The Earth Story

Humans and Monkeys (Part 3 of 3)

Finally, in our journey through the evolution of humans, we move on to the genus homo. Within this genus there are 2 main species we shall discuss today; Homo erectus and Homo sapiens neanderthalensis (though others are also important, including Homo sapiens, Homo floresiensis and Homo ergaster). Home erectus (picture 1) is named after its ability to stand upright and is noticeably important among the evolution of humans for their use of sophisticated tools for breaking up food and their use of fire. This control of fire is evidenced by the finds of burnt bones and rocks in caves in South Africa dated to 1.6 million years ago. It should be noted, however, there is no archaeological evidence yet of Homo erectus cooking food, only of using fire as a heat and/or light source. It is thought that Homo erectus was the first hominid to live in small family groups, functioning as hunter-gathers. Up to this point in time all hominin remains were found in Africa, however, it is thought Homo erectus was the first to migrate out of Africa approximately 2 million years ago.

Homo sapiens first arrived in Europe 45,000 years ago and are known as Cro-Magnons (after a cave in south-west France). This species later developed art and sculpture.

Homo neanderthalensis (or Neanderthals as seen in picture 2) is named after the Neander Valley in Germany and pre-dates Cro-Magnons by 400,000-25,000 years, leading to the belief that the two co-existed for approximately 20,000 years. Neanderthals typically had large brains, a brow ridge, barrel chests and large noses. By their skull morphology it can be seen they had a higher larynx and their tongue was higher in their mouth than humans today, suggesting they may have only been able to make slow and limited sounds. DNA sequencing has also revealed many were likely to have had ginger hair and that they often interbred with Cro-Magnons leading the European genome to today contain 1-4% Neanderthal DNA.

In conclusion, there were at least three interbreeding Pleistocene (2.6 – 0.01 million years ago) hominins and as such modern humans share DNA with their predecessors such as the Neanderthals.

~SA

Part 1: http://on.fb.me/1EcPExd Part 2: http://on.fb.me/1FrFZKk Pictures: http://bit.ly/1ETtCkq Homo erectus reconstruction by John Gurche; photographed by Tim Evanson. http://bit.ly/1LbFeno Neanderthal reconstruction by Tim Evanson.

Humans and Monkeys (Part 2 of 3): Hominoids and Hominins

Hominoids evolved from Old World Monkeys 25 million years ago. They can be categorised by an enlarged braincase, lack of tail and retention of grasping toes. This group contains apes seen today including the chimpanzee, bonobos, orang-utans and gorillas. The group can be split into the lesser apes (known as Hylobatidae) which includes gibbons and the Hominidae (Orangutans, Gorillas and Chimpanzees). Hylobatidae are arboreal (live in trees) and bipedal (walk on two legs).

Hominins however diverged from the Pan genus (chimpanzees) 6 million years ago. Despite all the photos seen on the internet showing human evolution, this was not a linear process. Hominins developed over a long time through many species, with some lines going extinct and other times when several species existed simultaneously. Despite this fact due to the nature of the fossil record we only know about some of these species in detail. The first hominin we know about in detail is Ardipithecus.

Ardipithecus lived between 6 and 4.4 million years ago in Ethiopia, was around 1.2m tall, and weighed 50Kg. Ardipithecus still had a chimp-sized brain and blunt teeth (thus was an omnivore). Most importantly however Ardipithecus kept its grasping big toes, meaning it was likely to have still been arboreal, however, this was the first hominin capable of bipedalism seen through its pelvic structure.

Australopithecine is known as the Southern Ape; there were at least four species of this Ape that lived from South Africa to Ethiopia between 4 and 2 million years ago. Most Australopithecines were between 1 and 1.5m tall, however, sexual dimorphism (the difference between a female and male of a species) was shown with males being up to 1.5x the mass of females. Like Ardipithecus, Australopithecine had long arms and fingers, meaning it too was adapted to tree climbing. However, it also had feet and short legs which were suited to bipedal movement on the grasslands. Bipedal movement was beneficial as it gave australopithecine a height advantage for spotting predators and they could use their arms while moving.

There are two famed ‘types’ of Australopithecine, gracile and robust. The most famous skeletal example of Gracile Australopithecines is Lucy, a 40% skeleton of a female Australopithecus found in Ethiopia. Like other gracile Australopithecines, Lucy was a lightly built omnivore and was bipedal. We know Australopithecine were bipedal as Laetoli, Tanzania shows 2 sets of australopithecine footprints walking side by side, dated to 3.7 million years old.

Robust Australopithecines are also known as Paranthropus (meaning beside human). They were around between 2.7 and 1.2 million years ago. Paranthropus was particularly noticeable due to its strong sexual dimorphism, skull crest, large jaws and teeth. Finally, the last link we know about in detail between Australopithecus and the genus Homo is known as Habilis (or handyman), yet scientists are still debating whether this group were Australopithecus or a Homo. The first specimen of Habilis was found in Tanzania by the Leakey family. Habilis lived between 2.3 and 1.4 million years ago, is thought to have had some basic vocalisation, and began to use some stone and bone tools. Next up, the Homo Genus.

~SA

Part 1: http://on.fb.me/1IHsyoK Pictures: http://bit.ly/1Ga5oHc Australopithecus reconstruction by Nachosan. http://bit.ly/1PIQLewParanthropus reconstruction by Nachosan.http://bit.ly/1JLcGA9 Homo Habilis Facial Reconstruction by Cicero Moraes. Further Reading: http://bit.ly/1bSxR7K The Smithsonian information page on ‘Human Fossils’

The Cradle of Humankind

Located 65 Km south west of South Africa’s capital city, Pretoria, is The Cradle of Humankind. The site includes the Sterkfontein Caves, where the famous 2.3 million year old fossil “Mrs. Ples” was discovered. The discovery was made by Dr Robert Broom and John T Robinson. Prior to 2010, the Sterkfontein Caves produced over 30% of hominid fossils ever found.

Including the Sterkfontein Caves and a massive complex of limestone caves, the site currently occupies over 45 000 hectares. There are close to 40 fossil-bearing caves across the site.

A massive number of homonin fossils have thus far been excavated from the many sites comprising the Cradle of Humankind, including some of the oldest ever discovered. A few of these fossils have been found to be almost 3.5 million years old.

It is theorized that hominins may have lived all across the African continent, but their fossils can only be found where the conditions for fossil formation are optimal. The hominin fossils found in dolomitic caves at the Cradle are often enclosed in a blend of limestone and breccia.

hominid – “group consisting of all modern and extinct Great Apes”

hominin- “the group consisting of modern humans, extinct human species and all our immediate ancestors”

Breccia – clastic sedimentary rocks made up of angular fragments. Often there are gaps between the angular fragments. These gaps are filled with a medium consisting of smaller particles that binds the rock together.

Renesh T

Image Source:

https://commons.wikimedia.org/wiki/File:Copy-of.mrs-ples-maropeng.jpg

References/Further Reading:

Kashmira Raghu BSc. Hons. MSc http://bit.ly/1lyU3b6 http://bit.ly/1IpOH9d http://bbc.in/1LSB6Nd http://bit.ly/1EN4f5U http://bit.ly/19hfUyi http://bit.ly/1xeqCAZ

https://blog.nationalgeographic.org/tag/rising-star-expedition/

The oldest Homo fossil

The Great African Rift Valley (along which the continent is being sundered apart by convecting mantle currents or a mantle plume rising from below) was the cradle of the human family, and fossils of our distant ancestors have turned up along much of its length. Ethiopia is famed for hosting the oldest remains of our genus and its ancestors found so far, including the iconic Australopithecine Lucy. The recent discovery of a lower jawbone and five teeth eroding out of a rocky slope turned up some 15 km from the Lucy site, and was dated by several methods as the earliest piece of our genus found so far, at 2.8 million years old (some half million years older than the next in line).

Like Lucy and many other important hominid fossils, it was found in the Afar triangle, the triple junction point where the Nubian, Somalian and newly separated Arabian plates meet, and start drifting apart. Nowadays the area is desertic, but back in our ancestor's time it was open grass and shrub land with tree lined rivers, though the evidence suggests that the area was considerably wetter when the new find walked the Earth than in Lucy's day, some 200,000 years earlier. This may indicate a climatic transition that killed off Australopithecus and promoted the development of the larger brains of the hominids.

Fossil hominids are very rare, and few specimens that date from 2-3 million years back help us fill in some major gaps in the evolutionary line of our species, since the period remains poorly understood since evidence is very scarce. As a scientist put it, you can put the entire collection of our ancestors remains for the whole million years into a shoebox and still have room for the shoes. When Lucy's species died out, two main lineages developed out of it, one of which led to us but no record of the transition period had turned up until now.

The jawbone shares some 'primitive' features with Australopithecus like the shallow chin bone while also having distinctive hominid characteristics, such as thinner teeth, and represents the earliest transitional specimen, right at the beginning of our genus. The remains are too scanty to know whether they are the first known species on our lineage (Homo habilis) or another, so far undescribed species. The site is being explored for further remains, and we'll keep you posted if anything interesting turns up.

Loz

Image credit: Brian Villmoare/PA

http://news.nationalgeographic.com/news/2015/03/150304-homo-habilis-evolution-fossil-jaw-ethiopia-olduvai-gorge/ http://www.theguardian.com/science/2015/mar/04/jaw-bone-discovery-in-ethiopia-is-oldest-ever-human-lineage-remains

http://www.npr.org/2015/03/05/390717001/jaw-fossil-in-ethiopia-likely-oldest-ever-found-in-human-line http://www.nature.com/articles/nature14224.epdf Orignal papers, paywall access:

http://www.sciencemag.org/content/early/2015/03/03/science.aaa1415 http://www.sciencemag.org/content/early/2015/03/03/science.aaa1343

Stepping Out: Laetoli Footprints

In 1976, Yale University paleoanthropologist Andrew Hill was working with Mary Leakey's research group on the excavation of an early-hominid archaeological site in Laetoli, Tanzania. Whilst conducting his work he unexpectedly stumbled across one of the most spectacular prehistoric discoveries ever made: a line of hominid footprints left in mud 3.6 million years ago.

Up until then, the earliest known human footprints were only tens of thousands of years old. Remarkably, Hill's Laetoli footprint trail was nearly 30 metres. It left us with an action replay of one of the first species of prehistoric hominids who walked upright on two legs.

The ideal surface material was created by a coating of volcanic ash from the nearby Sadiman volcano that settled on a sandy surface. When rain then fell, the sooty volcanic sediment became soft, like wet cement, and all the birds and small animals that walked on it left small prints. But they were joined by the track of two hominids, one large and the other smaller, trailed possibly by a third (child?), whose tracks share some of the larger individuals footprints.

A further eruption of dust from the volcano served to seal up the footprints for posterity before the rains returned and washed them away. A light rain then turned the ash into cement, which set solid. There, they remained until they were exposed by millions of years of gentle erosion.

These prints have led to all sorts of theories as to their origin, however they differ significantly from chimpanzee footprints and are not very different from those of modern humans, with an aligned big toe, heel, and an arched foot. Interestingly the smaller individual of the two (because they left shallower prints) is lopsided, bearing more weight on one side - perhaps carrying a baby? The sequence of depressions also reveal the pattern of walking, with an initial strike followed by a push off by the front toes, again like our own stride pattern.

The length of the footprints along the two trails are 19cm and 20cm, indicating that the individuals were probably about 120cm (4ft) and 152cm (5ft) tall. For the first time we had what amounted to a photographic record of pre-human intelligent activity that could be understood in terms of our present day movements, how amazing! A summer stroll on the beach could create the same impressions on the sand but only a marvellous accident of nature could preserve them.

~JM

Image Credit: https://abhsscience.wikispaces.com/Mary+Leakey

You can find more reading at: http://www.pbs.org/wgbh/evolution/library/07/1/l_071_03.html N. Agnew and M. Demas, 'Preserving the Laetoli Footprints' , Scientific America (September 1998), pp. 45-55. Mary D. Leaky and J. M. Harris (eds), Laetoli: A Pliocene Site in Northern Tanzania, Clarendon Press, Oxford (1987).

The earliest European footprint

The Lateoli footprints left behind by three Australopithecines 3.6 million years ago in our human cradle of Africa may be the most famous direct remnant of our past. I have stared awestruck in the more recent Cro Magnon era Grotte de Pech Merle in southwest France (though it may be Cougnac, my memory fails me) at a 15,000 year old footprint in glacial clay with an amazing arch and an incredibly broad open foot. On the Norfolk coast of England some prints 800,000 years old have been discovered, and recorded by 3D scanning before being destroyed by the waves.

The find is also the oldest evidence of human habitation in northern Europe, and was made last may during a low tide after rough seas had eroded the overlying sand away. There are three sets of older prints, all found in Africa. Up to five people walked on what is now the seashore, thought to be one adult male and several children, who were possibly foraging or hunting when they left their mark.

Their species remains indeterminate, but may have been Homo antecessor, whose remains have been discovered further south. Similar stone tools to theirs have been discovered in the area over the years. When these people came past, the British mainland was connected to the continent by a land bridge. The study of settlement patterns across Europe as the ice ages oscillated back and forth is being regularly rewritten as new finds and re analysis of old ones bring new evidence of occupation to light. Maybe the latest series of storms this winter will have revealed further joy for archaeologists and fossil hunters.

Loz

Image credit: Martin Bates

http://www.bbc.co.uk/news/science-environment-26025763 Original paper: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0088329

The oldest human DNA

A recent sequencing of mitochondrial DNA published in Nature is shedding a mysterious light on the complicated bush that is the Homo sapiens family. The genetic material came from a thigh bone excavated in the northern Spanish cave of Sime de los Huesos in the Atapuerca mountains, and is dated at 400,000 years old. It was found in the 1990's, along with the remains of 27 other people, and many cave bear bones. Scientists are unsure if the bodies were buries there or accumulated by some geological means.

The previous record was 70-80,000 years old, and belongs to the finger bone of our Densivan cousins found in another cave in the Caucasian Republic of Georgia. They co-existed with us and our Neanderthal cousins before becoming extinct. A debate is ongoing about the relative genetic contributions our cousins have made to our lineage through interbreeding.

The researchers developed a new technique allowing them to use highly deteriorated fossil DNA. Mitochondrial DNA occurs in all our cells, but not in the nucleus. These organelles help us to respire our sugars, and it is thought that they originally entered cells in as symbiotic bacteria hundreds of millions of years ago. In humans, mitochondrial DNA is inherited from the mother, and analysing its mutations at a known rate allowed us to bactrack to Eve, our last common female ancestor who lived in Africa around 100,000 years ago.

This new technique is expected to spread and revolutionise our understanding of human origins as excavated fossils from all over the world are analysed using this technique. It can also help us to estimate the level of genetic variation within populations of ancient man, which would help resolve several problems currently bedevilling human taxonomy (see http://tinyurl.com/mz767xo)

The researchers were surprised to find that the Atapuerca specimen shared more genetic commonalities with Denisovan man than with us or Neanderthals, though they physically resembled the latter. Neanderthal genes are found more densely in western European populations, while Denisovan ones are more prevalent in Siberia and Polynesia, and it was thought that there was a clear geographical divide between the sub species. With these Denisovan types coming from far western end of the Neanderthal zone in Spain, a reassessment of their previously thought range is needed.

Wherever we look, the story of human evolution gets more complicated, with multiple sub-species co-existing, hybridising and interbreeding. Disentangling the relationships between humans over the last half million years is now possible, and we look forward to exciting results in the coming years, and a possible thickening of the branches on the human bush. The team intend to tackle the harder to analyse nuclear DNA in order to build a more complete understanding of the makeup of this particular proto-Spanish population. They hope to learn whether they are a common ancestor of all three known sub species of human, or something else altogether.

Image credit: Javier Trueva

http://www.nature.com/news/hominin-dna-baffles-experts-1.14294 http://news.nationalgeographic.com/news/2013/12/131204-human-fossil-dna-spain-denisovan-cave/ http://www.scientificamerican.com/article.cfm?id=earliest-human-dna-shows-unforeseen-mixing-with-mystery-population http://www.theguardian.com/science/2013/dec/04/oldest-human-dna-discovered-spanish-cave

Original paper, paywall access: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12788.html

Fossil skulls create confusion in human family tree.

Science published a paper describing the first complete and best preserved hominid skull ever found, discovered with four different skulls and associated with primitive stone tools and extinct animal remains. They were excavated at Dmanisi cave in Georgia, dated to the Pleistocene 1.8 million years ago and have sparked a controversy over our evolutionary past.

They are relatively complete and their state of preservation is excellent, displaying several never observed details. A study of their anatomy comparing variation within the group and other finds elsewhere alongside their occurrence together suggest that what were once thought to be several distinct species of Homo (ergaster, gautengensis, habilis and rudolfensis) may be anatomical variations of a single species: Homo erectus. It is (or they are) also the oldest human ancestor(s) so far discovered outside Africa.

The site was once a watering hole, and the remains were found in carnivore dens where the carcasses had been dragged for consumption. They are thought to have died within centuries of each other (as good as dating resolution gets). The comparison within the group revealed that while they appeared quite different, their variation was comparable to that between modern human individuals or that of our closest relatives the chimpanzees. A single population of hominids excavated together seems to have a wider variation than previously thought.

The team points out that had the skulls been found in Africa, or the newly published skull and jaw had been found separately, they would almost certainly have been assigned to different species by taxonomists.

The researchers then compared them with skulls from Europe and Africa, and found that what had been labelled as several species coexisting with erectus displayed a similar amount of variation, suggesting that several branches of our family tree have been misperceived as separate. It suggests that Homo erectus was more variable than scientists have thought up until now. The quality of this find may force a reassessment of lineages described as separate branches in Africa, though there is (for obvious reasons, since careers may be at stake) strong resistance to the idea.

Opponents suggest their analysis is wrong, and point out that they seem like very primitive H. erectus, and may well even be an entirely new species. No doubt a flurry of papers and finds over the coming years will bring some clarity.

It is always hard to draw precise taxonomic lines between extinct species, since the usual criterion (whether they can successfully interbreed to produce fertile offspring) cannot be applied. The question is whether significant variation in fossils encompasses several species or the innate differences within one species. We covered a similar controversy over Archaeopteryx possibly being displaced as the earliest bird at http://tinyurl.com/k3xksm7, in which we discussed some of the elements that cause these difficulties.

In this case, sexual differences, variation within a species and other factors may have misled us into classifying one species as several. Had the main skull and jaw been found separately they would have been assigned to different species. Whatever the solution to the mystery of why five different (or one) species were buried at the same time in cave sediments, they allow us to compare the range of physical traits present in our ancestors living at that time, show us that early hominids migrated early to the Caucasus and may lop some branches off the currently recognised human evolutionary tree.

Loz

Image credit: M. Ponce de León and Ch. Zollikofer, University of Zurich/Science

http://www.theguardian.com/science/2013/oct/17/skull-homo-erectus-human-evolution Further photos: http://www.livescience.com/40503-dmanisi-ancient-human-skull-photos.html http://www.nytimes.com/2013/10/18/science/fossil-skull-may-rewrite-humans-evolutionary-story.html?_r=0 Original paper, paywall access: http://www.sciencemag.org/content/342/6156/326.abstract?rss=1

Footprints on the Sands of Miocene Time...

One day on the beach of Crete in the late Miocene, a bipedal creature walked through the sand, perhaps enjoying a day at the seaside.

One day on the beach of Crete in 2002, a Polish geologist named Gerard Gierlinski walked along the same seaside while on his vacation and saw... the tracks left by that creature of so long ago. Many tracks, not just one, with no tracks from forelimbs, that had to have been left by an animal walking upright. On two feet. Just like you and me.

Gerard and team returned to the site in 2010, and the hard work began. They scanned the footprints, they sampled the rock strata, and the results were so extraordinary that even the research team seemed astonished, showing a conservative difficulty to fully accept the implications of their own conclusions.

The rocks imprinted by these footprints are shallow carbonate sands. They contain microfossils, foraminifera that allow comparative dating. The sands are overlain by a rock formation associated with an abrupt and well-studied environmental change (the Messinian Salinity Crisis). This stratigraphy allows a spot-on determination of their date: the layer marked by the footprints are 5.7 million years in age! This is two million years older than any other hominid footprints yet discovered. And they aren't even in Africa.

Let's compare this age again: the well known hominid footprints at Laetoli, left in volcanic muds in Tanzania, are dated at 3.7 million years in age. Previous to that time, it is presumed that our ancestors walked on all fours, much in a style similar to chimpanzees. The last common ancestor of humans and chimpanzees has been estimated to have lived some 4 to 8 million years ago, though these dates are still open to heated discussion, with 7 million years as an accepted compromise.

So... if these footprints are indeed hominid, then the applecart of human paleontology has once more been overturned, upset to a degree that would require a complete re-think of early hominid history. There aren't supposed to be hominids walking around the beach of Crete, not to mention the plains of Africa, at this date in the late Miocene. Is it possible these aren't hominids, but some other life form that on occaision walks bipedally, you know, like bears or chimps? Comparison of footprints have been made, and there's simply no match -- except with your own tootsies.

There's only one way to test this theory: visit Crete, and leave your own footprints in its glorious sands and wait around 5.7 million years to see what they look like.

"Here about the beach I wandered, Nourishing a youth sublime, With the fairy tales of science, and the long result of Time." Tennyson

Annie R

With thanks to Charalampos Fassoulas of the Natural History Museum of Crete and Geopark Psiloritis, a co-author of the recently published study. Photos used with his courtesy.

Read more: http://bit.ly/2eRmfGv https://e-storieskritis.blogspot.gr/2017/09/blog-post.html http://nhmc.uoc.gr/el/news/human-fossil-footprints G.D. Gierlinski, et al., Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?, Proc. Geol. Assoc. (2017), http://dx.doi.org/10.1016/j.pgeola.2017.07.006 xxx–xxx.

Early Humans Face Fiery Flare-Ups

Humans have been living alongside nature's most volatile features since the beginning, with the most prominent discoveries of our early ancestors scattered along the East African Rift, a volcanically active zone that stretches from Ethiopia to Mozambique and marks where the continental plates are pulling apart. A new study of the geochronology of volcanic activity in the Ethiopian segment of the rift confirmed a previous theory that a major magmatic pulse of eruptions hit the Ethiopian Rift approximately 320 to 170 ka (In the notation for geologic time spans, ka = thousand years ago, Ma = million years ago). Using stratigraphic study of the volcanic deposits and both argon and radiocarbon dating of the deposits themselves, scientists from Ethiopia, the UK, and the USA recreated a detailed record of large eruptions at 4 volcanic centers which formed calderas and ejected large volumes of volcanic materials. The frequency of the volcanic deposits show that, during this period, the events were occurring at 5 times the average eruption rate for the past 700 ka.

This Mid-Pleistocene flare-up in volcanic eruptions coincides with the arrival of anatomically modern humans - Homo sapiens - in the evolutionary record around 200 ka. The landscape of the rift and human evolution are linked: in the rift zone, faulting and calderas create basins which often result in lakes and river basins which influenced where the hominid populations lived. The more hospitable environment of the rift also provided a corridor for migration, easier than through the highlands on the rift's flanks. The environmental change from large eruptions would have also influenced hominid speciation. The tephra (rock fragments ejected into the air) and ignimbrite (pumice fragments from pyroclastic flows) deposits from the eruptions would have spanned 40 to 100 km, which as the authors point out, is enough to span the width of the rift and block migration along it. Ash and acidic rains would have reached further, and disrupted the ecology of the rift lakes, altering the food chains that the human population relied on.

Further study is needed, but the population bottlenecks which resulted from the devastation of a highly eruptive period could have been a key driver of human evolution. Humans are still drawn to the wide rift valleys and bountiful lakes; today, the rift valley is home to a population estimated at more than 10 million, and this advance in our understanding of the volcanic record sheds light on how the dynamic environment of the East African Rift not only influenced human lives in the far past but may in the future as well. -CEL

Sources: http://go.nature.com/2eF4Yhx http://on.doi.gov/2ebl8RC

Image: A volcanic eruption at Nabro Volcano in neighboring Eritrea, 2011. Courtesy: NASA, http://bit.ly/2dyGsh9

The Valley of Bones: Olduvai Gorge

West of the volcanic slopes of Ngorongoro Crater, which was covered in another post not long ago, there is a deep cut across the landscape that interrupts the wide Serengeti Plains in northern Tanzania. A dry, winding ravine exposes layers of lava and ash, and within them, the traces of early human evolution. Named for a European misunderstanding of the Maasai word for wild sisal flowers, oldupai, Olduvai Gorge has a rich history of paleoanthropological finds, grueling excavations, and intriguing characters.

A German expedition in 1913 found an astonishing number of fossil animal bones, and a skeleton of Homo sapiens that was estimated by the discoverers to be 150,000 years old, based on the age of the rock unit. Oldoway Man, as he was called, would have been the earliest modern human to have been found at the time, and controversy over the dating lasted decades. Later estimates put the skeleton closer to 20,000 years, with the suspiciously complete skeleton buried in a grave that had been dug into the older rock; the rock layer the bones were found in consists of lacustrine (lake related) sediments, so that if the body had been deposited at the same time as the sediments, the skeleton ought to have been broken up and separated by the water.

WWI and the ensuing rounds of "who's got the colony" prevented further work until 1931, when Louis Leakey arrived at the site and, on his first day, found stone hand-axes, evidence of early tool-making. Though animal fossils and stone tools were abundant, it took until 1959 for the next spectacular hominid find in the gorge, when Mary Nicol Leakey uncovered fragments of a skull of an unknown species of australopithecine, a hominid genus that evolved in East Africa around 4 million years ago. She named the species Zinjanthropus boisei, though the specimen itself, which was dated to 1.75 million years (mya), was familiarly known as the Nutcracker Man for its strong jaws. Today the species is designated Paranthropus boisei.

Beyond the individual finds, Olduvai Gorge is remarkable for capturing the sequence of hominid occupation that unfolds there. The gorge cuts through deposits from an ancient lake, interrupted by periodic volcanic deposits; the lake provided a hospitable habitat for hominid development combined with easily datable volcanic rocks. Before Paranthropus, the site was home to Homo habilis ("handy man"), a species that was also first identified at Olduvai and named after the stone tools found in the gorge. Homo habilis is dated at the site from 1.9 mya, with Paranthropus overlapping from 1.8 to 1.2 mya. Another hominid species, Homo erectus, occupied the area from 1.2 to 0.7 mya, followed by Homo sapiens approximately 17,000 years ago.

Olduvai Gorge continues to reveal secrets about early human evolution - excavations are ongoing, and modern research also focuses on using geology and geophysical techniques to take a more big-picture view of the gorge. The Olduvai Landscape Paleoanthropology Project takes a "landscape" approach to look at wider population-scale patterns by reconstructing the ecosystem of the lake basin and identifying locations (springs, streams, etc) where hominid populations may have clustered and remains may be found. There is a wealth of information that can be uncovered from not just the bones themselves but the valley that holds them; one dry lake bed and one dusty gorge have allowed us to explore 2 million years of our own history as the family Hominidae.

-CEL

Image: Author Sources: "Born in Africa: The Quest for the Origins of Human Life," Martin Meredith Blumenschine et al 2012. http://bit.ly/1MKM0Cl