For some people the process of evolution is a difficult concept to grasp. For sure, evolution is a counter-intuitive idea. We don’t experience evolution in our daily lives. It only makes sense when we look beyond the surface of things; evolutionary concepts require a long-term view. Perhaps the biggest stumbling block towards understanding evolution is the disconnection between our lives and the evolutionary timeline. If we compared the history of the Earth to the length of a person’s arm, all of human history could be wiped out with a single stroke of a nail file.
Still, despite much scientific evidence for evolution, many people are not convinced. They may look for supernatural explanations for the existence of life, or conclude the question is beyond human understanding. How is it possible that all life evolved from single cell organisms? How did even a single cell evolve? And how did life diversify into millions of species? To get a grasp for evolution we need to shift our attention from the finished product to the process.
Evolution is indeed a process, which is ongoing. And it has no finished product in mind. Evolution can be defined as gradual changes and development over time. However, there is a mechanism that generates those changes, which Darwin called natural selection. Perhaps Darwin’s greatest insight was recognizing the power of natural selection. It is similar to an algorithm, because nature selects positive survival and reproductive traits. It also discards negative survival and reproductive traits. The process is cumulative and continuous from generation to generation. Once the process began improvements to life were inevitable, even though specific outcomes were not guaranteed.
The Card Game
As a thought experiment we can use the analogy of a card game to show how natural selection works. The analogy is not perfect, because there are subtleties in evolution that are complicated. The exercise is meant to provide a simple analogy for natural selection.
Although it was not known in Darwin’s time, we now understand that life is controlled by genetic information. Essentially, it is genes that are passed on through the generations. In our analogy it is more useful to view the cards as genes, and a hand of cards as a group of genes (or an individual life form). The game has 4 basic ground rules:
1) The deck of cards represents the gene pool: We need to assume multiple decks, because the same genes exist simultaneously in other individuals and are copied many times over. Each card carries information, which may or may not survive each reshuffling. For example, the 5 of spades is one gene and the 10 of harts is another gene.
2) The shuffling symbolizes the generations: Every time the cards are shuffled and handed out, it’s like a new generation. The cards are always being rearranged in different combinations.
3) The players act as natural environments: The players select which cards they want to keep. Just like nature favors different genes in different environments, each player will select different card combinations. In our game some players are playing poker, others cribbage and others bridge. Therefore, the poker player represents a specific environment, such as an ocean.
4) The goal of the game is to collect the best hand possible: Every player keeps the cards they want, and discards the ones they don’t want. The poker players will collect different card arrangements than the bridge players. But all the cards come from the same card pool. This selection process is done with every deal.
For natural selection to work the process had to work in the primordial period. The creation of life on earth probably did not start in an instant of time. It is more likely that the building blocks (atoms and molecules) were assembling for a long time; nature was favoring stable patterns. Richard Dawkins points out in The Selfish Gene:
“The earliest form of natural selection was simply a selection of stable forms and a rejection of unstable ones.”
Just like today, things that last are stable arrangements of atoms (whether living or nonliving). Consequently, life began in a fuzzy period where forms were interacting and assembling. At some point the forms acquired the ability to replicate (with occasional errors). The errors are necessary for evolution; this would be like randomly adding new cards to the deck (like a 15 of diamonds). Eventually, simplicity grew into increased complexity; small patterns grew into larger patterns. This is also what happens with the game of cards.
Exact patterns would be difficult to recognize in the first few hands. Nevertheless, there would still be cards that are more desirable than others. Generally, an ace or a face card is better than a numbered card. But there are exceptions, which depends on the type of game and the combination of cards. With each reshuffling patterns will emerge, where eventually an onlooker could identify the game each player is playing. This is analogous to the time when stable patterns would be recognized and classified as organic life (that’s if someone where watching).
Reshuffling the Deck
We can now see how the process of reshuffling the deck, selecting and discarding the cards would work. It would not take too many hands to achieve almost perfection. Each player would select for their specific game, just like nature selects for its specific environment. All the hands would contain some of the same cards, but in different combinations. Nature mixes the genes in the same way.
The power of natural selection is the continual selection and discarding process, which occurs at unfathomable timescales. Successful genes are kept from generation to generation, random gene mutations are added, and remixed in endless combinations. Only the best of the best survive the process. That is why an after-the-fact view of evolution can be deceiving. Incredible order can emerge without a design and a planned outcome.
Our card game never ends; the players are always looking to make improvements, no matter how small. Many poker players will end up with a Royal Flush (the best possible hand). Bridge hands will end up with every card of the same suit or all aces and face cards. This is where our analogy doesn’t quite measure up. In real life the environments constantly change, which drives evolution to adjust. It’s like occasionally changing some rules to each card game, which will force the players to change their hands.
I hope this thought experiment helps to conceptualize how evolution can accomplish a seemingly daunting task. The basics of natural selection are only a starting point towards understanding evolution. Evolution is a messy process of trial and error, an incalculable amount of trials and errors, which muddies the water. Yet the time involved is critical to the process (more than 3 billion years).
Knowledge of evolution is fundamental towards understanding all life on earth. The life sciences could not progress without it. Our own bodies function as a result of evolution and much of human behavior has evolutionary roots. It has been said that, “Evolution is not something you believe in; either you understand it, or you don’t.”
References: Richard Dawkins, The Selfish Gene (Oxford: Oxford University Press, First published 1976, Second edition 1989, 30th anniversary edition 2006).