Gy3021 Past Human Environments

Nicholas Drake

April 2002

 

The past six billion years of Earth’s history has been one of drastic change. In only the last 500 million years, life has evolved into multi-cellular organisms. This period in Earth’s history is known as the Cambrian explosion. Single cellular bacterium evolved into multi-cellular organisms that thrived throughout marine environments. Without geophysical or environmental boundaries to development, and with a suitable cultivating climate, populations of species can development un-hindered.

 

Following the Cambrian explosion to the present Holocene, over 30 billion species have evolved, with only an estimated 30 million species present today that means that 99.9% of species that have evolved with Earth are now extinct[1]. The adaptations and evolutionary characteristics are shaped from generation to generation in individual species, with geographical/environmental change bringing the need for species variation. For example, Darwinian evolutionary science articulates the differences between bird populations within the archipelago of the Galapagos Islands. Differences between the morphological appearance and the species that live on islands pre-requests the need for evolutionary speciation for survival. For example, on some islands, South American finches have strong, thick beaks to over-turn rocks in search of food; on neighbouring islands, the same bird species has evolved a different beak, longer and thinner as a result of bark-dwelling insects that form the finches diet[2].

 

Both catastrophes and evolution are dynamic and unpredictable by nature, yet catastrophes and evolution are the key to adaptation and species’ survival. For the context of this essay, evolution must be discussed in terms of both human and other species evolution in order for survival through catastrophes and extinctions.

 

To understand human evolution including why species moved as they did across the landmasses of Earth must include appreciation of extinction and disaster events, and their intensities as an integral part of natures’ management of populations.

 

Catastrophes such as earthquakes, flooding, drought, disease, tectonic uplifting, climate change, solar variability and asteroid impact have occurred and will occur in the future. It is only the scale and intensity of the events that determines the overall destructive ability.

Small-scale catastrophes can have a dramatic impact on localized populations and may bring about a change to the ecological framework of an environment, although only individual species and their populations may be affected.

Large-scale catastrophes and natural disasters can alter the geomorphic blueprint of an area (such as tectonic uplifting of mountain ranges), and in turn alter climate to that area. As a result the environment is altered with a huge initial loss of biodiversity.

Following these events, biota enters a ‘survival of the fittest’ scenario in that species adaptation to the new environment is the key to survival.

 

Geological time dating back to the Cambrian period of 540mya was divided into three era’s separated by two major catastrophes by the French anatomist Baron George Cuvier in late 18^th century. The Palaeozoic (ancient life) of 540mya-250mya caused by chemical changes in the atmosphere, which led to the Mesozoic (middle life) between 250mya-65mya; divided by the fore mentioned KT boundary, which leads into the Cenozoic (modern life) with distinct glacial and solar cycles dominating environmental change from then onwards.

 

Large-scale scientifically proven (Iridium, a rock found in asteroids can be found at the KT boundary) global extinction events such as the asteroid impact that brought about the extinction of the dinosaurs at the Cretaceous–Tertiary boundary (known as the KT event) of 65million years ago brought distinct change to the atmosphere causing an in-ability of vegetation to photosynthesise. It has been calculated that the KT event reduced marine and terrestrial biota between 75-85%.

 

The largest geological extinction event so far documented was at the boundary between the Permian and Triassic boundary of around 251mya. It has been estimated that up to 95% of all species became extinct during this cataclysmic event. The exact mechanism for this destruction is still debatable, some scientists believe that ‘hypercanes’ (Very massive hurricanes) were responsible for thousand mile an hour winds across the surface of the planet. The mechanism to generate these hypercanes is theoretical in nature such that an asteroid impact, undersea volcanic eruptions or up-welling of volcanically heated water could raise the temperature of the oceans surface, providing plenty of warm, moist air to fuel runaway hurricanes[3].

 

Homo-sapiens have evolved amid a high point of global biodiversity. We are but one of millions of species that live on Earth, the product of half a billion years of life’s flow, lucky survivors of at least 20 biotic crises[4]. Ancestors of the homo-sapien were not as geographically distributed or as numerous as populations today and habitats were found mainly in-between the tropics.

 

Background or natural extinctions are a natural process which Darwin may conclude as the ultimate survival of the fittest, genetically. A species can become extinct if it does not maintain the essential biological processes needed to sustain life. Darwin states that “species become extinct if they prove adaptively inferior to their competitors”[5] I would add to this “…to their competitors and the environments in which they live”

 

It is documented that to survive an extinction event, a species’ needs three important characteristics of behaviour[6]:

- Populations must be distributed over a wide geographical area – This ensures that an extinction event occurring on a species that is widely distributed has less chance to completely eradicate that species.

- The methods of seed dispersal must favour distribution over a wide area – Such as fish that lay their eggs into currents ensuring that the eggs travel long distances

- Population numbers specifically can enhance a population’s ability to survive – A population of 2-3 individuals is far more prone to extinction than a large populous mass such as 20-30 animals.           

 

The most important implication of extinction events is the opportunity presented to successive species, forming the rebounding nature of biological evolution to levels that match if not exceed the pre-catastrophe period in terms of populations sizes and species’ developed intelligence at adaptability. The collapse of the dinosaurs saw the extinction of Earth’s mega-mega fauna but mammals which had co-existed with dinosaurs for more than 150mya were crucially quicker to adapt to changing environmental conditions and so filled the gap that dinosaurs left, leaving possibilities of species expansion. This concept of a silver lining of evolutionary booming following extinction events has implications for the survival of Earth’s biodiversity and human development throughout history.

 

During the Miocene period of 23.5mya-5mya, Earth experienced drastic cooling. During the Early and Middle Miocene, ‘greenhouse’ conditions prevailed, with warm, humid and ‘equible’ (greenhouse) climatic conditions, increased biodiversity and increased evolutionary turnover. However during the Middle to Late Miocene, ‘icehouse’ conditions prevailed, with cool, relatively arid, less biodiversity and decreases in evolutionary tendencies. This altered global climate, and led to the opportunity of human evolution.

 

Hominid evolution has occurred in the past 5mya. Numerous suggestions have been offered by anthropologists and scientists as to unravelling the complex series of ancestral mammals that led to the Homo-sapien but whatever mammal humans are derived from, our mere presence is a result of our adaptability to change.

During the past 5mya, there have not been any global extinction events. The dominant environmental stresses presented to our ancestors during the past 5mya has been the well-documented Ice-Ages and the solar variability cycles named the Milankovitch forces.

 

In relation to Milankovitch’s forces, 2.8mya there was a shift of dominant solar cycles to that of Axial Tilt which operates on a 41,000 cycle. This helped to define the boundary into the Pliocene.  During the successive geologic period named the Pleistocene, there were switches in which of the three forces is most dominant and affects the Earth’s surface the most. Between 1.8 and 0.78mya during the Early Pleistocene, Earth experienced a dominant 41,000yr cycle of glacial and inter-glacial periodicities. Between 0.78 and 0.125mya the 100,000 cycle of Eccentricity became the most prevalent and in the Late Pleistocene up to 10,000 years ago the last-inter glacial cycle was dominant[7].

As early as 35,000 years ago three species of the Homo family lived together on Earth. The exact reason for homo-Neanderthalis’ extinction may be due to a slow ability to change to environmental or climatic changes, unlike the homo-sapien which dominates today.

“Humanity’s ailing non-sapien branches must have suffered a slow attrition of numbers in the face of such climatic instability and as a result of more adaptable Homo-sapiens faster growing populations”[8].

 

And so with this information relating to solar variance, it is clear that in the period following 10,000 years ago, biological diversity and the dominance of the homo-sapien has had an un-challenged succession to domination of planet earth. Although it cannot be said that we actually control the mechanisms behind the working of the planet, our power both technological and industrial has catapulted homo-sapiens far further than any other species.

What also must be drawn to attention is the ability of modern man to create the extinction of other species. No other species can itself destroy another and yet mankind has been responsible for the extinction of many species. As the Clovis people’s spread through North and South America 11,000 years ago, mass extinctions of large mammals coincided with the migration of mankind. “Large animals disappeared not because they lost their food supply, but because they became one”[9]

 

So, in conclusion, human evolution has been a product of both intelligent adaptability following environmental change and part of a ‘lucky’ chance existence, that may not have ever evolved had the order primates of millions of years ago been wiped out at any stage. The complexities of evolution and extinctions are a single part of the operations of planet Earth.

There are thousands of variables in environmental change including some that may be influenced by the operations of modern man’s industry however historically, external and natural events serve to limit the explosion of species’ resulting from opportune habitats.

 

It is widely accepted that homo-sapiens are a product of evolution which means in turn that homo-sapiens will evolve. I believe there to be two potential evolved homo-sapiens. One is AI or Artificial Intelligence, created by mankind, and the second evolution is that of homo-sapiens with an altered biological make-up, resulting from the environmental change brought about by our current fossil fuel burning and globalisation of industry and pollution.

 

In relation to other species; even though homo-sapiens are one branch off a tall tree of evolved primates, our destruction of other species is tremendously short-sighted in that all species have a right to life on Earth and yet we view ourselves at the top of the food chain with no responsibilities for environmental management but the exploitation of resources for our personal or commercial gain. The extinction events spanning back throughout time reduce biodiversity on average between 25-75% and yet at the rate we are destroying habitats, environments and slaughtering so many animals and fish every day that our future is not only bleak in terms of climate change but a lonely one if no other animals exist.                (1,837 words)