Evolution of humans
Homo sapiens.
Species.
Size.
Hominids.
Cooking.
Languages.
Neanderthals.
Agricultural revolution.
Farming.
We belong to the species of Homo sapiens.
As recently as 10000 years ago, we had other Homo species.
Homo floresiensis and Denisovan are close relatives, which are extinct now.
Homo sapiens are about 200 thousand years old.
The Homo Genus dates back to 1.6 million years.
Homo Erectus is one of our very early ancestors.
We Homo sapiens are unique in many ways compared to the animal world.
Even if we compare ourselves with our closest relatives, the chimpanzees , bonobos and gorillas, we are unique.
It is apparent we are a unique species in many ways.
Our ancestors lifespan was around 40 years.
Most of them died prematurely.
We have the luxury of dying from old age.
It is only after Charles Darwin published the ‘ On the origin of species’ in 1859,
people started to realise that life on Earth evolved gradually.
99.9% of all the species that existed have gone extinct.
Evolution leads to new species through the process of speciation .
Modified varieties of existing organisms thrive because they are able to exploit an ecological niche.
A species becomes extinct when it is no longer able to survive in changing circumstances.
Typically a species becomes extinct within 10 million years.
When one species becomes extinct it creates opportunities for others.
When many species disappear at once, it is a mass extinction.
In this case the rate of speciation increases dramatically.
Many new species emerge at the same time.
Mass extinction are extremely rare events.
In the past 540 million years, there has been only 5 mass extinctions.
The most recent was the Cretaceous-Paleogene extinction, which is called K-Pg in short.
This occurred 65 million years ago, when 70% of all life became extinct.
Scientists believe that K-Pg was caused by one or more natural catastrophes.
There was an asteroid impact on the Earth, and possibly increased volcanic activity.
This released masses of dust and ash into the atmosphere.
The global climate changed drastically.
Plants were not able to photosynthesise.
Most animals which could not adapt went extinct.
In the oceans a marine invertebrate called ammonites, that dominated the seas for 500 million years disappeared.
The mammals that did adapt and survive were small creatures, about the size of rats.
The laws of physics determine the size to which plants and animals can grow.
Arthropods like insects and spiders, are as large as they can get,
based on the limits of their respiratory and circulatory systems which work by diffusion.
Arthropods because they do not have lungs and circulatory systems like mammals.
They cannot supply their tissue with oxygen, if they got bigger.
During the carboniferous period there was much more oxygen in the atmosphere.
During this time there was 30 centimetre long spiders, and dragon flies with 1 meter wingspan.
Mites reached the lower limit of possible size of arthropod design.
If they got any smaller, they cannot metabolise properly.
Plants have also reached the limits of how big they can get.
The vascular tissues that carries water and nutrients from the root to the leaf tip,
is subject to gravity and pressure differences within the cells of the planet.
The giant redwoods are about as big as trees can get.
The reason dinosaurs were bigger than mammals, is because they were cold blooded.
They required less energy to maintain their metabolisms.
A mammal the size of a dinosaur would require ten times more food.
Whales benefit from the buoyancy of their habitat, which offsets the gravitational stress on bones and joints.
They grow so large because their food source, like plankton, krill, or squid, are plenty and easy to obtain.
Homo sapiens is a medium sized hominoid.
Conditions were just right for life on Earth to emerge, 3.7 billion years ago.
The K-Pg extinction was necessary to create the right conditions for mammalian life to flourish,
and intelligent life to evolve.
Grass, cereal and bamboo became widespread after the cretaceous period.
These played a significant part in human evolution.
In the millennia following K-Pg, the world was dominated by birds.
Birds are the descendants of avian dinosaurs.
Some groups like crocodiles also flourished.
Grasses changed the landscape.
The global forest of the carboniferous period giving way to steppe and savannah.
This happened at the time of the Miocene, 25 million years ago.
This change allowed mammals to dominate.
Species of grazers appeared along with the animals that preyed upon them.
The evolution of primates goes back to at least 65 million years.
Grasslands were essential for the emergence of our species.
Upright walking, tool use and increasing brain size have been attributed to grass lands.
Our earliest human predecessor diverted from a common ancestor,
with the forest dwelling chimpanzee 6 million years ago.
This was the time when the African savannah was prevailing against woodland and dense forest.
This possibly led to bipedalism.
Bipedalism freed the hands, which could be used for other purposes.
The first primates to walk upright were the australopithecines, a genus that evolved 4 million years ago.
The Homo Habilis evolved from them.
Their brains were no more sophisticated than modern day chimpanzees.
Homo Habilis was about half the size of modern humans.
It had opposable thumbs, that separate hominids from other primates.
Opposable thumbs helped them to develop more accurate fine motor skills.
Homo Erectus was possibly a descendent of homo Habilis.
It was the first species to start controlling the environment.
The species might have started using fire 1.5 million years ago.
The management of fire is a significant development in our evolution.
Fire allowed night activity.
It provided heat and light.
It protected from insects and animals.
Fire allowed us to cook food.
This is possibly the most important long time benefit of managing fire.
Cooking food, especially proteins, improves nutrition.
It makes it more digestible and allows us to absorb more calories.
Cooking also increase the amount of potential food available.
It helps the body to break down starchy carbohydrates in leaf stems, roots, and tubers.
These are not part of the early hominid diet.
Their diet consisted of nuts, berries, fruits, raw meat, and vegetables.
Cooking food means that it is partially digested before we eat it.
Compared to apes we have a smaller mouth, weaker jaws, a smaller stomach and a 50% shorter intestine.
Cooked food takes less time to chew.
We probably spend an hour each day eating, while chimps spend 6 hours in eating.
It is likely that cooking helped in the development of language, for sociological and physiological reasons.
Homo Erectus was the first hominid to live in hunter-gatherer societies.
Effective cooperation within these groups would have required some form of communication.
Over a period of time languages developed.
Earlier species used proto-language.
They lacked the syntax and structure of true speech.
The morphology of our ears suggest that auditory sensitivity of Homo Erectus was similar to humans.
Homo sapiens were the first to develop fully formed speech.
It was the final evolutionary step to our modern way of life.
Homo sapiens and Neanderthals co-existed for about 100 thousand years.
Neanderthals were better adapted to cold weather.
They were shorter limbed, barrel chested and stronger.
They lived in colder climes around the 50th parallel north,
and south of the line of glaciation during the last ice age.
Despite their bigger brains they were not more intelligent.
They failed to develop sophisticated survival strategies.
They never invented arrows or throwing spears.
Their hunting technique without this was possibly more dangerous.
Their larger size also meant that they require 350 more calories per day.
This could be a disadvantage when food was scarce, or competition is fierce.
Homo sapiens were hunter gatherers.
The main disadvantage of hunter-gathering is that there is an upper limit on the number of people it can support.
Smaller or weaker groups are pushed into extreme environments.
The Neanderthals lived in smaller communities.
They could not develop alternative survival strategies like farming.
Whatever the reasons, the Neanderthal species did not survive.
They were extinct 24000 years ago.
For Homo sapiens the shift from hunter gathers to farming was a gradual process.
In the middle to upper palaeolithic period, 80 to 70000 years ago,
specialisation began to emerge.
Communities focused on a smaller selection of game and gatherings.
In coastal areas bespoke tools such as fish hooks and nets.
Else where groups in forest areas started forest gardening.
Useful plants species were identified, protected and improved.
Undesirable plants were eliminated.
Later on foreign species of plants were introduced.
Initially hunter-gatherer was done along with forest gardening.
Over time, possibly due to pressure of population, a pastoral life style, became more established.
The first agricultural revolution took place during the Neolithic period, 10000 years ago.
This was a complete change in the process of energy management.
Earlier energy was procured directly from plants and animals, by hunting and foraging.
Now energy was stored in domesticated stock and grasses.
This led to a significant change in management of both land and labour.
Agricultural tied down people to the single place.
Animals were also domesticated so as to live in the settlement.
This is the process by which wild wolves, became tamed domestic dogs.
Cats and dogs have similar intellectual capabilities, yet it is the dog which became man’s best friend.
This was not due to size or strength, but due to behaviour.
Dogs are simply friendlier than cats.
Scientist have bred dog like animals from wild wolves.
The heritable characteristics are the effects of epigenetics.
Epigenetic changes are responses to the environment and external stimuli.
Dogs can be used to hunt, herd or provide protection.
Goats and sheep were domesticated for milk, wool and fur.
Cows could be used to plough fields and provide fertiliser.
Selective breeding is as old as farming itself.
The earliest crops were wheat, barley, lentil, pea, chickpea, bitter vetch and flax were some of the oldest crops.
They had high calorific value, and good seed retention properties.
By selective breeding, farmers developed better and better strains of these crops.
With improvements in agriculture, for the first time there was surplus of food.
Settled civilisations stored food in granaries.
The availability of food led to population expansion.
The settlements grew larger.
Communities developed specialised workers and more advanced tools.
Villages and towns developed, in which goods, services and ideas could be exchanged.
Farming was a much harder way of life, then hunter-gathering.
The size of hunter-gatherers ranges shrank, with pressure of population.
Farming was a necessary strategy for survival.
The nutrition standards of farming communities were inferior to hunter-gatherers.
The average height of adults reduced from 178 cm to 168 cm.
This reduced height persisted till the 12th century.
In parts of the world where competition for resources, was not fierce, like North America, Australia and Africa,
the hunter-gatherer life prevailed.
The shift to organised food production supported a denser population.
To operate effectively, these bigger societies required decision making and organisation.
This paved the way for government and the social elite.
Food surpluses meant that, communities could develop specialists like soldiers,
priests, politicians, bureaucrats, etc.
The agricultural revolution can be seen as a response, to the population- food energy crisis.
This was a milestone in the evolution of humans.