Some creationist somewhere is right now making the claim that, “In all the time scientists have been ‘watching’ for evolutionary change, they’ve never ‘caught’ a species transitioning into another one.” Well, the easy response to that remark is that all species, everywhere are in the midst of transitioning — the complicating factor is how damn slow it all is. So I decided to make a picture to bring some perspective to evolution’s immense sluggishness…
Notice the red spot in the top left corner of the image below. That is actually a scaled representation of how long we’ve been on the “look-out” for evolutionary changes, about 150 years. On the scale that we’re working on here, you can see that 150 years appears almost as a dot, but it does have a little length. You can see that the red portion is at the end of a longer, squigglier line that ends at the box labeled “Homo sapiens,” that’s the point on this timeline where our species first showed up (about 200,000 years ago). The next even longer and squigglier line terminates at a box labeled “Homo erectus.” In the current “species” discussions around human evolution, Homo erectus is considered to be our direct previous ancestor, originating about 1.8 million years ago.
Now Homo erectus is very similar to modern humans. It had a brain about 74% the size of Homo sapiens, its forehead is less sloping, and its teeth are smaller — otherwise, not a lot of difference. So consider that timeline. If we wanted to “witness” a change such as the increasing brain size between Homo erectus and Homo sapiens, we would have to be “watching” for the same period of time we have been — times 12,000.
We are not going to see something like an ape giving birth to a human, not ever — no matter how long we watch. Actually, if you see that, get down on your knees and pray, because you have just seen a real miracle and the best evidence for God, ever.
As a footnote, I should mention that over the summer Richard Lenski published a paper in which an E. coli strain he had been working with continuously for twenty years evolved an ability to ingest citrate. Since the lack of citrate transport is considered a defining characteristic of the E. coli species, we may have finally “caught” just such a species-to-species transition in the act. Creationists have been unimpressed — but then, they are the ones waiting for a baby to be born from a gorilla.