Chapter 2: The Last Hominin Standing

The last common ancestor between chimpanzees and humans lived 8-11 million years ago in Africa and perhaps part of the Mediterranean region. The LCA had no real resemblance to humans or chimps, but they shared similar DNA and behaviors. The LCA was four feet tall, lived in trees and on the ground in small groups, and ate fruit, leaves, and fungus. Common behaviors existed between chimpanzees and the LCA, including relationships, fights, makeups, and sex. They both used twigs to poke at bugs or lizards and rocks or wood to crack open nuts. About 7-8 million years ago, the last common ancestor branched into the hominins and the panins. 

Early Glimpses of Human Creativity

It is important to differentiate ape versus hominin fossils, which can be done by looking for bipedalism. Bipedalism, a trait that hominins possess but apes do not, is marked by a skull that sits on top of the spinal column at approximately 90 degrees, a foramen magnum directly under the skull, and a wider pelvis. Hominins also have smaller canine teeth than apes.

The first hominin ancestor is highly debated, but there are three very possible contenders. Each of these primates are ape-like, but their fossils show evidence of bipedalism and smaller canines.  These three contenders are Sahelanthropus tchadensis (Chad, between 6-7 mya), Orrorin tugenensis (Tugen Hills region of central Kenya), and Ardipithecus ramidus (Eastern Africa, 4.4-5.8 mya). Ardipithecus may have been the first in the hominin lineage to carry things with their hands and also showed little sexual dimorphism. 

Lucy, an Australopithecus afarensis found 3.2 mya, was an adult female and the most complete hominin fossil at the time she was discovered. Lucy proved to proved to scientists that humans became bipedal before brain size increased. Furthermore, other Australopithecus afarensis found at the site Dikika in Ethiopia demonstrated the evolution of human creativity. In 2010, researchers found evidence of butchery, opportunistic scavenging, stone tools at Dikka from 3.4-3.6 mya. This is the first evidence of marks by stone tools and sharp flakes to cut meat from bones and carry it to safety. In 2015, researchers discovered the earliest evidence of definite stone tools near Lake Turkana in Kenya from 3.3 mya. This was an incredible creative feat! These hominins had to rely on communication and collaboration to make stone tools, but had brains only half the size of humans. 

Humans Emerge from the Evolutionary Bush

It is likely that Australopithecus afarensis is the shared common ancestor between all hominins. Around 2.5-2 mya, three types of hominins existed: Paranthropus in Eastern and Southern Africa, slender forms Australopithecus afarensis and sediba in Southern Africa, and a slender form that we now call Homo in Eastern and Southern Africa. Adaptive radiation was a key component of this diversification. Humans (genus Homo, species sapiens) are the only hominins still in existence today after a 7 million year hominin evolutionary time scale because we adapted the best to our environment- we got bigger brains, smaller teeth, but mainly we became more collaborative and creative. 

Little Winners

1.8 million years ago, most members of the genus Homo were five feet tall with only a few tools and many predators. They managed to survive because they were creative. Homo lived in groups of around 15-25 people and collaborated to acquire resources. By using only vocalizations and signs (because there was no language yet), Homo worked with one another to learn when predators were dangerous and developed plans to steal the meat from predator’s carcasses using tools. Collaboration was crucial because some members would stand guard while the others ran to steal the meat. The development of such tactics and increased collaboration between Homo likely led to the demise of other hominins nearby.

E Pluribus Unum?

Over the 2 million year history of Homo, there were many populations with varying sizes and behaviors. The four groups of Homo included early forms (Homom habilis and rudolfensis, naledi), middle-range forms (Homo erectus, egaster, antecessor), later forms (Homo heidelbergensis, floresiensis, and neanderthalensis and the Denisovans), and us (Homo sapiens sapiens).  The one line that humans share some DNA with is the Heidelbergensis-Neanderthal line. They lived 400,000-30,000 years ago in Northern Africa, Europe, Middle East, and parts of Central Eurasia and showed signs of high levels of creativity with their stone and wood tools, fire making, art and jewelry. They had large bodies and brains. The Heidelbergensis-Neanderthals are not our ancestors, but it is very likely that our ancestors mated with them. 

Our Shared Trajectory

 Any two humans across the world are much more genetically similar than any two chimpanzees. Humans are all part of the same sub-species. 

“We are among the most genetically cohesive and most widespread of any animal on the planet” (47)

This demonstrates how misguided our views of race are today. We are so genetically similar and are all on the same evolutionary trajectory, regardless of the color of our skin.

Homo sapiens sapiens are the only hominin lineage left. Why? Creativity.