Evolution Lecture 1

Evolution of the Environment

• The evolution of the environment with definite biosphere zones facilitated the evolution of higher animals, including humans.
• Oparin (1938) suggested the following phases of evolution:
  • Atomic phase
  • Molecular phase
  • Organic phase
  • Colloidal phase
  • Autocatalytic phase
  • Primordial cellular phase
  • Autotrophic phase
  • Prokaryotic phase
  • Eukaryotic phase

Origin of Life

• The Earth is also known as 'the blue planet' or 'the planet with life', originating about 4.8 billion years ago.
• The primitive atmosphere of the Earth contained nitrogen, hydrogen, and carbon, but no oxygen or ozone, all found in the atomic state due to extreme heat and ultraviolet insulation.
• Chemical evolution continued for about 2,000 million years, resulting in the appearance of various inorganic and organic compounds, including N2, H2, CH4, NH3, CO, CO2, H2O, etc.

Lamarckism

• Lamarckian theory is also known as the 'Theory of Inheritance of Acquired Characters' or the 'Theory of Use or Disuse of Organs'.
• According to Lamarck's theory, as giraffes stretched to reach high branches, their necks lengthened, and this was passed on to their offspring.
• The basic ideas of Lamarckism are:
  • Complex plants and animals are produced from simpler ones over time under the influence of nature.
  • Living organisms have a tendency to continuously increase in size.
  • There is a change in the needs of an animal due to changes in the surrounding environment, resulting in the formation of new organs to cater to the needs of the animal.
  • If an organ is used continuously, it will become more powerful, but if it is not used for a long time, it will gradually weaken and eventually disappear.
  • The characters acquired during the lifetime of individuals will be transmitted to the next generation.

Critical Analysis of Lamarckism

• Lamarck based his idea of use and disuse on the evidence of vestigial organs and rudimentary organs.
• Weismann (1890) provided experimental proof against the assumption of inheritance of acquired characters.
• Weismann proposed the 'Theory of Continuity of Germplasm', stating that only changes in the germ cells are inherited, and somatic changes are not inherited.

Neo-Lamarckism

• A few scientists, notably Herbert Spencer, Haeckel, Gadow, etc., have supported Lamarckism in a modified form, known as Neo-Lamarckism.

Darwin Influenced by Others

• Malthus' "Essay of the Principle of Population" (1798) influenced Darwin's idea of natural selection.
• Darwin hypothesized natural selection as a means by which selective survival of individuals with superior attributes gradually changes the average characters of the population over many generations.

Additional Evidence Supporting Darwin/Wallace Theory

• Molecular biology, DNA, and genetic code, gene expression support the theory of evolution.
• Developmental biology provides insights into an organism's evolutionary history.
• Human embryos with gills, tails, and fur demonstrate evolutionary connections.

Darwinism

• Charles Darwin (1809-1882) categorically explained organic evolution in detail.
• Darwin's theory of evolution was shaped by the gradual changes in scientific beliefs during the 18th and 19th centuries.

Distinguishing Features of Species

• Galapagos tortoises have distinct shell shapes varying according to their island of origin.
• Examples of distinct species include the Rhea of South America, the Emu of Australia, and African ostriches.

Alfred Russel Wallace

• Alfred Russel Wallace (1823-1913) independently came up with the idea of natural selection.
• Darwin and Wallace published a joint presentation on their ideas in 1858, and Darwin published a detailed treatment in the Origin of the Species in 1859.