By Matthew Munson, Virginia Tech
Ever since the completion of the Human Genome Project in 2001, it has become an almost-idiom in the scientific community that “less than one percent of human DNA actually means anything.” However, the thought that a three meter long DNA molecule could only be one percent useful is one of the biggest misconceptions in science to date. Although it is true that less than one percent of DNA in the human genome codes for polypeptides used in normal functioning of the human body, the other ninety-nine and some odd percent of DNA is far from irrelevant.
By contrast, the vast majority of the human genome that some consider extraneous has more temporal wisdom than any human carrying it. The large, non-coding sections of DNA in the human genome are not junk, but have simply outlived their purpose for one reason or another. Through fairly simple and well understood chemical modifications, these sections of DNA have been silenced and entombed in the human genome periodically throughout history. But thanks to the technology scientists now have at their disposal, the evolutionary artifacts in our DNA have been given a voice once again.
First, let’s take a step back and look at the human organism and its place in history. Evolutionarily, humans are the end of the line; we’re hot off the evolutionary press and we are the most complex organisms to walk the Earth yet. But what kind of implications does this have for everything that came before us? Are they inferior organisms to humans? It is easy to adopt that style of thinking with as many ways as humans have found to shape the world around them. But from a different perspective, one could say that humans have been the cumulative effort of every other, less evolved organism that has come before them.
In the past few decades, the study of biochemistry has launched the scientific community to a whole new level of understanding how the body functions at the cellular and molecular level. From all of the research on organic reactions and the enzymes (coded for in DNA) that facilitate them, scientists have made an immense discovery: metabolism is conserved in almost every organism on the planet. From single-celled eukaryotes to human beings, the way organisms take in energy sources and materials from their environment and use them to harvest energy and run biological processes is almost the same. So what does this mean from an evolutionary standpoint?
It means that all of the organisms studied (plants and animals alike) must all be able to perform roughly the same reactions internally to utilize the energy sources that Earth provides. And as any good biochemist will emphatically tell you, all of the organic reactions that we have mapped are all the direct consequences of enzymes serving catalytic functions inside of the organism’s cell(s). Following this train of thought, a very important connection between the living inhabitants of Earth brings itself to light: not only do different organisms metabolize in the same way, but they must carry the same information to code for the same enzymes that are performing these catalytic functions.
This may not seem startling at first, but now let’s look at the implications of the scientific community making this connection. First, if humans and single-cellular organisms can perform the same functions with the same compounds, this suggests that around the time that organisms were evolving, conditions on Earth must have been roughly the same. This puts a major marker on our geologic time scale, as the Earth was radically different before the dawn of the organic era. Earth must not have changed all that much since whenever the first living organisms appeared. Another important implication of discovering the huge genetic similarities between organisms is that an evolutionary order based on the capabilities of organisms can be established. For example, fermenting bacteria are single-celled organisms that oxidize glucose to ethanol in order to harvest energy from the sugar molecule. Humans also metabolize glucose and perform fermentation (glycolysis) as the first step in their metabolic pathway. However, at the point when fermenting bacteria would end the process and start over with a new molecule of glucose, human cells will continue to oxidize glucose and produce a much higher energy yield per molecule of glucose than the bacteria. This well-known example highlights an important consequence of the human genome project, which is the ability to follow a process through a series of organisms and see the improvements and modifications made over time to help certain organisms evolve when the “natural standard” no longer made the cut. When organisms became larger than a single cell and organized into groups of specialized cells like those in tissues, a better energy solution was provided by evolution. This leaves a trail for the scientists of today to follow back to its origin.
Now that we’ve discussed some of the secrets that looking at DNA with a 21st century eye have uncovered, I’ll ask you to look towards what it could tell us in the future. The ninety-nine percent of DNA that may have been labeled “junk” seems a lot more useful now that we know what it really is. The huge portion of the human genome that does not code for actual human proteins isn’t nonsense; it’s evolution’s leftovers! The silenced portions of the human genome were once vital for an organism’s survival, but are no longer needed or have been replaced with a better gene for the job. So although the Human Genome Project was completed almost fifteen years ago, the work it left was to take the newly-sequenced DNA and make sense of it.
Thanks to computer modeling and new technology in the field of genetics, making sense of the human genome’s non-coding regions is now possible indeed. Scientists can approximate where in the remnant DNA old genes’ borders were, and can attempt to model their protein products for characterization and determination of function. Who knows what research on this “junk DNA” could bring in the coming years?
Studying the DNA leftover in the human genome from evolution’s work is a lot like studying a scrapbook that nature has left cleverly coded in each and every one of us. Who knows what prehistoric functionality lies hidden in our genome? Who knows what diseases have already come about and were conquered by some other organism? The cure could be somewhere in our nucleic acid. It is not a stretch of the imagination to think that our DNA could contain every other organism’s genome as well, provided they came before us evolutionarily. Thus, our human genome has taken on a new role as evolution’s scrapbook, just waiting to shed light on our past and what may come next.