Why is it so difficult to reconstruct evolutionary changes from the fossil record?

Question

This is an exam question on evolution. I would have thought it would be easy to reconstruct them.

Answer 1

There are a lot of reasons.

For one, fossils ALMOST NEVER form. Most things that die are eaten by other things, even if it's only by worms, fungi, or bacteria. To get a fossil, then, you have to have very special conditions - getting sucked into a tar pit or being buried in a flash-flood. You have to die in a way that prevents anything else from getting to you. Not easy.

To make matters worse, usually the only thing that a fossil preserves are really hard tissues. Your own body has enough bacteria and the like in it to turn all your soft body parts to mush, even if you are buried in silt. That means that fossils give us very little information about the creatures themselves - if one species had blue eyes and another green eyes we'd never know it. There has been long-standing arguments over whether some dinosaurs had fur or not!

And if all that weren't bad enough, there are lot of things that can destroy fossils even after they are formed. Underground water flows can erode them away. They can be crush and warped with the pressure of other rocks. Or some other creature might think they're nifty and build a nest out of them or something (don't laugh... it happens).

Add all this up and we're probably lucky to know anything about any species at all. And the amount we know about each varies widely - stupid creatures that liked to play in tar pits are easy to find (trilobites), but if you're looking for a clever creature that doesn't hang out near rivers and is mostly soft tissue (human ancestors), you're probably out of luck.

Hope that helps!

Answer 2

The fossil record only represents about 15% of the life that has ever existed, so think of the 85% of creatures that have died since the earth formed that we may have never even seen. So any animal or population of animals (or plants) demonstating a physical difference from its counterpart (in the same species) that would eventually become a trait of a whole new subspecies for example is more likely never to be found as a fossil. The odds against any form of preservation are very low. So recontructing a progression of such changes is hard without any physical evidence.

Answer 3

Ignore fuwad...
But the chances of being fossilized are incredibly slim. First off, an organism needs to die in the right sort of environment: somewhere where this is almost immediate burial by sediments. A lot of dinosaur fossils are found in a lucustrine sediment--dirt laid down by water deposits, like a lake or a river. The beautifully preserved feathered dinosaurs from China are normally found in lake deposits--the animal died, sunk to the bottom of the lake and was promptly covered, preventing immediate decay and allowing today's paleontologists to find these 'feathered dragons'. Once the critter is dead, it helps to avoid being scavenged by carnivores.
I'll try to put it in numbers: if you die, you have roughly a 1 in a 1000 chance of dying in the right environment, avoiding scavenging to become fossilized...another 1 in a 1000 chance of surviving the geologic activity that can occur over the course of millions of years...another 1 in a 1000 that you will be brought to the surface for someone to find.... So for any given individual, its about 1 in a 1,000,000,000 chance of being fossilized and then found. You can see how lucky paleontologists are to find what they are finding and they make new discoveries every year!

Answer 4

YOU HEATHEN!!!! thats cuz 'evolution' doesnt exist, its all a ploy by the liberal devilcrats along with global warming to hand this country and Israel over to Osama Bin Laden, Hes running for president you know! There where Dinosaurs the large two-three story carnivorous mammals and we lived amongst them. We as mere soft fleshy tasty humans had no problem with taming them, for we had Christ on our side! In the Beginning a mere 6,000 years ago, God got bored and said LET THERE BE LIFE and it was good ALL GOOD, WHAT YOU DONT BELIEVE ME! Why this is scientific proof behold my sources!!!!