7. Evolutionary Biology

7. Evolutionary Biology

7.1 Life and Its Origin

• Oparin-Haldane Theory:

  • Proposed independently by Alexander Oparin and J.B.S. Haldane in the 1920s, this theory suggests that life originated from simple organic compounds present in the early Earth’s atmosphere, which combined in the presence of energy sources (like sunlight and lightning) to form more complex molecules.
  • The conditions of early Earth (reducing atmosphere) facilitated the formation of amino acids and other biomolecules, leading to the development of primitive life forms.

• Miller and Urey's Experiment:

  • In 1953, Stanley Miller and Harold Urey conducted an experiment to test the Oparin-Haldane hypothesis. They simulated the conditions of early Earth by mixing water, methane, ammonia, and hydrogen in a closed system and subjecting it to electric sparks (simulating lightning).
  • The experiment resulted in the production of amino acids and other organic compounds, supporting the idea that the building blocks of life could form under prebiotic conditions.

7.2 Evidences of Evolution

• Morphological Evidence:
  • Comparative anatomy shows similarities in the structure of different organisms, indicating a common ancestry. For example, the forelimbs of mammals (like humans, whales, and bats) share a similar bone structure despite having different functions.
• Anatomical Evidence:
  • Vestigial structures, such as the human appendix or pelvic bones in whales, are remnants of features that served a function in ancestral species, providing insight into evolutionary history.
• Paleontological Evidence:
  • The fossil record documents the existence of species that no longer exist and shows gradual changes in form over time, illustrating the process of evolution.
• Embryological Evidence:
  • Similarities in embryonic development across different species suggest common ancestry. For example, vertebrate embryos exhibit similar structures, such as pharyngeal arches, at early developmental stages.
• Biochemical Evidence:
  • Molecular biology studies reveal similarities in DNA and protein sequences among different species, indicating shared genetic heritage. For instance, humans and chimpanzees share about 98% of their DNA.

7.3 Theories of Evolution

• Lamarckism:

  • Proposed by Jean-Baptiste Lamarck, this theory suggested that organisms evolve through the inheritance of acquired characteristics. For example, he believed that giraffes developed long necks by stretching to reach higher leaves and passed this trait to their offspring. This theory has largely been discredited.

• Darwinism:

  • Proposed by Charles Darwin, this theory emphasizes natural selection as the mechanism of evolution. Darwin posited that individuals with advantageous traits are more likely to survive and reproduce, passing these traits to the next generation. The concept of "survival of the fittest" encapsulates this idea.

• Neo-Darwinism:

  • An updated version of Darwin's theory, incorporating Mendelian genetics. Neo-Darwinism combines natural selection with genetic inheritance, explaining how variations arise and are transmitted in populations, leading to evolutionary changes.

7.4 Human Evolution

• Position of Man in the Animal Kingdom:

  • Humans belong to the kingdom Animalia, phylum Chordata, and class Mammalia. They are classified in the order Primates, which also includes apes, monkeys, and lemurs.

• Differences Between New World Monkeys and Old World Monkeys:

  • New World monkeys (e.g., capuchins, spider monkeys) are found in the Americas and typically have prehensile tails and flat noses. In contrast, Old World monkeys (e.g., macaques, baboons) are native to Africa and Asia, lack prehensile tails, and have downward-facing nostrils.

• Differences Between Apes and Man:

  • Humans (Homo sapiens) differ from other apes (such as chimpanzees and gorillas) in several ways, including bipedalism (walking on two legs), larger brain size, advanced tool use, and complex language.

• Evolution of Modern Man from Anthropoid Ancestor:

  • The evolutionary lineage of modern humans traces back to a common ancestor shared with other primates. Fossil evidence indicates that early hominins, such as Australopithecus, exhibited both ape-like and human-like traits.
  • The genus Homo emerged around 2 million years ago, with species like Homo habilis and Homo erectus showing increasing brain size and tool use.
  • Homo sapiens appeared around 300,000 years ago and eventually became the only surviving species of the genus Homo, characterized by advanced cognitive abilities, culture, and social structures.