Your Body is a Spaceship – Your Genes are the Crew

DNA strand genes genetic information

Imagine that your body is merely a vessel, a temporary host to an immortal ‘crew’. This crew is equipped with all the tools for survival, and their sole mission is to ensure that they transfer themselves on to the next host. Ideally, the next ‘spaceship’ will be stronger, fitter and better able to survive the next journey. If they fail to do that, billions of years of evolution and adaptation will be in vain. Welcome to the world of true time-travelers; the crew is none other than your genes.

What are Genes?

Genes govern all life on our planet. They provide instructions for the creation, maintenance and repair of ‘spaceships’. The ‘spaceship’ in this case can mean the human body, but also the body of every animal and organism that ever lived. The genetic information stored in our DNA has traveled over billions of years in evolutionary history to reach us now, changing and adapting along the way, with each version better than the last.

Nucleotide Bases and DNA

Genetic information is stored in a very simple format. There are 4 basic building blocks that genes use, in the form of 4 nucleotide bases: adenine, thymine, guanine and cytosine. Adenine and guanine belong to a group of molecules known as purine, while cytosine and thymine are pyrimidines. Both purines and pyrimidines are widely found in nature. Caffeine, for example, is a purine, sharing a similar structure to guanine.

adenine guanine cytosine thymine chemical structures
Chemical structures of nucleotide base pairs adenine, guanine, cytosine and thymine

The 4 bases are better described as 2 pairs because adenine binds to thymine, and guanine to cytosine. Two strands of nucleotide bases often find themselves bound to each other by a multitude of pairings, becoming what we know as deoxyribonucleic acid (DNA). DNA is a large molecule and is most stable in a ‘double helix’ conformation often portrayed in diagrams and symbols.

DNA strands blue background genes
The DNA double helix is composed of two strands joined together by base pairs

From DNA to Proteins to Life

As mentioned, the base pairs in DNA hold the key to life. But how? It turns out that these base pairs represent a language that our cells can understand. We have machinery that can unzip this DNA, read the instructions inside, then produce the proteins we need to survive.

Every three base pairs from adenine (A), thymine (T), guanine (G) and cytosine (C) spell out the code or ‘codon’ for a particular amino acid. For example, the amino acid alanine is coded for by the 3 base pairs GCA, and glutamine is coded by CAA. There are 20 amino acids in total; some of these amino acids are produced by our bodies naturally, while we must obtain others from our diet.

In cells, DNA is transcribed into RNA before the codons are translated into amino acids. RNA is identical to DNA except that the thymine nucleotide is substituted with uracil (Source)

These amino acids chain together to form proteins, each with different functions. Proteins might be cytochrome enzymes that help with metabolism, they might produce pigmentation for the color of our eyes, they can silently work in the background as part of cell signaling mechanisms.

All the processes and functions of our body are overseen by proteins. In this manner, everything that we need to survive is encoded in our genes. Genes that have been passed on from our parents, who received it from their parents, going all the way back to the origin of life.

How Genes Influence Their Carriers

The Time-Traveling Gene

Genes – these instructions within our body – have therefore been time-traveling from the very first gene through the bodies of our ancestors. Successful versions of course, or they would not have come this far. Gene lineages abruptly end if they cannot be passed onto the offspring of an individual. But not all combinations of genetic information are created equal. Genes would not be effective if they didn’t exert an influence on the traits – or the phenotype – of an individual.

That is to say, the instructions must be able to exert their effects on the spaceship in an observable way. A gene (or a group of them) must produce beneficial traits, which as a result is able to increase the chances of survival or reproduction. Beneficial genes in a bird, for example, might include those that code for sharper claws (hunting), or brighter feathers (mating).

sharp claws phenotype genes
My, what sharp claws you have

When the carrier dies, the specific set of instructions is lost forever. That is why reproduction occurs, so that the carrier’s genes can remain ‘immortal’ through a younger host. Therefore genes that provide carrier the best chance to stick around long enough to reproduce are the most successful ones, often passed on to the next generation.

Genetic Mutations

On rare occasions, DNA is not properly replicated and mistakes occur in certain genes. Base pairs can be erroneously added, deleted or substituted. There are mechanisms in place to repair or remove such errors, but they can fail and allow the mutant genes to slip through undetected.

Sometimes, these mutations don’t cause any change to the overall phenotype of the organism – these are known as silent mutations. Other times, they alter the function of a key process in the organism. This usually results in an overall detrimental effect, with the embryo terminating development or the individual born with genetic defects. There is great interest in gene therapy these days that look to cure genetic diseases by altering the mutations that are responsible.

On extremely rare occasions, mutations to a gene give rise to changes that bring tangible benefits to an individual. In birds, this might lead to even sharper claws or brighter feathers. Beneficial mutations increase the chances of the individual passing its genetic information on to the next generation.

Of course, this wouldn’t be considered evolution unless the specific traits that improve survivability are passed on as well, which requires that the mutations occur in gametes – the cells that are responsible for reproduction, such as sperm and egg cells.

Humans have known for hundreds of years that traits in the parent organism are more likely to be transferred to their offspring. Genetic modification of animals and plants through selective breeding has brought us docile, domesticated wolves (dogs!) and crops with a higher yield.

Additional Section: Are Genes ‘Selfish’?

The Gene-Trait Relationship

As mentioned, genes code for proteins, which in turn affect the processes and features of an individual, also known as traits. In birds, genes code for traits like feather color or claw sharpness. In humans, genes would code for hair color or handedness.

We must understand, however, that there is no single gene that precipitates ‘sharp claws’ or ‘bright feathers’. Rather, traits tend to arise from a combination of factors. That is not to say that a single gene – all other things being equal – is not able to drive sharper claws. But multiple genes and environmental factors decide the final outcome, making a ‘sharp claw’ gene difficult to pinpoint.

The relationships between genes are so complex that trying to understand the big picture through individual genes is an impossible task. Sort of like trying to explain how a spaceship is able to zip through space by analyzing each individual component separately.

So, why, then, do genes work together in the first place? Or do they, for that matter? It turns out that it is not enough to be the ‘best’ gene and hope to be consistently passed on to the next generation. All genes are inherently ‘selfish’ in that they care only for their survival, but must work together to produce a viable carrier that functions well as a whole.

Genes Forced to Work Together

We can take apart the DNA of an individual and analyze each gene solely, based on the traits that it confers. We end up with a list of ‘good’ and ‘bad’ genes; the good ones improve the organism’s chances of survival, whereas bad genes decrease these odds. You might be thinking that if genes were ‘selfish’, each would simply evolve to become the ‘best’ version of itself and hope that its carrier survives long enough to reproduce!

The problem lies in the situation that there is only one body carrying an abundance of genes, both ‘good’ and ‘bad’. A ‘good’ gene in the company of surrounding ‘bad’ genes that decrease the organism’s odds of survival might be thought of as unlucky, but if such a situation arises consistently then it cannot be considered a good gene at all. Even if the good gene conferred the best version of that trait, it wouldn’t be passed on to the next generation.

The crew in your body are forced to stick together, no matter the consequences. They either all make it out alive, or none of them do – there is no in-between. They are therefore forced to work together with a goal to sustain their body long enough for sexual reproduction to take place.

If genes could exit individually by, for example, being sneezed out, this would be the preferred mode of genetic information transfer. Like viruses looking for hosts to replicate, the best genes would simply ‘infect’ other hosts, ensuring its survival.

Alas, genes only work together because they have to. While it is the nature of genes to have a form of ‘selfishness’ embedded within them, they know that they are stuck. Like crew members on a spaceship, they must learn to survive together, or not at all.

brown grizzly bear looking sad claws
We hope you enjoyed this short interpretation of a key concept in evolutionary biology!

The last section of this post is inspired by author’s interpretation of “Survival Machines” in ‘The Selfish Gene‘ by evolutionary biologist Richard Dawkins.

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