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Twenty three hundred years ago, Greek naturalists circulated the idea that all life forms on Earth started from a single source and changed over time by natural means. The idea was quickly quashed by religious leaders who deemed it a threat to their prestige and growing economic and political power. The idea, however, lingered within the scientific community for two thousand years before it burst onto the public stage when Charles Darwin published his book, “On The Origin Of Species,” in 1859.
Strong opposition to the idea by some religious and political leaders continues to this day and, in my opinion, for the same reasons. Molecular biologists and geneticists have proven that, except for the Archaeans, the DNA of all living things contain some of the same genes present in the descendants of our oldest ancestors, bacteria, and the genes are similarly located in each. This is powerful evidence that life did indeed evolve from a single source, but how? What mechanism could have produced all the diverse life forms that have ever lived on Earth?
Want to know?
Many people say they don’t want to know because evolution theory contradicts long-held religious beliefs. Changing those beliefs might weaken their hope for a God who made each of us the way we are, warts and all, for a specific purpose. A God who walk sand talks with us while we are living; a God who provides us an eternally happy afterlife.
Understood.
For those who do want to know, living things change over time by mutations in some of the genes they pass to their offspring. Almost everything about any living thing is determined by the genes it received. A gene in is composed of a specific number, usually thousands, of just four nucleic acids that geneticists refer to by “letters”—A, T, G, and C. The letters are strung together on dual strands in pairs, and arranged in a unique sequence. Since A only bonds with T, and G with C, opposite an A on one strand will always be a T on the other. The same is true for G and C. When viewed through an electron microscope, the structure looks like a spiral staircase. The dual structure is called a chromosome, a DNA molecule, or simply DNA. Human DNA has about 3 billion base pairs or 6 billion “letters.”
Until reproduction begins, the DNA molecule’s two strands are attached at both ends by repeating units of six base pairs of the “letters” TTAGGC. This is true whether the DNA is in the cell of a tree, fish, bird, human, or any other living thing. The attachment prevents contact with the ends of other chromosomes in the cell.
All human cells have 46 chromosomes except for their sex cells, which have 23. When it comes time for the cell to reproduce, an enzyme unties the ends and separates the strands. The cell then makes a copy of one strand to pass to the next generation. On rare occasions, a copying error changes one or more of the genes on the chromosome. The cell might make an incorrect number of “letters” or might make the correct number but position them in the wrong place. The mutation might have no significant effect on the offspring receiving it or might cause immediate death or a horrible birth defect. When mutated genes are not too harmful to the offspring receiving them, the next generation’s population will have individuals with some different traits than the previous one. In time, the population will be composed of individuals having multiple inheritable variations of the same trait.
These changes in the composition of the gene pool—repeated over a 3.5 billion year period and acted upon by natural selection in ever-changing environmental conditions and sudden reductions in the size of the gene pool due to group isolations—explains how all living species have evolved from single-celled bacteria.
If you want to gain a better understanding of the scientific theory that is the basis for all the biological sciences, or are just curious to understand why it is so threatening to so many, read my book, Settled Science, and my commentaries here on some of the social and religious implications of the book’s contents.
See if you agree with any of them.
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Evolution Blog 
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