What The Hell Is Evolution Anyways?
There is an argument to be made for evolution as science's richest concept. All of life's variation is a product of the evolutionary process. Shrubs and fungi. Blue whales, woolly mammoths, and the T-Rex. Your uncle Gary. More astonishingly, this diversity can all be explained by a few simple principles.
Evolution is the process through which life adapt to Earth's different environments. Resources are scarce in nature. The most well-adapted life forms are able to thrive, survive, and reproduce. Poorly adapted life forms face death, via starvation or predators. This intense struggle to eat and mate is replicated across the globe. Evolution leads to amazing strategies for securing a share of the communal pie. Let's look at the simple principles (mutation, inheritance, and natural selection) that drive life's blossoming.
Mutation
DNA is the main mechanism behind evolution. All life is rooted in DNA, as are the differences and similarities we see between species. Every individual animal, plant, insect, bacterium, and fungi has a unique DNA sequence. However, these unique sequences are part of a shared history. This history stretches from the origin of life on Earth to the present day. How did this diversity arise from our original shared ancestor? Through time, and DNA mutations.
We need to understand two important concepts regarding DNA and evolution: genomes and phenomes. A genome is the DNA 'code,' the chemical instructions that tell our bodies how to grow and replenish. A phenome is the expression of the DNA, the set of appearances and functions that the genome creates. The genome and phenome are related like a piece of sheet music and the performance of a song. Sheet music contains the instructions for how the song will sound. It doesn't contain any of the music itself. A performance contains the musical expression of the instructions, but there is no evidence of the instructions to the performance's audience. You can appreciate the song (phenome) without understanding the sheet music (genome). However, understanding composition (evolution) is much easier with an understanding of the sheet music (genome).
Once we have a grasp of the genome and phenome distinction, we can understand how mutations in a DNA sequence create life's diversity. DNA functions through replication of the genome, our chemical code, in order to express an organism's phenome. This replication process has incredibly high accuracy. However, it isn't 100% accurate. These few points of inaccuracy are mutations in DNA replication. Both the accuracy and imperfection of this process are important. The high accuracy ensures that DNA replication is effective. This way, it produces correct genetic outcomes rather than random, useless combinations. The imperfection of the process ensures that mutations occur in the genome. These mutations are accompanied by new features in the phenome.
These mutations can be a blessing, a curse, or irrelevant. A key thing to remember here is that a mutation isn't intrinsically good or bad. What makes it good or bad is how the organism can utilize it in its environment. Long necks are great for helping a giraffe pick leaves off tall trees. But what if their environment had no trees? What if giraffes had to catch mice off the ground? A long neck would be a hindrance. Mutations either spread in the gene pool or die off, based on their success. Either way, they are passed down via our next aspect of evolution: inheritance.
Inheritance
Inheritance in evolution is the ability of parents to pass their genes on to their offspring. For the sake of clarity, we will focus only on sexual reproduction here. This is where each parent provides half of the genetic material for the child. We can trace the branches of the genetic tree from single-celled organisms to all of the currently existing species, including ourselves. Genetic inheritance retains this rich history in all of our DNA. Humans share common DNA with:
Chimpanzees (98.8%)
Mice (90%)
Dogs (84%0
Chickens (65%)
What do the differences in these numbers tell us? Roughly how far back on the genetic tree that our respective lineages split because of mutations. All life is related by some common ancestor, but at varying distances. You are related to both your first and fourth cousins through some distant great-grandparent, but share a higher percentage of your genome with your first cousin.
Inheritance, like mutation, has elements of both randomness and structure. The structure comes from having one complete genome. It is composed of half of each parental genome. The randomness comes from the unpredictable consequences of combining two distinct genomes. Also similar to mutation, these combinations can have positive, negative, or neutral results for the child's phenome.
The value of an inherited genome is again based on how well it allows the child to function in its environment. If the two longest-necked giraffes mate, their child will very likely also be able to eat the highest leaves. The energy from this food will allow it to grow, and eventually mate with another long-necked giraffe.
Why will this well-adapted giraffe seek out another long-necked mate? Neck length is a 'sexy' characteristic for giraffes. Longer necks mean more food. More food will allow the child to continue the genetic line. There is little real difference between this and how men view big-breasted women. Inheritance is the process for passing down mutations that produce successful adaptations. How do we judge whether an adaptation is successful? Through our final aspect of evolution: natural selection.
Natural Selection
The theory of natural selection was Charles Darwin's awesome contribution to our knowledge. From his investigations, Darwin uncovered the inner workings of life's struggle to carry on. What he found was that nature's scarce resources puts life forms under constant pressure. What does this pressure force them to do? Adapt.
Nature is violent. Life in the wild is often brutal. Organisms compete in literal life or death games of cat and mouse, lion and gazelle, or bird and worm. Weakness is punished almost immediately by death. However, the fear of predators or starvation drives innovation. Killers become more tactical and ruthless. Prey becomes craftier or quicker. Social groups emerge with safety and feeding as the prime motivators. Even predators band together, like in a wolf pack. These adaptations are weapons in the ongoing war for survival. This is Darwin's natural selection. This is the deadly game that initiated the blossoming of life's diversity.
We can now combine our three principles for a birds-eye view of evolution. Genome mutations occur during DNA replication. These mutations are expressed in the organism's phenome. This phenome determines how well-adapted the organism is to its local environment. Adaptation is measured by the ability to feed and breed. Inheritance ensures that a well-adapted phenome is passed down to children via the genome. Organisms with well-adapted, 'sexy' characteristics are more likely to mate with one another. This increases the amount of these well-adapted genes in a species, increasing their chances of survival. Nature is the testing ground for these organisms. Natural selection is the process that separates those who can from those who can't.
Almost all non-human life, along with the majority of human history, is governed by the primal goals of feeding and breeding. Traits are refined as the game of life is played over and over. Species flourish and die off over countless generations. As this bloody spectacle plays out, we begin to get a view of the incredible creativity that evolution produces. Evolution's clever problem-solving has produced functions like:
sight
flight
muscles
communication
cooperation
photosynthesis
hibernation
symbiosis
intelligence.
Intelligence has also given us the power to appreciate the scale of the evolutionary process, along with its body count.
Applications of Evolutionary Thinking
To close out, I would like to apply evolutionary thinking, specifically DNA mutation, to a couple common riddles. This will show how we can find evolutionary solutions to problems that seem to have no logical answer. I highly recommend applying evolutionary principles whenever you are curious about animal behaviour. An explanation is often right under our noses. These explanations also unveil examples of evolution's rich diversity and adaptability.
Skeptics of evolution frequently state the objection that, if we evolved from monkeys, how come monkeys still exist? Can we be checkmated that easily? No. The key to this question lies in our common ancestor. Human's closest genetic companions are chimpanzees and bonobos. We share almost 99% of our DNA with these two. This shows that our branching point on the genetic tree is very recent in evolutionary terms. While still a long time in human years, life on Earth is roughly 3.8 billion years old. Our common ancestor, neither human, chimp, or bonobo, underwent a DNA mutation in its genome. This caused the split in the genetic branch. We have only grown more distant from our ape cousins since then, but our genome shows how closely entwined our histories are.
Finally, the eternal mind-bender. What came first: the chicken, or the egg? We are all familiar with the logic loop that this causes in our minds when we normally think about it. This is because of our assumption that the bird laying the chicken egg is itself a chicken. In fact, it isn't. The first chicken egg was the result of a DNA mutation in one member of the chicken's most recent ancestor species. This mutation caused a branching of the genetic tree. What resulted was a new species, ready to live out its illustrious history of crossing roads and being fried in Kentucky. Evolutionary thinking allows us to process these questions that are otherwise riddles. This shows its practical power, to go along with the awe-inducing consequences.