Standardized and systematic investigations have suggested that living entities of today are a result of a prolonged and incessant chain of events causing changes referred to as organic evolution. The expansive biodiversity that prevails on Earth to this day is attributed to this evolutionary phenomenon, occurring over thousands of years.
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Organic Evolution Definition
“Changes in the genetic makeup of species in a population as a result of responding to environmental changes is organic evolution”
Living entities possess the basic characteristic of reproducing. Entities being reproduced can sustain life only if there is proper coordination and adaptation with the changing environment. To maintain harmony in the ecosystem, changes must be endured and suitably adapted. Structural changes in living entities can be permanently integrated through changes in the genetic composition.
Evolution is a gradual and continuous process.
Theories Of Organic Evolution
Evolution corresponds to change in the form and behaviour of organisms between generations. It refers to change within a lineage of populations between generations.
A number of theories were put forward to substantiate and describe the evolutionary process. Some of these theories are listed below:
I. Darwin’s theory of evolution
Organic evolution by Charles Darwin is emphasized as “Descent with modification” stating that the present complexities in animals and plants are as a result of evolution from simpler forms that existed earlier through eventual changes.
Darwin’s book on “Origin of Species” in 1859, was the earliest one to put forward the theory of evolution through natural selection which stated that the entities, as a result of alterations in the inherited behavioural and physical characteristics, undergo changes over a period of time. These changes allow species to better adapt to changing environments, helping in the survival of offspring.
One of the best-sustained theories has been the evolution of natural selection backed by evidence from a range of scientific disciplines such as genetics, geology, palaeontology, developmental biology, etc.
The theory highlighted the main points as per Brian Richmond, which are – “All life on earth is connected and related to each other” and diversity of life is as a result of modifications of populations through natural selection wherein few characteristics were selected in an environment over others. Many times the theory is referred to as “survival of fittest” which can be misled more often.
Origin of Whales
First edition of “On the Origin of Species” had Charles Darwin speculating about the role of natural selection leading to a mammal on land turning into a whale. As part of a hypothetical example, Darwin used North American black bears known to prey by swimming with open mouths.
It is important to have a fundamental understanding of the mechanism of natural selection to comprehend the origin of whales. The phenomenon of natural selection can alter a species in a small way leading to a change in the colour/size of a population over generations. This is referred to as microevolution.
In addition to this, the process of natural selection can accumulate changes and create an altogether new species referred to as macroevolution. This can transform amphibious mammals to whales, dinosaurs to birds and ancestors of apes into humans.
Darwin also went to describe a natural selection form based on the success of an entity to attract a mate, a process referred to as sexual selection. Antlers of male deer, the plumage of peacocks are good examples of the characteristics, which were evolved in this type of selection.
Incorporation of genetics and Darwin’s theory is referred to as modern evolutionary synthesis, which came after Pobiner stated that Darwin noted the pattern of evolution only and could not put forward the mechanism. It came after the discovery of how genes encode different behavioural or biological characteristics and their inheritance.
At the level of genes and DNA, the behavioural and physical changes occur making natural selection possible. These changes are known as mutations which are raw information on which evolution performs, added Pobiner Random errors in replication of DNA repair, radiation or chemical damage can lead to mutations. These are mostly neutral or harmful and rarely beneficial. This tends to become prevalent in the upcoming generation spreading in the population.
II. Lamarckian Theory Of Evolution
The first theory of evolution was Lamarckism proposed by Jean Baptiste de Lamarck, the outline of this theory came into the picture in 1801 only. He is responsible for coining terms “Annelida” and “invertebrates”.
4 main factors are:
- Internal vital force – this force causes all living things and their component parts to be continually increased
- Effect of environment and new needs – environmental changes have an impact on living entities causing them to change leading to new needs. These needs generate new structure altering habits of entities
- Use and disuse of entities – more usage of organs causes it to develop better, disuse of organs leads to degeneration
- Inheritance of acquired traits – characteristics adapted as a result of all these above factors passing on to the next generations. It is a continuous process. These variations are accumulated over generations leading to the formation of a new species.
Examples In Support of Lamarckism:
- Webbed toes of aquatic birds
- Evolution of giraffe
- The disappearance of limbs in snakes
- Flightless birds
- Flat fishes
- Cave dwellers
Mechanism Of Organic Evolution
The phenomenon of genetic variation is basic for organic evolution. It is upon this that selective forces act for evolution to take place. The mechanism of evolution emphasizes on:
- Descent and genetic differences which can be inherited to the next generation. Genetic drift, migration, mutation, natural selection as mechanisms of change
- Significance of genetic variation
- Consequences of a reduction in genetic variation and random nature of genetic drift
- Impact of various species on each other’s evolution process via co-evolution
- Role of differential reproduction, variation, heredity in evolution by natural selection
Evolution is observed in a population as it contains genes in the gene pool, changes in this pool cause evolution.
It is a driving force for evolution. It can be a random change in the genetic composition having an impact on the gene pool of a population. This alteration in the nature of DNA in 1 or more chromosomes produces new alleles, hence a cause for genetic variation. Natural selection is decisive in mutation to eliminate the less-fit, allowing survival of fittest.
It occurs when entities are left up to an environment where survival of fittest is observed. These characteristics when inherited in offspring reproduce a population better suited to the changing environment. Traits from less-fit entities are less likely to be passed to the upcoming generation. In natural selection, the significant selective force is the role of the environment.
For instance, the ability to attract and mate can also be seen as a measure of fitness. Those who are better adapted, produce comparatively more offspring, passing on their genes at a higher success rate compared to the entities that are less adapted.
Migration of entities may cause a cluster of them to move to a new geographical location. When the migratory entities interbreed with the newly introduced population, they result in the addition of new genes to the already existing gene pool as a result of the local population, thereby contributing to the gene flow.
For instance, when pollens are blown by wind beyond the reach of the parent plant population, gene flow takes place. Some animals can be shifted away from a herd compelling them to move to a new location, interbreed and introduce new genes to the pool.
It can take place when a small population moves to a new geographical location, establishing in a completely isolated area. For instance, when a few fishes are introduced in a lake, the population evolves over time into a different one from the parent ones. This process does not take place in densely populated areas.
Development of Species
A particular group of entities sharing a number of traits with the ability to interbreed with each other, leading to the production of fertile offspring are species. These usually share the same gene pool.
Speciation is the evolution of species taking place when a specific population is isolated as a result of barriers, geographically. This phenomenon can also take place with the development of reproductive barriers. For instance, when a population tends to develop anatomical hurdles leading to difficulties in mating with members of the same population, a new species takes form. Species can also develop as a result of spatial differences and timing of sexual activity.
Paleontological Evidence Of Organic Evolution
Palaeontology is the study of fossils. They are formed with the remains of entities, plants which get implanted into water or soil, thus preserved for years together. In appearance, they resemble skeletal, moulds, footprints or are intact in snow. With these studies, similarities can be drawn between entities from the present and ancestors.
Fossils were preserved in the form of hard structures of setae, spicules, chitinous and spiny exoskeleton, shells, bones, scales, feathers, teeth and hair of previously dwelled entities.
Fossils are formed from living entities that lived earlier. An animal becomes fossil when immediate changes take place in the environment. Most fossils are formed as a result of petrifaction where organic matter is replaced by minerals such as lime, sand, oxides of iron and so on. Here the decomposers decay the dead entities and organic matter. Here, precipitation of minerals takes place forming hard rock like structures resembling dead entities.
There are four types of fossils –
- Altered fossils – formed as a result of Petrification, these are changed fossils. Most fossils are of this type such as Eusthinopteron, Archaeopteryx fossil and Ayshaea
- Unaltered fossils – they are the dead bodies of entities that lived earlier and are unchanged fossils as the name suggests. Example – Hexapod fossils, Wooly mammoths in ice mountains of Siberia
- Coprolites – faeces fossils of entities that lived earlier. It assisted to decide if the faeces is of omnivore, carnivore or herbivore, not of a specific animal.
- Moulds – impressions of leaves, foot and bodies of entities that lived earlier. Typically, this type houses plant fossils.
Evidence For Organic Evolution
Organic evolution is not a hypothetical concept. Some evidence can provide proof depicting existence and occurrence of organic evolution. The evidence includes:
- Vestigial organs
- Homologous organs
- Analogous organs
- Connecting links
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Frequently Asked Questions on Organic Evolution
What is the effect of plate tectonics on organic evolution?
Organic evolution can be caused as a result of isolation contributing to the introduction of new genes to the gene pool. Plate tectonics produces geographic isolation which enables divergent evolution in the species that are isolated, thereby safeguarding them from any competition.
What is an example of organic evolution?
Process of Organic evolution produces genetic modifications in a species or inside a cluster of species with time. Examples of this phenomena are Evidence of missing links in Archaeopteryx, wings of birds and insects – analogous organs.
Who proposed the theory of organic evolution?
Jean-Baptiste Lamarck in the early 19th century formulated the transmutation of species theory, which was the first fully-formed evolutionary theory. Later in 1858, Charles Darwin alongside Alfred Russel Wallace released a new theory of evolution substantiating Darwin’s theory of Origin of Species in detail.