The Possible Role of Nondisjunction in Evolution

A common objection to natural selection as the mechanism for evolution is that while it may act as an editor, it cannot be an author. That is, it may change genetic information through mutation, but it cannot cause genetic information to increase. And they are right, but genetic information can still increase across the generations of organisms through a process called nondisjunction. This occurs when an unequal amount of genetic material is passed on to two daughter cells after the process of a cell dividing. One cell will have slightly less genetic material, and the other will have slightly more. The most famous example of nondisjunction is the kind that causes Down’s Syndrome, when a human embryo receives three 21st chromosomes from its parents rather than the normal number of two. But nondisjunction can occur regarding any chromosome in any organism and may not even involve chromosomes at all, such as in the case of bacteria.

Let us imagine that three billion years ago, a bacterial cell was dividing, but because of a chemical malfunction, slightly less genetic material ended up in one daughter cell, and slightly more in the other. The cell with less material will probably end up smaller, while the cell with more material may end up larger, because a greater amount of genetic material can produce a greater amount of proteins, the molecules that provide the structural basis for all organisms. Larger cells (assuming the reproductive potential of the different cells was the same) would have an advantage over smaller cells in the race to gain food, thus natural selection would favor larger cells.

If this process was repeated many times, then it is possible that over a billion years a bacterial cell would have emerged that had hundreds of times more genetic material than the first primitive organisms that arose on Earth about four billion years ago. And that would have enabled the evolution of more complex organisms than bacteria…including us!

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