According to the standard DNA model only about 2% of human DNA codes for amino acids. Amino acids are used by the cell to, among other things, construct proteins and catalyze reactions. The proteins, in turn, are used to construct structures (such as hair and skin) while the catalysts allow our cells to function by helping process materials and chemicals for use.
This leaves 98% of our genome as “non-coding”. In 1972, Susumu Ohno ignorantly claimed that these sequences were functionless leftovers of the random process of Evolution. He coined the phrase, “Junk DNA“. It is today recognized that much of our non-coding DNA serves any number of functions, such as: maintaining structure, controlling which genes are expressed and acting as hooks for RNA to attach to when copying segments of “coding” DNA. It reminds on of the equally as ignorant “vestigial organ” theories of the 19th century; where many organs were thought to be useless throwbacks to a different time.
Of course, humans and other creatures do have vestigial “features”. These are features that have lost either part of all of their functionality because of selective pressures (environment), sexual selection (it looked bad) or mutation. Now, there is no scientific consensus on exactly how much of our DNA is actually just broken junk. However, this part is certain to grow with time. Eventually, if the genetic load becomes too heavy, our species will become extinct.
This leads us to the conclusion that ancient peoples (at some time in the past) had what are now broken functions in full working order. From research into the ancient past, we can tell that those humans who came before us were an amazing lot. With foot falls in the mud clocking them at 23 miles per hour (and accelerating), strength that makes us modern folks look like wimps, larger brains, amazing memories that could remember huge amounts of information (including oral traditions like the ones used when Moses wrote genesis) and even giants, we can definitely see how, in many ways, we are less than those who came before us.
Now this concept of becoming “less” over time kind of sums up what “Genetic Load” is. For example, if we take Biblical history as fact, we can see clearly how human life spans began to shorten after the flood. It is well known today that anytime a creature is reduced to only a few members (like 8), any genetic problems present in that number become a permanent addition to the genome quite quickly. So us modern folk are victims of broken, non-functional DNA passed down from our ancestors.
It’s not only humans, however, who suffer from this misfortune. The modern cheetah and panda populations are nearing extinction. As population loss creates a sudden rise in genetic load, these creatures are quickly approaching genetic non-viability; According to natural selection, their time is up.
So, if genetic load is slowly destroying life on earth, how long do we have? What does it say about how long we have been here? What about evolution and its millions of years?
Here’s the skinny. If most of the human genome is discovered to have purpose (little is classified as junk) then the human genome has a small genetic load. If most of the DNA is useless junk then humans have a large genetic load. It’s that simple.
Now, we inherit approximately 60 to 200 mutations per generation via our parents’ reproductive DNA. Although most of the changes are neutral, they do represent change and can combine to either benefit or harm the genome. Fortunately, we can run simulations to discover how quickly genetic load builds over time, taking into account such factors. The simulations, however, are only as accurate as the numbers entered.
Here is where both creationists and evolutionists must begin making assumptions and creating models. A creationist will take straight forward approach, counting the neutral, beneficial and destructive mutations. This reading leads to a human race doomed after only a few hundred generations. On the other hand, evolutionist models rely heavily on Junk DNA. If humans are a million years old, there must be large regions of useless DNA that have and will continue to absorb most of the mutations while the protein coding and useful non-coding regions are left mostly unharmed (in a similar way to how Jupiter protects the earth from asteroids). This leads to using numbers that are different than those used by creationists and viability up to 10k generations and beyond.
In the end, simulations aside, it seems to me that this entire issue of genetic load and viability revolves around two rates which are scientifically measurable. Since we know how quickly genetic load accumulates, the only thing left to measure is how quickly it degrades our viability. Here, however, is the second point where the creationist and evolutionist models diverge.
In the creationist model, the genome started with zero genetic load; It was perfect when created by God. After the fall, it began to degrade as it was attacked by viruses, exposed to carcinogens or attacked by other mutation causing factors (including the human race being reduced to 8 people). In the evolutionist model, the genome is in constant flux. Mutations that are destructive are kept in check through selective pressures (sexual selection, fitness, etc) and are absorbed by junk DNA while beneficial and neutral ones are spread. This keeps the genetic load from ever reaching the extinction point (1) and allows for new functions to be created.
One of these models relies on a lot of “must haves” and “probably’s”; In other words, a lot of assumptions that we can’t validate. The other model relies on known values and measurements that corresponds to a known historical and anthropological discoveries. I’ll leave it to you to figure out which is which.