Homo ergaster skull (KNM-ER 3733). This fossil specimen dates from around 1.8 million years ago, and was discovered in 1975 in Koobi Fora, on the eastern shore of Lake Turkana, Kenya. This well-preserved fossil skull is that of a mature female. H. ergaster is an extinct hominin species from the same genus as modern humans.

Source: BBC

By Melissa Hogenboom

Our ancient human ancestors were an elusive lot. Their remains are literally thin on the ground, and even when fossils are unearthed it is rare for them to be complete. Sometimes they must be pieced together from dozens of fragments.

That is why a staggering find in 1984 excited the entire field, and continues to do so today over 30 years later.

Turkana boy

It was a skeleton of a young boy, discovered at Lake Turkana in the deserts of northern Kenya. He died when he was about eight years old and his bones sank into the sediments of the lake, where they were preserved for 1.5 million years. He was, and is, the most complete early-human fossil ever discovered.

Yet “Turkana Boy” is just one of many early human fossils discovered near the lake. Together they span four million years of human evolution. This one spot has told us a huge amount about where we came from and how our ancestors lived.

Today Lake Turkana lies in the midst of a dry, hostile desert environment. But this was not always the case.

About two million years ago, the lake was much larger and the surrounding area was greener. Since then, rapid changes in the climate have periodically caused the lake to shrink, and occasionally it has disappeared altogether.

Before long fossils of numerous species were tumbling out of the ground

During the wetter times, it was an ideal place for early humans to live, and when they died it was a perfect place for their remains to fossilise. That’s because Lake Turkana lies in a volcanic area, where tectonic activity can move Earth’s crust and create new layers. It is within these layers that fossils from different time periods are found.

“Those are all great circumstances where you can have bones that get buried in the sand and that becomes sandstone,” saysFred Spoor of University College London in the UK. Periods of heavy rainfall have since eroded many of these layers, exposing the fossils more clearly.

Lake Turkana was once much wetter (Credit: Nasa/Wikimedia commons)

Excavations at the lake started in 1968 when Richard Leakeyof the Turkana Basin Institute led a group to the eastern side, known as the Koobi Fora. It was an enormous area, but aerial views had suggested that there were lots of fossils to be found.

“My idea was to start at one end and work our way to the other end,” says Leakey. The first few years were “a bit of an adventure”, but before long fossils of numerous species “were tumbling out of the ground”.

Humans used to be a diverse group of species, not just one as we are today

In 1972, Leakey’s team uncovered the skull and some limb bones of a 1.9 million-year-old Homo rudolfensis, known as “skull 1470“.

The discovery reinforced an idea that was emerging at the time: that there was not a single line of early humans, but multiple lineages. It was already known that three other species were living in Africa around the same time: H. habilis, H. erectus and Paranthropus boisei. H. rudolfensis added to this diversity.

In other words, humans used to be a diverse group of species, not just one as we are today. Later finds from Koobi Fora suggest that the three Homo species coexisted between 1.78 and 1.98 million years ago.

But it was not until the discovery of Turkana Boy, also known as Nariokotome Boy, that we began to learn about perhaps the most important of these species: H. erectus.

The lake reveals four million years of human evolution (Credit: Richard Bizley/SPL)

“Turkana Boy is one of the monumentally important fossils that radiates new questions about human evolution,” says paleoanthropologist John Shea of Stony Brook University in New York, US.

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