Walking with Cavemen episode guide

The science of episode two: Blood Brothers

Why two million years ago?

We chose to set our next story two million years ago because the fossil evidence indicates that there were several species of upright-walking hominids around at the same time. During this period, many different species of animals were experiencing dramatic changes.

These adaptions happened because the plants in Africa were changing around 3 to 2.8 million years ago. Africa went through a process of drying, causing woodland to shrink back further and be replaced by grass. This in turn prompted new animals to evolve to exploit the new food sources, and new predators to evolve to exploit them.

An ice age caused this upheaval.

Ice Age

The creation of the Himalyan mountain range dramatically altered rainfall patterns in East Africa, drying out Africa over many millions of years. But between 3 and 2.8 million years ago, changes in the Earth’s orbit made the seasons more extreme: The summers became hotter, the winters colder. This caused the polar ice caps to expand, locking up reserves of water and causing a drop in rainfall, drying Africa still further.

	Paranthropus boisei

Why boisei?

A whole host of features in their skulls tell us that Paranthropus boisei was a unique species. They were impressive creatures with dish-shaped faces and enormous molars that were four times the size of our own. Wear patterns on their tooth enamel show that they used these big molars to break down hard, gritty food. Chemical analysis of their teeth shows they must have been eating certain kinds of papyrus and bullrushes.

For all these reasons, it seems that boisei, if not a herbivore, had adapted to strongly favour a specialist diet of tough vegetation.

In our story, we suggest two reasons that boisei lived in a harem structure with a dominant male, rather than a more fluid social grouping. Firstly, the skulls of male boisei have a large saggital crest down their top and back, which is lacking in females. In modern-day primates, such as gorillas, this phenomenon - called sexual dimorphism - is usually seen in species where a male mates and protects a select group of females.

The second reason we employ the harem social structure is because it is usually found in primate species whose food is uniformly distributed, like the tough roots or shoots of vegetation.

Paranthropus boisei’s heavy jaws and teeth allowed them to eat the tough vegetation that other hominids and primates were not so well adapted to. But when the African environment changed again, they were too entrenched in their evolutionary niche to keep up with what was happening around them.

Why habilis?

Although the details of many homininds are argued over by anthropologists, Homo habilis and its classification is particularly controversial. Many of the habilis fossils that have been found have been categorised differently by different anthropologists.

One important specimen is OH 7. Found at Olduvai Gorge in Tanzania, the hand bones resemble later species of the genus Homo, rather than the australopithcines. In another fossil, OH 24, the skull bones are thin and the brain case is larger than hominid predecessors. It also has a short, straight face with teeth that show it was an omnivorous species.

Generalists versus specialists

We know of at least half a dozen hominid species that existed at the same time in Africa, including a generalist called rudolfensis, which we feature in the film. We centre our story on boisei and habilis because they are the two best-recorded species at this time.

Oldowan tools

The name Oldowan comes from Olduvai Gorge, where Mary Leakey defined and described the tool-making industry. The stone tools come from the lowest rock strata at the site, which are close to two million years old. Although there is no hard and fast proof that habilis made the earliest Oldowan tools, these tools were found in the same fossil layers as this hominid. Homo habilis has the delicate hand bones to be able to manipulate them and the large brain capacity to make and use them. Scientists believe that stone technology evolved in parallel with the expanding brain and socialisation of Homo.

Next: Episode three - Savage Family