Close

October 19, 2016

DNA Replication and Mutation – Our Mysterious Evolution

We can’t discuss the evolutionary processes without first discussing Deoxyribonucleic acid, better known as DNA. All forms of life on Earth utilise strings of DNA to store the information which directs cell reproduction and carries cellular information forward to be utilised by future generations of offspring. DNA is itself located inside of cells, either at the nucleus (nuclear DNA) or in a smaller subdivision of the cell called the mitochondria (mitochondrial DNA).

It is certainly not my intention to enter into a lengthy biological thesis on genetics, one which I am not even suitably qualified to deliver, I will just offer a very basic understanding of the key areas of this topic before we return to the story of human evolution. Hopefully, my short introduction to the topic will at least serve as the bare essentials for anyone that has almost no knowledge of this specific area of biology.

DNA structure and coding

As you can see in the image above, DNA takes the form of a double helix, with two spiralling strands of a sugar phosphate substance woven one about the other, correctly these strands are called nucleotides. These nucleotides are linked together by bridges called base pairs. Base pairs carry the actual chemical based information that programs cell division as well as other biological processes.

DNA utilises what can be considered a language, of sorts, with an alphabet containing just four letters, A, T, G and C. These letters each correspond to a compound; Adenine, Thymine, Guanine and Cytosine. There is also what we can think of as a full stop which ends each series of letters. The letters are paired together in the DNA base structure, hence the term base pairs. This pairing is clearly depicted in the image above where we can also see that letter A pairs with T, whilst C pairs with G.

Genes are the basic physical and functional unit of heredity, they are essentially further combinations of these four compounds, formed from what we can think of as three letter words called Codons. There are 64 possible codon combinations. Within the biological system, genes are translated into proteins, these proteins then operate rather like tiny biological machines with pre-programmed functions. Proteins are themselves constructed from amino acids, of which 20 different types are available.

This is perhaps the shortest and most simplistic summary that can be given in respect to this area of genetics, by all means, do consider reading further about genetics on an appropriate website, such as that of the National Human Genome Research Institute, which can be found at www.genome.gov.

DNA has incredible self-replication abilities, that is to say, that it makes almost exact copies of the various required gene sequences available to new cells during the process of cell division (in which a cell splits into two cells). This replication ensures that the correct instructions are always being provided for biological growth and all other cellular processes, generation after generation. To further ensure that serious genetic problems do not occur amidst this process (mutations) DNA also carries a great deal of redundancy, consider the fact that despite there being 64 codons there are only 21 possible meanings these codons can carry. This means that any corrupted information can be safely dropped, with the correct information being then taken from an otherwise redundant area of the coding. Of course, this process can still be overwhelmed, such as in cases where high radiation levels damage too much of the DNA for redundancy to prevent mutation.

Even our very elementary look at genetics should give us the understanding that we are dealing with a highly complex process, it is certainly difficult to use words like luck or chance when discussing how this all works, although even they do at times seem to play some role. Genetic expression is a rigorously organised process. It is pretty mind-bending to then see how the same process would eventually cause a small rodent, something similar to a mouse, to eventually morph into something akin to a chimpanzee. Yet, all the current thought in evolutionary theory holds that this is exactly what occurred, with an early rodent-like mammal eventually evolving into the first of the primates. No matter how long we allow, no matter how many generations of mice produce offspring, we would logically expect to see only more mice, at the most extreme we might believe a new type of mouse-like rodent could eventually arise. DNA just strikes us as too good at the replication process it controls to allow for anything but this to happen, when it does fail in any major way the severely mutated foetus is almost always naturally aborted by the mother’s reproductive system. If a severely mutated mouse survives the birthing process it would remain limited to breeding with other mice that do not carry the same mutation.

Typically, at least with complex life forms, two parents are involved in reproduction. Because of this, we should not expect offspring to be identical to any parent, information is taken from both parents, the child is then an expression of a selection of the available genes from both parents. Indeed, the developing offspring has access to information passed down from all previous generations, this additional information is stored at the cellular level within what we call the gene pool of the parents. This gene pool includes any slight mutations that have made their way down through viable individuals, this is why we see so much variation of form within any single species, including differing eye colours, hair colours, head shapes and dozens of other notable traits. The collection of accumulated minor mutations does not, however, give any obvious mechanism for new offspring to diverge so greatly from their parents that they might be considered members of a new and separate species.

Sometimes different traits within a population group might offer a specific benefit, for example, smaller heads might allow an animal access to more reserves of a usually difficult to access food type. During a time of shortage, those members of the population with the food attaining benefit will be more likely to survive the famine than those without it, this means the resultant population will on average be noticeably smaller headed than previous generations. We refer to this process as natural selection and it is perhaps the only easily observable type of evolution, it is not anywhere near as radical as a population group suddenly becoming a new species. Natural selection is seen as one of the key supports to the reality of evolutionary theory. Recent observations of beak size adaptation amongst a finch population offers strong support for these types of changes being at times fairly radical and quite fast occurring.

“This research tells us that a complex trait such as beak size can evolve significantly in a short time when the environment is stressful,” Rosemary Grant said. “We know that bacteria can evolve very quickly in the lab, but it is quite unusual to find a strong evolutionary change in a short time in a vertebrate animal.” – B. Rosemary Grant, senior research biologist, emeritus, in ecology and evolutionary biology [1]

If we are to fully accept the reality of evolutionary theory, for which the fossil record provides strong support, we have to seek out viable explanations for why DNA replication can fail so spectacularly over longer periods. How could lower mammals, specifically a group of rodents, end up on a reproductive journey that involves so much genetic error it eventually leaves their offspring as higher primates? The entire chain of mutations would have to produce viable organisms at each stage, able to attract mates and interbreed, the mutations would also have to be beneficial, or else they would place offspring at odds with natural selection (survival of the fittest). Lady luck would really have to be smiling on the changing population throughout the entire process.

There are perhaps a number of possible explanations for the genetic mutations that eventually cause offspring to transition into an entirely new species from their parents. Keep in mind that no matter how gradual the changes might be, no matter how similar the parents and offspring, the final change can be thought of as radical, because the result is an entirely new species. Here below we can very briefly explore some conceivable mechanisms for evolution of species, one or all of these could be involved in the story.

Non-coding DNA

We have talked a little about coding and gene expression, what can be thought of as the key role DNA plays in life and evolution. Yet, the truth is, around 98% of the human genome is still fairly mysterious. Some estimates are that up to 15% of the genome relates to biological expression of an organism, whist much of the remainder has other complex functions yet to be fully unravelled, this is known as non-coding DNA. There is some suspicion that this non-coding DNA may have the ability to select new genetic expressions from a pool of possibility, to direct evolution in some sense that we are yet to comprehend. Might there be something hidden in this non-coding DNA which directly triggers sudden leaps in an organisms’ genetic make-up, mutating it into entirely new types of species?

Epigenetics

Epigenetics, is the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself. To some degree it suggests there is a continual modification of DNA expression directed by the organism’s own consciousness, it’s reactions to direct environmental experiences, occurring at a sub-conscious level. Any organism that lives through a lot of stress will more likely produce offspring adapted to such stress. In plants and small animals there is evidence of quite drastic adaptions in form after only three generations have been so-stressed. At present, the research into epi-genetic effects in human beings is at an early stage, but there is every reason to suspect epi-genetics has played a crucial role in human evolution (and all evolution).

Cosmic radiation

Radiation of the high energy variety is not a natural ally of biological life. The odds of a positive mutative trait arising from a high energy event are wildly low, yet we must consider the possibility that there is a direct, occasionally positive, role for such events in the evolutionary process. Mutation rates have been heavily increased, multiple times, by extreme energy events emanating from space. Sources for such events include solar storms, supernovae, pulsars and galactic core explosions.

Panspermia

There is a school of thinking within science that DNA may have been deliberately engineered by advanced extra-terrestrial intelligence and then seeded throughout the cosmos. Life on Earth may have been programmed to evolve right from the very start, with specific coding for this to occur being hidden in the very language of the DNA code. In this scenario there is also room to consider the possibility that any such advanced intelligences might also be visiting Earth to perform further modifications, upgrading organisms on Earth whenever they see that it benefits their mysterious designs.

Morphic Resonance

There exists a theory in biology which posits the existence of energy fields that define the biology of species. DNA would thus not be the sole source of potential structure, but rather it acts as a receiver of information from the field of the species, the information is downloaded and then translated into instructions which modulate physical form. Over time the energy field itself adapts, by means of an ongoing feedback loop, and thus reshapes subsequent individuals.

What we can say for sure is that evolution requires a mechanism by which successful mutations lead to members of a species eventually transitioning into a new species. DNA specialises in perfect replication, something has to be operating against that understood biological imperative.

 

[1]Gene behind ‘evolution in action’ in Darwin’s finches identified. biologynews.net

Leave a Reply

Your email address will not be published. Required fields are marked *