Fundamentals: DNA. Evolution: It’s natural for DNA to change

All living organisms have DNA. DNA is like the blueprint or the instructions for a living cell. As you’ll see throughout this book, in addition to DNA, living cells are packed full of “nano-machinery” that can read the DNA and “execute its instructions.” The instructions embedded in DNA are critical for the cell’s survival.

Cells and DNA can be compared to a computer and its hard drive. The computer hard drive holds all the information that is necessary to “run your computer.” The information is stored as tiny magnetic dots and dashes in the hard disk. Like Morse code, the little magnetic dots and dashes are the “language” that the rest of the computer can understand. Perhaps the most essential information on the hard drive is the operating system, like Windows or Mac OS.

This information includes all images and sound files that make up what you see and hear when your computer boots up, as well as the software that makes your keyboard, mouse, screen, webcam, and microphone work. Without a hard drive, and the dot and dash information it contains, your computer would not function.

The computer has many parts other than a hard drive. These include your screen, keyboard, mouse, cooling system, graphics, central processing units, battery, and more. All of these “parts” together are required to “bring your computer to life” when you press the power button. The hard drive needs the other computer parts so that the information stored on it can be accessed, read, and executed.

The computer parts also need information on the hard drive so they can operate and communicate with each other. By changing the dot and dash information in the hard drive, a computer can behave very differently. Over the last 40 years, the operating systems of computers have evolved substantially because they have been repeatedly updated and modified by computer developers.

DNA is simply a different medium for storing information. Rather than tiny magnetic dots and dashes on the hard disk, DNA is a microscopic string of tiny molecules called nucleotides, and it is the order of the nucleotides that make up the language that the cell knows how to read. Also, just as the tiny magnetic dots and dashes on a hard disk can be modified and changed, so too can the string of molecules that make up DNA. In other words, DNA can be altered.

In the natural world, DNA can spontaneously change due to environmental factors, or due to cell malfunction. Environmental factors like ultraviolet light, gamma radiation, chemicals in the environment, viruses, and even molecules produced by other living organisms can all have an “editing” affect on DNA. Just like deleting an important file on your computer can change how your computer operates (or whether it will even turn on), a small change such as deleting some DNA nucleotides can have a profound impact on a living organism.

It is extremely important to realize that DNA is not a permanent chemical. While it is quite stable, DNA is highly susceptible to modification.

The changeability of DNA is the basis of evolution. It is why every organism is unique and why there is such a fantastic array of living organisms in the world around you. For billions of years, the nucleotide sequence making up the DNA of living cells has changed time after time. DNA nucleotides are constantly being erased, duplicated, inverted, jumbled up, and combined with other organisms’ DNA. DNA molecules can even be copy-pasted and cut-pasted through chemical reactions!

The genetic history of humans is a great example: Did you know that 5 to 8% of human DNA is made from viruses that once infected our ancestors? An example of a type of virus that can add its DNA to your genome is the Human Immunodeficiency Virus (HIV), which is a class of virus called retroviruses. HIV infects human immune cells, then copies its nucleic acid into human cells so that these human cells will keep this new DNA and make more of the virus. This shows that human DNA has not been solely human since “the beginning.” Rather it is the accumulation of DNA from different organisms in nature as well as natural changes to the DNA sequence over time. When enough DNA is transferred, duplicated, removed, or otherwise modified, this leads to an organism that looks and behaves differently from its parent.

It can take thousands, millions or billions of generations for changes in DNA to accumulate to the point where an organism becomes unique. When minor DNA changes happen even one thousand times, the “Great-one-thousandth Grandparents” can look very different than its “Great-one thousand Grandchild.” It may even result in a different species! Let’s write this out so you can see what 1000 generations look like:

That is a lot of grandparents! Do you know who your great-one thousand grandparents were? Do you think they looked just like your grandparents? In humans, 1000 generations of minor DNA modifications require about 15 thousand years. In microorganisms, 1000 generations of minor DNA modifications can happen in days. Considering that a microorganism’s lineage goes back billions of years, that provides a lot of opportunities for generations to change and evolve.

Life on earth started with the simplest of life forms, with simple DNA blueprints. Through billions of years and an unimaginable number of incremental changes to the DNA blueprint, we now see countless species of microorganisms, plants, fungi, insects, and mammals such as humans.