Neo Darwinian approach to evolution takes into account the scientific evidence brought about by the discovery of genes and of the DNA molecules which constitute the basic device enabling all living beings on our planet to replicate, from the simplest cells to the most complex organisms, including bacteria, viruses and other parasites, plants, vertebrates, mammals, hominids, and modern man "homo sapiens"... Evolution since the beginning of life on earth in the most simple form is thought to have progressed through replication, reproduction or multiplication of living beings, with natural selection and "fitness for survival" as the basic process: organisms, fittest for survival, replicate reproduce and multiply in greater numbers at each next generation, due to positive variations of their characteristics which enable them to adapt to environmental stress and competition from other living beings (predators). Organisms unfit for survival, because of injurious or neagtive variations of their genetic characteristics, do not attain the age of replication or they transmit these injurious negative variations to their off-spring and the latter in turn do not replicate reproduce or multiply, so they gradually become extinct as carriers of such negative variation.
The question involves many aspects of science. Biological evolution brings us first to the origins of life on earth and to the origins of the earth part of the solar system and from there to the origins of the universe.
Our planet earth is an integrate part of the solar system and our sun is believed to have started 4.55 billion years ago. Evidence that the age of the earth and the age of the sun is 4.5 billion years is based on the decay of nuclear isotopes and as such is not contested except by so-called creationists who still maintain that the earth is much younger, and are the continuators of ancient biblical views.
The solar system itself is part of the universe which is believed to have started before then i.e. 14-15 billion years ago, by the "big-bang"; all the matter of the universe was contracted in a small ball of infinite density and temperature, which exploded and started to expand.
See links to theory of the Big Bang:
The hot big bang model
Cosmology: The Study of the Universe
The age of the universe is subject to debate: see Big bang vu par un astrophysicien français. The origin of the universe results from the theory of relativity, or generalised theory of gravity as first expressed by Isaac Newton, while the theory of relativity is owed to Albert Einstein in the early 20th century.
When our planet earth was formed as a satellite of the sun, it was initially a cloud of dust and gas turning around the sun by gravity in nearly circular orbits. Under the force of gravity, adjacent particles collided and aggregated, eventually producing the earth and planets. Initially, our planet earth was a mass of hot metals, rock and gases; it is believed that our planet earth, still in the throes of volcanic eruptions and battered by falling comets and asteroids, remained inhospitable to life for about half a billion years after its birth together with the rest of the solar system, some 4.5 billion years ago.
There is evidence of advanced forms of life that existed on earth at least 3.5 billion years ago. At that time, the conditions propitious for the existence and survival of living matter had therefore gradually developed. Among these conditions were the presence of oxygen, carbon dioxide, water, and light which all living matter we know on earth need. These elements resulted from the cooling of the earth of which volcanic activity was the apparent process and which was widespread over the whole surface of the earth as well as impacts of falling meteorites and asteroids. When conditions propitious for living beings existed, the first very simple organisms appeared, were able to survive and more importantly to reproduce. This is described as the prebiotic or proterozoic era.
Evidence that the cooling period before life appeared lasted less than half a billion years, is given by fossil microscopic elements of life in the oldest known rocks of the earth. The oldest rocks found on Earth are 3.5 to 3.6 billion years old and are noted as Archean era by geologists (as dated by various nuclear decay methods). Such rocks have been found in North America, Greenland, Australia, South Africa, and Asia. In rocks of that age, fossilised imprints of bacteria have been found that strangely look like cyanobacteria, the most highly evolved photosynthetic organisms present in the world today. Most of these rocks are of sedimentary origin i.e. due to erosion, but they include constituent minerals which are dated as old as 4.1 to 4.2 billion years (noted as Priscoan era by geologists), i.e. less than half a billion years after the birth of the earth. The constituent minerals are enriched in the lighter carbon-12 isotope over the heavier carbon-13 isotope; this is an indication of biological carbon assimilation, which attests to forms of life as old as that age of 4.1-4.2 billion years. Rocks of that age are very rare. See the geological time scale.
In addition to being dependent on the chemical composition of the planet (carbon, carbon dioxide, oxygen, nitrogen, water, light, etc…), all living beings are interdependent. Plants depend on carbon dioxide, water, light to produce carbon biomass in their living process and they reject oxygen in the atmosphere. Animals depend on oxygen rejected by plants for their living process. All species, living on the same planet Earth, form the planetary ecosystem. One single organism cannot occupy the whole planet and provoke the extinction of all the others. So some form of equilibrium has to exist, at least for some time. This interdependance results, for every living being, in a struggle for survival, by reproduction, generation after generation and during this process some variations occur over a long period of time.
In replicating for thousands of generations, it is believed that evolution took place by natural selection, the fittest organisms i.e. those whose characters gave them some advantage in responding to perturbations in the environment and to competition from other organisms struggling for their own survival, prospered more and further as time elapsed. It is observed in geology that more complexity appears in all living organisms, meaning that fittest organisms are capable of responding more and more efficiently to natural perturbations and competition by other organisms. Fossils, the first representatives of this complexity of living beings, first appear in our rock records some 600 million years ago, i.e. the Cambrian period (see the geological timeline). No fossils of that degree of complexity, are found in rocks of older age. It therefore took about 2.4 billion years to reach this stage from the time that is believed to be the start of life on earth i.e 1.5 billion years after the Earth was formed in the solar system.
It is believed that modern man results from the evolution of primates over many millions of years. It is believed that modern man we call "homo sapiens", which populates the whole planet today, appeared between 200000 and 100000 years ago in East Africa at a time when glaciation covered most of Europe and Asia. From there homo sapiens migrated to the different parts of the world; See map of migrations of homo sapiens as results from thousands of mitochondrial DNA analyses.And mitochondrial genomics explain....
If the time span of 4.5 billion years since the formation of the earth is compared to one calendar year, a time span with which we are familiar, then modern man "homo sapiens" appeared between the last 30 minutes before the end of the year (150 000 years). If we refer to the time elapsed since conditions propitious for the development of life were there (1 billion years), then "homo sapiens" appeared between 350 days after the first evidence of life started on earth . This indicates the length of time taken by the process of evolution to reach the highest known stage of complexity of living matter, modern man, or "homo sapiens".
Every human being has a brain which appears to be man's most remarkable organ. The human brain enables man to perceive the world outside of him, as well as to act on, and communicate with, the world and his fellow men. The human brain is a set of hundreds of billions of nerve cells called neurones that all interconnected together, thus enabling all our senses and perceptions, our conscience, our memories. We start by acquiring the sounds and the language of the family and community in which we are born, in an innate manner, within the first three years of our life. In this process, we acquire the sounds and words that designate objects, notions of cold, hot, big, thin, and sentiments like content or unhappiness, etc... The acquisition of language by man, within such a short time after birth, has to be based on an innate mental capacity (his brain) which extends not only to learning the particular words used in his community, but also to acquiring the order and variation of words used (grammar and syntax) in the particular language of his community, a feature which gives him the capacity to discourse. Man's brain, and his language enable him to acquire, with the only limitation of his individual mental capability, a feature which varies within a relatively narrow range, all the knowledge, know-how, crafts etc. developed and accumulated by "homo sapiens" during the past 150 000 years, at his particular time of living, in his particular community, and in his particular geographical and environmental situation.
If we extend the play of this process in space and time, we can say that all human beings collectively, in their respective geographical locations, generation after generation, have built distinct cultures with their arts, crafts, implements, rules and law, government, science and technology, music, painture, sculpture, medicine, etc… And because of the interchange between such cultures permitted by the extraordinary capacity of man's brain and language, distinct cultures interpenetrate and a global culture is gradually emerging.
So it appears that once our gene machine is built from the genes transmitted by our parents and ancestors, our brain or meme machine takes over and builds us up to the stage attained by the cultural environment of our time, in its geographical location and with the effect of interpenetration of cultures of the distinctive communities. We in turn are transmitting our genes to our descendants. According to the process of sexual reproduction, by which each sex transmits half of its genes to its offspring, we share our descendants with people living at the same time as we; more we go down into the future, more of us are sharing descendants; many of us today are therefore co ancestors of many descendants that will live many generations in the future. Likewise, we are the descendants of many co ancestors. This view enables to understand the fallacy of having an infinite number of ancestors e.g. each of us has 2 parents, 4 grand-parents, 8, 16, 32 above etc. so in a 1000 years, or approx. 40 génerations we would have 2 exponent 40, ancestors a number so high as to be stupid to express... Instead, all of us share common ancestors, likewise as many of us today are common ancestors of those who will live a thousand years from now. The distance in number of generations that separate any of us living on the planet today, depends on the geographical location. Two people living today in France, will have a common ancestor relatively near in the past, say less than a thousand years; the same applies for two people living in Ladakh. But two people living today, one in France, the other in Ladakh, will have a common ancestor much farther away in the past.
The concept of memes as described so far poses a number of crucial observations.
Genes and memes are believed to be two processes of the evolution of man. Genes are related to biological evolution, whereas memes are related to cultural evolution. The questions which interest me are in fact questions that have always troubled man i.e. who are we, where do we come from and where are we going?
Memes are concepts, thinking patterns, behaviours, perceptions, expressions of emotions, know-how, held in an individual's memory which can be transferred to another individual's memory by means of exchange of spoken language, pictorial representations, playing and hearing of music. Memes are found in all the domains of human culture like sculpture, dance, theater, astronomy, architecture, economics, medecine, mining and processing of metals and minerals, etc...The concept of memes was first used by Richard Dawkins, a biologist and neo Darwinist, lecturer at the University of Oxford. The idea of "memes" is the application of biological evolution to culture. Biological evolution teaches us that human beings are made of a combination of genes transmitted by many generations through sexual reproduction, and time. One individual having two parents, each parent having two parents, and so on, that individual shares the genes of 32 persons, 16 male and 16 female, that lived 5 generations earlier than he (2^5 is 32); the time span of 5 generations is approximately 100 years. Over 100000 years which is thought to be the age of man as known today, the number of criss- cross transmission of genes by sexual reproduction, forms a huge and complex network tree, of which all the human beings of today are the result.
According to Brian Sykes, Professor of Human Genetics at Oxford University, all Europeans descend from just seven women, which he names the founders of seven clans. They arrived between the past 45,000 and 10,000 years, each establishing a family which today amounts to millions but still bears the genetic signature of its founder.
See details: The seven daughters of Eve by Bryan Sykes.
and "The mitochondrial Eve"
and mitochondrial DNA in fossil hominids
See also population growth estimates of "homo sapiens", since 8000 years BC.
See also the theory of evolution by Charles Darwin:
"the descent of man" and "the origin of species".
Mis à jour le 01/04/2016 pratclif.com