The origin and evolution of life The beginning
The origin and evolution of life
The beginning of life • Throughout history, there have been many explanations for the origin of life: THEORY OF SPONTANEOUS GENERATION • Idea: life can appear from inanimate objects. • Today, it seems incredible that people believed such things. However, by observing some phenomena in daily life, it could appear possible that inanimate objects produce living things. For example, if a piece of meat is left for several days in a warm, damp place, flies and larvae appear. • Until the 17 th century, theory of spontaneous generation could not be proved wrong
The beginning of life: theory of spontaneous generation • In 1668, Francesco Redi, demostrated that the larvae found in rotting meat came from fly eggs.
The beginning of life: theory of spontaneous generation • In the 19 th century, Louis Pasteur demostrated that microorganisms did not come from spontaneous generation. The theory was finally rejected. 1. Pasteur placed meat soup in two flasks and bent the neck into an S-shape. 2. He sterilised the liquid by heating it. After several weeks he observed that the soup had not decomposed 3. He cut the neck of one of the flask and after a few days he observed that the soup in this flask had decomposed Conclusion: The S- shaped neck let air into the flask, but not microorganims. When the neck was broken, microorganims could enter and cause decomposition
The beginning of life: Oparin´s theory • At the beginning of the 20 th century Alexander Oparin developed a theory about the origin of life that is still the basis for the hypotheses accepted by most scientists today. • According to Oparin: 5. formed 3. temperature later 6. 2. The Some Thenewly reactions of the stable were biological molecules were fell so the water vapour coacervates started by electric divided and 1. A series of 4. The atmosphere organic molecules insulated from thethis, water in the multiplied. charges from To storms, do spontaneous chemical joined together tocalled make inside structures condensed. Intense they intense synthesisied ultraviolet reactions ocurred bigger molecules. Some coacervates. Thisthe continuous rain was molecules radiation (nucleic from acids) Sun, between the of them, such as proteins insulation was not produced and primitive that and were continuous capable volcanic of atmosphere´s and polysaccharides, complete, so therethis was seas were formed. The replication. eruptions. These From components (CH 4, H, were the future an exchange molecules recently-formed organic point provided onwards, theofhuge the life NH 3, H 20) 4000 million components of living between the water and molecules that amount resulted ofaccumulated energy from this years ago. There was things. the coacervates. in the seas. These seasno process needed could to start be The the oxygen gas in the more stable coacervates were much warmer and described reactions. as The ansynthesis organims. primitive atmosphere. survived, the less stable less deep than today. This of simple was the organic origin of all ones disappeared. Oparin called them “the cells. molecules began primordial soup”
The beginning of life: the present-day hypothesis • Oparin´s theory is still the most widelyaccepted today. Many experiments have proved the first stages of Oparin´s theory, but none have been able to prove the complete model. • In the mid-20 th century, Stanley Miller conducted an experiment to test part of Oparin´s hypothesis.
The beginning of life: the present-day hypothesis 1. He put a mixture of gases that were believed to make up the primitive atmosphere into a container. 2. This mixture was then subjected to high-voltage electric discharges. 3. The reaction produced various organic compounds, such as amino acids, that are the basic chemical components of all living things.
The beginning of life: the present-day hypothesis • There have been two main additions to Oparin´s theory: – Small organic molecules will join together to form large biological molecules, such as proteins, when certain minerals are present. This is why scientists think this process probably happened in areas with clay or muddy soil, not in water – The first nucleic acid to appear probably would have been RNA. DNA, which is more complicated and stable, is believe to have evolved later.
Evolutionary theories before the 20 th century • Along human history there have been two main theories on the existence and variety of life: – “Static” theories – Evolutionary theories STATIC THEORIES • Carl Linnaeus (1707 -1778) : – different species were reated separately and independently by God. – Species are static or unchanging. It was accepted until the beginning of the 19 th century. • Georges Cuvier : – At the end of the 18 th century, he used scientifically reasoned arguments to reinforce theory that species were static. – According to Cuvier, the existence of fossils from species that had disappeared was due to the catastrophes that had happened during the Erath-s history, like the great
Evolutionary theories before the 20 th century • At the beginning of the 19 th century, these ideas were questioned. • Scientist started to think on the possibility that all living things had a common ancestor, this is a common origen from which all criatures from this planet have evolved. • However it took a long time to accept these ideas for two main reasons. : – The process of evolution is slow and cannot be perceived in a human generation. – The theories of evolution went against the religios doctrine of the time
Evolutionary theories before the 20 th century EVOLUTIONARY THEORIES • LAMARCKISM or theory of inheritance of acquired characteristics. – Lamarck (French naturalist, 1744 -1829) was the first to develop a reasoned theory of evolution. – As Cuvier, he studied fossils, but he observed that there were fossils that had an intermediate appearance between older and present-day organisms. This made him think that one has developed from another. – States of Lamarck´s theory: • Animals developed structures and organs that they needed to adapt to their environment. (adaptative force) • These new characteristics were transmitted to their descendants and so changes were produced that modified
Evolutionary theories before the 20 th century EVOLUTIONARY THEORIES • Lamarckism is no longer accepted. Modern advances in genetics have disproved the idea of the inheritance of acquired characteristics • DAWARNISM or theory of Natural Selection – Charles Darwin (British naturalist) and Wallace developed this theory in the mid 19 th century. Present-day explanations of biological evolution are based on this theory.
Evolutionary theories before the 20 th century • Basic principles of Darwinism: 1. The individuals that make up any population of living things have anatomical, physiological and behavioural differences. 2. Each type of organism produces more offspring than actually survive to reproductive age. The number of individuals in each species remains more or less constant, so it can therefore be deduced that many die. 3. There is competition between the new-born individuals for space and food (struggle for existence). This esplains why many individuals are born but don´t survive. 4. Individuals whose variations help them survival in a certain environment are favoured over those who are badle adapted (survival of the fittest) 5. The surviving individuals produce the next generation, so that the most favourable variations are transmitted to the
Evolutionary theories before the 20 th century – This theory is based on the concept of natural selection • Sumarising: 1. The individuals that have the most advantageous characteristics survive and their frequency in the population increases progressively. 2. Others who do not have these cahracteristics are disadvantaged, which leads to the gradual disappearance of these less favoured traits. 3. After many generations, significant changes are produced in the population and new
Lamarckism 1. Original short necked ancestorand 2. Keeps stretching neck to reach leaves higher up on tree 3. And stretching… 4. And stretching until neck becomes progressivel y longer.
Darwinism Giraffes originally had a certain variety of length of necks and legs Natural selection favoured the individuals with longer necks and legs, whoproduced more offspring Over time, there were increasing numbers of giraffes with long necks and legs
Evidence of evolution – Nowadays there is so much evidence for evolution that most scientists now regard it as a proven fact. • ANATOMICAL AND MORPHOLOGICAL EVIDENCE – Three types of organs have been found that provide morphological and anatomical evidence: Human Horse Whale Bat – Homologous organs: • Same structural pattern but different functions. • They are proof of divergent evolution. • Example: the development of different limbs in mammals
Evidence of evolution • ANATOMICAL AND MORPHOLOGICAL EVIDENCE – Analogous organs. – They fulfill the same function but have a different evolutioanry origin. – They are proof of convergent evolution. – Example: the wings of insects and birds
Evidence of evolution • ANATOMICAL AND MORPHOLOGICAL EVIDENCE – Vestigial organs. – These are the evolutionary remains of organs which tend to disappear because they no longer have a function. – Example: The wings of the flightless kiwi bird.
Evidence of evolution • FOSSIL EVIDENCE • Fossils from related species have been found from different eras. Slow, but clear changes can be observed in these fossils. Example: horse. One toe per foot (the side toes atrophied) Three toes on its feet, only the middle toe rested on the ground (beginning to adapt to the grasslands. Teeth for eating leaves. Four toes on its front feet and three on its back feet. . Teeth for eating leaves
Evidence of evolution • FOSSIL EVIDENCE • When fossils are compared to present-day species, generally an increase in diversity and complexity can be seen. • Fossils have been found of organisms with intermediate characteristics which later evolved into different groups. • Example: Archaeopteryx, an amal with a beak, wings, teeth and a tail. It was an intermediate organism between reptiles and birds.
Evidence of evolution • EMBRYONIC EVIDENCE • Some embryos from different species are similar, which shows that there is a clear evolutionary relationship between them. The similarities between embryos are greater and last for more time in groups that are closely replated to each other
Evidence of evolution • BIOGEOGRAPHYCAL EVIDENCE • The geographical distribution of certain animal and plant species can only be explained by theory of plate tectonics and theory of evolution.
Present-day theories of evolution • NEO-DARWINISM • The discoveries that have helped scientists understand the mechanisms that cause variety between individuals are: o Mendel´s laws, which explain hereditary traits and their transmission mechanism. o Sexual reproduction, which gives rise to gene combinations that are different from those of the parents. o Genetic recombination, which happen during meiosis. o Mutations, which causes rapid cahnges in genes. • So to the ideas of Darwin we just have to add: o The variety between individuals of the same population is caused by mutations and genetic recombination. o Natural selection does not act on the individual in isolation, but on the population it belongs to.
Human evolution • Humans are mammals which means that they are subject to the same evolutionary mechanisms as all other living things. • Our closest relatives are the great apes. From them , the genus Homo evolved around 4 million years ago. Humans as we know them today (Homo sapiens) appeared only 40. 000 years ago. • There is consensus on three basic steps that allow us to trace the path from the ancestor we share with chimps and gorillas, who lived between 5 and 10 million years ago, up to us. They are: the bipedalism, the cephalization and language.
Human evolution BIPEDALISM • There are two keys to determine the position of an individual while walking, the orientation of the foramen magnum (skull) and footprint. • In the Australopithecus (6 Ma ago) the thumb already is directed forward and not one-sided, as the gorillas. (the thumb gives boost to walking). It is considered the first hominid and the first walking upright. • The bipedalism advantages: o It frees your arms and hands while walking. This allows to use them for other actions. o In an area of strong insolation, such as Africa, it reduces the amount of radiation received. o It extends the visual field in areas with tall grass, allowing better location of food and predators.
Human evolution CEPHALIZATION • It occurred 2. 5 million years and also in Africa. There arose a species (Homo habilis) that looks similar to Australopithecus but with a larger skull and capable of making tools. • The increase in the size of the brain in relation to body continues until the current human. • But the brain is an organ very expensive in energy terms and its development must be done at the expense of reducing others body organs. In our case eating habits were changed. From herbivores we move to being scavengers which allows to greatly reduce the digestive tract. • The use of tools allowed us access to a lot of resources that previously we didn't use, which
Human evolution LANGUAGE EMERGES • 200, 000 Years ago emerged in Africa a new species from which all humans today descend, Homo sapiens. • One of its main characteristics is that in addition to increasing the size of the brain, its shape changed. • This change involved a change in reasoning mechanisms, it appeared the symbolic thought and language. • The cave paintings, the carving of figures, and complex burial rituals are attributed to Homo sapiens.
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