Out of Africa: The Origin of Our Species (Part 4)

Homo Habilis

Note: I started reading Africa: A Biography of the Continent by John Reader. The following posts will basically summarize what I find interesting in the book as I’m reading it. None of the ideas or thoughts are of my own.

The earliest known tools come from sites in Ethiopia and elsewhere in East Africa from 2.4 million years ago (at the latest), and they have only ever been found in association with gracile hominids, not the robust kind (see Part 3: Robust vs. Gracile Australopithecines). The bipedal ancestral hominids existed without the benefit of stone tools for more than a million years and then started making them around the same time that robust australopithecines appeared in the fossil record. There may have been a drastic climatic change or something else that caused some species to specialize, and took others into extinction. For instance, the number of hyena species declined rapidly, which increased the opportunity for hominids to scavenge carcasses and in the process develop tools to break open bones and slice up flesh. Stone tools were also used to process vegetables and nuts.

Stone tools enabled hominids to do with their hands what other animals did with their teeth. These gracile hominids, the earliest toolmakers, came to be known as Homo Habilis, i.e. “handy man”. The Homo Habilis externalized the processing of food while carnivores ripped open carcasses and tore flesh from the bones with their teeth, and as the robust hominids munched on mounds of low-grade plant foods. Furthermore, the brain of the Homo Habilis was appreciably larger than the earlier hominids: gracile or robust. Together, brain size and the capacity to make tools were the accepted definitions of humanity in its true and earliest expression.

However, tools at this point were only used for cutting and cracking food products. Using tools for hunting requires a much higher sophistication. The hominid toolkit remained unchanged for almost a million years, consisting of cobbles with the ends knocked off to make a sharp edge, until around 1.5 million years ago, when the robust became almost extinct, and more than one species of hominid had already evolved into the scene.

Oldowan tools used during the Lower Paleolithic period

Bipedalism marks the divergence that led hominids away from the ancestral hominoid stock, but brain size and a more sophisticated toolmaking denote the ancestors of the modern humans.

It was found that robust hominids were present at the same time as Homo Habilis, and the species seem to have shared the expanse of East and southern Africa for several hundred thousand years. Different ways of life minimized the chances of competition and conflict.

Around 1.6 million years ago, Homo Habilis and the robust were joined by a third hominid, Homo Erectus. Homo Habilis disappears from the fossil record shortly after. The robust continued to occupy their specialized vegetarian niche for another half a million years, before they too become extinct at about one million years ago. Homo Erectus was then the sole surviving hominid, and becomes the most widespread and longest-surviving of the known candidates for human ancestry.

The most completed specimen of an ancestral hominid ever unearthed was that of a boy, presumed to be less than twelve years old, whose body became entombed in mud west of the present Lake Turkana about 1.6 million years ago. The Turkana boy was over 1.6m tall, and given the chance to grow to adulthood he would’ve probably reached 1.8m tall. His brain size was approaching 900cc.

Watch: National Geographic Education - Discoveries at Lake Turkana

Brain size (cc) vs. Time (millions of years)

To be continued...

Out of Africa: The Origin of Our Species (Part 3)

Australopithecus (robust vs. gracile)

Note: I started reading Africa: A Biography of the Continent by John Reader. The following posts will basically summarize what I find interesting in the book as I’m reading it. None of the ideas or thoughts are of my own.

At about 2.5 million years ago a new heavily built Australopithecus appeared, one that had a much larger body compared to its head size. Its teeth were also correspondingly large, with a chewing surface four to five times the size of the earlier gracile australopithecines, and so they were called “robust” australopithecine or Paranthropus (from Greek παρα, para "beside"; άνθρωπος, ánthropos "human"). Their scull is of heavy and solid appearance, with a broad flat face, solid cheekbones and brow ridges, a low braincase, a prominent crest of bone running from the forehead to the back of the skull, and a massive lower jaw (Figure 1).

Figure 1 - Robust Australopithecus or Paranthropus

Because of Australopithecus robust’s large chewing size, it was unable to apply a great force on any certain point to crack open bones or hard nuts. The purpose was to be capable of prolonged bouts of chewing. So what were they eating that needed to be processed in such large quantities? It must’ve been foodstuff that contained a large proportion of indigestible material.  When their teeth were examined with an electron microscope and compared to those of orangutans (fruit eaters), rhinoceros (grazers), giraffes (browsers), cheetahs (carnivores), and hyenas (scavenger and bone eaters) the greatest similarity was found with the orangutans, indicating that the robust australopithecines had eaten fruit in large quantities just as they were picked up from trees, i.e. including flesh, skin, hard shell, pods, and seeds, which they had to chew into a digestible mass. Their powerful jaw muscles that moved these massive set of teeth separated the robust australopithecines apart from the rest of the hominids, and this specialization served them well for a while. They were able to spread from Ethiopia to South Africa at about 1.6 million years ago. But evolution has taught us that too much of specialization also drives a species into extinction. According to our fossil records, about one million years ago, the robust Australopithecus reached a dead end.

Meanwhile, the gracile Australopithecus also evolved to specialize, but towards an advantage that allowed many of its generations to multiply, and these advantages were tools and intelligence.

To be continued...

Watch: The Ape That Took Over The World (BBC Documentary)

Out of Africa: The Origin of Our Species (Part 2)

Australopithecus (ramidus, afarensis, and africanus)

Note: I started reading Africa: A Biography of the Continent by John Reader. The following posts will basically summarize what I find interesting in the book as I’m reading it. None of the ideas or thoughts are of my own.

Lucy, an Australopithecus Afarensis, was found in Ethiopia in the 1970s. This fossil is the earliest known candidate for human ancestry. The deposits in which it was found dates from 3.2 million years ago. Lucy stood at 122cm and weighed 30kg. The configuration of the pelvis and lower limbs tell us that Lucy and her kind walked upright. But also, her arms were long relative to her body size, and her fingers and toes were curved, which indicate that Lucy and her kind retained the ancestral primates’ ability to climb trees. It was very likely that trees provided them an escape from predators, and they may have spent the nights sleeping on top of rocky edges or branches.

Figure 1 - A representation of Lucy in the Smithsonian, Washington, D.C. (Wiki)

While other carnivores hunted from dusk till dawn the hominids slept in a safe place, and during the day they would’ve encountered some carnivores but there wasn’t really competition for food since meat wasn’t as essential to the omnivorous hominids. For hominids, a little meat provides enough proteins for quite a while, and too much of it is not that healthy. If protein consumption exceeds 50% of the daily total calorie intake for a prolonged period of time the liver function will be seriously strained. This is especially true when the meat consumed is low in fat. Consumption of purely lean meat would kill a human within weeks!

Fat is essential to good health. Most game that roams the African planes are very rich in protein, whereas most of the fat is found in the braincase and marrow of the animals. It’s very possible that hominids looked for bones and carcass more often than the flesh to fulfill the necessary intake of fats. The prey’s marrow and its scull tend to be left after the predators consume the meat and after the scavengers pick at bits and pieces that were left, which gave hominids the chance to get to the needed fat. Besides, plant foods constituted the main part of a diet; they are pretty rich with proteins too, so the fat intake from game was sufficient for the purposes of the hominids if game meat was too difficult to get to. However, at migration sights meat was plentiful, so this is most likely where the ancestral hominids’ pre-adaptation towards a bipedal mode of locomotion was gradually adopted. 

What’s fascinating about our ancestral hominids is that from the 5 million year old australopithecine (the oldest known), to Australopithecus Ramidus (existed 4.4 million years ago), to Lucy (3.2 million years ago), and on to Australopithecus Africanus (2 million years ago) (Figure 2), represents a span of about 150,000 generations without any physical change that would indicate a significant shift in the way of life. They were nomads that walked the old African continent, moving towards whatever they could feed on, and away from whatever they needed to escape; day in and day out. It seems that the generalized (as opposed to specialized) form and lifestyle of these small bipedal primates functioned successfully in various climatic and ecological conditions within those 3 million years.

Figure 2 - A representation of Australopithecus Africanus (Smithsonian)

I'll end this piece with a few pictures that were taken during our vacation to Addis Ababa, Ethiopia, in December of 2011.

An archaeological site

Scenery from the suburbs of Addis

On our way to the archaeological site

A replica of what was found of Lucy's bones in the National Museum of Ethiopia 

A replica of the standing Lucy

A market place in the suburbs of Addis

A national park not far from Addis Ababa

A lonely turtle on the museum grounds

To be continued...

Out of Africa: The Origin of Our Species (Part 1)

Aegyptopithecus & Kenyapitchecus

Note: I started reading Africa: A Biography of the Continent by John Reader. The following posts will basically summarize what I find interesting in the book as I’m reading it. The pictures are taken from Google Images, and some of the definitions are from Wikipedia. None of the ideas or thoughts are of my own.

Figure 1 - Aegyptopithecus

Aegyptopithecus = Ægypto + pithekos 

= from Greek Αίγυπτος (meaning: Egypt) + πίθηκος (meaning: primate or ape)

Aegyptopithecus is the earliest known candidate for ancestry of the ape and human lines (Figure 1). 

The fossil ape was found in the Fayum region of Egypt 35 million years ago (Figure 2). 

This was back when the African continent was still an island, cut off from Eurasia (i.e. Europe + Asia) and North America by sea (Figure 3). 

Figure 2 - Fayum, Egypt

Much of North Africa is desert land today, but back then it was a well-watered landscape, lush with forests that were gapped by open fields.

This small arboreal primate that lived in trees was about the size of a domestic cat; with long limbs, and all four capable of grasping branches as well as conveying food to the mouth. Their brain size was larger proportionately to body weight in comparison to other mammals of the time.

Evolution of species generally happens because of climatic change, and/or because of competition for resources. About 30 million years ago Africa, with the Arabian Peninsula attached, bumped to Eurasia.

Figure 3 - Earth at 60-40 million years ago

18 million years later (making it 17 million years ago) a baboon sized, quadruped, arboreal, fruit-eating primate called Proconsul existed on Rusinga Island close to the Kenyan shore of Lake Victoria (Figure 4). Four species of Proconsul have been classified to date: P. africanus, P. heseloni, P. major and P. nyanzae. They mainly vary in size.

Some of the same traits that the Proconsul carried were later seen in Kenyapithecus, which existed 15 million years ago. However, Kenyapithecus had a more modern set of teeth.

After Kenyapithecus, the fossil record that we have today of primates is almost nonexistent until about 5 million years ago when Australopithecus was found to exist. Footprints of Australopithecus afarensis that date from 3.7 years ago were found in Laetoli, Tanzania. A striding bipedal gait is unique to humans, so the Laetoli fossil footprint is the earliest known evidence to us of humanity’s existence. 

Figure 4 - Proconsul

So within those 10 million years (15 million years ago and 5 million years ago) the process of human evolution within the fossil record is still hidden. This is the period when our ancestral species acquired the upright stance and the striding bipedal gait.

To be continued...