A Fortuitous Planet (Part 3)
Cultural evolution makes humans unique
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Why didn’t humans evolve to swim in the water or have tentacles? Evolution on an early Earth could have taken any number of paths. The story of life on Earth is a story of evolution's ceaseless search for advantageous characteristics. This search led to increasingly complex creatures where the whole became greater than the sum of individual parts. Humans evolved, however, to become the first species that could largely break free of evolution’s genetic limitations.
From Prokaryotes to Eukaryotes
We now understand that life likely formed in Earth’s early oceans around 3.8 billion years ago. As I discussed in A Fortuitous Planet Part 2, the “primordial soup” was likely a mix of carbon-rich molecules, stirred and churned under the heat of direct sunlight. In these conditions, some believe, life arose because it could dissipate energy more effectively than simple matter could. This is in accordance with The Second Law of Thermodynamics; that energy in the universe will trend toward dissipation. Life can reduce the entropy within itself by taking in energy, but in doing so, it raises the entropy of the universe around it.
In order for this nascent life to maintain its filial duty to laws of entropy, it also had to have two important capabilities; the ability to reproduce or replicate, and the ability to adapt to a changing environment around it. Without these attributes, life would have inevitably perished as environmental challenges would have quickly overwhelmed its ability to survive. Replication/reproduction and evolution are the primary mechanisms through which life attempts to adapt and multiply.
Early life, per our fossil record, was comprised of prokaryotic cells. These are small simple cells that lack organelles or distinct nuclei. The lack of specialization and structure in these early cells limited their size and capabilities. Nonetheless, they were hardy and prokaryotes persist to this day. They were also numerous enough in Earth’s oceans that they literally changed the climate. Over millions of years, some of these species evolved to absorb sunlight and perform photosynthesis. In the process, they released oxygen into the atmosphere, which until that point had been mainly comprised of carbon dioxide.
Some 1 billion years after the emergence of prokaryotic life, or about 2.7 billion years ago, larger and more complex cells began to emerge. How this happened is not fully understood. Some believe that anaerobic prokaryotes, literally suffocating in an increasingly oxygen-rich atmosphere, evolved to survive by living inside aerobic cells in a symbiotic fashion. Over time, two species became one with their DNA commingled. This endosymbiotic origin is now generally accepted, if not proven. These larger cells, called eukaryotic cells, had developed distinct nuclei and organelles with specialized functions and were far more complex and capable than their ancestors.
At the end of the day, however, the size of a cell is inherently limited by the laws of physics because they are bound tightly to the square-cube law. This law holds that as a cell grows larger, its internal volume grows at a cubic rate while its surface area grows at a square rate. In other words, the membrane of the cell, the sole window through which it must acquire nutrients, energy, dispose of waste, and otherwise interact with the world around it, cannot grow as fast as its internal area. Thus, past a certain size and complexity, the membrane’s surface-to-area ratio becomes insufficient to maintain cellular functions.
Life eventually found a path around this limitation by combining many like-cells together into one single organism, which in certain instances was beneficial to the survival of the species. This happened about 1 billion years later, or 1.7 billion years ago, when the first multicellular organisms, similar to algae, emerged. Over time, evolutionary pressure saw some segments of these cells begin to specialize and develop specific functions. Much like how the specialization of components within eukaryotic cells expanded cell capability, specialization between cells, creates a whole that is greater than the total sum of parts. The result was the first modern plants.
Replication and Reproduction
You have probably noticed at this point that life on Earth was dominated by simple, single-celled organisms for much of its history; the process of evolution was painfully slow. This is, in part, because the transmission of genetic information was very limited. Early life replicated or cloned itself. Evolution had to wait for fortuitous mutations to emerge, happy errors in the copying of genetic material between generations. With that said, Horizontal Gene Transfer, we have learned, also played a significant role, allowing the transfer of genetic information horizontally between some organisms.
Over time and through a complex and murky process, evolution led to the ‘advent’ of sexual reproduction. In this process, genetic information could be passed from one generation to the next by combining the DNA of two or more members of the species. Through this method, bad mutations could be swept out of the gene pool more quickly and the mixing and matching of DNA made it more probable that advantageous traits would appear than by random chance alone.
Over time and aided by new means of passing genetic information, cells became increasingly specialized and distinct. Some became sensitive to light, others to heat and sensation. Some developed the ability to pump blood and bring nutrients to limbs and organs, others formed neural connections that resembled increasingly complex computers that could take in electrical data from other cells and could use that data to solve problems. Humans are among the beneficiaries of this increased complexity and specialization.
Humans also developed a few key advantageous physical aspects that were crucial to our emergence as the dominant species on Earth. Those physical attributes include the ability to walk upright, or bipedalism. This was important because it frees our hands and arms to lift and carry objects. Opposable thumbs were also crucial in this regard, making it possible for us to manipulate objects with a precision that is unmatched by life before us. Perhaps, however, there was no greater evolutionary invention than our large complex brains and our vocal cords.
Humans developed the ability to communicate by creating vibrations in the air and this led to the emergence of complex language that allows for the rapid exchange of information. We also evolved the “theory of mind” or the ability to understand that other individuals possess emotions and knowledge that we do not; the core of human social interaction.
This is important because it sped the process of evolution, or the passing of information, further. We no longer had to wait for genetics to do the work; humans could learn and teach each other information that was beneficial for the survival of the species within generations rather than between them. We could also, for the first time, receive and transmit information between members who were not genetically related.
The advantages of this capability cannot be understated. Ideas are ‘nonrivalrous', my use of an idea does not deprive anyone else’s ability to use that same idea. With cultural evolution, new methods of making tools, hunting practices, and even techniques for making clothing could be transmitted quickly. Oral stories could be shared across many generations, preserving knowledge and history. While biological evolution certainly shaped human social groups, cultural evolution enabled those groups to be larger, more complex, and allowed for greater specialization of skills and abilities within the group.
Thus, cultural evolution continued the climb up the evolutionary ladder. With each step on the next rung, from the earliest life to the arrival of humans, the transmission of information became increasingly rapid. Every rung of the ladder saw life (generally) become increasingly complex and components more specialized. This process continues to the present, with human organizations, corporations, governments, and technological advances enabling ever-faster sharing of information and higher degrees of specialization.
Bringing It Together
In sum, from the gravitational singularity sprung simple elements and the laws of physics, including the concept of entropy. Over billions of years, chemical evolution in the furnaces of stars produced more complex elements, including Carbon. Carbon readily bonds with other elements, making it a key building block of complex molecules. These molecules took on characteristics that differed from their constituent elements. Some of these molecules eventually arranged themselves into forms that would accelerate entropy. These forms, what we call life, could evolve on their own, passing information at an increasingly rapid speed until it too created new kinds of cells and higher levels of specialization within and between them.
Ultimately, genetic or biological evolution, culminated in a species that could pass information among its living and unrelated members. This “cultural evolution” was the final step. It was the ‘dematerialization’ of information that enabled humans to (partially) break free of evolution’s physical limitations and eventually develop and share better means of obtaining energy for survival. This included early attempts at controlling and growing other life forms, what we call agriculture, the bedrock of all future human progress.
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