Revision: 12th Std >> Origin and Evolution of Life MAH-MHT CET (PCM/PCB) Origin and Evolution of Life

Autogenesis is another term for spontaneous generation, meaning self-origin of life from non-living matter.

Abiogenesis is the concept that living organisms can arise naturally from non-living substances.

Evolution is a slow and continuous process whereby complex forms of life have emerged from simpler forms over millions of years.

Mutation breeding, sometimes referred to as “variation breeding”, is the process of exposing seeds to chemicals or radiation in order to generate mutants with desirable traits to be bred with other cultivars.

The proportion of an allele in the gene pool, to the total number of alleles at a given locus, is called gene frequency.

Organic evolution can be defined as slow, gradual, continuous and irreversible changes through which the present-day complex forms of the life developed (or evolved) from their simple pre-existing forms.

The total genetic information encoded in the sum total of genes in a Mendelian population is called gene pool.

Differences between individuals of the same species that arise naturally and can be passed to offspring are called variations.

The origin of new species by gradual modification is called speciation.

The fittest individuals in nature are most likely to reproduce and pass on their good qualities to their offspring. It is called natural selection.

The modern version of Darwin’s theory of natural selection, which incorporates genetics as the source of variations, is called Neo-Darwinism.

The structural, morphological change in chromosome due to rearrangement is called Chromosomal aberrations.

Insertion of a vector into the target bacterial cell is called transformation

Gene flow is the movement of genes into or out of a population. Gene movement may be in the form of migration of organism, or gametes or segments of DNA Gene flow also alters gene frequency, causing evolutionary change.

Any random fluctuation (alteration) in allele frequency, occurring in the natural population by pure chance, is called genetic drift.

The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation. 

The preserved remains, impressions, or traces of ancient organisms found in Earth's crust, which provide evidence of past life and evolution, is called a fossil.

Fossils are preserved remains or impressions of past organisms found mainly in sedimentary rocks, and their study is called palaeontology.

According to A.E. Emerson, speciation is the evolutionary process by which new species arise due to genetic divergence and isolation.

The process of formation of a new species from the pre-existing species is called speciation.

Bipedalism is a major type of locomotion that involves movement on two feet instead of four.

• Hardy–Weinberg’s principle states that allele frequencies in a population remain constant from generation to generation in the absence of evolutionary forces.
• The total collection of all alleles in a population is called the gene pool.
• Genetic equilibrium means no change in allele frequencies over time.
• If p is the frequency of dominant allele and q is the frequency of recessive allele, then
  p + q = 1.
• Genotype frequencies are expressed as:
  p² (AA) + 2pq (Aa) + q² (aa) = 1.
• Any deviation from Hardy–Weinberg equilibrium indicates that evolution is occurring.
• The principle helps in detecting the role of natural selection and other evolutionary forces.

• The theory of special creation states that life originated on Earth through a supernatural event beyond scientific explanation.
• It proposes that all plants, animals, and humans were created in their present form by a divine power.
• This theory is supported by religious texts and beliefs, such as the Bible and Hindu mythology.
• Since it is based on faith and not observable or testable, it lies outside the scope of scientific study.

• Natural selection, proposed by Charles Darwin, explains evolution as a process where organisms with favourable variations survive and reproduce.
• Organisms produce more offspring than can survive, leading to a struggle for existence.
• Individuals with useful variations are better adapted to the environment and are selected by nature (“survival of the fittest”).
• These favourable traits are inherited by successive generations, resulting in gradual evolution and formation of new species.
• Darwin presented this theory in his book On the Origin of Species (1859), which became a landmark in evolutionary biology.

• Fossils are the preserved remains or impressions of organisms buried under the Earth due to natural disasters.
• The study of fossils helps understand the organisms that lived millions of years ago and their evolutionary history.
• The carbon dating method measures the radioactivity of C-14 to estimate the age of fossils and ancient remains.
• Willard Libby developed the carbon dating method and received the Nobel Prize in 1960 for this invention.
• Fossil records suggest that vertebrates have gradually evolved from invertebrates over geological eras.
• Fossils occur in various forms such as petrification, compression, impressions, moulds and casts, coal balls, and unaltered fossils.

• The geological time-scale represents the entire history of the Earth and helps correlate geological and biological events in proper sequence.
• The Earth’s crust is made of layered rocks, and radioactive dating techniques estimate the age of the Earth to be about 4.5 billion years.
• Earth’s history is divided into five major eras: Archaeozoic, Proterozoic, Palaeozoic, Mesozoic, and Cenozoic.
• Each era is further divided into periods and epochs, marked by changes in climate, plant life, and animal life.
• The time-scale shows the gradual evolution of life, from simple unicellular organisms to complex plants, animals, and humans.
• Major events such as the origin of life, rise and extinction of dinosaurs, and evolution of mammals and humans are recorded in the geological time-scale.
• Scientists believe Earth is currently entering a sixth mass extinction (Anthropocene), mainly due to human activities causing rapid loss of biodiversity.

• Human evolution began from simple unicellular organisms, eventually giving rise to ape-like animals around 15–20 million years ago, during the late Miocene period.
• Carl Linnaeus classified modern man as Homo sapiens, under the order Primates, which includes monkeys and apes.
• Evolutionary changes such as bipedal locomotion, erect posture, increased brain size, reduced body hair, and the development of chin and forehead marked the shift from primitive apes to early humans.
• Fossil records—especially from Asia and Africa—reveal how early ape-like ancestors gradually evolved into gibbons, orangutans, gorillas, and eventually humans.
• Ramapithecus, an early ancestor known from jaw and tooth fossils, is considered a prehuman form that walked upright, initiating the journey toward modern humans.