Chapter 1: The Kinship of Apes and Humans

From my childhood visits to the zoo, I vividly remember the time spent observing the orangutans. Their elongated fingers, the way they sought shelter during rain, the tenderness they showed toward their offspring, and their stretching after prolonged periods of inactivity captivated me. At times, watching them felt akin to observing fellow humans in a park. I felt a profound connection, as if I could sense their thoughts and emotions.

As an anthropologist now, that childhood sense of connection has evolved into a clearer understanding of our relationship with these remarkable creatures. Great apes are our closest living relatives.

In the past, our planet was home to a diverse array of relatives, including Homo erectus, which closely resembled modern humans, and Paranthropus boisei, which appeared quite different. Each species carried vital information regarding our shared ancestry—genetic, behavioral, biological, and geographic insights that contribute to our understanding of humanity's interconnectedness.

Today, Homo sapiens stands alone as the sole surviving member of the Homo genus. However, within our broader family, the Hominidae, four genera of great apes remain: humans, chimpanzees, gorillas, and orangutans.

Currently, there are about 7.67 billion people inhabiting the Earth. In stark contrast, the wild populations of chimpanzees are estimated to be fewer than 300,000, wild orangutans less than 120,000, and gorillas, whose numbers are difficult to ascertain, are estimated between 100,000 and 200,000. All great apes face the threat of extinction, with humans being the only exception.

The gravity of these numbers is evident to anyone concerned with conservation efforts. Species are lost to extinction daily, largely due to habitat destruction driven by economic interests and rampant consumerism. Wherever humans establish their presence, biodiversity often suffers.

The loss of great apes is particularly tragic because they represent the last remaining threads of our ancestral web. Once they are gone, the invaluable information they provide about our origins will vanish with them. Great apes play a crucial role in anthropology, where researchers seek to understand the past to inform the present. If the preservation of biodiversity isn't sufficient to motivate action, the potential to uncover our human narrative should serve as an additional impetus for their conservation.

Chapter 2: The Evolution of Bipedalism

One of the most defining characteristics of humanity is our ability to walk upright on two legs. Some anthropologists argue that this trait has contributed significantly to our success as a species, as it frees our hands for carrying objects over long distances and for tool-making.

However, evolution does not occur in isolation; it acts on existing bodies that navigate the world. Our ancestors transitioned from four-legged movement to an arboreal lifestyle, which has resulted in modern humans experiencing challenges like lower back pain and joint instability. The emergence of bipedalism suggests that the benefits of upright walking outweighed its drawbacks.

Anthropologists aim to answer crucial questions: When did bipedalism arise? How did it develop? Why did it occur? To seek answers, scientists examine two primary sources: the fossil record and our great ape relatives.

Great apes provide a unique lens into our evolutionary past that no other species can offer. The fossil record reveals signs of bipedal traits in ancient species such as Orrorin tugenensis (approximately 6 million years ago) and Ardipithecus ramidus (around 4.4 million years ago). The famous "Lucy," or Australopithecus afarensis, dated at 3.2 million years old, demonstrates that even after adopting bipedalism, many traits linked to arboreal living persisted. This is still observable today; for instance, reaching overhead for an item is possible due to our shoulder joint's evolution for swinging between branches.

Yet, fossils are scarce, and researchers have yet to uncover direct ancestors demonstrating the transition to bipedalism. Hence, anthropologists turn to the great apes for insights.

Orangutans were the first to diverge from the lineage leading to Homo sapiens about 13 million years ago. Today, they spend a significant amount of time in trees and exhibit a locomotion style known as quadrumanous scrambling, allowing them to grasp branches with their feet as adeptly as with their hands. Often, they maintain an upright position by gripping high branches and standing bipedally.

Gorillas, which branched off from our lineage around 7 to 8 million years ago, are the largest of the great apes and predominantly inhabit the ground. They utilize knuckle-walking, moving on all fours using their knuckles rather than their palms. While they can walk upright like humans, their skeletal structure is not optimized for this, making bipedalism slow and energetically taxing for them.

Chimpanzees, our closest living relatives, diverged from our lineage approximately 5 to 6 million years ago. They inhabit both trees and the ground, employing knuckle-walking and vertical climbing, as well as hand-over-hand swinging. Under certain circumstances, they too can walk bipedally while sometimes carrying food for their young.

These behaviors provide anthropologists with a means to explore the origins of bipedalism in ways that fossils alone cannot. Some researchers speculate that our ancestors began knuckle-walking before gradually adopting upright walking after diverging from gorillas and chimps. Others propose that bipedalism originated in trees during our split from orangutans, with millions of years of evolution subsequently shaping gorillas and chimps in different directions. Some even suggest that bipedalism arose post-split from chimps.

Regardless of which theory prevails, the ability to draw these conclusions hinges on the continued existence of our ape relatives. They offer a lens into our evolutionary journey, providing insights into aspects of humanity such as language, tool usage, and childhood development. While they are not identical to us, they share significant commonalities.

Once the great apes disappear, we will lose an irreplaceable connection to our evolutionary history. Without them, the 7.67 billion of us will feel even more isolated.