Ask A Scientist© Biology Archive

Author:      Danielle Wilson
Text:        What proof is there for Evolution?

Response #:  1 of 2
Author:      Dr. R. Topper
Text:        First let me say that I am not a biologist, but a chemist.  So I 
do not have a very detailed answer to your question.  I first want to say that 
scientists have a very special meaning for the word "proof."  In fact, it is 
so difficult to "prove" a scientific theory that I can honestly say that there 
are NO pieces of scientific knowledge that have actually been "proved."  
Scientists come up with a theory, and then they test it in as many ways as 
they can, looking for evidence or information which will either prove the 
theory to be impossible, or maybe verify some of the theory's predictions, or 
change the theory a little.  Most theories start out because someone has done 
a lot of experiments, or a lot of studies, to look at something, and then they 
make a general guess as to how that thing works.  This is called a "theory" in 
science.  However, if we guess how things are based on what someone else tells 
us, or based on what we read, that is not a "theory" to a scientist but a


"guess."  After all of that, I guess you would like to hear some EVIDENCE 
supporting evolution.  One piece of evidence is based on our DNA molecules.  
Every single cell in our bodies contains DNA, a special molecule which 
literally makes us what we are.  Our DNA is almost EXACTLY the same as gorilla 
DNA, and is even closer to DNA obtained from fossils of ancient ancestors of 
human beings.  There is much more evidence, but I will let the biologists take 
over.

Response #:  2 of 2
Author:      Jim Murray
Text:        Dr. Topper is right that it is hard to prove a theory beyond 
doubt.  This is particularly true in science because scientists can be very 
skeptical.  The approach many scientists take is to try to disprove a theory.  
That way they know it is false.  Evolution is a theory that has not yet been 
disproved.  It is always best to define one's terms before explaining 
something.  Evolution, in this context, is how life in general changes over 
time.  There is little doubt that life on earth has changed over time.  It is 
believed that 99% of all the species that have lived on earth, are now 
extinct.  Extinction of a species is one way in which life evolves.  That 
evolution occurs within populations of life forms on earth is well supported.  
Scientists measure gene frequencies and protein structures in a group of 
organisms, and then see how those frequencies and structures change over time.  
Another term you might have heard is "natural selection."  It is not the same 
as evolution.  Natural selection simply means that some individuals reproduce 
more than others, and which leave the most offspring is due to forces at work 
in nature.  If a rabbit made a lot more noise than its neighbor, then it might 
be more at risk of getting eaten by a lynx or an eagle.  If it gets eaten, it 
will not reproduce anymore.  Natural selection has also been shown to occur in 
nature in many instances.  Charles Darwin proposed that this process of 
natural selection might cause evolution in nature.  And that this evolution by 
natural selection could have been the major force that made so many species of 
organisms.  This was a controversial theory then because it was contrary to 
what most people believed about how g-d created each species himself.  Today, 
most all people familiar with the evidence for evolution of life on earth, 
accept it as the best explanation for the diversity of life.  There are two 
large lines of evidence to support this theory.  The first is fossils.  The 
other is HOMOLOGY.  All life on earth, according to evolutionary theory, 
evolved from common ancestors.  All life on earth is related to each other; we 
are all of the same family.  Modern whales have hip bones in their flesh that 
they do not use because they do not walk.  They probably evolved from mammals 
that did walk.  Paleontologists have found a fossil whale called Pakicetus 
that has more developed rear legs.  Older whales should look more like their 
ancestors if evolution is correct.  Without evolution, we could not understand 
why whales have hip bones.  I should also emphasize that homologous structures 
do not have to be used for the same purpose.  Whale flippers and human hands 
are homologous, but are used in very different ways.  Another interesting 
fossil is Archaeopteryx.  This was a dinosaur that had feathered wings, like 
birds.  Bird and dinosaurs have a common ancestry.  This fossil has teeth, 
although no bird has teeth.  It has the skeleton of a dinosaur, but the 
feathers of a bird.  It shows that there was a time when the difference 
between birds and dinosaurs was not obvious.  Birds are the only remaining 
species from the dinosaur line.  Homology is a complicated concept.  It means 
that two structures are similar because they are related genetically.  If two 
structures are similar but not related then they are only analogous.  The 
wings of birds and insects are analogous.  They both are used to fly, but in 
different ways.  They are not related animals.  Many differences between their 
structures make this apparent to the keen observer.  But the wing of a bat and


the wing of a bird are homologous.  They both contain the same bones.  Both 
have an upper arm bone (humerus), both have a radius and ulna (lower arm 
bones), and both have wrist bones and metacarpals and digits.  They were both 
derived from the same genetic plan.  Look up homology in a biology text for 
more examples.  There is a growing mountain of evidence that supports 
evolution.  It will never be proven true because we can not know for sure.  
But by using the scientific method, we can make a good guess, based on careful 
observations of the earth as it exists today.  A long answer to a short 
question.  Because evolution is a complicated theory.  Keep asking questions.  
And do not take anybody's word for it, go out and see for yourself!