Evolutionary Theories

What is Evolution?

Evolution refers to the gradual change in a population's genetic composition over successive generations. It is based on well-substantiated evidence that has been tested repeatedly and is accepted by the scientific community.

Evolutionary Theory

• Theory of Natural Selection

• Theory of Use and Disuse of Organs

• Theory of Inheritance of Acquired Characteristics

Evidences of Evolution

What pieces of evidence show that evolution happened?

What is the significance of looking for evidences?

Evidence for Evolution:Many genetic, anatomical, physiological, archaeological, and geographical discoveries have been made that support the theory of evolution; these include:

• Biogeography

• Fossil Record

• DNA/Protein sequences

• Comparative Anatomy

• Embryology

Biogeography

Biogeography reveals how the distribution of organisms across regions supports evolutionary processes. For example,

• The presence and evolution of marsupials in Australia, isolated from other continents, demonstrate unique evolutionary outcomes.

• Islands often have species closely related to those on the nearest mainland but evolved unique traits due to isolation and different environmental pressures.

A classic example is the finches on the Galapagos Islands, studied by Charles Darwin, which evolved from a common ancestor to adapt to diverse ecological niches, showing variations in beak shapes, sizes, and functions.

Fossil Records

Fossils are the preserved remains and traces of past life. Depending on structure, composition, and/or role, fossils can be classified as:

• Preserved remains

• Traces of organisms that lived in the past

• Imprints of external features or plant tissues without organic materials

• Compression fossils: animal or plant tissues in sedimentary rock with more organic material.

Comparative Anatomy

Comparing the anatomy of present day, transitional, and ancestral organisms gives insight into similarities and differences. Structures can be classified into:

• Homologous Structures: Different external appearances but derived from a common ancestor. Examples include the pentadactyl limb and vertebrate hearts.

• Analogous Structures: Structures that may appear similar due to similar environmental pressures but do not share a recent common ancestry. Examples include wings of birds and insects.

• Vestigial Structures: Anatomical structures that no longer serve their original function, but indicate shared ancestry. Examples include wisdom teeth and the tailbone.

Comparative Embryology

Vertebrates share several developmental characteristics, including a hollow dorsal nerve cord and pharyngeal pouch. The more closely related two species are, the more similar their embryos appear earlier in development.

Molecular Homogeny

This involves comparing the sequences of DNA, genes, and proteins. The fewer genetic differences between species, the more closely related they are, allowing for measurement of evolutionary distance quantitatively.