CBSE Class 12 Biology Evolution Flow Chart

This Class 12 Biology Chapter 7 Evolution flow chart notes page for CBSE board exam preparation covers the evidences of evolution, adaptive radiation, biological evolution with Darwin and Lamarck, the mechanism of evolution with Hugo de Vries, Darwin and the Hardy-Weinberg principle, and a brief account of evolution through geological time.

1. EVIDENCES OF EVOLUTION

Evidences of evolution :
1. Paleontological evidences show that life forms varied over time and certain life forms are restricted to certain geological time spans.
2. Comparative anatomical and morphological evidence shows:
    Homologous organs leading to divergent evolution
    Analogous organs leading to convergent evolution
3. Bio-chemical evidences: similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry.
4. Anthropological evidences:
    Appearance of resistant organisms or cells
    Industrial melanism, shown by the moth Biston betularia and Biston carbonaria
    Artificial selection of domesticated wild animals and crops by man

2. ADAPTIVE RADIATION

Adaptive radiation is the evolution of different species in a given geographical area, starting from a point and radiating to other areas of geography (habitat).

Examples of adaptive radiation:
1. Darwin's finches (a small black bird) with original seed-eating features.
2. Australian marsupials and placental mammals in Australia.

3. BIOLOGICAL EVOLUTION

Biological evolution flow chart:
• Evolution of new colonies of bacteria within days when the
• Key concept of Darwin: branching descent and natural selection. Under natural selection, organisms with favourable heritable variations get better survival to reproduce and leave a greater number of progeny.
• Lamarck theory:
    1. Evolution of life forms had occurred by the use and disuse of organs, e.g., vestigial organs (wisdom tooth).
    2. Inheritance of acquired characters, e.g., elongated neck of giraffe.

4. MECHANISM OF EVOLUTION

Hugo de Vries:
1. Mutation causes evolution, not minor variation.
2. Mutations are random and directionless.
3. A single step mutation causes speciation (saltation).

Darwin:
1. Minor variations cause evolution.
2. Variations are small, gradual and directional.

Hardy-Weinberg Contribution

Principle: Allele frequencies within a population are stable and remain constant from generation to generation. p² + 2pq + q² = 1

Factors affecting the Hardy-Weinberg principle:
• Gene migration or gene flow
• Genetic drift
• Mutation
• Recombination
• Natural selection, which can be stabilising, directional or disruptive

5. BRIEF ACCOUNT OF EVOLUTION

Time and organisms in the evolution of life:
1. 3 billion years ago: first non-cellular form of life.
2. 2000 million years ago: first cellular forms of life appeared.
3. 500 million years ago: invertebrates formed.
4. 320 million years ago: seaweeds and plants existed.
5. 350 million years ago: fishes with stout and strong fins could move on land and go back to water. The coelacanth, called lobefins, evolved into the first amphibian.

[Figure: Table titled Brief account of Evolution with two columns, Time and Organism, and five rows as listed above.]