3 Periods of the Stone Age: Paleolithic - Mesolithic - Neolithic

The study of the evolution of human race on this planet, which has almost nine million different species of animal and plant life to date, is divided into two great periods: Prehistoric and Historic. The Prehistoric period studies the appearance of the first hominids or ancestors of man and his evolutionary process from 5 million years ago until the invention of writing in 4 000 B.C., when man began to transmit news about himself, reporting his existence. Here the Prehistoric period ends and the Historic Period begins to this day.

This first stage in the evolution of mankind, which is substantially longer than the second, is further subdivided into two stages according to man’s relationship with his environment and with the materials he used. Therefore, we have the Stone Age, during which Man fundamentally used stone to fabricate the tools he needed in his daily life, and the Metal Age, when humans learned, with the help of fire, to fuse some minerals to transform them into metals, and later use them as tools.

The Origin of Life
After so many years of development, advances in science and technology, the origin of life remains a mystery that continues to challenge and baffle scientists. The “big bang” of biology, a definitive and irrefutable theory on the origin of life that is accepted by all, has yet to be discovered. No one has so far managed to recreate the real conditions of primitive Earth when life first appeared; that is to say, no one has been able to turn back the clock and recreate the conditions that favored the transition of inorganic nonliving matter into organic living matter.

The recreation in laboratory of environments that could be similar to that of primitive Earth did not result in the appearance of life form. The old Aristotelian derived theory of spontaneous generation harbored by some, that fully-formed complex living organisms could arise naturally and spontaneously from nonliving matter, has long been put to death once and for all by Louis Pasteur in the nineteenth century with his famous swan-neck flask experiment, from which he concluded that “life only comes from life”.

“The most complex machine man has devised – say, an electronic brain – is child’s play compared with the simplest of living organisms,” wrote American biologist and Nobel Prize winner in Medicine, George Wald. “The especially trying thing is that complexity here involves such small dimensions. It is on the molecular level; it consists of a detailed fitting of molecule to molecule such as no chemist can attempt.”

We know that the force of gravity was responsible for the agglutination of matter and space dust, and the formation of planets and stars. It is unknown if there is an analogous force in biology that causes different organic molecules to come together to form a prokaryotic cell.

To date, all that biology has been able to establish is that, under very peculiar conditions, inorganic molecules can be transformed into organic molecules, but the transition from these simple organic molecules like amino acids to something that is complex enough that it can self-replicate, and endowed with metabolism, remains a great mystery. It is known, however, that the microorganisms at that period used methane or hydrogen for metabolism instead of oxygen: they were organisms with anaerobic metabolism. Fermentation is a modern example of this type of metabolism.

Long before photosynthesis, and the eukaryotic cells that perform it, the first living beings on our planet would have the aspect of single-celled microorganisms or prokaryotic cells, like today’s bacteria and archaea, and would have lived in extreme environments, next to thermal springs in the primitive seas, nourishing themselves from the reactions between inorganic substances. From these first living beings, those capable of carrying out fermentation emerged, later the photosynthetic and, lastly, the heterotrophic beings, that is, living beings that, unlike plants, are not able to produce their own food.

The Evolution of Species
Then God said, “Let the earth put forth vegetation: plants yielding seed, and fruit trees of every kind on earth that bear fruit with the seed in it.” (…) And God said, “Let the waters bring forth swarms of living creatures, and let birds fly above the earth across the dome of the sky.” (…) And God said, “Let the earth bring forth living creatures of every kind: cattle and creeping things and wild animals of the earth of every kind.” And it was so. Genesis 1:11, 20, 24

The theory of evolution of species that Charles Darwin published in 1858 is the result of empirical research conducted during his voyage to the Galapagos Islands, which led him to conclude that life on this planet comes from a common stock, that is, that all living beings on this planet, both plants and animals, are related. All individuals have common ancestors.

The diversification of living beings or the evolution of species occurs by adaptation to the environment and natural selection – the better equipped, the strongest, prevail over the weakest or, as the proverb says, “the weak do not recite history”. Those that best adapt to the environment will eliminate their rivals and manage to pass on their genes to the next generation because the females instinctively allow themselves to be fertilized by the strong and reject the weak.

The first living beings appeared 3.5 billion years ago and one billion years later, the first photosynthetic living beings appeared, followed by the eukaryotes soon after. Around 543 million years ago, there was a period of great explosion of evolutionary changes in life form on this planet known as the Cambrian Period; there are many fossils that document this phase of life on Earth.

The first living beings were the microscopic organisms, primitive plants and invertebrates (worms and arthropods). Fish were the first vertebrates to emerge. It was 570 million years ago that plants invaded the dry land from the sea. Some animals had already done so before, but they did not stay on dry land permanently, because there was no food available there.

Animals came on dry land periodically, but remained most of the time in the sea: these were the amphibians. About 438 million years ago, they began to increase their time on land and 30 million years later, they evolved into reptiles. From the reptiles, evolution took two different paths: some reptiles evolved into mammals and others into birds.

Around 360 million years ago, the dinosaurs reigned on our planet. Some time later, the mammals which already coexisted with the dinosaurs but were insignificant began to stand out. About 245 million years ago, the dinosaurs became extinct and the mammals increased in number due to the absence of predators. About 66 million years ago, the primates appeared. Then 55 million years ago, the common ancestor of the pongids and hominids evolved. The earliest hominids emerged 8 million years ago.

Ontogenesis and Phylogenesis
Ontogenesis recapitulates phylogenesis by postulating that there is a similarity between the aspect of the embryonic stages of the human fetus, from conception to birth, and the development of the different life forms, from the unicellular origin to the human being. It is a discarded theory today, but it is close to the analogy that is often established between different fields of knowledge.

From the conception of an individual to his birth, the evolution of life on Earth is recapitulated, from the single-celled origin to the complexity of a human being. The diverse forms that the embryo acquires in its development resemble, in some way, the forms that life has assumed in the evolution of the species, from the prokaryotic archaea to the human being.
 
Furthermore, after birth, the development of an infant to self-awareness, that is, until he realizes that he exists as a person and begins to communicate, he recapitulates the evolution of the human race from the last primate that was not yet bipedal and did not speak to the Homo sapiens who stand erect walking upright and have the ability to communicate.

The Evolution of Human Life
For these reasons the Teaching Authority of the Church does not forbid that, in conformity with the present state of human sciences and sacred theology, research and discussions, on the part of men experienced in both fields, take place with regard to the doctrine of evolution, in as far as it inquires into the origin of the human body as coming from pre-existent and living matter - for the Catholic faith obliges us to hold that souls are immediately created by God. Humani Generis, 36 – Pope Pius XII, 1950
   
“There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” Charles Darwin, The Origin of Species, 1858

Charles Darwin never said that humans evolved from the present day monkeys. According to the British naturalist, humans, monkeys, chimpanzees and gorillas, all have a series of common ancestors. These ancestors lived on the African continent about 6 and 5 million years ago. Scientists named this species the Sahelanthropus tchadensis.

After this, between 5 and 3.5 million years, the Australopithecus afarensis emerged. Lucy, found in Ethiopia, belongs to this family, which marks the moment when the human race learned to walk. A little later, 2.6 million years ago, the first human tools appeared. Following this, 2.5 million years ago, the Homo habilis appeared, so called for the use he made of the tools.

The mastering of fire took place 1.5 million years ago; food began to be cooked about one million years later, and 400 thousand years ago, Homo neanderthalensis left Africa to inhabit the western part of Eurasia. The Homo sapiens remained in Africa. Then 350 thousand years ago, the Neanderthals developed and occupied Eurasia, from Portugal to Siberia.

About 100 thousand years ago, the Homo sapiens left Africa and appeared in Israel. Five thousand year later, they arrived in Malaysia, and 55 thousand years after that, in Australia. At that same time, they invaded Europe, defeating the Neanderthals or interbreeding with them. About 28 thousand years ago, we have the last evidence of the Neanderthals who became extinct. Fourteen thousand years ago, the Homo sapiens passed from Siberia through the Bering Strait and entered America through Alaska, gradually moving south, until they occupied the entire continent.

The Paleolithic or the Old Stone Age (2.5 million BC – 10 000 BC)
In this era, human beings were nomadic and did not build permanent dwellings. Because of this, they lived in caves, and had to compete with wild animals for this type of habitat. When food in that region was used up, families had to migrate to another region.

They lived by hunting small, medium and large animals, fishing and gathering fruits, leaves and roots. The economy during the Paleolithic phase was subsistence, that is to say, the group did not amass or produce for trade, but only for their own survival.

This period is also known as the age of chipped-stone tools. The first humans, who mastered and knapped stones, had the practice of producing materials by taking two stones and hitting them together to generate sharp points. These artifacts served, especially, for cutting meats and animal skins. They used instruments and tools made from pieces of bones and stones (axes, spears, staves, knives etc.). The goods produced were for collective use and property.

The Discovery of Fire
One of the greatest discoveries of this period was the production of fire through two processes. The most rudimentary was the friction of two stones over a pile of dry straws. The sparks produced ignited the straws.

In a second more elaborate procedure, a small stick was turned in a hole made in a piece of dry wood. This method, through friction, generated heat that passed to the straw, creating the fire.

• As we have commented in another text, fire had a great importance for the cohesion of families and communities, because everyone gathered around the fire for warmth. Since no one wanted to be left out in the cold, fire acted as a deterrent to antisocial attitudes.
• It allowed the light of the day to extend into the night, and because it was impossible to work at night, the two or three hours of tenuous light served for cultural events, to share experiences and for the handing down of culture from parents to children.
• The light in the night promoted safety of human beings in relation to animals that hunted at night, as it served to scare them away.
• However, the most important use of fire at that time was in the preparation of food. Cooked or roasted food has improved human diet. Certain foods are more nutritious cooked than raw. Fire and cooking of food are responsible for population growth and human survival.
• Finally, it was precisely fire that allowed humans to move from the Stone Age to the Metal Age.

The Social Organization
The men organized themselves in small groups, where the leader was the strongest and the most skilled. The men had the task of hunting, fishing and protecting the group. The women had the job of preparing food and caring for the children.

Communication
The communication in this period was based on the emission of some sounds (noises), without the elaboration of words, and physical gestures. Another widely used form of communication was cave paintings (drawings made on cave walls). Through these drawings (cave paintings) men marked time, exchanged experiences and transmitted messages and feelings.

Rituals
In the Paleolithic, men already performed funeral rituals. Archaeologists have found, in various regions, ceramic pots with human remains and personal objects inside caves. Religious rituals were also performed with the use of fire.

Hominids that lived in the Paleolithic Period
Australopithecines, Homo habilis, Homo erectus, Neanderthal Man or Homo neanderthalensis, Homo sapiens and Cro-Magnon Man, the earliest known European.

The Mesolithic or the Middle Stone Age (10 000 BC – 8 000 BC)
The Mesolithic is an intermediate period of the Prehistory, between the Paleolithic and Neolithic periods. This phase did not occur in all the regions of the world, but only in those where glaciation or the ice age had the most considerable effects.

In this intermediate period, the human being became more related to nature and began to make the first experiences of its domination. The nomadic lifestyle and dependence on external food did not allow development. Man learned to domesticate animals rather than hunt them, thus always having food at his disposal. On the other hand, instead of gathering fruits, plants and roots, he began to cultivate them. In this way, he managed to maintain a certain independence from the environment.

According to these regions, many humans maintained a life similar to that of the Paleolithic, depending on whether they were more dedicated to the domestication of animals or the cultivation of crops. The shepherds would be nomadic, for they followed their herds to pasture, while the farmers settled on the most fertile lands near the rivers.

The Neolithic or the New Stone Age (8 000 BC – 4 000 BC)
The Neolithic is also known as the New Stone Age. The beginning of this period is marked by the end of the ice age, a period when almost the entire planet was covered in ice, and ended with development of writing in Sumer in the Mesopotamia region.

The development of agriculture has allowed human beings to have a life less dependent on nature. With this advancement, they no longer needed to gather wild fruits, vegetables and roots, although these activities continued to be practiced.

The domestication of animals (goats, oxen, pigs, horses and birds) also contributed to the improvement in the quality of life. Together with agriculture, the domestication of animals allowed man to significantly increase the amount of food produced, eliminating the dependence on hunting.

As a result of the development in agriculture and the domestication of animals, humans ceased to be nomadic (with no fixed address) to become sedentary (with fixed address). This fact enabled the development of the first communities (tribes, villages, towns and cities). These first communities developed along the banks of rivers and lakes. In addition to meeting basic needs, water took on a new role in human life: the irrigation of crops.

With the increase in food production, the need for storage was created. In the Neolithic period, there was a great development of ceramic art. Vessels and pots were shaped and fired. According to archaeologists, the first ceramic objects were made around 8,500 years ago.

In the first communities that were formed, it became necessary to organize the work. The men were in charge of hunting, fishing and safety of the community (military protection function). The women were left with the tasks of caring for their children, agriculture and food preparation.

With the increase in production came the surplus. In addition to storing for periods of greatest need, men began to exchange these products with other communities. This was the beginning of trade economy.

With more food, there was a significant increase in population. This fact led to the need for more advanced forms of administration, including the establishment of more specific leadership and task allocation within the community.

In the Neolithic, men began to build more resilient dwellings because they needed to remain in fixed locations. Houses of wood, clay and blocks of stone were built in the villages. On the banks of rivers and lakes, stilts were more common (wooden houses with stakes fixed at the bottom of the river or lake).

The first civilizations arose and developed in the Neolithic period. Among them, we can mention: the Mesopotamian civilization (between the Tigris and Euphrates rivers) and the Egyptian civilization (along the banks of River Nile, northeastern Africa).

Conclusion: Unlike animals that have always lived at ease in a symbiotic relationship with Nature, survival and development for humans required an emancipation from it. The use of instruments, made of stone was the first act towards freedom.

Fr. Jorge Amaro, IMC

3 Metabolism Factors - Fuel - Oxidizer - Ignition

After writing about photosynthesis as the process by which plants transform energy into matter, we now address the reverse process: the transformation of matter into energy. Plants burn part of the matter they produce in order to survive and they do so in the same way as other non-vegetative living things. The only difference is that plants only burn what they themselves produce – they are therefore completely independent, while other living beings burn what plants produce because they cannot produce their own food.

In this sense, we are talking about metabolism, which is in fact, a slow controlled combustion reaction where there is an ignition – the moment when the living being is born and begins to inhale oxygen which is the oxidizer for all combustion – and a fuel, the food consumed by each living being. Before we talk about this slow combustion that takes place inside each living thing, let us talk about combustion in general.

The Process of Combustion
Combustion is a chemical reaction between two substances: a fuel and an oxidizing agent, that is, something that facilitates or makes the combustion possible. The oxidizer is always oxygen, and all fuels have something in common: they are of organic origin, that is, they were once living organisms with carbon chains linked to hydrogen or oxygen atoms.

If this is the case then how does our star, the sun, carry out combustion where there is no oxygen and no organic matter? Combustion on Earth is a chemical reaction. Inside the sun and all the stars, combustion is a nuclear reaction; in other words, the pressure inside the sun is so immense that energy is released by nuclear fusion of hydrogen nuclei into helium. 

Back to our reality on Earth, for a combustion reaction to take place, it is not enough to just have a fuel; we need an oxidizer to help in the process or to make it possible. Take a lighted candle, for example – it can burn for hours until all the wax is burned off; but if we put it under a glass dome, it will continue to burn only until all the oxygen is used up. Without the oxidizer and still with a lot of fuel, the flame will nevertheless go out.

In addition to the fuel and the oxidizer, there is still a third component that is essential for combustion: the ignition. The candle does not come lit, someone has lit it; even in the presence of oxygen, the candle would not burn if it isn’t first ignited. Even gasoline, which is far more flammable than a candle, does not burn in the presence of oxygen unless it is ignited. In the case of gasoline, the ignition may even be the heat in the air.

Let us recall that in the second stage of photosynthesis, carbon dioxide is combined with hydrogen to form matter. In combustion, that matter is oxidized, that is, it is combined with oxygen O2 to form carbon dioxide CO2 and water, releasing energy or heat in the process. The energy that is released, shall we say, is the very energy that a plant had previously obtained from the sun and has been amassed in the fossil fuel, be it coal, wood, oil or natural gas.

The Fuel
This is any substance that reacts with oxygen in the air, releasing light and heat. In this way, fire is the process by which matter releases its energy or becomes energy. Whatever the substance, it is always the result of a past photosynthesis. Fuel is amassed or stored up energy, it is matter that can transform into energy, back into something it once was. All it needs is a start, a starter engine, and the presence of an oxidizer which is oxygen.

For much of human history, fuels were from plants, alcohol, vegetable oils such as castor oil, and animal fats. During the first industrial revolution, the first fossil fuel came into use – mineral coal – which for a long time had fed the first man-built engine: the steam engine.

Then came petroleum and its derivatives, diesel, kerosene, and gasoline; also natural gas, first for domestic use, later for industrial use. Finally, nuclear energy emerged, resulted from the fission of uranium atoms, releasing energy that is then harnessed by the principle of the steam engine to move electric generators.

The Oxidizer
We have said that most of the fuels are of organic origin. The same can be said of the oxidizing agent, oxygen. As we have seen in speaking about photosynthesis, oxygen is a component of water; there is no free oxygen in space; what little there is, it is part of the water molecule and exists in space as ice. The same thing happens on Earth: oxygen is in the water and the water is in the sea.

In order to release oxygen from water, we need a source of energy to break water molecules by the process of electrolysis. However, this process does not happen in nature – the natural process from which oxygen is released is by photolysis which occurs in the first stage of this process.

It is plants, both terrestrial and aquatic, that release oxygen into the air when they photosynthesize. If our air is currently composed of 21% oxygen which allows and facilitates all the combustion taking place on our planet, both the active ones without as well as the slow ones within all living beings including plants, we owe it all to the cyanobacteria that have been making oxygen at the bottom of the oceans for millions of years, bubble after bubble, with the help of the sun.

The Ignition
Like we have said earlier, a fuel in the presence of the oxidizer does not burn if it is not ignited. There must be a kick-start. Even our universe needed a starter, and its kick-start was the Big Bang. All combustion reactions need to be started; after that everything progresses automatically. Like the domino tiles placed upright one after the other, the tiles will not fall sequentially without a tipping force on the first tile to initiate the chain reaction.

Ignition can be defined as the minimum temperature at which a fuel begins to burn incessantly. In the early days of mankind, when fire was first discovered, ignition was triggered by the friction between two sticks of wood until a spark occurred. Today all combustion reactions are initiated by an electrical spark or a match. Gasoline engines need a spark to initiate the chain reaction; in diesel engines, the diesel is heated and compressed until it explodes on its own.

The Discovery of Fire
Fire is an active combustion in which and by which substances called fuels are combined with oxygen in the air, producing light, heat and carbon dioxide. The technically correct definition, however, does not fully satisfy our amazement and willingness to understand it. We can’t help but be intrigued with this reality. As if by magical arts, it seems to be present everywhere; when invoked or summoned, it becomes visible and cannot be ignored because it burns, destroys, warms, modifies, melts, and then disappears. Nothing remains as it was, it destroys some realities and creates others, before disappearing again and becoming invisible until summoned or invoked again. Fire and its true nature have always intrigued the human beings. Let us see how the Greek mythology treated this reality.

Prometheus Stole the Fire from the gods
In the Greek mythology, it was the Titan Prometheus, with the condescension of Zeus, who created human beings that should have been obedient to the gods. Always benevolent to his creatures, Prometheus climbed Mount Olympus to steal the fire from the gods in order to provide the humans with the best weapon to master nature.

The human civilization progressed rapidly after that, and this displeased Zeus greatly who punished Prometheus by having him chained to a rock. Every day an eagle sent by Zeus came to eat the Titan’s liver, which re-grew every night only to be eaten again by the eagle on the following day. Despite his agony, Prometheus never repented of his rebellious act and was eventually freed from his torment many years later by the demigod, Hercules who was renowned for his strength.

In this myth, Prometheus is exalted for his intelligence, and more important than strength, for his altruism as the benefactor of humanity, for the risk he took and that despite so much suffering, he did not regret what he did for humanity. The progress of mankind is owed to the fact that man is as creative as God. But even with his creativity, he needed fire in order to truly master nature; with fire, man can blend the existing elements and create new ones. Without fire, he would remain in the darkness of ignorance.

It is impossible not to see in Prometheus certain similarities with Christ of the Christian religion. He represents great resources, notably his remarkable intelligence and prudence, but he also follows the idea of rebellion against established power, the liberation of the oppressed, the sacrifice of self without counting the cost, and finally the creation of a new system to which all have access: the Kingdom of God.

The Fireplace
Fire has not only allowed us to associate and mix elements of different nature, like the fusing of metals and the invention of new stronger alloys, but it has also attracted human beings to gather around it and form communities. The need to stay warm, not to die of cold by being excluded from the fire or from the community, led humans to overcome individualism and to create cohesive communities.

This is the reason why the fireplace evokes in us the fraternal feelings of harmony, peace and love; until very recently, the families of a village were counted by fires: the number of fires of a village was the number of families in the village.

Even today, love is symbolically represented as a fire in countless poems. There is a sonnet by the Portuguese poet Camões that attests to this use of fire as a symbol of love: “Love is a fire that burns yet burns unseen.” In fact, love unites two different people, creates bond, conquer individualism, creates equality between people, and creates alliances, harmony, and fraternal coexistence.

For thousands of years, around the campfire, culture circulated and were handed down by oral tradition: grandparents passed on to their children and grandchildren what they themselves had received from their own parents… Winters were long and longer still were the nights; during the day there was no time for coexistence as it was necessary to fight for life. So beckoning is the fireplace, the reminiscent of our ancestral life, that today there are television channels that broadcast a lit fireplace 24 hours every day!

Fire and Civilization
It was the mastering of fire that helped human beings pass from the Stone Age to the Metal Age. It is true that humans have already seen fire in the volcanoes, or a fire caused by the lightning in a thunderstorm, but they did not know how to invoke it, how to provoke it. The mastering of fire was important to create the first objects of clay and metal. Fire in the preparation of food gave man access to new sources of protein, an improved diet and better absorption of food.

For centuries, the fire remained trapped in the bonfire or in the forge of metals and in the potter’s oven. With the industrial revolution, an engine that functioned like a furnace was invented, which boiled water from which steam would exit to move the pistons that drove the wheels of a locomotive. From here to the propulsion engines, cars, ships, airplanes, rockets, was a short step.

We can read the history of human civilization as the history of fire and its use. Finally, we have the nuclear energy which transforms the heat released by the fission or the splitting of atoms and transmitted to water into mechanical energy to move the electric generator, producer of electricity.

The Genesis of Life
What is the origin of life on Earth? How did inorganic matter become organic matter? How did inanimate atoms and molecules transform into animate matter? Abiogenesis is the science that studies this transition. So far, there have been many theories proposed to explain how inorganic inert matter becomes organic living matter, but none without empirical evidence. That is to say, so far no one has managed to create life in a laboratory from inorganic matter.

The first living being or organism that appeared on our planet was a cell without nucleus, therefore prokaryotic, and without membrane. It appeared 4 billion years ago and is therefore almost as old as our planet which was formed 4.5 billion years ago. These bacteria were the archaea and cyanobacteria that began to carry out photosynthesis and paved the way for other life forms.

Later on, somehow, these cyanobacteria were associated, forming eukaryotic cells with nucleus, reducing the cyanobacteria to the chloroplast of these cells. Cyanobacteria still exist, they predate plants and animals, not being one nor the other; but is at the origin of two life forms: plant and animal.

Contrary to what seems logical, animals, not plants, were the first to leave the sea and populate the land. But if the animals were the first, what did they eat on land since there was nothing at the time? The animals were amphibians and they lived most of their life in the sea, but probably came on land to escape their predators or to lay eggs. However, it is known that the algae colonized the coastal rocks 1.2 billion years ago. Animals were the first to come ashore, but plants were the first to establish above water.

Even though cyanobacteria are also known as “blue-green algae”, they are strictly speaking not algae as the latter are restricted to eukaryotes, they are rather photosynthetic prokaryotes, the only prokaryotes able to produce oxygen.

Combustion and Respiration
Since combustion is the process by which combustible materials are oxidized with a release of energy and carbon dioxide, then, similarly, respiration consists of the oxidation of foods like glucose, amino acids and fatty acids, resulting in the production of energy and carbon dioxide. Until now there is no difference between the two, but in respiration not only is energy formed, other products are also formed, that is, more matter. This is why it is called metabolism, that is, a change or transformation.

Broadly speaking, this would be the only difference. However, if combustion instead of being complete is incomplete, that is, instead of being rapid it is a slow combustion, matter is also obtained, as in the case of respiration or metabolism. Think about how charcoal is made from wood: one places all the wood together in a pyre and cover the pyre with soil, leaving only one hole at the bottom and another at the top of the pyre. The wood burns in slow combustion because we limit the entry of oxygen and after a few days, we have all the wood turned into charcoal. If the oxygen was not limited, we would get ashes instead in no time.

The same is true of a long distance runner: if after the first minutes of running, on feeling tired from the increased heart rate, the athlete begins to breathe through his mouth and does not limit the oxygen intake, he will quickly tire and after spending all the glucose, he’ll have to stop. However, if he limits his intake of oxygen, he will force his body to change the fuel, so that instead of using glucose which burns rapidly and consumes a lot of oxygen, he will start to burn fatty acids which burn without the help of oxygen. In this way, he can run for a long time without altering his breathing or heart rate.

Another physical process of slow combustion is the degradation and rusting of metals, iron in particular. Over time, all objects containing iron, and there are many of them since iron is the most widely used metal, and even steel which is said to be stainless but under certain humid conditions, end up oxidizing, that is, burning or degrading due to the presence of oxygen.

Respiration or the Breakdown of Glucose
Glucose is the most widely used fuel inside living beings; the breakdown of glucose releases the energy that is contained in its chemical bonds. Glucose has 6 carbon, 12 hydrogen and 6 oxygen atoms, and in each bond between atoms there is an energy content. As glucose decomposes, energy is liberated and used by the body. Respiration completely breaks down glucose, turning it into energy and inorganic matter, such as carbon dioxide. There is yet another process that breaks down glucose, but only partially, since it transforms it into other organic products; this process is called fermentation.

Metabolism
According to the definition found in the dictionary, metabolism is the set of transformation that chemical substances undergo inside living organisms. It is these reactions that allow a cell or a system to turn food into energy, which will be used by the cells so they can multiply, grow and carry out their functions.

Metabolism is divided into two stages: catabolism (where there is degradation or breakdown of compounds) and anabolism (where there is the synthesis or formation of compounds). Let us recall that photosynthesis is also a two-stage process, and that the second stage cannot take place without the first. The process of making glucose and the process of its degradation, breakdown or decomposition, are similar.

Photosynthesis, which makes glucose from smaller molecules, is an anabolic constructive pathway; cellular respiration or metabolism, on the other hand, where glucose is broken down into smaller molecules, is a catabolic degradative pathway.

We have seen that in photosynthesis plants make their own food and part of it is used for their own consumption. The making of the food is photosynthesis; its use for self-consumption and growth is metabolism. Therefore, the plant cell is in some way more complex than the animal cell; it has a unique organelle that is lacking in animal cells: the chloroplast, through which it carries out photosynthesis. On the other hand, like the animal cells, it has the mitochondria by which it performs metabolism.

In metabolism, the anabolic phase of the cell uses glucose to construct cellular elements, to replace them when they are damaged or aged, and also for growth. In the catabolic phase, energy is released that maintains the constant temperature of the organism and the general functioning of all the tasks of the same organism.

Metabolism is a controlled combustion and it is not possible without the use of oxygen. In this combustion, the fuel is the proteins, fats and carbohydrates which, combined with oxygen in the air from respiration, produces energy which is used for the general functioning of the body, but is also partly stored for later use, and for the growth of the body. Everything in the universe obeys these same laws, functions in the same or in an analogous way.

In conclusion, if the plant life photosynthesis uses energy to make matter, the animal life metabolism burns that matter to make energy. Animal life metabolism as well as all man-made engines work under the same three principles.

Fr. Jorge Amaro, IMC