Tuesday, June 27, 2023

Climate Change & Us; WSF: Brave New Prehistoric World; WSF - Rewriting the Story of Us


This diagram by the study authors shows how climate change driven by astronomical forces — such as tilt in the earth’s axis and changes in the shape of the Earth’s orbit around the sun — has influenced ice ages and consequently, human evolution. Photo: Nature

Climate change and us: What really shaped
human evolution last 2 million years

Climatic shifts determined where food was available, driving
migration and adaptations, according to the study

Published: Thursday 14 April 2022

[edits & arrangements mine - re slater]


Ancient humans likely evolved in response to climate shifts by settling and adapting to newer habitats, according to a new study.

Climate change driven by astronomical forces — such as tilt in the Earth’s axis and changes in the shape of the Earth’s orbit around the sun — has influenced how much solar radiation reaches the planet, the study published in Nature noted.

This spurred the Ice Age and the warmer interglacial periods, according to researchers. These climatic shifts determined where food was available, driving migration and adaptations, the study noted.
“Astronomically-forced past climate change determined where ancient humans lived and how their habitat and food-preferences changed over time due to adaptation,” Axel Timmermann, lead author of the study and director of the IBS Center for Climate Physics (ICCP) at Pusan National University in South Korea, told Down To Earth.
The researchers mapped the habitats of five human lineages: Homo neanderthalensis, Homo erectus, Homo heidelbergensis, African Homo — Homo habilis and Homo ergaster — and Homo sapiens.

Previous studies have investigated the link between climate change and human evolution. Even though the idea is old, there has been very little hard data to support this hypothesis quantitatively, Timmermann added.

The researchers tried to address this gap by combining data on well-dated fossil remains and archaeological artefacts. A supercomputer helped them reconstruct the earth’s climate history over the past two million years.

According to their analysis, Homo erectus and Homo sapiens had the most extensive habitats:
  • While Neanderthals were more concentrated in Europe,
  • the early African homo found refuge in eastern and southern Africa.
  • Homo heidelbergensis settled in southern Africa, east Africa, and Eurasia [(e.g., The Levant/India - re slater)], the study determined.
Though all five human species showed a preference for a particular habitat, they responded to climate shifts, the researchers highlighted.

For example, Homo heidelbergensis and Neanderthals had to migrate from Northern Europe when ice ages made the region cold and dry, Timmermann explained.

So, they moved south to the Mediterranean, which had enough food available. When glacial conditions ended, forests moved northward quickly, and so did animals and Homo heidelbergensis and Neanderthals, he added.

Timmermann and his colleagues also found that around two to one million years ago, early African hominins preferred stable climatic conditions, staying back in narrow habitable corridors.

Homo heidelbergensis, on the other hand, migrated and adapted to make use of a much wider range of available food resources in new environments. A major climatic transition about 800,000 years ago triggered this migration, the study found.

“Archaic humans either had to adapt to the new environment or migrate to different regions,” Timmermann said,

Homo heidelbergensis became global wanderers by reaching remote regions in Europe and eastern Asia, Elke Zeller, PhD student at Pusan National University and co-author of the study, said. “Climate conditions are strongly connected to food security,” Timmermann added.

The researchers also went a step further by documenting when and how one species developed into another. When major ice age cycles began, Homo heidelbergensis split into two groups: European and African, the study suggested.

Around 400,000-500,000 years ago, the European group may have gradually evolved into Neanderthals, Timmermann pointed out.

And around 200,000-300,000 years ago, the African group likely developed into the earliest Homo sapiens in the southern [(and eastern - re slater)] part of the continent, according to the study.

Persistent harsh climate conditions could trigger a gradual transition from one species to another, the expert added.

In the future, the team plans to gain a clearer picture of ancient humans by studying the impact of past climate change on human genetic diversity, Timmerman said.


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BRAVE NEW PREHISTORIC WORLD

1:07:31
Brave New Prehistoric World
Premiered May 4, 2023

Recent breakthroughs in dating ancient samples of DNA and human remains have led to a radical reassessment of human origins.
At least ten other early human groups–some with the cognitive capacity to make art, jewelry and herbal medicines–occupied the planet at the same time as our ancestors, Homo Sapiens, and some of their genomes live within us today.
Leading archeologists and paleoanthropologists join Brian Greene to discuss how these surprising new insights are transforming our understanding of early Humans.
This program is part of the Big Ideas series, supported by the John Templeton Foundation.
Participants: Rebecca Ackermann Thomas Higham Sheela Athreya Viviane Slon


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Rewriting the Story of Humankind

0:02 / 1:40:51
Rewriting the Story of Humankind
Premiered Jun 9, 2023

What attributes set our species apart? Taming fire? Expressing artistically? Solving problems creatively? Recent discoveries that have already upended humankind’s origin story by expanding our family tree, are now challenging long-held assumptions about what makes us special.
Paleoanthropologist Lee Berger is a leading figure in these breathtaking developments and he joins Brian Greene to discuss how new discoveries are now rewriting human history.
This program is part of the Big Ideas series, supported by the John Templeton Foundation.
The live program was presented at the 2023 World Science Festival Brisbane, hosted by the Queensland Museum.
 
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Evolution of Earth's Climate & Biological Life to the Holocene Age of Modern Civilizations



Evolution of Earth's Climate & Biological Life
to the Holocene Age of Modern Civilizations

To speak to humanity's origins must also be to speak to the conditions of the Earth which allowed the human species to evolve through it's lineages. The history of the Earth's many varied climate changes over the aeons is complex and complexly evolving. Below is a recommended link to investigate in detail each age as listed. They tend to be lengthy because of the detail involved. It is recommended that they are read beyond the introductory paragraph's copied below.

R.E. Slater
June 27, 2023



History of Earth's Climate
1. Precambrian

Introduction

Visible tangible life in the form of trilobites and other animals appeared for the first time in Cambrian. That is why the traditional boundary between the distant geological past and the period of life on Earth, is defined at the start of Cambrian. Cambrian is the first part of Phanerozoic, which traditionally denotes the era, where life has existed on Earth. This article is about the climate during the whole period before Phanerozoic that often is referred to as Precambrian.


The geological eons in Precambrian - Hadean was the burning inferno right after Earth's creation. The first rocks, that we know about, were formed in Archean, water vapor condensed, and an atmosphere of nitrogen and methane was created. Proterozoic was the eon when cyanobacteria produced oxygen, iron and methane were oxidized, and life emerged in the late of the period on the bottom of the sea. Several very severe ice ages occurred in Proterozoic that is the Huronian, Sturtian, Marinoan and Gaskiers ice ages. Phanerozoic denotes the period of life on earth...

1. Introduction

Phanerozoic denotes the part of the Earth's history, where life has been.

Paleozoic is the longest of the Phanerozoic eras. It was the period of early life where plants, corals, mollusks, insects, fish, and many other living organisms emerged. Paleozoic is divided into six geological periods, which are the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.

It is common to call the widespread explosion of life for the Cambrian explosion. The Cambrian climate is assumed to have been temperate. The Ordovician and Silurian periods had a warm greenhouse climate only interrupted by the Andean-Saharan Ice Age. Devonian and Carboniferous were periods of considerable stability until the Karoo Ice Age at the end of Carboniferous. In Permian dominated a harsh and dry continental climate on the enormous Pangea continent.


Hadean was the glowing inferno just after Earth was formed. In Archean the first rocks, which we know about, were formed, water vapor condensed and an atmosphere of nitrogen and methane came into being. In Proterozoic cyanobacteria produced oxygen that oxidized iron and methane. Also in Proterozoic occurred several very severe Ice Ages that is the Huronian, Sturtian, Marinoan and Gaskiers ice ages. At the end of the period, life emerged on the seabed.

However, the early geologists, who defined and named the geological periods, knew nothing of fossilized bacteria from Archean or the exotic Ediacaran fauna in the late Proterozoic. They had found the fossilized trilobites from the Cambrian, and therefore they believed that it was during that time life emerged on Earth, and therefore it should be marked by the start of a special geological era, which was characterized by life namely Phanerozoic.

Phanerozoic has been divided into Paleozoic, Mesozoic and Cenozoic that we can call Earth's antiquity, medieval and modern times. Paleozoic was the era of early life and is the subject of this article. Mesozoic was the era of the dinosaurs; and Cenozoic is the age of mammals....

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History of Earth's Climate
3. Mesozoic


1. Introduction

Phanerozoikum is the name of the part of Earth's history where there was visible tangible life. It is divided into Paleozoic, Mesozoic and Cenozoic, which are popularly called the Earth's ancient, medieval and present.

Mesozoic was the period of the dinosaurs. The period is further divided into Triassic, Jurassic and Cretaceous.

Start of Mesozoic with the beginning of Triassic was characterized by the harsh and dry continental climate of the gigantic Pangaea continent. Pangaea's split up in the following Jurassic period paved the way for a hot and humid greenhouse climate with little temperature difference between low and high latitudes. The temperature in Cretaceous was even higher, and most of the world was most likely covered with damp forests.


The surface of the Hadean Earth was a glowing chaos, characterized by intense radioactivity and an atmosphere of toxic gases. In Archean Earth's surface was solidified, the atmosphere consisted of nitrogen and methane, and the first cyano-bacteria occurred. In the Proterozoic methane and iron was oxidized and an atmosphere with oxygen was formed.

Phanerozoic represents the part of Earth's history, where visible tangible life existed, from the appearance of the trilobites in early Cambrian until the emergence of humans and historical time.

The Phanerozoic is divided in Paleozoic, Mesozoic and Cenozoic that can be called Earth's antiquity, medieval and modern times.

Paleozoic was the period of early life where plants, insects, fish, mollusks, corals and many more living organisms developed. Mesozoic was the era of the dinosaurs and is described in this article, and Cenozoic is the age of mammals...

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click here to enlarge chart

History of Earth's Climate
4. Tertiary


1. Introduction

Phanerozoic is the part of Earth's history, where there has been visible tangible life. It is divided into Paleozoic, Mesozoic and Cenozoic, which are popularly called the Earth's antiquity, medieval and present.

Cenozoic is the age of mammals. Tertiary is the name of that part of the age when there were no humans. It is the earliest and longest-lasting part of Cenozoic. Tertiary means the third (age). The five periods of the Tertiary are Paleocene, Eocene, Oligocene, Miocene and Pliocene.


The geological periods - Hadean was the glowing inferno just after the Earth's creation. In Archean the first rocks were formed, an atmosphere of nitrogen, methane was formed and water condensed. In Proterozoic cyanobacteria produced oxygen that oxidized iron and methane, at the end of the period life emerged on the seabed. The entire period prior to Phanerozoic is often called the Precambrian, as it was previously believed that life originated in the Cambrian (earliest period of the Paleozoic) some 500 million years ago.

Phanerozoic - which denotes the period of life on earth - is divided in Paleozoic, Mesozoic and Cenozoic. Paleozoic was the period of early life, when plants, insects, fish, mollusks, corals, and many others living organisms were developed. Mesozoic was the era of the dinosaurs and Cenozoic is the age of mammals, which latter is further divided in Tertiary and Quaternary.

Tertiary denotes that part of the age of mammals when no humans existed. The climate of Tertiary is the subject of this article.

There are more and newer definitions of geological periods adopted at international geological congresses. Some divide the Tertiary into the periods Paleogene and Neogene, others let Quaternary start later in more accurate harmony with human appearance. However, the traditional period-division seems the author most suitable for a popular presentation....

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History of Earth's Climate
5. Pleistocene


Introduction

Phanerozoic is the part of Earth's history, where there has been visible tangible life. It is divided into Paleozoic, Mesozoic and Cenozoic, which are popularly called the Earth's antiquity, medieval and present.

The Cenozoic is the age of the mammals. The part of the Cenozoic, where man has existed is called Quaternary, which means the fourth (age). Quaternary is composed of the periods Pleistocene and Holocene.

However, the Pleistocene lasted 2.6 million years, which is far, far more than the Holocene, which so far has only lasted about 11,000 years. Basically, the Holocene is just another inter-glacial, of which have already been many in the Pleistocene, but it is in this very special inter-glacial that human civilizations have evolved and all of the known history has taken place, and therefore we find this period in the geological and climatic history of Earth immensely important.

But, this article will deal with Pleistocene.

Pleistocene is the period in Earth's history that we commonly refer to as the Ice Age. Through much of this period, the Earth's northern and southern regions were covered by kilometer thick glaciers. It is important to recognize that the Pleistocene was a series of real ice ages, separated by relatively short interglacial periods. The Pleistocene started 2.6 million years ago and lasted until the termination of the Weichsel glaciation about 11,711 years ago.


Timeline of Earth's geological periods. Time progresses from right to left. The glowing inferno just after Earth was formed is named Hadean. In Archean water condensed and an atmosphere of nitrogen and methane was formed together with the first rocks that we know about. In Proterozoic cyano bacteria produced oxygen, which oxidized iron and methane, at the end of the period life emerged on the seabed.

Phanerozoic represents the era in which there has been visible tangible life. It is divided in Paleozoic, Mesozoic and Cenozoic. Paleozoic was the period of early life. Mesozoic was the time of the dinosaurs, and Cenozoic is the era of mammals, which latter further is divided into Tertiary and Quaternary. Tertiary represents the age of mammals and means the third (time). Quaternary means the fourth (time) where not only mammals but also humans existed.

Pleistocene is the first and most part of Quaternary and the subject of this article.
Holocene is marked with red and is slightly visible to the left...

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History of Earth's Climate
6. End of Pleistocene


1. Introduction

Last glacial absolute maximum took place about 26,500 to 19,000 years ago. The ice sheet covered then the whole of Scandinavia and the Baltic region down to North Poland and Germany. In North America, the ice cap extended down to the Great Lakes between Canada and the United States.


Cenozoic is the period of mammals, which followed the Mesozoic which was the period of the dinosaurs. Tertiary is that part of Cenozoic where no humans existed, and Quaternary represents the part of Cenozoic when there were humans. Quaternary is subdivided into Pleistocene and Holocene. Holocene represents the present which basically is a Pleistocene interglacial period. The climate in the last phases of the Pleistocene is the subject of this article...

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History of Earth's Climate
7. Holocene


1. Introduction

If you want to know what the climate was like in the Holocene, simply take some outerwear and go out into nature and look around. Holocene refers namely to the present since the end of the Weichsel glaciation.

The interglacial Holocene has supported the development and growth of human civilizations, it has been the cradle of civilizations, not to say their uterus. It started around 11,700 years before present with a sudden warming from the cold period called Younger Dryas. In only ten years time the temperature in Greenland rose with an impressive 8 degrees, which corresponds to that North Europe's climate was replaced with a Mediterranean climate. It is not known, what caused this rapid rise in temperature.



Cenozoic is the period of the mammals, which followed the Mesozoic that was the period of dinosaurs. Tertiary is that part of Cenozoic, where no humans existed , and Quaternary means the part of Cenozoic, where humans exist. Quaternary is composed of Pleistocene and Holocene. Pleistocene is the period that we in common language call the Ice Age. Holocene represents the present, which basically is a Pleistocene interglacial period. Holocene is represented by the thin red line on the far left. The climate of the Holocene is the subject of this Article.

During the following one thousand years, the temperature increased so that climate became several degrees warmer than today. About 8,000 years before present, in Hunter Stone Age, occurred the hottest period throughout the Holocene. This initiated the warm period called the Holocene Optimum, which lasted almost until about 4,500 years before present, whereafter the temperature continued to drop through bronze age, iron age and historical time until it reached a low point in "The Little Ice Age" in the years 1600- 1700. Within the last few hundred years, the temperature has again increased, but not to such heights as in Hunter Stone Age.
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The Origin of Humanity



The origin of our species

By Jenny Wong and Lisa Hendry

Our Human Evolution gallery explores the origins of Homo sapiens, tracing our lineage since it split from that of our closest living relatives, the chimpanzee and the bonobo.

Gallery developer Jenny Wong tells us more....

The gallery takes visitors on an epic journey spanning the last seven million years.

Starting in Africa with our early hominin relatives (who are more closely related to us than to chimpanzees), visitors will travel forward in time to meet our ancient human relatives as they spread into Europe and Asia. The journey ends with modern humans as the only surviving human species in the world today.

Along the way, visitors can see star specimens from the Museum collections, and get to grips with some of the latest research shedding light on our past.

Conservator Effie Verveniotou and human origins researcher Dr Louise Humphrey examine the oldest nearly complete modern human skeleton ever found in Britain before it goes on display in the gallery. Cheddar Man lived around 10,000 years ago.

A great saga

The story of human evolution is not one of neat, linear progression with a concrete beginning and end. Instead, it is a tale of a family tree whose complex and bushy branches stretch over many millennia and continents. It features a changing cast of ancient hominin relatives, evolutionary dead-ends and many unknowns. Adaptation, survival and extinction provide the dynamic backdrop to this story.

By piecing together fossil traces, scientists are revealing what our ancient relatives were like, how they were related and how they adapted to life in different landscapes and challenging climates.

Meet the ancient relatives

Entering the gallery, visitors meet hominins like us and our extinct australopithecine relatives, comparing them to non-hominins like the chimpanzee to explore the differences.

The human lineage split from the chimpanzee lineage around seven million years ago. Fossil evidence relating to the earliest hominins that lived after this split is scarce, but it provides important clues about how our ancient relatives lived.

From the six- to seven-million-year-old Sahelanthropus tchadensis skull found in Chad, we know that they had evolved small canines, while six-million-year-old Orrorin tugenensis leg bones show that they exhibited primitive bipedalism (walking on two legs).

Visitors can further investigate the key hominin traits of habitually walking upright and having small canines that aren't used as weapons, using an interactive digital touchscreen.

The 3.5-million-year-old Laetoli canine belonging to Australopithecus
afarensisis the oldest hominin fossil in the Museum's collection

Visitors to the gallery will also be able to see a replica of one of the most famous bipedal hominins, the Australopithecus afarensis known as Lucy, who lived around 3.2 million years ago.

By around two million years ago, several australopithecine species like Lucy had evolved and spread across southern and eastern Africa. Fossil remains show that they had adapted to survive in different ecological niches by altering their diets.

Scientists think that some form of australopithecine is likely to have given rise to the next phase of human evolution, the genus Homo.

What is a human?

There have been many species similar to us that have lived over the last two million years. Some co-existed with modern humans in Asia and Europe as recently as 40,000 years ago.

Who these relatives were, and how they lived, is the subject of the next part of the gallery.

Apart from our species, the gallery features eight other kinds of human: Homo habilis, Homo rudolfensis, Homo erectus, Homo antecessor, Homo heidelbergensis, Homo floresiensis (nicknamed 'the hobbit'), Homo neanderthalensis (the Neanderthals) and the recently discovered Homo naledi. The mysterious Denisovans, who may or may not turn out to be a distinct species, also make an appearance.

Scientifically accurate Homo neanderthalensis model by Kennis & Kennis. Neanderthals
survived in Europe until the species went extinct about 39,000 years ago.

Fossil specimens, casts and other objects on display provide a series of snapshots in time, offering visitors glimpses of our ancient relatives' lives.

Exhibits include a flint handaxe possibly made by Homo heidelbergensis and a butchered rhino skull whose brains were extracted and eaten by ancient humans in Sussex, England around 500,000 years ago.

Visitors can investigate a Neanderthal burial and other clues about Neanderthal behaviour, such as innovative tools, which suggest minds capable of creativity and invention.

Coming face to face with a scientifically accurate Neanderthal model, visitors will see how physically adapted they were to cold climates.

The tiny Homo floresiensis highlights another way in which our ancient relatives adapted to their environment, becoming smaller in response to the limited resources available in the island environment of Flores, Indonesia - a process known as island dwarfism.
Fascinating firsts

Visitors will encounter some of the exciting research Museum scientists have recently been involved in as part of the Ancient Human Occupation of Britain and Pathways to Ancient Britain projects, including the discovery of the oldest human footprints in Europe.

In 2013, erosion of the Norfolk coastline exposed a preserved trail of footprints dating to around 900,000 years ago. Analysis suggests they were left by a small group of humans, perhaps some of the first to set foot in Britain. You can touch a replica footprint in the gallery.

An area of the 900,000-year-old footprints found at Happisburgh, Norfolk,
with an enlarged photo of footprint eight showing toe impressions

Other star specimens in this part of the gallery include the Broken Hill skull of Homo heidelbergensis - the first early human fossil found in Africa - and the Gibraltar 1 skull, which was the first adult Neanderthal skull ever found. Gibraltar 1 has recently been sampled for ancient DNA, with the results eagerly awaited.
A new view into the past

With advances in the extraction and analysis of ancient DNA and the sequencing of both Neanderthal and Denisovan genomes, scientists are revealing in more detail how our ancient relatives could have looked and behaved. They are also pinpointing what exactly we have inherited from our closest ancient human relatives.

We know that interbreeding with these ancient humans allowed Homo sapiens to acquire genes that improved their chances of survival, and some of these genes remain in many of us today.

Some of the DNA inherited from Neanderthals seems to have been involved in boosting immunity, for example, while a gene variant inherited from Denisovans - present today in Tibetan populations - may enable better survival at high altitudes.

Gibraltar 1, the first adult female Neanderthal skull ever discovered

Out of Africa

The final part of the gallery explores how our species, Homo sapiens, originated in Africa, before dispersing around the world and becoming the only surviving species of human left today.

Modern humans evolved in Africa around 200,000 years ago. They have a higher and more rounded brain case, smaller faces and brow ridges, and a more prominent chin than other ancient humans.

Casts on display include modern humans fossils found in Africa (about 195,000 years old), Israel (around 100,000 years old) and Australia (around 12,000 years old).

These fossils show that rather than springing fully formed from Africa, typical modern human characteristics instead built up over time. They also suggest that there may have been at least two waves of migration out of Africa - one dating back to around 100,000 years ago and another to around 60,000 years ago.

Outside of Africa, we are all descendants of those who left in that second wave of migration.

Evolving culture

Artefacts in this final zone of the gallery highlight the craftsmanship and ingenuity of modern humans, as well as early symbolism and cultural practices such as cannibalism.

Human skull fashioned into a cup. Museum scientists Dr Silvia Bello and Prof Chris Stringer have been researching cut marks on bones from Gough's Cave in Somerset, England, to understand more about the behaviour of humans who lived there 14,700 years ago. | Read more

A changing story

Human evolution is a puzzle with thousands of fossil pieces and billions of DNA fragments. As new fossils continue to be uncovered and added to the human family tree, new dating techniques and climate data are providing a more accurate picture of the conditions in which our ancient relatives evolved.

Improved DNA techniques will help determine where each species fits within the family tree, and give us further insights into recent and ongoing human evolution.

Museum scientists and collections are playing a key part in shaping one of the most exciting fields in science today. We're delighted to be able to show visitors some of this work in the gallery.

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How we became human

By David Urry and Lisa Hendry


Today, we sit alone on the only remaining branch of the human family tree. But we are only one character in the story of human evolution.

To truly understand who we are, we must look at how we got here and the key physical traits that make us human.

Bipedalism

The ability of humans to comfortably stand on two feet for extended periods of time marks us out from almost all other animals.

This feat has come about over time through a series of anatomical changes to our skeleton, affecting our cranial base, spine, pelvis, femur, knees and feet.

Australopithecus sediba (centre) and modern human (far right) skeletons
are adapted to walking upright, but a chimpanzee's skeleton (left) isn't.

These features serve as useful identifiers in the fossil record of likely bipedalism in our ancestors, the earliest evidence of which may come from the six-million-year-old Orrorin tugenensis.

But it's not until Homo erectus came on the scene about 1.9 million years ago that we see the long-legged form, similar to our own, that makes us so well suited to running and walking over long distances.

Big brains

Humans are big headed - our brains are around three times larger than would be expected for an animal of our size.

The brains of our early hominin relatives (species more closely related to us than to chimpanzees) were not especially large. Australopithecine brains were little bigger than those of other apes, about the size of a grapefruit.

Australopithecus africanus had a much smaller brain than humans

It isn't until the emergence of the genus Homo that we begin to see a more significant increase in the size of brains, dominated by a swelling of the cerebral cortex.

Between 1.8 million and 700,000 years ago the average brain size of Homo erectus doubled, and the brains of Neanderthals and Homo sapiens are even larger.

What caused this drastic increase in size is unclear, but it was made possible by changes in diet that allowed humans to extract more energy from their food. The production of tools and fire that allowed pre-processing of plant foods - reducing the work load of jaws, teeth and digestive systems - probably played a part. So did access to meat, a rich source of protein.

A larger brain is clearly linked to a number of distinctly human traits: the ability to create more complex tools, more advanced hunting techniques, complex social structures and the advent of language.

This 400,000-year-old spear tip made from yew wood was whittled to a
point with a stone tool. It would have made a lethal weapon for hunting with.

Similar sized sexes

Although not as obvious a human trait as some of the others, a reduction in sexual dimorphism - the difference in size and shape between males and females - is closely linked to one of the most important human features of all: widespread cooperation in a population.

High sexual dimorphism in most primates is associated with competition between males for access to females. Most commonly, this leads to males having much larger bodies and canine teeth, which are used in displays of aggression.

A chimpanzee bares its large canine teeth. Male chimps have much larger canines than female chimps and use them to signal aggression, unlike humans. © Sergey Uryadnikov/ Shutterstock.com  |  Read more

A chimpanzee bares its large canine teeth. Male chimps have much larger canines than female chimps and use them to signal aggression, unlike humans. © Sergey Uryadnikov/ Shutterstock.com  |  Read more

All known hominins have smaller canines than our closest living relatives, the chimpanzees and bonobos. Among some of our early hominin relatives, such as Australopithecines afarensis, we see quite a large difference in body size between males and females. But species in the genus Homo start to show a level of sexual dimorphism similar to our own.

Why is it an important trait for becoming human?

Since reduced sexual dimorphism correlates with less aggression between males, it is likely to be associated with greater cooperation within a population and probably made the development of successful societies and civilisations much easier.

Childhood

The existence of a childhood appears to be an important development on the road to becoming human. We define it as the period of time following infancy, when the youngster is weaned but is not able to care for itself.

It is essentially an extended period of growth with continued rapid development of the brain. This period allows us to learn the complex set of skills and social intricacies that equip us to exist in complex human societies.

Childhood also brings with it another, less obvious benefit for human populations.

Unlike most primates, we are still relatively helpless once we stop feeding on our mother's milk. A child is therefore still dependent on the care of others. Importantly however, provision of care is not limited to the mother, but could instead come from a grandmother, elder sibling, or another close relative.

This frees up the mother's time, enabling her to engage in other activities and also to have another child much sooner than would be possible if she was still nursing.

An extended childhood appears to have first developed in the Homo genus. The beginnings of this are found in Homo erectus after about 1.9 million years.

A precision grip

Although other animals use tools, our mastery is second to none, and distinctly human. Ultimately, it stems from the development of a precision grip, the result of changes to the anatomy of the hand. One of the key anatomical features that has enabled this is the presence of a little projection of bone called the metacarpal styloid process.

This bone allows us to apply greater amounts of pressure to the wrist and palm. Together with changes in the proportion of our digits, it means we can squeeze objects between our thumb and the tips of our fingers.

Considerable manual dexterity was needed to carve this harpoon point from reindeer
 antler. Around 14,000 years old, it was found in Kent's Cavern, Devon.

A chimpanzee, by contrast, is unable to touch the tip of its thumb with the tips of all its fingers, and as a result does not have the same manual dexterity.

Some of our more distant relatives such as Australopithecus afarensis, including the famous fossil known as Lucy from 3.2 million years ago, also lacked a precision grip. But recent research using CT scanning suggests that Lucy's close cousin, Australopithecus africanus, may have possessed the required anatomy and grip to wield stone tools more than three million years ago.

This grip may have become even more refined by the time of Homo erectus 1.8 million years ago. Coupled with an increased intelligence, it has equipped humans with incredible influence over the world around us.

This film shows the making of a Levallois core and flake, an innovative stone tool developed by the Neanderthals and early Homo sapiens.

Around 300,000 years ago, they began to shape stone cores from flint that they could carry as a kind of toolkit. They would strike off flakes from this portable core and skilfully turn them into tools for specific purposes such as cutting, scraping, piercing and carving.

You can learn more about our origins and evolution in the Museum's Human Evolution gallery and this feature about the origin of our species.
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