Human Evolution

Last week I wrote about how the Sun, along with the planets, were thought to have been formed. This time I will say a bit more about the colonisation of the land, a bit about extinctions and then talk about our human evolution and its history.

An artist’s conception of Devonian flora.

I said last week that the Huronian ice age might have been caused by the increased oxygen concentration in the atmosphere, which caused the decrease of methane (CH4) in the atmosphere. Methane is a strong greenhouse gas, but with oxygen it reacts to form CO2, a less effective greenhouse gas. Oxygen accumulation from photosynthesis resulted in the formation of an ozone layer that absorbed much of the Sun’s ultraviolet radiation, meaning unicellular organisms that reached land were less likely to die, and as a result Prokaryotes began to multiply and became better adapted to survival out of the water. These microscopic single-celled organisms have no distinct nucleus with a membrane and include bacteria. These organisms colonised the land, then along came Eukaryotes, an organism consisting of a cell or cells in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus. For a long time, the land remained barren of multicellular organisms. The supercontinent Pannotia formed around 600Ma (that is 600 million years ago) and then broke apart a short 50 million years later. Fish, the earlier vertebrates, evolved in the oceans around 530Ma. A major extinction event occurred near the end of the Cambrian period, which ended 488 Ma. Several hundred million years ago plants, probably resembling algae and fungi, started growing at the edges of the water, and then out of it. The oldest fossils of land fungi and plants date to around 480 to 460Ma, though molecular evidence suggests the fungi may have colonised the land as early as 1,000Ma and the plants 700Ma. Initially remaining close to the water’s edge, mutations and variations resulted in further colonisation of this new environment. The timing of the first animals to leave the oceans is not precisely known, but the oldest clear evidence is of arthropods on land around 450Ma, perhaps thriving and becoming better adapted due to the vast food source provided by the terrestrial plants. There is also unconfirmed evidence that arthropods may have appeared on land as early as 530Ma. The first of five great mass extinctions was the Ordovician-Silurian extinction and its possible cause was the intense glaciation of Gondwana, which eventually led to a snowball Earth where some 60% of marine invertebrates became extinct. The second mass extinction was the Late Devonian extinction, probably caused by the evolution of trees, which could have led to the depletion of greenhouse gases like CO2 or the eurotrophication, the process by which an entire body of water or parts of it, became progressively enriched with minerals and nutrients. It has also been defined as “nutrient-induced increase in phytoplankton productivity”. This meant that 70% of all species became extinct. The third mass extinction was the Permian-Triassic, or the Great Dying event, possibly caused by some combination of the Siberian Traps volcanic event, an asteroid impact, methane hydrate gasification, sea level fluctuations and a major anoxic event. In fact, either the Wilkes Land Crater in Antarctica or the Bedout structure off the northwest coast of Australia may indicate an impact connection with the Permian-Triassic extinction. But it remains uncertain whether either these or other proposed Permian-Triassic boundary craters are either real impact craters or even contemporaneous with the Permian-Triassic extinction event. This was by far the deadliest extinction ever, with about 57% of all families and 83% of all living organisms were killed. The fourth mass extinction was the Triassic-Jurassic extinction event in which almost all small creatures became extinct, probably due to new competition from dinosaurs, who were the dominant terrestrial vertebrates throughout most of the Mesozoic period. After yet another, the most severe extinction of the period around 230Ma, dinosaurs split off from their reptilian ancestors. The Triassic-Jurassic extinction event at 200Ma spared many of the dinosaurs and they soon became dominant among the vertebrates. Though some mammalian lines began to separate during this period, existing mammals were probably small animals resembling shrews. The boundary between avian and non-avian dinosaurs is not clear, but Archaeopteryx, traditionally considered one of the first birds, lived around 150Ma. The earliest evidence for evolving flowers is during the Cretaceous period, some 20 million years later around 132Ma. Then the fifth and most recent mass extinction was the K-T extinction. In 66Ma, a 10-kilometre (6.2 mile) asteroid struck Earth just off the Yucatan Peninsula, somewhere in the southwestern tip of then Laurasia and where the Chicxlub crater in Mexico is today. This ejected vast quantities of particulate matter and vapour into the air that occluded sunlight, inhibiting photosynthesis. 75% of all life, including the non-avian dinosaurs, became extinct, marking the end of the Cretaceous period and Mesozoic era.

Yucatan Chicxlub Crater in Mexico.

A small African ape living around 6Ma (6 million years ago) was the last animal whose descendants would include both modern humans and their closest relatives, the chimpanzees, and only two branches of its family tree have surviving descendants. Very soon after the split, for reasons that are still unclear, apes in one branch developed the ability to walk upright. Brain size increased rapidly, and by 2Ma the first animals classified in the genus Homo had appeared. Of course, the line between different species or even genera is somewhat arbitrary as organisms continuously change over generations. Around the same time, the other branch split into the ancestors of the common chimpanzee and the ancestors of the bonobo as evolution continued simultaneously in all life forms. The ability to control fire probably began in Homo Erectus, probably at least 790,000 years ago but perhaps as early as 1.5Ma, but it is possible that the use and discovery of controlled fire may even predate Homo Erectus and fire was possibly used by the early Lower Palaeolithic. It is more difficult to establish the origin of language and it is unclear as to whether Homo Erectus could speak or if that capability had not begun until Homo sapiens. As brain size increased, babies were born earlier, before their heads grew too large to pass through the pelvis. As a result, they exhibited more plasticity and thus possessed an increased capacity to learn and required a longer period of dependence. Social skills became more complex, language became more sophisticated and tools became more elaborate. This contributed to further cooperation and intellectual development. Modern humans are believed to have originated around 200,000 years ago or earlier in Africa as the oldest fossils date back to around 160,000 years ago. The first humans to show signs of spirituality are the Neanderthals, usually classified as a separate species with no surviving descendants. They buried their dead, often with no sign of food or tools. But evidence of more sophisticated beliefs, such as the early Cro-Magnon cave paintings, probably with magical or religious significance, did not appear until 32,000 years ago. Cro-Magnons also left behind stone figurines such as Venus of Willendorf, probably also signifying religious belief. By 11,000 years ago, Homo sapiens had reached the southern tip of South America, the last of the uninhabited continents, except for Antarctica which remained undiscovered until 1820 AD). Tool use and communication continued to improve, and interpersonal relationships became more intricate. Throughout more than 90% of its history, Homo sapiens lived in small bands as nomadic hunter-gatherers. It has been thought that as language became more complex, the ability to remember as well as to communicate information resulted so ideas could be exchanged quickly and passed down the generations. Cultural evolution quickly outpaced biological evolution and history proper began. It seems that between 8,500BC and 7,000BC, humans in the Fertile Crescent area of the Middle East began the systematic husbandry of plants and animals, so true agriculture began This spread to neighbouring regions, and developed independently elsewhere until most Homo sapiens lived sedentary lives in permanent settlements as farmers. It was also found that those civilisations which did adopt agriculture, the relative stability and increased productivity provided by farming allowed the population to expand. Not all societies abandoned nomadism, especially those in the isolated areas of the globe that were poor in domesticable plant species, such as Australia. Agriculture had a major impact; humans began to affect the environment as never before. Surplus food allowed a priestly or governing class to arise, followed by an increasing division of labour which led to Earth’s first civilisation at Sumer in the Middle East, between 4,000BC and 3,000BC. Additional civilisations quickly arose in ancient Egypt, at the Indus River valley and in China. The invention of writing enabled complex societies to arise, record-keeping and libraries served as a storehouse of knowledge and increased the cultural transmission of information. Humans no longer had to spend all their time working for survival, enabling the first specialised occupations, like craftsmen, merchants and priests. Curiosity and education drove the pursuit of knowledge and wisdom, and various disciplines, including science, albeit in a primitive form, arose. This in turn led to the emergence of increasingly larger and more complex civilisations, such as the first empires, which at times traded with one another, or fought for territory and resources. By around 500BC there were more advanced civilisations in the Middle East, Iran, India, China, and Greece, at times expanding, other times entering into decline. In 221BC, China became a single polity, this being an identifiable political entity, a group of people who have a collective identity and who are organised by some form of institutionalised social relations, having the capacity to mobilise resources. They would grow to spread its culture throughout East Asia and it has remained the most populous nation in the world. During this period, famous Hindu texts known as Vedas came in existence in Indus Valley civilisation. They developed in warfare, arts, science, mathematics as well as in architecture. The fundamentals of Western civilisation were largely shaped in Ancient Greece, with the world’s first democratic government and major advances in philosophy as well as science. Ancient Rome grew with law, government, and engineering and then the Roman Empire was Christianised by Emperor Constantine in the early 4th century but then the Roman Empire declined by the end of the 5th century. Beginning with the 7th century, the Christianisation of Europe began. In 610AD Islam was founded and quickly became the dominant religion in Western Asia. The ‘House of Wisdom’ was established in the Abbasid era of Baghdad and Iraq. It is considered to have been a major intellectual centre during the Islamic Golden Age, where Muslim scholars in Baghdad as well as Cairo flourished from the ninth to the thirteenth centuries until the Mongol sack of Baghdad in 1258AD. Meanwhile in 1054AD the Great Schism between the Roman Catholic Church and the Eastern Orthodox Church led to the prominent cultural differences between Western and Eastern Europe. In the 14th century, the Renaissance began in Italy with advances in religion, art, and science. At that time the Christian Church as a political entity lost much of its power. In 1492AD, Christopher Columbus reached the Americas, thus initiating great changes to the New World. European civilisation began to change beginning in 1500AD, leading to both the Scientific and Industrial revolutions. The European continent began to exert political and cultural dominance over human societies around the world, a time known as the Colonial era. Then in the 18th century a cultural movement known as the Age of Enlightenment further shaped the mentality of Europe and contributed to its secularisation. From 1914 to 1918 and 1939 to 1945, nations around the world were embroiled in World Wars. Following World War I, the League of Nations was a first step in establishing international institutions to settle disputes peacefully. After failing to prevent World War II, mankind’s bloodiest conflict, it was replaced by the United Nations and after that war, many new states were formed, declaring or being granted independence in a period of decolonisation.The democratic capitalist United States and the socialist Soviet Union became the world’s dominant super-powers for a time and they held an ideological, often violent rivalry known as the Cold War until the dissolution of the latter. In 1992, several European nations joined in the European Union and as transportation and communication has improved, both the economies and political affairs of nations around the world have become increasingly intertwined. However, this globalisation has often produced both conflict and cooperation. As we continue in this beautiful world though, we are at present having to cope with a world-wide pandemic for which no cure has yet been found. We are researching and looking for vaccines that it is said will at least reduce the adverse effects of Covid-19, however many do not believe that these same vaccines are what we need. As a result, a great many deaths are still being reported in countries right across our world. Some say it is a man-made virus, others are suggesting conspiracy theories, but I feel sure that just as in the past other viruses have been beaten, this one will also be. However, in the meantime we should surely behave responsibly and work together to help reduce the spread of this virus, no matter what our thoughts, ideas or beliefs may be. So that in years to come, others may then look back and learn, in order for all life on Earth to continue.

This week, a simple quote…

“The purpose of life is a life of purpose.”
~ Robert Byrne (22 May 1930 – 06 December 2016)

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