Lesson 24: Evidence for Evolution

1. Molecular Biology Evidence

• Molecular biology evidence refers to the similarities in the structure and function of organic molecules found in different species, reflecting their shared ancestry.

• Specific examples:

• Genetic Code: All living organisms today share a universal genetic code, indicating their close relationship.

• DNA Structure: The DNA of all living organisms is made up of the same four nucleotides: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). The arrangement of these nucleotides determines the diversity of genetic information across species.

• Protein Structure: Proteins in all living organisms are made up of approximately 20 amino acids. Different combinations of these amino acids create diverse proteins that perform specific functions for each species.

Note:

• Molecular biology evidence is the most compelling support for the theory of evolution, as it reflects the direct genetic connection between species.

• Advances in molecular biology research continue to provide more evidence supporting evolution.

2. Homologous and Analogous Structures

2.1. Homologous Structures

• Definition: Homologous structures are organs that share a common origin and basic structural plan but may differ in shape, size, and function due to adaptation to different environments.

• Examples:

• Bird wings and bat wings: Both have the same bone structure (humerus, radius, ulna, carpals, metacarpals, and phalanges) but differ in shape, size, and function due to their adaptation to different flight styles.

• Human arms and cat legs: Both share the same bone structure (humerus, radius, ulna, carpals, metacarpals, and phalanges) but differ in shape and function because they perform different tasks.

2.2. Analogous Structures

• Definition: Analogous structures are organs that have different origins and different structures but have evolved to perform similar functions due to adaptation to the same environmental conditions.

• Examples:

• Bat wings and insect wings: Both serve the function of flight, but their structures are completely different. Bat wings are modified forelimbs, while insect wings are outgrowths of the exoskeleton.

• Whale flippers and the forelimbs of terrestrial animals: Both structures function in locomotion in water, but they have different structures. Whale flippers are modified hind limbs, while the forelimbs of terrestrial animals are derived from the forelimbs.

Note:

• Homologous structures provide strong evidence for shared ancestry, while analogous structures exemplify evolutionary adaptation.

3. Vestigial Structures

• Definition: Vestigial structures are organs that were fully developed in ancestors but are now reduced or non-functional.

• Examples:

• Appendix in humans: A remnant of the cecum, it plays a crucial role in herbivores but is reduced in humans due to changes in diet.

• Pelvic bones and femur in snakes: Remnants of hind limbs in their ancestors, they are no longer used for locomotion.

Note:

• Vestigial structures demonstrate common ancestry and the process of evolutionary adaptation.

• The presence of vestigial structures shows how species adapt to their environment, with unnecessary organs gradually diminishing.

4. Summary

• Molecular biology evidence, homologous structures, and vestigial structures are key evidence for the theory of evolution.

• This evidence showcases the close relationship between species, adaptation to the environment, and the evolutionary descent from a common ancestor.