1. Introduction to Evolution:

(i) Evolution is the gradual change in traits of living organisms that are determined by genes.
Charles Darwin's book On the Origin of Species by Means of Natural Selection was published in 1859.

(ii) Darwin explained the mechanism that causes organisms to change over time. The process that we call evolution. His explanation shows how all forms of life could have evolved from a universal common ancestor.

2. Selective breeding of dogs:

(i) Artificial selection is the selective breeding of plants and animals to include beneficial traits in them. This is also called selective breeding.

(ii) Artificial selection can only change traits if they are due to the dogs' genes and not to the environment.

(iii) If something is changed during a dog's lifetime, the offspring of that dog will not inherit the changed trait.

(iv) Artificial selection can only work if there is variation in the genes. If there is no genetic variation in a breed, then it is impossible to select individuals with more desirable traits to breed the next generation.

3. Mutation:

(i) Mutations are changes to the base sequence of a gene.

(ii) A mutagen is a substance that causes an increase in the frequency of mutations.

(iii) The most important features of gene mutations are:

(a) Mutations are random

(b) Mutations are heritable

(d) Mutations can change protein structure

(e) Mutations can be beneficial, harmful or neutral

(iv) Sickle-cell anaemia, a genetic disease, is caused due to change of one base in the gene coding for the beta-chain of haemoglobin.

4. Adaptation:

(i) Adaptations are features (or changes to features) that make an organism better fitted to its environment.

(ii) Different adaptations are needed if an organism's environment changes.

(iii) Only heritable traits are considered to be adaptations.

(iv) Being better adapted gives an organism more chance of survival. This is sometimes referred to as survival of the fittest.

(v) Skin colour in humans is an example of adaptation.

5. Natural Selection:

(i) Natural selection happens when the best-adapted individuals in a species survive and reproduce, passing on genes to their offspring.

(ii) Characteristics that can be passed from parents to offspring are heritable.

(iii) Variation is the range of differences between members of a species.

(iv) The well-known examples of natural selection are the development of antibiotic resistance in bacteria and beak size change in Darwin's finches of the Galapagos Islands.

(v) Variations inherited through generations and repeated differently help form species that are different from their ancestors. This type of selection, done by nature, leads to the diversity of species that we see around us. This is the explanation of Darwin's theory which is known as the Theory of Natural Selection.

(vi) Natural selection can cause more significant changes, but only if these three conditions are met:

(a) There is variation in the population.

(b) The variation is at least partly heritable.

(vii) Industrial melanism exhibits natural selection. It is a term that describes how some animals change colour in response to environmental changes caused by pollution. The best example of this is shown by the peppered moth.

6. Evidence of Evolution from anatomy:

(i) The anatomical structures and physiological functions of different species provide evidence of evolution.

(ii) Scientists compare and contrast types of anatomical features, known as homologous structures, vestigial structures, and analogous structures, to understand how closely related different organisms are.

(iii) Homologous organs are the organs of different species having the same basic structures and similar embryonic origin, but different functions.

7. Evidence of Evolution from DNA:

(i) Organisms that are in the same species have genes with very similar base sequences.

(ii) Organisms that are in different species have far more differences in their genes.

(iii) The more closely related two individuals are the fewer differences in the base sequence of their DNA.

(iv) Differences in the base sequence of DNA accumulate over time, so are used to estimate how long it is since two species diverged from a common ancestor.

(v) Computer analysis of base sequences can generate "tree of life" diagrams that show the likeliest evolutionary history of a group of organisms.

(vi) All organisms can be traced back to a universal common ancestor, about 4 billion years ago.

(vii) Evidence from DNA was used to produce the tree diagram of canids (species closely related to dogs).

8. Evidence of Evolution from embryos:

(i) Embryology, the study of the development of the anatomy of an organism to its adult form, provides evidence for evolution as embryo formation in widely divergent groups of organisms tends to be conserved.

(ii) The structures that are absent in the adults of some groups often appear in their embryonic forms, disappearing by the time the adult or juvenile form is reached. For example, all vertebrate embryos, including humans, exhibit gill slits and tails at some point in their early development.

9. Evidence of Evolution from fossils:

(i) The study of fossils is known as Palaeontology.

(ii) Sequences of fossils show progressive change over time, including gradual transformations from one life form to another.

(iii) There is an increase in the complexity and diversity of organisms from the oldest to the youngest rocks that matches how we would expect life to have evolved.

(iv) Some major groups of organisms have disappeared permanently from the fossil record.

10. Extinct species:

(i) Many species of plants and animals that once lived on Earth are no longer found anywhere and are therefore extinct.

(ii) Fossil records tell us that very large numbers of species have died out during five brief periods in the Earth's history. These are called mass extinction events.

What is mutagen give an example ?

Important Questions on Evolution

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