Genetic similarity and ... watermelons?

From: (Wesley R. Elsberry)
Subject: Re: Please explain...
Date: 27 Oct 1994 09:34:40 GMT
Organization: Dept. of Wildlife and Fisheries Sciences, Texas A&M University
Lines: 61
Message-ID: <38ns7g$>

In article , JONATHAN REXIN wrote:


 JR> Also something else to ponder... a "Deep Thought" if you will.
 JR> Human DNA is 98% the same as chimpanzee DNA what keeps them from
 JR> being somehow related, also the water content of a watermelon and
 JR> a cloud are approximatley the same, what keeps them from being
 JR> related :)

Let's see how deep this thought is...

DNA is sampled from two species. The sequences are correlated, and a measure of similarity is found. This measure is always less than 100% across two species.

Now, let's sample a cloud's water and a watermelon's water. Let's "sequence" the water molecules... in one, it is H2O,H2O,... and in the other, it is H2O,H2O,...

The "water sequencing" reveals that a cloud and a watermelon are identical. Now, given that clouds and watermelons are not actually identical, what conclusion do we make? Most people will figure out that "water sequencing" is not a good measure of similarity: any two items containing water will give the same "sequence".

Now, let's sequence the watermelon's DNA and the cloud's DNA... What? The cloud doesn't have DNA? What a shock...

In a roundabout way, I hope I have gotten across the point that your "deep thought" is actually rather shallow, more like an empty pie tin at the bottom of a high jump, since the analogy given fails from several different viewpoints to be analogous.

A page by Wesley R. Elsberry