Discuss briefly the evidence of organic evolution.

Paleontological Evidence (Fossil Records)

Fossils provide a historical sequence of life, demonstrating changes in organisms over time. The fossil record shows a progression from simpler to more complex forms. Transitional fossils, exhibiting characteristics of both ancestral and derived groups, are particularly compelling.

• Archaeopteryx: A classic example, possessing reptilian features like teeth and a bony tail alongside avian features like feathers.
• Tiktaalik: A “fishapod” exhibiting features of both fish and tetrapods, illustrating the transition from aquatic to terrestrial life.
• Evolution of the Horse: The fossil record of horses shows a gradual increase in size, reduction in the number of toes, and changes in tooth structure, reflecting adaptation to grassland environments.

Comparative Anatomy

Comparing the anatomical structures of different organisms reveals similarities that suggest common ancestry.

• Homologous Structures: Structures with similar underlying anatomy but different functions, indicating shared ancestry (e.g., the pentadactyl limb in mammals, birds, reptiles, and amphibians).
• Analogous Structures: Structures with similar functions but different underlying anatomy, resulting from convergent evolution (e.g., the wings of insects and birds).
• Vestigial Structures: Remnants of structures that had a function in ancestral organisms but are now reduced or non-functional (e.g., the human appendix, pelvic bones in whales).

Embryology

The study of embryonic development reveals striking similarities between different species, particularly in the early stages. This suggests a common ancestry.

• Von Baer’s Law: States that the general features of a large group of animals appear earlier in development than the specific features of smaller groups. For example, vertebrate embryos all possess gill slits and a tail at some point, even if these structures are lost or modified in the adult form.

Biogeography

The geographical distribution of species provides evidence for evolution. Species tend to be more closely related to other species from the same geographic area than to species with similar lifestyles from different areas.

• Darwin’s Finches: On the Galapagos Islands, Darwin observed finches with different beak shapes adapted to different food sources, demonstrating adaptive radiation.
• Marsupials in Australia: The prevalence of marsupials in Australia, despite their limited distribution elsewhere, suggests that they evolved in isolation after Australia separated from other landmasses.

Molecular Biology

At the molecular level, all living organisms share a common genetic code (DNA and RNA). Similarities in DNA sequences, proteins, and other biomolecules provide strong evidence for common ancestry.

• Universal Genetic Code: The fact that all organisms use the same genetic code is a powerful argument for a single origin of life.
• DNA Hybridization: The degree of DNA hybridization between species reflects their evolutionary relatedness.
• Molecular Clocks: Mutations accumulate at a relatively constant rate, allowing scientists to estimate the time of divergence between species.

Direct Observation of Evolutionary Change

Evolution can be directly observed in some cases, particularly in organisms with short generation times.

• Antibiotic Resistance in Bacteria: The rapid evolution of antibiotic resistance in bacteria is a well-documented example of natural selection in action.
• Insecticide Resistance in Insects: Similar to antibiotic resistance, insects can evolve resistance to insecticides.
• Industrial Melanism in Peppered Moths: During the Industrial Revolution, the frequency of dark-colored peppered moths increased in polluted areas due to their better camouflage against soot-covered trees.