Since at least the time of the ancient Greek philosophers, we have been comparing the human race to the other animals that inhabit this world. We're driven by the same instincts and urges as animals, yet humans are infinitely more complex in emotion and thought. Several breakthroughs in the past two centuries have helped us explain this. And yet, many questions remain.
In the 18th century, Carolus Linnaeus designed a Latin-based naming system for the planet's species and labeled ours Homo sapiens, meaning "wise man." In 1859, Charles Darwin published his theories about natural selection, or how species change by adapting to their environment: Those individuals with successful traits are more likely survive to pass on those traits. After many generations, therefore, the whole species rejects some traits and adopts others.
Such an evolution from chimpanzee to human would take many millennia. Fortunately, archaeologists have uncovered many different kinds of fossils of extinct species that exhibit similarities to both chimps and humans. By examining bone structure, teeth and DNA, researchers can make educated guesses as to these species' mobility, diet, brain size, age — and how we might be related.
Hominids are the group of species that includes humans, chimpanzees, gorillas and orangutans in addition to their immediate ancestors. (Hominins are a subfamily of hominids that includes the genus Homo and its immediate ancestors or relatives). The history of hominids is not a straight line from chimps to humans, but rather a diverse family tree that's still being debated and assembled as we find more fossils. We'll explore the species that came before us, many of which thrived for much longer than Homo sapiens have been around.
It's an exciting time for archaeology because we're still discovering fascinating artifacts and fossils that clue us in to the history of hominids. As recently as 2009, archaeologists found "Ardi," a surprisingly intact skeleton of the species Ardipithecus ramidus, one of the earliest known species of extinct hominids. Ardi and her family existed about 4.5 million years ago in what is now Ethiopia [source: Roberts].
Paleoanthropologists are interested in studying how our hominid ancestors moved. Specifically, they'd like to pinpoint when and how bipedalism developed, which is a significant advancement that distinguishes us from our primate ancestors because it is more energy efficient than walking on four limbs.
Finding so much of Ardi's skeleton, rather than just the skull and teeth of the species we had found before, was a major discovery. It revealed much of Ardi's body structure. Ardi's arms and fingers were long with short palms and wrists that were likely flexible. The pelvis was short and broad, and the feet could both grasp and support bipedalism. All of this suggests that Ardi climbed trees, could probably walk on two feet and didn't use her knuckles for walking much [source: Roberts].
Other environmental evidence suggests Ardi lived among trees and shrubs, which called into question the prevailing theory at the time that bipedalism developed on the savanna [source: Smithsonian].
Luckily, we know quite a bit about Australopithecus afarensis. Since the 1970s, archaeologists have discovered many specimens of the species in Kenya, Tanzania and Ethiopia. We have much of an adult skeleton and most of an infant skeleton in addition to fragments of limbs, mandibles and crania.
One specimen, nicknamed "Lucy," was about 3.5 feet tall (about 1 meter), and another specimen, named "Kadanuumuu," meaning "big man," was 5 feet to 5.5 feet tall (1.5 to 1.7 meters). As we can see, this species had significant sexual dimorphism, meaning males and females of the species were different sizes, unlike Ardipithecus ramidus for instance. Paleoanthropologists speculate that males and females of the ramidus species were more likely to have shared tasks such as food gathering and childcare, whereas afarensis males were more likely to have competed for dominance. Some argue, however, that the smaller and larger specimens of afarensis don't represent males and females of the same species but rather completely different species [source: Roberts].
From dating layers of volcanic ash, experts estimate afarensis lived about 3.7 million to 3 million years ago. Based on afarensis's teeth, experts guess he ate mostly plants including fruit, leaves and seeds — but also possibly lizards [source: Smithsonian].
The species' skulls reveal a small braincase but large face and jaws. With long arms and curved fingers, the species probably climbed trees. But the thorax, leg shapes and knee joint suggest the species walked upright. All this indicates that afarensis could be a direct ancestor of the genus Homo, and therefore all humans.
The species Australopithecus africanus holds a special place in the history of archaeology and paleoanthropology because its discovery and identification as an early hominid in the 1920s helped us identify Africa as the home of human ancestors.
Living between 3.3 million and 2.1 million years ago in South Africa, africanus had a bigger brain and smaller teeth than the older species afarensis. Its face is also shorter and more closely resembles a human face. Evidence from the long arms, mobile shoulders and large hands indicate the species could climb, but the leg, pelvis and foot bones suggest this species was also bipedal [source: Roberts].
Paleoanthropologists once thought this species to be a hunter and even called it the "killer ape" because of evidence of broken animal bones near the hominid fossils. However, experts now believe that, rather than being the hunter, africanus was likely the hunted. Other predators probably preyed on these animals found near africanus, and dental evidence suggests africanus mostly ate plants and probably insects and eggs [source: Smithsonian].
Living between 2.3 million and 1.4 million years ago across Tanzania, Ethiopia and Kenya, Paranthropus boisei thrived for about 1 million years. Unfortunately we have yet to uncover any specimens for the body or limbs, but we do have a few specimens of the skull, jaw and teeth that indicate how fascinating this species was.
Boisei is nicknamed "nutcracker man" because of its large teeth and strong jaws. However, wear on the teeth suggests that although they could chew hard foods, they commonly didn't. The skull is short from front to back but has wide cheekbones and wide eye sockets. The fact that boisei's face didn't project as much as earlier hominid species suggests a progression toward more humanlike characteristics.
Another significant aspect of this find was that it marked the first use of a method called potassium/argon (K/Ar) dating for determining the age of volcanic ash. This was helpful because volcanic ash covered the surface, forming a lasting layer. When we discover fossils in between layers, we can reliably narrow down the age of those fossils. And, in some cases, volcanic ash even captured and preserved footprints of ancient hominids. After this development, paleoanthropologists found that the process of human evolution is far older and longer than previously believed.
In addition, the discovery that boisei lived at the same time as Homo erectus helped paleoanthropologists determine that the history and lineage of hominids was not a straight line but a tree with various branches [source: Smithsonian].
Fossils of Homo habilis show evidence of long arms and a projecting face more similar to apes, but the species also had more humanlike traits than older species, including a larger brain and a smaller face and teeth [source: Smithsonian]. Perhaps members of this species adapted smaller teeth as they learned to eat more energy-efficient foods that required less chewing [source: Roberts].
Paleoanthropologists speculate that this species could be associated with the earliest known evidence of bones that had been cut and hammered. This would mean they ate meat and bone marrow, and dental evidence does not contradict this idea.
Although Homo habilis's name means "handy man," it may not have been the first hominid to make stone tools, as was once thought. We've found stone tools that date back to a period when several hominids existed, and they date earlier than the oldest known member of the genus Homo [source: Smithsonian].
Homo habilis lived 2.4 million to 1.4 million years ago across Kenya, Ethiopia and South Africa, and you'll notice that this is the earliest example of the genus Homo. However, classifying it as thus required tweaking the definition of the genus by lowering the brain size requirement. In 2000, archaeologists discovered both a comparatively young habilis fossil at only 1.44 million years old and a slightly older Homo erectus at 1.55 million years old. Discovering these in the same region of northern Kenya suggests that these species didn't evolve one after the other, but rather co-existed [source: Smithsonian].
Because many of the fossils we unearth are incomplete and tell only a partial story, categorizing them into distinct species becomes fuzzy and controversial. Such is the case with Homo georgicus, which may not be its own species, but rather a member of Homo erectus. Regardless, the trove of this hominid's fossils found in Dmanisi, Georgia, is fascinating.
Archaeologists unearthed several skulls and jaws in addition to fragments of limbs, hands and feet. These fossils date to 1.8 million years ago and represent the earliest known hominid to have lived outside of Africa. Although proportionally georgicus was similar to modern humans in body structure, this species had a relatively small brain and stood shorter at just under 5 feet tall (1.5 meters).
Amazingly, one of the skulls shows evidence that the individual survived for a while after having lost all of his or her teeth. In a more primitive culture, this would have been impossible. But this is evidence that a supportive societal structure existed and helped take care of this individual [source: Roberts].
In 1984, archaeologists discovered a striking example of Homo ergaster in the skeleton known as "Turkana Boy" (after having been found in Turkana, Kenya). Before, all we had to tell us about ergaster was a lower jaw, but Turkana Boy is a nearly complete skeleton, revealing much more. He had a narrow pelvis that indicates he was very comfortable walking upright on two feet. His arms were shorter and his legs were longer than his predecessors.
What's perhaps most striking is how tall Turkana Boy was. Although he was likely not fully grown, he grew to 5.25 feet tall (1.6 meters) before he died, meaning ergaster is the first of the genus Homo we know of that reached the height of modern humans [source: Roberts]. It is difficult to estimate the age of death for many hominid fossils because they also had different growth patterns and a shorter adolescence than modern humans, but judging from the teeth, experts believe Turkana boy was probably 8 or 9 years old [source: Smithsonian].
Other fossils have been found in Tanzania, Ethiopia and South Africa. Homo ergaster lived 1.9 million to 1.5 million years ago, and its name means "workman," stemming from the fact that the species made tools from stone, such as the Archeulean handaxe. This was a hand-held stone tool that was forged from striking flakes off to form a sharp edge, possibly used for butchery or chopping wood.
Evidence of Homo erectus or "upright man" was originally discovered in 1891 on the island of Java in Indonesia. This species lived as far back as 1.8 million years ago to as recently as 30,000 years ago. Skull fossils show that this species had a long cranial vault housing a relatively large brain, in addition to a wide face and strong brow.
Most of what we have of erectus consists of skulls, jaws and teeth, but we also have one complete thighbone. These have been discovered across Asia, and some similar-looking fossils have been found in Africa, but researchers debate whether these belong to the same species.
Considering the limited fossil record for this species, Paleoanthropologists have still been able to surmise that erectus was tall and walked upright. The handaxes found in Africa are notably absent in Asia, however, suggesting that the species likely left Africa before their invention or that they made tools from other available materials [source: Roberts].
Having lived in Europe 600,000 to 200,000 years ago (during the Middle Pleistocene era), Homo heidelbergensis was likely the first hominid species to have lived in a cold climate. To thrive in such an environment necessitated several momentous innovations. This included building shelters: In France, evidence of postholes dates back 400,000 years.
They also probably mastered fire: In Israel, evidence of burnt wood and tools forged in fire date to 790,000 years ago [source: Smithsonian]. Evidence of various sturdy tools and large butchered animal remains suggests that heidelbergensis was also an adept hunter.
This species got its name because it was first found near Heidelberg, Germany, in 1907. Since then, archaeologists have discovered a nearly complete skeleton including a skull that housed a large brain within the range of modern human size. The pelvis is slightly wide, prompting the nickname "Elvis." Indeed, heidelbergensis shares many similarities with modern humans, and the exceptions are often closer to the fossils of Neanderthals, suggesting this species might be our common ancestor [source: Roberts].
Neanderthals, aka Homo neanderthalensis, are the closest known relative to modern humans, and we have uncovered several complete skeletons of the species. We therefore know quite a bit about them, but much remains unclear — including how exactly Neanderthals fit into our family tree. Evidence shows that modern humans interbred with Neanderthals but that we didn't evolve from them.
This species thrived across Europe and even into Asia. They tended to be shorter and wider than modern humans. They had wide shoulders, strong arms and legs and a large, deep chest. Paleoanthropologists speculate that the short stature could have been an adaptation to deal with the colder weather to conserve body heat. Another possible explanation is that this sturdier, tougher build was an adaptation to a brutal lifestyle. Indeed, the fossil remains show many injuries [source: Roberts]. They hunted animals and ate a lot of meat, but they also enjoyed seafood and plants. Plaque found on molars has revealed remains of starch grains [source: Smithsonian].
Neanderthal brains tended to be even larger than our own, and evidence of their culture suggests behavior that was worlds apart from earlier hominids. They buried their dead, wore primitive clothing and even made ornamental objects. This prompts questions about the relationship of brain size to social behavior, innovation and imagination.
Paleoanthropologists are interested in the question about how modern intelligence, behavior and culture evolved. Did it evolve alongside our physical evolution or did it happen more quickly? We may never definitively answer this question, but with each new fossil unearthed, we get closer to understanding our ancient ancestors.
Washington state's rhino-shaped cave is one of the strangest fossils ever discovered. HowStuffWorks explain how it came to be 15 million years ago.
Author's note: 10 Extinct Hominids
Without having studied hominids before, several things struck me in my research. First, the age of these specimens is astounding. It's difficult to fathom how the world would look so long ago. That we have any fossils this old and we know so much about them is incredible. And yet, I don't want to make the mistake of thinking we know more than we do. Although we have sophisticated technology to inspect age, teeth, DNA, etc., many of our conclusions about their lives are only educated guesses. New fossils continually call into question previous notions. Clearly, we still have a lot to learn about the exact origins of humanity.
- How Archaeology Works
- How Fossils Work
- How Evolution Works
- How Intelligent Design Works
- How Dinosaurs Work
- How Carbon-14 Dating Works
- Are humans really descended from apes?
- How are humans different from our ancestors?
- How has radiocarbon dating changed archaeology?
- Why is Mesopotamia called the cradle of civilization?
- What can archaeology teach us about humanity?
- Who was the first archaeologist?
- 10 Historical Misconceptions
- Abramiuk, Marc A. "The Foundations of Cognitive Archaeology." MIT Press, 2012. (Jan. 30, 2015) http://books.google.com/books?id=yf25055KtvsC
- Nelson, Richard William. "Darwin, Then and Now: The Most Amazing Story of the History of Science." iUniverse, 2009. (Jan. 30, 2015) http://books.google.com/books?id=je2Ms5kQCNcC
- Roberts, Alice. "Evolution: The Human Story." Dorling Kindersley Limited, 2011. http://books.google.com/books/about/Evolution_The_Human_Story.html?id=lXeTXj2vctgC
- Smithsonian. "What does it mean to be human?" Smithsonian Museum of Natural History. Jan. 29, 2015. (Jan. 30, 2015) http://humanorigins.si.edu/