3: Life

Life on Earth began about 3.5 billion years ago. All life shares a universal genetic code; this strongly supports the premise that all living things share a universal ancestor. Evolution through various forms of selection (natural, sexual, and cultural) led to increasingly complex organisms over billions of years, culminating in the primates that were our evolutionary ancestors

3. Life

We don’t know exactly when the first life forms came to exist on Earth.

We can only trace back to the point where we have evidence of life and assert that life originated sometime before that time. The earliest direct evidence of life on Earth (so far) are microfossils of microorganisms mineralized in 3.465-billion-year-old Australian Apex rocks. The illustration below shows the photographs of these life forms, along with drawings to help visualize their shapes.

QQQ 13 microbes shapes.

How did we go from ‘no life’ to ‘life?’

This issue needs to be explored, but I don’t want to explore it here. Another book in the series, The Meaning of Life, is a kind of prequel to Fact-Based. There is one thing in our past that is pretty hard to explain, and that is the evolution of something called ‘The Genetic Code.’ This code is the foundation for all life on Earth, from the earliest microbes to modern humans. The word ‘code’ tells us that there are sequences in DNA that mean something: they can be ‘decoded’, and get the results read.

In Earth life forms, the code is ‘read’ by a ‘code reading molecule’ called the ‘ribosome.‘ Special DNA encodes for ribosomes called rDNA. The coding is complex but the bottom line is that all higher beings (Eukaryotes: all living things with cells — at least one — that contain a membrane-bound nucleus or more than one cell, at least one of which has a nucleus) have the same DNA sequences and the ribosomes are the same. (Humans are eukaryotes; so are all fungi, all plants, and all protozoa). Lower beings (Prokaryotes, any living without clear cells or nuclei) also have ribosomes which are coded by rDNA. Although the ribosomes in these lower life forms are slightly different than those in higher life forms, they are the same among all prokaryotes. This means there are only two kinds of ribosomes in all Earth life forms.

Both the code itself and the decoding structures (ribosomes) are incredibly complex. All life-forms have them: they are the things that make the reproduction and construction of complex parts of living things possible. Many scientists have gone over the evidence and determined that it is not mathematically possible for this code (which is identical in all life forms) and the decoding structures (two forms, both of which read codes the same, but identical among their class), to have come to exist spontaneously, either as a single event or as a series of events. In other words, this code wound up existing here on Earth somehow other than through chance mutations and combinations of elements and chemicals on Earth. The first to make this connection was Francis Crick, the co-discoverer of the genetic code. He discusses what is left, after we rule out the possibility of spontaneous creation, in the book ‘Life Itself.’ When he published this book, it was seen as a kind of speculative fancy. It went against everything people believed about the way life came to exist on Earth. (Both religious and secular people have explanations for this. If Crick is right, both of these groups are wrong.)

The book The Meaning of Life takes up the same issue. We have a very large amount of new evidence to help us understand this issue that didn’t exist in 1981 when Crick wrote his book. If we want to understand the human condition and gain full awareness of exactly what the existence of the thing we call ‘life’ implies, we need to go into some pretty complex topics.

Universal Common Ancestry

What happened to cause more complex animals to exist? What happened to cause humans to exist?

In 1859, Charles Darwin published the book on The Origin of Species. This book proposed that it is possible (Darwin uses the term ‘not incredible’) that all life on earth started with a common primordial form, and evolved from there due to the process of natural selection. He writes:

On the principle of natural selection with divergence of character, it does not seem incredible that, from some such low and intermediate form, both animals and plants may have been developed; and, if we admit this, we must likewise admit that all the organic beings that have ever lived on this earth may be descended from someone primordial form. (PDF of the book available in references section of PossibleSocieties.com website.)

Recently, scientists given a formal name to the theory Darwin described. They call it the ‘Universal Common Ancestry’ theory, or “UCA.” Understanding the UCA theory is important because it provides a foundational understanding of the realities of the world before evolution began, which can then be used to test this theory of evolution itself.

Before we look at evolution, let’s first explore how scientists have confirmed the UCA theory and the evidence supporting its validity. This evidence comes from an the analysis of DNA.

DNA, or ‘deoxyribonucleic acid,’ is a molecule in the nucleus of the cells of all living things that have cells. In 1954, Francis Crick, Maurice Wilkins, Rosalind Franklin, and Charles Watson built models of DNA that revealed it contained coded messages within its structure.

Crick and Watson early DNA model

DNA is made up of sequences of amino acids that code for proteins and other complex molecules that are needed for life. The coding molecules are incredibly tiny, and it took roughly a half century for scientists to build machines that could read these codes. These machines are called ‘gene sequencers.’

In the early 2000s, Douglas Theobald and a team of researchers at the University of Colorado obtained funding to use gene-sequencing techniques and statistical analysis to evaluate the UCA theory. If different organisms had different origins — in other words, if they were not all ‘descended from a single primordial form’ — we would expect different coding methods to be used to code for complex molecules in different life forms.

Scientists can investigate the Universal Common Ancestor (UCA) by analyzing DNA sequences for various proteins across different organisms. For instance, they might sequence the genes of Treponema pallidum, the bacteria responsible for syphilis, and then sequence human DNA, often using their own DNA as samples. By comparing these genetic codes, they can draw conclusions about the origins of these species. If the species had entirely separate origins, we would expect them to use different genetic coding mechanisms. If their origins were similar but not identical, some parts of the coding mechanisms would match while others would differ. However, if the coding mechanisms are found to be identical, it would strongly suggest that both the syphilis bacteria and humans share a common ancestor.

If scientists sequenced a wide range of life forms and found similarities in some of them, but not all of them, it would suggest evidence for common ancestry among those with all these similarities. The more similarities they found, the higher their confidence would be in a shared ancestry. If they discovered that every single code was identical, they would be virtually certain that all these life forms share common ancestry.

The team published their findings in 2010. They found that the gene sequences for various proteins were not just similar but identical in all living things. They used statistical tests to determine how likely this is to be a coincidence. Here are the findings from their paper:

UCA is at least 10^2,860times more probable than the closest competing hypothesis. Notably, UCA is the most accurate and the most parsimonious hypothesis. Compared to the multiple-ancestry hypotheses, UCA provides a much better fit to the data (as seen from its higher likelihood), and it is also the least complex (as judged by the number of parameters). [Theobald, Douglas L. “A Formal Test of the Theory of Universal Common Ancestry,” Nature 465, 219-222 (May 2010).]

If scientists sequenced a wide range of life forms and found similarities in some of them, but not all of them, it would suggest evidence for common ancestry among those with all these similarities. The more similarities they found, the higher their confidence would be in a shared ancestry. If they discovered that every single code was identical, they would be virtually certain that all these life forms share common ancestry.

This means that the probability of observing such genetic similarities by chance is approximately 1 in 10^2,860 —a number so large defies human comprehension. To put this in perspective, let's consider some astronomical numbers:

There are estimated to be about 10⁸² atoms in the observable Universe, and, if the universe did in fact have a ‘big bang’ origin, about 10¹⁷ seconds have passed since the Universe's estimated beginning. If you had all of the necessary materials and could create DNA-based life in as many different places as there are atoms in the Universe, and you repeated this process once each second for all the time since the Big Bang, you would have created life 10⁹⁹ times. Even with this astronomical number of attempts, the chances of producing the observed genetic similarities by coincidence are vanishingly small.

In fact, you would need to repeat this entire experiment—creating life 10⁹⁹ times—approximately 102,860 times before you would have a 50/50 chance of producing one world with these similarities purely by coincidence. This number, 10^2,860, represents a 1 followed by 2,860 zeros—a number so large it defies human comprehension.

In other words, it is not a coincidence that all life forms on Earth use the same genetic coding sequence in our DNA. We can conclude that we have a common ancestry with a greater degree of certainty than we know just about anything else in science. This puts the theory of Universal Common Ancestry among the most well-supported ideas in all of science, comparable to fundamental theories in physics or chemistry.

Dating Artifacts

When Darwin was alive, scientists didn’t have any scientific tools that would give accurate dates on artifacts.

People had to rely on inference from the things they accepted and believed. Western scientists, trained as many of us, were taught that nothing in the Universe is older than 4,004 BC. For most of the last several thousand years, people in the Western world were required to accept this belief; those who did not, were guilty of heresy and could be put to death. While the rigidity of this requirement eased during Darwin’s time, it was still uncommon for people to openly claim that anything was older. Naturally, if nothing is older than 4,004 BC, then all artifacts were assumed to have come to existence sometime between that date and today.

In 1949, while working at the Lawrence Livermore National Laboratory at the University of California in Berkeley, William Libby discovered the first truly scientific dating method. This process uses the radioactive decay cycle of carbon and is called ‘radiocarbon dating.’ (See textbox below for more information.)

Radiocarbon Dating: Gamma radiation from the Sun changes stable carbon-12 to radioactive carbon-14 at a fixed rate, and carbon-14 degrades to carbon-12 at a known rate; the relative ratios of these two kinds of carbon have reached an equilibrium billions of years ago. The new carbon-14 created exactly equals the carbon-14 that disappears, and the ratio stays the same.

All plants ‘breathe in’ carbon; they take in carbon dioxide and convert it to sugars using photosynthesis. Animals eat plants, taking the plant’s carbon into their bodies. Once the plant or animal dies, it stops taking in carbon and there is no more carbon-14 being created (it is only created in the atmosphere due to the sun’s UV rays), so the relative ratio of carbon-14 to carbon-12 falls, as the number of carbon-14 falls. Eventually, after about 50,000 years, the carbon-14 has all disappeared and there is none left.

During the first 50,000 years after the death of a plant or animal, the ratio of these two isotopes of carbon changes from its natural ratio in the atmosphere to zero. Scientists can measure the ratios of these two isotopes in a sample and go to a chart that tells them how long that carbon has been out of the atmosphere, to within a few years. *

Scientists began using this method in 1950 and found it to be extremely reliable. To determine just how reliable it was, they needed to find other events that occurred at a known time in the past and test artifacts from those events to see if they obtained the expected results.

We know from many sources that Mount Vesuvius in Italy erupted on August 24, 79 AD. This eruption buried many towns before the people could escape, encasing them in lava with the exact date of their death recorded on their date books and calendars. We can test the radiocarbon dating method by dating artifacts left by Mount Vesuvius. Other known eruption dates allow us to verify dates going back a very long way. This process has been tested many times and is virtually 100% accurate giving us great confidence that this method determines accurate dates.

Over the 65 years since radiocarbon dating was perfected, scientists have developed many other scientific dating methods. Radiocarbon dating is most effective for items of recent origins (less than 50,000 years). Older artifacts can be tested with a similar method that measures the breakdown of potassium into argon. By cross-referencing the results of many different tests, we can determine and have determined that these tests are extremely accurate.

As of 2024, scientists have come up with many reliable and useful dating techniques based on other elements with extremely long decay cycles. Most of these techniques only work for organic artifacts—those that were once alive—by determining when they stopped taking in air, water, and food, meaning when they died. New methods such as optically stimulated luminescence (OSL), are being developed to measure the amount of exposure that rocks, and anything has had to light. By cross-referencing results from various tests using different technologies, scientists can get increasingly accurate scientific dates for artifacts of all kinds.

Evolution

The chart below lists the ages of the oldest samples of various living things dated so far. We don’t know exactly when these organisms first appeared on Earth; they may have been here significantly longer than shown. However, the figures below represent the minimum time we know for certain that these life forms have been on Earth:

Ø For the last 3.4 billion years, simple cells (prokaryotes) have existed;

Ø For the last 3.4 billion years, cyanobacteria performing photosynthesis have existed;

Ø For the last 2 billion years, complex cells (eukaryotes) have existed;

Ø For the last 1.2 billion years, eukaryotes which sexually reproduce have existed;

Ø For the last 1 billion years, multicellular life has existed;

Ø For the last 600 million years, simple animals have existed;

Ø For the last 500 million years, fish and proto-amphibians have existed;

Ø For the last 475 million years, land plants have existed;

Ø For the last 400 million years, insects and seeds have existed;

Ø For the last 360 million years, amphibians have existed;

Ø For the last 300 million years, reptiles have existed;

Ø For the last 200 million years, mammals have existed;

Ø For the last 150 million years, birds have existed;

Ø For the last 130 million years, flowers have existed;

Ø For the last 60 million years, primates have existed.*

How did one life form change into another?

Darwin’s theory, which is more than 150 years old, has held up and remains consistent with the discoveries made since. Darwin describes the process of “natural selection,” the most important underlying process of evolution, in this way:

As more individuals of each species are born than can survive; and as, consequently, there is a frequently recurrent struggle for existence, it follows that any being that varies even slightly, in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. Due to the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.

Over time, beings with advantageous traits replaced those without them. The basic capabilities of the most capable beings on earth increased steadily, over billions of years. By 60 million years ago, primates existed—Primates being the ‘family’ that includes humans. Our ancient ancestors were present in this world 60 million years ago.

Paleogenomics

The field of Paleogenomics is the study of the evolution of DNA. It is a brand-new field. This is an excerpt from a 2019 article about the field:

The recent accumulation of plant genomic resources has provided an unprecedented opportunity to compare modern genomes with each other and to infer their evolutionary history from the reconstructed genomes of their most recent common ancestors (MRCA). This method of ancestral genome reconstruction was initially used to investigate 105 million years of eutherian (placental) mammal evolution. Eutherian genomes are surprisingly stable and affected by only a limited number of large-scale rearrangements during evolution. Higher rates of such chromosomal shuffling have been reported for the branch extending from the great ape ancestor to the ancestor of humans and chimpanzees, which diverged after the Cretaceous–Paleogene (K–Pg) boundary, at a time when the dinosaurs became extinct.

Computational reconstructions of mammalian ancestral genomes were instrumental in suggesting that environmental changes may have driven genome plasticity through chromosome rearrangements. These changes may also have led to new variations in gene content and gene expression that gave rise to key adaptive biological functions.

Paleogenomics is a new field and so far, it hasn’t produced any results that conflict with the evolutionary analysis of other sciences. The lack of conflict, however, is an important finding. If the previous work on evolution had been incorrect, the DNA results would have shown discrepancies. The fact that there are “no conflicts” gives us great confidence that the researchers who have studied evolutionary processes were on the right track and that all the basic processes that Darwin proposed are indeed operating.

Primates

Mammals had already existed for 140 million years before the first primates emerged. Over this immense period, nature selected mammals with higher intelligence for survival. The gradual increase in intelligence eventually led to animals that were so different from than their predecessors that they were an entirely new classification of beings. Sometime between 65 million and 60 million years ago, the highly intelligent mammals that are classified as “Primates” came to exist.

Primates are mammals with these specialized features:

Grasping hands with fingernails (rather than claws) and fingerprints.

Large brains relative to their body mass.

Vision is their primary sense, and they are highly visually oriented.

They normally give birth to one offspring at a time.

They have very long periods of growth & development.

They tend to live in long-lasting social groups.

Primates are the only class of animals that take natural products and use them to manufacture tools.

Incomplete remains of primates have been found and dated to 60 million years while the oldest complete skeletons go back 55 million years. These skeletons were discovered by scientists at Beijing’s Institute of Vertebrate Paleontology and Paleoanthropology in 2013.

Evolution did not stop when the first primates emerged. All primates reproduce sexually, and sexual reproduction creates new combinations of genes—and entirely new animals—with each birth. Once these new generations existed, they had to compete with their peers for resources. Those with lesser intellectual skills and abilities were less likely to perish before they could mate, while those with greater skills were more likely to carry on the species.

Every 1,000 years about 500 generations had the opportunity to surpass their peers. Over the span of a million years, some 500,000 generations had this same opportunity.

The individual changes didn’t need to be large. Over this immense period, tiny incremental changes accumulated to bring about enormous differences.