PART II: HUMAN ORIGINS AND THE ASCENT OF MAN
One of the most challenging aspects of understanding evolution is our difficulty in processing the perception of time, particularly when it comes to grasping scales of duration that extend beyond our daily experiences. The human brain struggles to quantify both ends of the time spectrum: the very short and the very long. Evolution is a prime example of a process that operates on a timescale of hundreds of millions of years, similar to the millions of light-years when discussing distances between stars. ( In this article, I will be using MYA, an acronym for “millions of years ago” )
A frequently asked question about evolution concerns how fossils are dated and the timescales involved, which span millions of years. One method of dating fossils involves looking at the age of the sedimentary rocks in which they are found. Radioactive dating is the most accurate technique, based on the predetermined “half-life” of radioactive elements in plant and animal remains. Radiocarbon dating measures the remaining carbon-14 in organic specimens. Some radioactive elements, like Potassium-Argon (K-Ar), have a half-life of 1.3 billion years, while others, such as Rubidium-Strontium (Rb-Sr), possess even longer half-lives.
However, our minds can generally comprehend only a certain amount of time—about a generation is manageable. A person’s lifespan typically covers three generations: a child, a parent, and a grandparent, with a centenarian potentially adding a great-grandparent to this mix. Today, we define a generation as approximately 25 years, but this figure was lower in the early stages of human development. For most people, a photo album featuring our parents and grandparents serves as the primary memento of our ancestry. It is rare to have relics from our great-grandparents. Beyond that point, knowledge of our lineage often becomes sparse.
Richard Dawkins’ book, “The Magic of Reality: How We Know What’s Really True,” addresses this concept of time and our understanding of ancestry. Dawkins, a British evolutionary biologist known for works like “The Selfish Gene” and “The God Delusion,” discusses human evolution and helps readers gain a better sense of time by theoretically identifying ancient generations. In this book, he organizes a series of pictures tracing back through generations.
Suppose you were to pull a picture card from 20 generations (about 500 years) back; you might find a Filipino ancestor as a Spanish conquistador. Pulling from forty generations back could reveal an Indigenous ancestor, such as an “ITA” from an Ifugao tribe
Tracing back to our modern human ancestors from 200,000 years ago (about 10,000 generations) may lead you to a Neanderthal, considering that approximately 2% of Asian DNA comes from Homo neanderthalensis.
If you keep pulling pictures of your ancestors and reach back 300,000 years (or about 12,000 generations), you will likely find a pre-sapiens ancestor, most probably a Homo erectus.
The genus Homo can be traced back about 2.5 million years, or around 125,000 generations. Going further back, approximately 3.7 million years ago, you would encounter Australopithecus afarensis, followed by early species of Homo, which might include Homo habilis.
If, out of curiosity, you pulled a card from 375 million years ago, who might you find? A fish! Yes, that’s what we were 18.75 million generations ago; our ancient ancestor was likely a Tiktaalik, a fish transitioning into an amphibian.
A creationist would have difficulty wrapping his head around this because his mindset on human origins stops 10,000 years back ( some even less at 6000 years ), a mere 400 generations ago, when, according to Genesis, Adam and Eve were romping around in the Garden of Eden. Human evolution, according to some creationists, is an Ape giving birth to a human, a notion that seems more fitting for the National Enquirer. How some people can believe this kind of trash is beyond me. To be fair, not all the 40% of creationists in the US believe this nonsense.
WHAT WERE WE BEFORE AND AFTER A FISH?
Considering the earliest living organisms, which existed 4.2 to 3.8 billion years ago, only simple life forms could develop and thrive on primitive Earth. Microscopic organisms like amoebae and paramecia inhabited the early aquatic habitats. Early photosynthesis, fueled by algae and other simple single-celled plants, contributed to the oxygenation of the atmosphere. More complex multicellular organisms, such as rotifers and dinoflagellates, emerged about 1.7 billion years ago.
Some unicellular organisms started living in colonies, giving rise to colonial organisms like sponges and corals. The precursor of bony fish appeared around 800 MYA, resembling the jawless ancestors of modern fish, like lampreys and hagfish. The first bony fish emerged at approximately 375 MYA. It is important to note that all early life existed in aquatic environments for billions of years.
The Tiktaalik was one of the first fish to gradually emerge from the water to become amphibians, thus able to breathe on land using their lungs and through their moist skin. Tiktaalik possessed many essential features that eventually became part of humans, including shoulders, elbows, legs, wrists, and a neck. This evolutionary step was crucial for developing tetrapods, leading to the emergence of amphibians, mammals, reptiles, and birds. Frogs and salamanders inhabit water and land; during their metamorphosis, their fins and gills disappear, replaced by legs and lungs. Many amphibians retain their aquatic beginnings as water-dwelling, gill-breathing tadpoles before metamorphosing into land-dwelling adults.
One notable transition in the evolution of these organisms on their way to becoming the first humans was the relatively brief period in which amphibians transformed into reptiles, including the great dinosaurs. Birds first appeared as flying reptiles like Archaeopteryx, followed by marsupials (specifically in Australia), mammals, and eventually primates. All of this evolution unfolded within the last 300 million years. This rapid evolution, exemplified by the Cambrian Explosion between 541 MYA and 530 MYA, resulted from various factors, such as climate fluctuations and continental drift. Rising oxygen levels and new food sources created new ecological niches, leading to rapid diversification among species.
There have been five major mass extinctions, beginning with the Ordovician-Silurian 440 MYA and culminating in the Cretaceous-Tertiary 65 MYA. These mass extinctions opened new environments with reduced competition, enhancing survivability and biodiversity. The aftermath led to the emergence of new ecosystems and a surge of new plant and animal species.
Even though we evolved from fish (and, by extension, all early life before fish from 3.5 billion years ago), many fish still exist today, just as there are thousands of reptiles, despite some evolving into birds. Evolution does not follow a linear trajectory where one species entirely replaces another. When a species evolves, it branches into various lineages, with some remaining unchanged in their original environment while others adapt to new niches.
Tiktaalik was the first vertebrate to inhabit the land, giving rise to tetrapods. Millipedes, spiders, and other insects, as the first land-dwelling animals, served as food for these tetrapods. The vast majority of fish remained in the water and continue to evolve to adapt to changing aquatic habitats. (A notable recent example is the tilapia, which has adapted to low-oxygen, muddy ponds in Africa, and the lungfish, which can hibernate and can breathe through their skin and survive in drying ponds until the rains return.) The common ancestors that gave rise to new species eventually became extinct. Tiktaalik, along with synapsids, therapsids, and cyanodonts (ancestors of mammals), is no longer present.
THE HUMAN TRANSFORMATION
Notes: Our transformation from our original ancestor, the Dryopithecus, 16 million years ago was a complex process of human evolution. For clarity, I have summarized this account and rounded some figures to enhance comprehensibility. I have also simplified some scientific names to only the genus or the species.
For instance, our distinct species could be accurately called Homo sapiens sapiens. Importantly, unlike today, many different varieties of humans coexisted and interbred, although not all were present simultaneously.
A recurring theme in evolution is that it is gradual, and there is a vast timeline, often spanning millions or tens of thousands of years, before a species becomes dominant. When similar environmental pressures arise, parallel species may develop simultaneously in different locations. As with any population, variations within species help ensure survivability in diverse environments.
The Dryopithecus is the common ancestor of the great apes (gorillas, orangutans, bonobos, and chimpanzees) and humans. This ape-like creature lived approximately 16 MYA. Fossils have been discovered in Africa, Europe, and India. While we share a common ancestor, our DNA confirms that we did not evolve directly from any of the apes living today. Chimpanzees and bonobos are our closest living relatives, and we diverged from them between 8 and 6 MYA
Following the Dryopithecus, we find the Australopithecus and Ramapithecus, which existed between 3.85 and 2.95 MYA in Ethiopia and Tanzania. Australopithecus afarensis survived for around 700,000 years. After this species went extinct, the first genus Homo became dominant between 3 and 2.8 MYA. This genus includes Homo habilis, Homo erectus, and Homo neanderthalensis, along with less well-known species like Homo antecessor, Homo heidelbergensis, Homo floresiensis, and the most recently discovered Homo naledi. While most of these species populated Africa, some spread to other parts of Europe and Asia. Key traits that distinguished these pre-Homo sapiens included skull size (reflecting brain size), dental structure (indicative of diet), and spinal curvature (related to posture and bipedalism).
The emergence of these species was not due to the movement of populations—clearly, they lacked the means to cross oceans and landmasses MYA. Instead, they evolved independently through a process known as “Adaptive Radiation.” The ecological niches in their respective environments exerted similar pressures that led to the development of these subspecies. Continental drift created new habitats and isolated populations. It is reasonable to suggest that where these species were geographically close, they likely interbred, leading to the emergence of more subspecies.
HOMO ERECTUS: THE MOST SUCCESSFUL HUMAN SPECIES THUS FAR
Homo erectus first appeared around 2 MYA and thrived until approximately 100,000 years ago, totalling 1.9 million years on Earth. For our species, Homo sapiens, to surpass this duration, we would need to continue for another 1,660,000 years, given that Homo sapiens neanderthalensis emerged around 240,000 years ago.
About 600,000 years ago, Homo erectus gave rise to Homo heidelbergensis, which simultaneously produced three distinct human species (all classified as Sapiens) across three separate continents: Neanderthals in Europe, Denisovans in Asia, and Sapiens in Africa.
Homo sapiens, meaning “wise man,” began to dominate after the existence of Homo neanderthalensis. By this time, Homo erectus was in decline, with only a few populations remaining in Europe and Asia. The Neanderthals and Sapiens coexisted in overlapping environments, with some interbreeding occurring between the two. Our species cohabited with Neanderthals for about 150,000 years until their extinction approximately 40,000 years ago in Europe.
Today, we, the Homo sapiens sapiens who migrated out of Africa, are the only known human species still alive ( so far as it is known ). Civilization, geopolitical boundaries, and sectarian fears have created artificial constraints on interbreeding patterns that once existed. Unlike in the past, when open niches facilitated the emergence of various human species (similar to dog breeds today), future generations of Homo sapiens and the diversity that may arise will likely result from reproductive technology rather than natural processes, especially as long as we continue to have significant societal inhibitions regarding sexuality.
Make no mistake about it: we continue to evolve. Look around and see how young people are so different from when we were young. There are thousands of variations within our species. While the changes are subtle for now—mainly because our environment has not undergone any catastrophic alterations—certain scenarios could drastically impact us. Events like a nuclear war or a giant asteroid striking Earth— which caused the extinction of the 165 million-year reign of the dinosaurs— could potentially wipe out the majority of our population. However, in such cases, there will likely be survivors whose genetic traits may render them resistant to radioactivity, for example. These individuals could carry on, leading to the emergence of a new human species (or even a new genus) that could repopulate the Earth, much like how it was millions of years ago!
Footnote:
Details, especially periods and extent of the evolutionary timeline, have been gleaned from Wikipedia. The vast amount of time involved lends to various discrepancies from different sources but reflects a general correlation.
Part III
– Evidence of Evolution
-Why “Intelligent Design” is not too intelligent
-The future of the Human species.
