The Origin of Life On the Earth: An Historical Account of Scientific Thought Part I - From the beginning of time until 1900

Introduction

Life is abundant on Earth. To date, we have identified more than a million life forms, but this pales in comparison to the vast majority of species still undiscovered. The number of extinct life forms is few thousand times more than the total number of life forms that presently exist. Over time, we have observed that the life can survive even in extreme conditions, like in the hottest volcanic springs, below the coldest ice of Antarctica, in the rocks below the sea floor, in barren deserts, in acidic conditions, and in places lacking oxygen. Even a century ago, such statements would be considered laughable.

Among all the existing life forms man takes pride in thinking he is the most intelligent. Man’s ability to generate new knowledge and to pass it on to the next generations has given the human species an immense advantage over other life forms. He grew stronger as time passed and successfully exploited nature to his gain. His hunger for knowledge is infinite. He found answers to many complex riddles posed by nature. Even in his efforts towards finding an answer to the origin of life question, man has made many discoveries and come up with theories that have helped shape the different fields in a variety of ways.

One important theory on the origin of life stands apart until the end of 19th century: spontaneous generation. Until the beginning of 20th century, spontaneous generation was the prevailing theory for the origin of lower life forms. Generation of higher life forms, like humans, were not studied exclusively in science. Those who tried to find an answer for the generation of higher life forms mostly relied on either religious texts or spontaneous generation.

The theory of spontaneous generation began because the existence of microorganisms was unknown. When an animal or plant appeared from no visible seed, then the first natural instinct was to attribute it to spontaneous generation. This simple thought led the first investigators to find a recipe for creating each new plant or animal. They tried to set up a controlled environment, and observe how life generates out of non-life, or from a putrefying body. Life appeared, but investigators could only fathom what they could see.

All the investigators were so busy in identifying such recipes that they could not shift their thoughts from it when a breakthrough came from Anton Van Leuwenhoek in the 17th century. Microscopes opened the doors for the new world of microorganisms. But most people, including Leuwenhoek, failed to consider the role of microorganisms in putrefaction or fermentation. Instead, most scholars were more comfortable with the age-old idea than to a fundamental shift in their worldview.

Moreover, many other ideas, in nature very similar to the theory of spontaneous generation, continued to boost it. Vitalism and Miasmata are examples for such theories. Interestingly, none of these theories had any credible scientific evidence in the modern sense, but they continued to support one another. To understand how this worked, let’s consider an experiment devised to test a theory ‘A.' Investigators would interpret the outcome of the experiment by taking another theory ‘B’ for granted. If theory ‘B’ is wrong, then the interpretation of the experiment is erred. It means theory ‘A’ still has no credible evidence.

Outside the scientific community, theories supporting the origin of life on Earth by natural means found support, or opposition, from scholars in other schools of studies such as theology and philosophy. Theologians and philosophers associated such theories with God. The general line of thought suggested that if the life generated on Earth through a natural process, then it would remove the need for a creator. Few exceptions took a different line of argument suggesting that it was God’s wish for the generation of life to happen naturally.

In 18th century philosophy, the idealistic thought became popular, which suggested a teleological principle for all life and opposed any explanation involving a natural means for the origin of life on Earth. But revolutions across Europe by the end of the 18th century resulted in strong support for the materialistic views. Skeptical materialist philosophers supported the theories attributing the origin to a natural means, such as spontaneous generation.

Another proposal for the origin of life on earth went almost unnoticed until the end of 19th century. This theory, now called panspermia, suggested that life exists throughout the universe. From this, an implication was derived suggesting the seeds of life from space, most likely through a meteorite, must have reached earth.  The nature of these seeds of life reaching the earth was not discussed by the proponents of this theory in the 19th century. Also, this might solve the problem of the origin of life on earth, but it will still open another question before us, the origin of life in the universe.

As we stepped into the 20th century, spontaneous generation had been rendered irrelevant in the wake of atmospheric germ theory. And panspermia had never gained the popularity that spontaneous generation did. There was a desperate need for new efforts and a new direction to understand how all life began. One of the most debated scientific theories in the history, Darwin’s theory of evolution by natural selection, gave this much-needed direction. Darwinism changed the way people looked at the life in general, and it affected everything that came after. Scientists took the idea derived from Darwinism forward and tried to form a strong hypothesis about the beginning of life. The discovery of double helix structure of DNA by James Watson and Francis Crick took this research to a whole new level, as scientists now tried to identify the process leading to the first building blocks of life. These efforts took two distinct directions. One, to identify the chemical process in early Earth conditions that could have resulted in the first building blocks of life. And two, to find evidence of life in space and confirm the method by which it came to early Earth. Both these efforts depended on Darwinism to explain how that first life led to every other life form on Earth.

When we learn all these efforts, one of the major complaints pointing to the lack of a conclusive answer for the big question takes a back seat, and our appreciation for the feasibility of different scientific proposals will only grow.

1

FIRST ATTEMPTS

The question of the origin of life is so fundamental that we can never be confident enough to know precisely where man’s efforts began. While many interesting theories were put forward in ancient religious or mythological texts from Babylon, Egypt, Mesopotamia, India, and China, they all involve the hand of a supernatural entity. The Greeks put together the first philosophical account of the origin of life, so we will begin our examination there.

Some theories from ancient Greek philosophy included divine presence. For example, in Thales’s theory where ‘everything’ comes out of the water, he considered water to be divine. But we still discuss Thales’s theory because it suggests a natural element or matter as the primary substance from which everything else came. The causality rules out the hand of the supernatural element in all following explanations.

Basic Elements

Thales of Miletus takes the credit for being the first in many fields. He was the first known Greek philosopher, the first Western scientist, and the first Greek mathematician. He is often called the father of science, but perhaps the "father of Greek science would be more accurate. Thales (c. 624–546 BC) was from a Greek city called Miletus. None of his direct writings are available now, and most of what we know about him comes from the writings of others. But his reputation speaks for itself. Based on his prediction of weather, Thales reserved all the olive presses in Miletus far in advance, only to sell or rent them later for a higher price. This is perhaps the first known future or option contract in the financial world. He also correctly predicted the first solar eclipse in the history of Greece on 28 May 585 BC, famously called the Eclipse of Thales."

Thales tried to explain natural phenomena based on rational reasoning rather than mythology. Based on his observations, he concluded that water is the primary substance and everything that exists came from it. He believed that the Earth was flat and floated on water. Though we don’t know how exactly he came to that conclusion, it appears that he observed how a moist substance would dry and turn into different forms of matter, so he applied that logic to Earth.

If Earth came from water, then everything on Earth came from water, which further implies that life too came from water. This notion suggests that the life originated from lifeless or inorganic matter. But Thales himself never delved into the specifics of how life came into being.

One of Thales’s students, Anaximander (c. 611–546 BC), had a different theory. In truth, it is a matter of debate whether he was a student of Thales or was a younger teacher at the Milesian school, a school of thought founded in 6th century Miletus, but Thales’s teachings nevertheless had an impact on Anaximander. He applied a similar rational process of reflection in the study of nature, but he came to different conclusions.

Anaximander is the first Greek philosopher to have documented his studies, but unfortunately, only one fragment is available now. So once again we must depend on other sources to learn about him and his studies. Anaximander observed that any given element has two properties of opposing nature. For example, wet and dry are two such properties that cannot exist together. He further noted that water could never be dry as its primary property is wet. This implied that any matter that comes from water must also be wet. This runs counter to Thales’s idea that everything, including dry matter, came from the water.

Instead of water, Anaximander posited that a primordial matter called apeiron or arche—terms he coined to describe his theoretical substance—was the source of origin for all life. He defined apeiron as the substance where all the elements along with all the properties are unified. He further explained how the basic elements eventually separated, and how the universe was created. In many respects, this idea is not so dissimilar from the push among today’s physicists for a Theory of Everything that would unite the fundamental forces of nature.

In support of his theory, Anaximander proclaimed that the Earth floats freely in infinite space, as it would need no support in any direction. His vision is similar to a ball suspended in a vacuum or water with equal pressure on all sides. This is possibly the first time in history that such an idea was proposed—a truly brilliant deduction for the era.

But Anaximander did not stop there. He proposed that life originated while the Earth was still forming, with fish or fish-like creatures emerging in the sea. This idea appears to be the result of his fossil study. He believed that the first animals were trapped inside the bark of tree and that they broke out of that bark as they grew. Anaximander thought that human infants couldn’t have survived independently on primeval Earth, so instead a primitive version of man would have stayed inside the mouth of a large fish. We can visualize this by comparing it with ovoviviparity in certain types of frogs and sharks. Here, eggs will remain inside the body of one parent. Once hatched inside the body, they receive nourishment from the egg yolk. When they are ready to survive in outside world, they move out of their parent’s body. In Anaximander’s theory, once men and women were able to survive on Earth and feed themselves, they came out of the host animal. This could only occur after a period when Earth was dry enough for humans to adapt themselves to the new conditions.

The idea that fish, or fish-like creatures, emerged from the sea and gave rise to man echoes the very basic idea of evolution that Darwin would deduce centuries later. Unfortunately, there is no way to know how Anaximander derived his evolutionary explanation for life on Earth, as there are no surviving accounts of his studies.

Anaximander did manage to pass down his ideas through others, though. Anaximenes of Miletus (c. 585–528 BC) and Pythagoras (c. 570–495 BC) were among Anaximander’s pupils in Milesian school. From his observations and logic, Anaximenes concluded that air was the primary principle from which everything else came. In essence, Anaximenes replaced Thales’s primary element of water with air, which then gave rise to all things.

Thales, Anaximander, and Anaximenes form the trio of Milesian School philosophers who made a permanent mark in the history of ancient Greek philosophy. Similar to Thales or Anaximenes, most influential philosopher of the time Heraclitus of Ephesus (c. 535–475 BC). The weeping philosopher believed that fire, which all other elements transform into and thus must be the cause of everything there is.

Clearly, many early Greek philosophers believed in one primordial element as the source of all life. It was water for Thales, apeiron for Anaximander, air for Anaximenes, and fire for Heraclitus. Empedocles (c. 490–430 BC), from Acragas city in Sicily, took a step further from his predecessors and argued that four classical elements constitute all other matter: water, earth, air, and fire.

Empedocles’s theory started with a primitive mixture of four classic elements—water, air, fire, and earth—but he soon built on them to include two powers called love and strife that control the mixture of elements. Love attracts the elements together, causing them to mix with one another; strife separates them. Love and strife acting on the elements in different proportions led to the creation of all things.

In Empedocles’s scenario, when the elements began to mix, various different organisms began to form. And when these organisms got together, strange hybrids appeared: Men with ox heads, oxen with human heads, and animals with both sexes. But they didn’t survive because they couldn’t adapt to the given conditions. Only those that could adapt to nature’s conditions survived, which are the organisms we see today.

Empedocles’s theory was a path breaker, and his ideas regarding animal adaptation would prove prescient. Empedocles had big ideas in other areas of study, too. Besides being a philosopher, Empedocles was also a poet, politician, and to a certain extent had knowledge of medicine. His death in circa 430 BCE is also the subject of legend. As the story goes, he jumped into Mount Etna, an active volcano in Sicily, to prove his immortality. It proved just the opposite.

Empedocles’s contemporary, Anaxagoras of Clazomenae (c. 510–428 BC) was a man who considered all the wealth or property he had a hindrance to his quest for knowledge. So he gave up all of it and immersed himself in a hunt for wisdom. He lived in Athens for about thirty years where he produced most of the significant works.

There are only a few fragments from a part of Anaxagoras’s book survived today. And most of the remaining work is available from other writers. Anaxagoras famously stated:

In everything, there is a portion of everything except Nous, and there are some things in which there is Nous also.

In other words, everything is in everything. This sounds similar to Anaximander’s theory of apeiron, but Anaxagoras has a different take on it. To him, there is one mixture that contains everything, and then there is Nous,—or the mind—which is the only thing that is independent of that mixture. Nous, which is infinite and pure, segregates the similar things from the mixture into different groups to form everything there is. But a portion of everything remains in each thing. Otherwise, Anaxagoras justifies, how could hair come from what is not hair, or flesh from what is not flesh? When things mix, a new thing forms. When they separate, it disappears.

Anaxagoras further argued that the primitive mixture included innumerable seeds of all living things. Men and all the animals formed from those seeds. The hypothesis that the life exists throughout the universe is today called panspermia [meaning ‘all seed’], and Anaxagoras was the first known person to come up with this idea. But his theory went against all orthodox beliefs of the time, and it was not taken lightly by Greek society. Indeed, this was not the only such theory put forth by Anaxagoras. Anaxagoras also tried to explain natural phenomena like earthquakes and eclipses. He stated that heavenly bodies are nothing but stones, and that the Moon has mountains just like the Earth and gets the light from the sun.

All these revolutionary ideas, as well as his close friendship with the Athens ruler Pericles, put him in a dangerous situation. Pericles (c. 495–429 BC) ruled Athens from 461 BC until his death. He was a prominent statesman, a defender of democracy, and a great orator. He gave importance to philosophy, education, arts, and literature. This brought Pericles and Anaxagoras close to each other, and Anaxagoras exerted significant influence over Pericles’s thoughts.

Athens reached its pinnacle during the so-called Age of Pericles, but his successes did not shield Pericles from political enmity. Pericles and his companions became targets of many charges, and Anaxagoras was eventually given a death sentence. Pericles defended him vigorously at trial and saved him from the death penalty. If not for Pericles, Anaxagoras could have been our first Socrates! After the trial, Anaxagoras moved to Lampsakos, escaping the death sentence as well as the dangerous epidemic known as the Plague of Athens, which claimed Pericles’s life in 429 BC. It is noteworthy to mention that Hippocrates, the father of Western Medicine, was on the ground fighting the very same plague at the time!

After Anaxagoras, the origin theories did not see any significant work for a while. But there was a clear development in the field of philosophy as well as science. This development reached a whole new level with Aristotle’s brilliant works, which included substantial work related to the origin of plants and animals.

Aristotle

Aristotle (384–322 BC) is, arguably, the most influential man who has ever lived. He is also the greatest polymath world has seen. The first true scientist, he mastered and contributed significantly