  Let me make this abundantly clear:  The Institute for Creation Research has not published a single falsifiable scientifically derived prediction which has held up to scrutiny.  Not one.  What they do is publish half truths and outright lies about evolution and the sciences contributing to our understanding of the process.

I’m not going to dismantle this website point by point as I’m sure it’s been done by someone more competent and eloquent than me.  However, I want to address a very common claim by Creation Scientists (sic!).   It is said that the geologic column is incomplete, and that there are huge gaps where there ought to be gradual change.

What these poor scientific illiterates do not understand is that according to the theory of natural selection, we should not expect to find a complete record.  In fact, the very things which cause speciation to occur would necessarily cause gaps in the fossil record.

To begin with, we must understand that speciation is a very, very long process in most cases.  In a single population, it is extraordinarily rare for a new species to just appear.  This is because of interbreeding.  Any new beneficial adaptation is overwhelmingly likely to be quite small, and it is also overwhelmingly likely to spread through the population relatively quickly, in evolutionary terms.

We must also confront a popular notion about species.  Species are not defined by their ability to mate.  Lions and tigers are different species, and yet, they can breed.  Breeding is necessary, but not sufficient, to label a species.  In other words, for something to be considered a species, it must be able to breed with itself, but just saying that two animals can interbreed does not make them the same species.  In determining species, one of the biggest factors involving breeding is whether they do so without outside interference.

With these two things in mind, we can examine how speciation does occur, and what the evidence would look like after millions of years.  In order for a particular population to become different enough from another population of the same species, there has to be isolation.  If there is no isolation, mutations will propagate through the whole population, and there will be no speciation event.  Let’s do a thought experiment with a rodent, some variety of rat.  Let’s suppose that this is a prairie rat, and it lives on a very large island.  Now, let’s suppose that a major geologic event occurs (what it is hardly matters) and the island is literally split in two, with a large body of water in between.  Some of the rats on both sides survived, and now we have two separate populations.

Since mutations occur essentially randomly, we should not expect both populations to continue down the same evolutionary path.  In fact, we’d be amazed if they did.  Instead, we will start to notice slight differences, even if the habitat of both populations is still quite similar.  Eventually, just from time and mutations, we will have two groups of animals that are different enough from each other that they will no longer interbreed if reintroduced.

The effect of culture upon speciation also cannot be overlooked.  The tiniest change in the expression of a gene can cause quite different social behavior.  Since we’re talking about rats, it’s worth mentioning that by introducing a single chemical into the brains of polygamous varieties of rodents, we can make them monogamous.  Since we know that this occurs, let’s suppose that one island of rats becomes monogamous while the other remains polygamous.  This, in itself, would probably be enough for scientists to make a case for a new species, since the two populations would not normally be socially compatible.

However, we’re trying to get at the fossil record, so let’s extend our thought experiment much farther into the future.  We need to imagine that enough time passes so that there are two species that are clearly recognizable by the fossil evidence.  This is only a matter of geologic time, so let’s suppose now that one population grows quite large while the other remains quite small.

Here’s where the trick comes in, and evolution predicts gaps in the fossil record.  Suppose now that the two bodies of land are reunited.  Perhaps sea level drops, and there is now a land bridge.  Again, the method doesn’t really matter.  In any case, if our new giant rats come back across the land bridge, we can easily imagine that they might directly compete with the small rats for resources, and might drive them extinct within only a few generations.  (We see this kind of competition all the time when we inadvertantly introduce species into new environments.)

Now, jump another few million years into the future, and let’s imagine that sea level has risen again, and an archaeologist is digging about on the original site.  What will he find?  He will see small rat fossils through one strata, and suddenly, all the small rats will disappear, and very large rats will take their place — with no intermediate fossils.

As you can see, it is precisely because some kind of separation is necessary for speciation, and because the geology of the earth is not constant, that we should not expect to find, anywhere in the world, a complete geologic column.  All we will ever find is bits and pieces, and we must also reconcile ourselves to the fact that parts of the geologic record are gone forever, reconstituted into the earth’s core, or buried under the sea, or pushed upwards into mountain peaks, only to be eroded away by wind and rain.

Luckily, we are not dependent on the geologic column for our proof of evolution.  The phyolgenetic record can be put together without any need for it.*  That, of course, is a topic for another blog, lest this turn into several chapters of a book.  Before I leave the subject of the geologic column, however, I should point out that we do have complete evolutionary records of several species as they evolve.  When I say complete, I do mean absolutely complete in all ways.  We have the specimens themselves, and we have their complete genetic data.

How can this be?  Quite simply, they’re all still alive.  These are called “ring species.”  The best known of these is the Herring Gull/Lesser Black-backed Gull ring.  If you look at each of these birds, they are quite distinctly different species.  Even non-scientists can easily tell them apart.  The thing is, if you start in England with a population of Herring Gulls and follow them around, population to population, you will journey around the North Pole to North America, across to Alaska, across Siberia, and back to England again.  All along the way, you will find interbreeding groups, but as you travel westward from England, the Herring Gulls begin to look more and more like Lesser Black-backed gulls until you get to the middle of Europe where they are undoubtably not Herring gulls anymore.  If you take one member of each “end group” and put them together, they will not breed.  However, if you follow the chain either forwards or backwards from Herring Gull to Black-backed gull, you get a continuous chain of interbreeding populations.  We literally can see a complete, living example of speciation through separation, with absolutely no gaps in the record at all.

So, thanks again, Russ, for inspiring me for another day.  Take care, my friend.

Herring Gull

Herring Gull

* This is not to say that the geologic column is useless.  Far from it.  Together with the DNA record, the two help us form a very parsimonious explanation of specific events in evolutionary history.  The geologic record helps us explain what we find in the DNA record, and vice versa.  That’s how science works.

Advertisements

Discussion

11 thoughts on “Gaps in the Fossil Record

  1. Hello, I just wanted to tell you that I agree with you beliefs so much. I have a blog where I talk about some of the same things. I’m going to mention your blog in my next post. Hope you don’t mind.

    http://thegayatheist.blogspot.com/

    Posted by Alex Cheney | March 18, 2009, 5:05 pm
  2. There is a slight problem with your rat postulation:

    The gaps argued for proof against evolution aren’t the slight gaps between species. No serious creationist has ever argued that animals lack genetic variability within the confines of their own type. The serious gaps are the ones that deal with biological classes of life.

    Perhaps if your story was about rats who seperated and one population became foxes, but then you would have the same problem that every biologist has… where are the half-fox/half-rat fossils?

    Posted by Rawxor | April 5, 2009, 6:33 am
  3. Rawxor, my illustration will work just as well with rats and foxes as rats and bigger rats. Did you not read further down where I explained the concept of a ring species? I want you to think for a few seconds about the differences between a rat and a fox. Both rats and foxes have a tail, four legs, ears, etc. What is the big difference between a rat and a fox? Foxes are bigger, right? Its snout is longer. Its tail is more… um… fox-like. So, imagine a rat that gets bigger. (Hmmm… hasn’t someone mentioned this before?) While it’s getting bigger, imagine that its snout is also getting ever so slightly longer. Imagine that its ears are getting ever so slightly more sensitive, and starting, by very small degrees, to stand erect on its head. Imagine that its legs are getting ever so slightly longer. Imagine that its tail is becoming ever so slightly less rat-like and more fox-like. If you imagine all these things happening in very, very small increments, you’re not doing anything different than imagining a rat turning into a bigger rat. You’re just allowing for multiple lines of genotype mutations instead of one.

    I’m puzzled by your rather strange assertion that there are serious gaps between biological classes. There are serious gaps in some fossil records, and that is to be expected. Some creatures lived in places where fossil formation was highly unlikely or nearly impossible. Some species lacked hard parts that lend themselves to fossilization. The thing is, there are really great fossil records for many animals. Horses are a great example. Have you never seen these? Take some time and dig into a good textbook. You may be astounded at how many virtually complete records there are. I’ll bet you didn’t know that we have recently found a spectacular fossil of a cephalopod that verified our predictions of how the gladius came to exist as a vestigial shell. We’re constantly filling in gaps as new fossils are discovered.

    Have you ever stopped to think for a moment about what you’re looking for in a “transitional fossil”? Let your brain wander for a moment, and imagine the possibility that evolution happens. If it does, it happens over generations, not within them, right? In other words, a mouse isn’t going to change into a fox while it’s alive. You’re never going to find a “rat-fox” because rat-foxes are not predicted by evolution. Also, consider that foxes are many steps away from rats on the evolutionary tree. You will never find a rat-fox, but you would certainly expect to find a rat-beaver, and lo and behold, that’s what we find. Rats and beavers, both being rodents, are very close to each other compared to rats and foxes. Look around you. Living transitional creatures are everywhere. There are tiny rats, bigger rats, bigger rats, and even bigger rats. There are rats that look a lot more like moles than rats, and rats that look a lot like chipmunks. There are moles that look a lot like prairie dogs. There are rats that swim, and have oily coats and thick tails, and… curiously enough, they look a lot like beavers. Oh, and we put them in a different family than rats, and call them a different “species” because they’re different enough from rats to have their own classification. The thing is, if you take all the living rodents in the world right now, you can see very clearly that there are easy, smooth transitions between them.

    Rawxor, the arbitrary line you draw between “biological classes” exists in textbooks, not in reality. We draw lines because we like to put things in boxes. The evidence is all around you that life is a continuum. Just pick a big clade and have a look at all the various living members of that clade. You can see evolution right now. All you have to do is look.

    Posted by hambydammit | April 5, 2009, 1:04 pm
  4. Hamby says:

    “Rawxor, my illustration will work just as well with rats and foxes as rats and bigger rats. Did you not read further down where I explained the concept of a ring species? I want you to think for a few seconds about the differences between a rat and a fox. Both rats and foxes have a tail, four legs, ears, etc. What is the big difference between a rat and a fox? Foxes are bigger, right? Its snout is longer. Its tail is more… um… fox-like. So, imagine a rat that gets bigger. (Hmmm… hasn’t someone mentioned this before?) While it’s getting bigger, imagine that its snout is also getting ever so slightly longer. Imagine that its ears are getting ever so slightly more sensitive, and starting, by very small degrees, to stand erect on its head. Imagine that its legs are getting ever so slightly longer. Imagine that its tail is becoming ever so slightly less rat-like and more fox-like. If you imagine all these things happening in very, very small increments, you’re not doing anything different than imagining a rat turning into a bigger rat. You’re just allowing for multiple lines of genotype mutations instead of one.”

    PG says:
    Hamby,
    You instuct the reader to let their brain wander and “Imagine” the evolution similar species as proof of evolution.

    Evolution is the only field of science that incorporates imagination into its scientific methodology.

    Posted by PG | July 31, 2010, 11:31 pm
  5. Hamby I did what you suggested and researched Horse evolution. Interestingly enough I read where the curators at the major museums actually pulled the horse evolution displays from the public view because they were so misleading.

    Here is what niles eldridge had to say…

    “The popularly told example of horse evolution, suggesting a gradual sequence of changes from four-toed fox-sized creatures living nearly 50 million years ago to today’s much larger one-toed horse, has long been known to be wrong. Instead of gradual change, fossils of each intermediate species appear fully distinct, persist unchanged, and then become extinct. Transitional forms are unknown” -Niles Eldgridge,

    “There have been an awful lot of stories, some more imaginative than others, about what the nature of that history [of life] really is. The most famous example, still on exhibit downstairs, is the exhibit on horse evolution prepared perhaps fifty years ago. That has been presented as the literal truth in textbook after textbook. Now I think that is lamentable, particularly when the people who propose those kinds of stories may themselves be aware of the speculative nature of some of that stuff.” -Niles Eldgridge

    Maybe you have a better example for me to research?

    ..

    Posted by PG | July 31, 2010, 11:47 pm
  6. Hamby says,
    “Rawxor, the arbitrary line you draw between “biological classes” exists in textbooks, not in reality”

    PG says:

    Hamby, The Phylogenetic tree in textbooks are specific and not simply arbitrary as you incorrectly state. The problem is precisly as you state, its not in reality!

    .

    Posted by PG | July 31, 2010, 11:53 pm

Trackbacks/Pingbacks

  1. Pingback: Gaps in the Fossil Record « Skepfeeds-The Best Skeptical blogs of the day - March 18, 2009

  2. Pingback: A Fertilized Egg is Not a Human Being « Life Without a Net - June 11, 2010

  3. Pingback: Topic Summary: Christian Smackdown « Life Without a Net - July 24, 2010

  4. Pingback: Frivolous Trivia « Life Without a Net - July 31, 2010

  5. Pingback: Archive: A Fertilized Egg is Not a Human Being « Life Without a Net - September 9, 2010

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow Me On Twitter!

%d bloggers like this: