Different Species With The Same "Junk DNA"

The Short Summary

The example below shows that two patterns have been found in the genetics of both cows and whales. Neither pattern is found in mice and horses. This implies that cows and whales inherited them from a common ancestor. I discuss how scientists checked if it was just a coincidence.

The Basic Idea

Most of your DNA is "junk". We call it that because the DNA sequence inside a "junk" region is never used to form a protein. The junk isn't after a Start codon, or else is right after a Stop codon, so the gene expression mechanisms simply never look at the junk. They skip over it. There is also "junk" which is inside a gene, but which is ignored when the gene is used. The details are complicated, but if you are interested, see Section Two of this Talk.Origins FAQ.

Junk DNA is inherited. Suppose we find a pattern in the junk DNA of two different species, and don't find that pattern in other species. Evolution can explain the situation by saying that the two species recently had a common ancestor, and both species inherited this pattern from their ancestor. In short, evolution suggests the family tree:

                ====================== species A without the pattern
 common         |
 ancestor ======|                  ====== species B with the pattern
 species        |   common         |
of A, B and C   ====ancestor===X===|
                    species        |
                   of B and C      ====== species C with the pattern

"X" marks where the pattern arose.

To the best of my knowledge, Creationism does not predict or explain such situations. Since the pattern is in the junk, one cannot argue that the pattern confers any short-term benefit or meets any need.

Of course, coincidences do happen. In the example below, I discuss how scientists checked to see if the pattern they'd found was meaningful or not.

An Example: Whales and Cows

You may have heard that the AIDS virus copies itself into its host's DNA. It can do this because there is a "reverse transcription" mechanism which leaves a so-called retroposon at some randomly chosen place in your DNA. There is a category of retroposon called a SINE (Short INterspersed Element).

A recent study found two different SINEs were present in the Hippopotamus, Cow, Sperm Whale, and Humpback Whale. Neither SINE was in the Red Kangaroo, Human, Mouse, Cat, Asiatic Elephant, Domestic Horse, Pig, or Bactrian Camel. This suggests the family tree

              ========================= kangaroos, mice, etc
  common      |
 ancestor ====|                   ===== cetaceans (whales,dolphins)
              |      common       |
                  that had the    |==== ruminants (deer, cows, sheep)
                  two reverse     |
                  transcriptions  |
                                  ===== hippopotamus

There are a number of ways to check if this is really the case. The first question is whether the patterns are just some random fluctuation of junk DNA. Randomness is ruled out for at least four different reasons.

Next, we have to ask if a retrovirus could have just infected several species. This also can be ruled out.

Next, we ask if the conclusion is believable. Could a land animal have evolved into a whale? The answer is that the land ancestry of whales is a century-old idea, and well-proven without this new line of evidence. The ancestry was originally suggested based on the fact that whales are mammals, with a placenta and live birth and mother's milk. The idea is confirmed (for example) by mitochondrial DNA similarities, by protein similarities, and by fossils of small whales with legs. Also, whales with vestigial hind legs are sometimes born.

Finally, we ask if this conclusion leads anywhere. To be science, it has to make predictions, that can be tested to see if they are right.

The answer is yes. From the standard biological taxonomy, we can predict that only artiodactyls ("even toed" mammals) have the patterns. So, we can test animals that aren't artiodactyls, like cats and iguanas. We can predict that since cows have the patterns, all ruminants should. So, we can test sheep and goats. We predict that all cetaceans have the patterns, so we can test dolphins and killer whales. Furthermore, we don't predict just that dolphins have the patterns. We also predict that dolphins have the patterns at the exact same genetic locations.

In fact, many of these predictions have already been tested, and so far they have always been correct.The Minke Whale, Baird's Beaked Whale, Dall's Porpoise, Short-Finned Pilot Whale, and Bottlenose Dolphin all had both patterns, and in exactly the predicted places. Sheep, the Reticulated Giraffe, the Axis Deer, and the Lesser Malayan Chevrotain also are as predicted.

To sum up: this evidence unambiguously says that whales and cows have a common ancestor.



Last modified: 12 January 2001

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