One of the questions commonly asked by creationists of those who study evolution is 'Why are there no transitional fossils?' To a creationist1, a transitional animal is clearly part one animal and part another. They have even been heard to ask, 'Show me a fossil that is half-fish and half-lion'!
This entry explains why there are no transitional fossils according to the creationists' definition - and why it's for a rather more straightforward reason than some people might think.
Time to Imagine
Imagine an album of photos of your family. You are on the front page, your father on the next, his father on the next and so on. Flicking between the first two pages, you and your father are clearly related, since you share physical characteristics such as the shape of your noses or the colour of your eyes. As you flip through the album, going back hundreds of generations2 it is immediately obvious that each family member is related to the next, thanks to their clear similarities. You may sometimes even find you share identical characteristics with some earlier ancestors, even though these traits 'go missing' in between.
On a whim, you stop flicking back and turn straight to your own photo. You pause, and turn back to where you were. Something is wrong. You and the man you were looking at share no similarities. He is short, you are tall, his face is round, yours is square. Yet you know that he is related to you. At some point in the intervening generations, you stopped looking like your ancestors. Fortunately, you have every single generation in between, so it is easy to see the transition between the ancestor and you, and it is easy to prove that your ancestor is your ancestor.
Now imagine the album going back billions of years, including every single generation of your family, all the way back to the first protobacteria. Flick through the album quickly, very quickly, and it's like a movie with excellent special effects: the protobacteria morphs smoothly into you, via several strange shapes on the way. It is still easy to see the change from goo to you. Every photo shows a small transition in the process of change. This is the level of evidence most creationists demand from scientists before they will accept that evolution occurs.
Now add a little reality to the image. Not every one of your ancestors is in the album. Some were camera-shy. Other photos were simply lost. Sometimes the photographer was not particularly skilled, and only took a photo of a head or foot. Over the millennia, the album has suffered as well, and been caught in fires, earthquakes, storms and accidents with dodgy plumbing, and has occasionally been used as raw material for collages3. Some of the photos have been shuffled during the album's violent history, with some groups of pages warped or even turned over. Many of the existing photos are damaged and incomplete.
Your family album now represents the true fossil record: it is still clearly a record of your family, but it is not as complete as you may wish. You will need to use a little detective work to get some of them back in the right order, using extra evidence such as the numbers printed on the back of the prints4. Flick through it now, and instead of the smooth morphing, there are occasional jumps in the images. You look at one 'kind' for a while, then come to a gap, so the image jumps from one form to the next, without the smooth transition being so obvious. The transition from protobacteria to you still happened, you just don't have all the photos to show it anymore. Losing the photos of your ancestors does not mean they never existed. They did exist — none of your ancestors simply appeared without having parents — it's just that the photos have been lost to the ravages of time. If you show the album to other people, they will still see your history, and understand 'where you came from', despite the gaps. The remaining photos show enough of the story to convince them. It is the same with real fossils: although we do not have complete fossils of every single organism that we could claim as an ancestor, the fossils we do have provide enough evidence and tell a compelling enough story that we can confidently say they show the true story.
Now you should understand why there are no fossils which fit the traditional creationist definition of 'transitional'. Each and every fossil is complete unto itself, every organism is a whole living thing, yet every one is transitional between the previous generation and the next.
Why are there no transitional fossils? They are all transitional!