Wednesday, October 13, 2010

Difficulties in Understanding Evolution: Dividing Lines of Species

There are many impediments to understanding the theory of evolution.  I really had to struggle out of the misinformation I had gathered about it in order to accept it as fact, and when I did, it was like a cartoon lightbulb appeared above my head.  It explains so much of the world around us!  No doubt many people have always accepted it as fact, and maybe some of the eureka! moment is lost on them.  But there are many people who do not accept it as anything other than an impossible fairy tale.  I believe that many of these doubters have an incorrect idea of what evolution really is (as I once did).  While I am in no position to correct all of the possible misunderstandings of the theory of evolution (I am a layman, and my own knowledge is severely limited), I can offer some helpful bits that I found very insightful.  For now, I will cover just one.

Imperceptible Progression

When someone looks at our ancestor's fossils, there are all sorts of skull fragments and long, confusing names to go with them.  To most of us, it doesn't mean much or help us to understand the importance of these fossils.  We all know about Homo sapiens, and most of us have at least heard of Homo erectus (I specifically remember this one sticking in my teenage mind because it sounded funny) or even Homo habilis.  There are many other lesser known fossil species such as Australopithecus africanus, A. boisei, H. rudolfensis, A. robustus, etc.  These fossils can be dubbed "missing links" in our ancestry, or as just other animals that have no link to humans - it all depends on your viewpoint.

Part of the problem is how we think about and understand what these species were, and what their fossils represent.  If we look at them as distinct species, or islands by themselves in the sea of history, we quickly lose the perspective of the evolutionary process.  That often gives rise to the silly notion that evolution says that a Homo erectus one day gave birth to a Homo sapien.  In reality, Homo erectus' always begat Homo erectus'.  Just like humans always beget humans.  If it is understood in its proper scale of time, each change in species is very small, and impossible to perceive in the moment.  Richard Dawkins, in The Greatest Show on Earth, puts it this way:
"As we trace the ancestry of modern Homo sapiens backwards, there must come a time when the difference from living people is sufficiently great to deserve a different specific name, say Homo ergaster.  Yet, every step of the way, individuals were presumably sufficiently similar to their parents and their children to be placed in the same species."
And just a bit further down the page:
"Think about the first specimen of Homo habilis to be born.  Her parents were Australopithecus.  She belonged to a different genus from her parents?  That's just dopey!  Yes it certainly is.  But it is not reality that's at fault, it's our human insistence on shoving everything into a named category.  In reality, there was no such creature as the first specimen of Homo habilis.  There was no first specimen of any species or any genus or any order or any class or any phylum.  Every creature that has ever been born would have been classified - as belonging to exactly the same species as its parents and its children."
It is people who feel the need to classify everything as to make it easy to reference later.  But this can cloud the understanding of what evolution says really happened to progress these species.  Species are evolving at this very moment, with each generation.  No child is an exact copy of their parent - they vary in many subtle ways.  But there would never be a time where an observer would classify that child as a separate species from its parent.

So if evolution is true, what would we expect the fossil record to show in regard to our ancestry?  We would expect to find the sort of transitional forms that we do in fact find!  The fact that there are several "landmark" fossil species along the way, and not every detailed transition is accounted for should not deter or confuse us.  Not every human ancestor who ever lived has fossilized, but if they had, we could theoretically place each skeleton in succession from the earliest ape to the modern human.  And at any given point in that line, we would see little to no change at all from one to the next.

Monkeys Climb Trees, We Build Ladders

Another important thing to remember is that evolutionary theory puts all living things into a tree, not a ladder.  It is an error of understanding to think that the fact that chimpanzees still exist is evidence that evolution is wrong.  To think that evolution says that life is like a ladder, where there are species just morphing into other species until we get humans is wrong.  Instead of a ladder, imagine a tree.  A tree has many branches, and each of those branches, traced back in time, merges back to the common trunk.  In addition, many branches split from other branches who then split again forming more branches, and any of those branches can split yet again, and so on, until you reach the very tips.  In this analogy, the trunk is the beginning of all life, and the tips of the branches are either the extinction of a species, or the current moment in history.  

Our little branch (and it is little!) can be traced back toward the trunk until it meets the "parent" branch that it split from.  In this case, this split created not just our tiny branch, but it also created another branch, going in a different direction.  This branch belongs to the chimpanzees.  As the tree shows, we did not come from chimps - both we and chimps came from a common ancestor.  The following image shows how this can be imagined with all of our human ancestors:

click image for full size
Provided by Donald Prothero, professor of Geology, Occidental College

If we follow the logic of the the branching tree, we can see that all species slowly evolved from other species, who have also slowly evolved from other species, and so on, until we are back at the beginning of life.  We are all related to each other, every living thing that has ever existed is our relation, no matter how distant.  Trace it far back enough, and you can find the common ancestor that both you and cats share.  Or you and spiders, or you and Triceratops!  Pick whatever you like, we are related.  It's a beautiful thing to realize.

Now maybe I was wrong.  Maybe nobody really has these misunderstandings blocking the way of them really grasping what evolution means.  But for me, these things were not so evident, and when I saw them, and understood them, it brought Darwin's theory out from the realm of the impossible and into the light of reality.

For a great book on the fossil evidence for evolution, check out Donald Prothero's Evolution: What the Fossils Say and Why it Matters.

For a more eloquent explanation of how chimps are related to us, please watch this.

For a wonderful online resource on evolution, click here.
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