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Miller-Urey experiment
1. In the 1950’s, biochemists Stanley Miller and Harold Urey, conducted an experiment.
2. It demonstrated that several organic compounds could be formed spontaneously by simulating the conditions of Earth’s early atmosphere.
3. It was a chemical experiment that simulated the conditions thought at the time to be present on the early Earth and tested the chemical origin of life under those conditions.
4. The two scientists sealed a mixture of water, ammonia, methane and hydrogen in a sterile flask.
5. The mixture was heated to evaporate water to produce water vapour.
6. Electric sparks were passed through the mixture of water vapour and gases, simulating lightning.
7. After a week, contents were analysed. Amino acids, the building blocks for proteins, were found.
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Embryological evidence
- Comparative study of the embryos of different animals show a great deal of similarity.
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Adaptive radiation
- Adaptive radiation is evolutionary divergence of members of a single phyletic line into a series of rather different niches or adaptive zones.
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Types of natural selection
Natural selection is of three types directional, stabilizing, and disruptive selection.
1. Directional selection occurs when natural selection favors one extreme of continuous variation. Over time, the favored extreme will become more common and the other extreme will be less common or lost.
3. Stabilizing selection occurs when natural selection favors the intermediate states of continuous variation. Over time, the intermediate states become more common and each extreme variation will become less common or lost.
4. Disruptive selection occurs when natural selection favors both extremes of continuous variation. Over time, the two extreme variations will become more common and the intermediate states will be less common or lost. Disruptive selection can lead to two new species.
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Mutation theory of Hugo de Vries
The salient features of mutation theory are as follows:
1. Mutations or discontinuous variations are the raw material of evolution.
2. Mutations appear all of a sudden. They become operational immediately.
3. Unlike Darwin’s continuous variations or fluctuations, mutations do not revolve around the mean or normal character of the species.
4. The same type of mutations can appear in a number of individuals of a species.
5. Accumulation of variations produces new species. Sometimes a new species is produced from a single mutation.
6. Useful mutations are selected by nature. Lethal mutations are eliminated. However, useless and less harmful ones can persist in the progeny.
7. Mutations appear in all conceivable directions.
8. All mutations are inheritable.
9. Evolution is a jerky and discontinuous process.
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Hardy-Weinberg principle
1. The Hardy-Weinberg principle states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
2. The Hardy-Weinberg equation is expressed as:
p2 + 2pq + q2 = 1
where p is the frequency of the “A” allele and q is the frequency of the “a” allele in the population. In the equation, p2 represents the frequency of the homozygous genotype AA, q2 represents the frequency of the homozygous genotype aa, and 2pq represents the frequency of the heterozygous genotype Aa.
3. The sum of the allele frequencies for all the alleles at the locus must be 1, so p + q = 1.4. Five factors that affect Hardy-Weinberg equilibrium are:
1) Gene migration or gene flow
2) Genetic drift
3) Mutation
4) Genetic recombination
5) Natural selection
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Sources of variation
Founder effect
It is the effect on the resulting gene pool that occurs when a new isolated population is founded by a small number of individuals possessing limited genetic variation relative to the larger population from which they have migrated.
Sewall wright effect
The sudden and random change in the allele frequency occurring in small or isolated populations by chance alone is called the Sewall wright effect.
Bottle neck effect
The phenomenon causing the reduction in the allele frequency and loss of some alleles from the gene pool in a random fashion is called bottle neck effect.
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Stages in Human Evolution
The following are the stages of human evolution:1. Dryopithecus
i) Ancestors of both man and apes.
ii) Lived in China, Africa, Europe and India.
iii) Predominantly herbivores
2. Ramapithecus
i) First remains were discovered from the Shivalik range in Punjab and later in Africa and Saudi Arabia.
ii) Lived in open grasslands.
iii) Thickened tooth enamel, robust jaws and shorter canines
iv) Usage of hands for food and defence.
3. Australopithecus
i) Fossils first discovered in 1924 in South Africa.
ii) Used stones as weapons and walked erect.
iii) 4 feet tall and weighed 60-80 pounds.
4. Homo erectus
i) Large cranial capacities
ii) Lived in communities.
iii) Used tools comprising quartz, bones and wood.
iv) Did collective huntings.
v) Use fire and lived in caves.
5. Homo sapiens neanderthalensis
i) Cranial capacity of Neanderthal grew from 1200 to 1600 cc.
ii) Some small hand axes had also been discovered.
6. Homo sapiens sapiens
i) Remains of Homo sapiens were first discovered in Europe and were named Cro-Magnon.
ii) The jaws are quite reduced, the modern man’s chin appeared, and the skull was rounded.
iii) Cranial capacity was about 1350 cc.
iv) Gathered food through hunting.
v) Cave art first appeared during this time.
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Evidences from morphology and anatomy
1. Comparative morphology and anatomy of individual organ and organ systems of diverse forms of organisms reveal their phylogenetic relationships and thus provides important evidences of evolution.
2. Homology is a relationship defined between structures or DNA derived from a common ancestor and illustrates descent from a common ancestor.
3. A common example of homologous structures in evolutionary biology are the wings of bats and the arms of primates.
4. Analogous structures are physically (but not genetically) similar structures that were not present the last common ancestor.
5. Bat wings and bird wings evolved independently and are considered analogous structures.
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