Human Evolution

Human evolution is the lengthy process of change by which people originated from apelike ancestors. Scientific evidence shows that the physical and behavioral traits shared by all people originated from apelike ancestors and evolved over a period of approximately six million years.

Theories of Evolution

Lamarck's Theory of Inheritance of Acquired Characteristics

Proposed by Jean-Baptiste Lamarck, this theory is based on two main principles:

1. Use and Disuse of Organs: Organs that are used frequently become stronger and more developed, while those that are not used deteriorate and may eventually disappear.

   • Example (Use): The long neck of the giraffe is explained by generations of giraffes stretching their necks to reach higher leaves, with this acquired trait being passed on to their offspring.
   • Example (Disuse): Vestigial organs in humans, such as the wisdom teeth, vermiform appendix, and the muscles that move the pinnae (outer ears), are considered to be remnants of organs that were once functional in our ancestors but are no longer needed.

2. Inheritance of Acquired Characteristics: Lamarck believed that the characteristics an organism acquires during its lifetime can be passed on to its offspring.

Darwin's Theory of Evolution by Natural Selection

Charles Darwin's theory, outlined in his book "On the Origin of Species," is based on the following key concepts:

• Variation: Individuals within a population exhibit variations in their traits.
• Inheritance: These variations are heritable and can be passed on to the next generation.
• Competition: Organisms produce more offspring than can survive, leading to a struggle for existence.
• Survival of the Fittest: Individuals with traits that are better suited to their environment are more likely to survive, reproduce, and pass on those advantageous traits.

Example: Adaptation of the Peppered Moth

Before the Industrial Revolution in England, the peppered moth was predominantly light-colored, providing camouflage against lichen-covered trees. A rare, dark-colored variant existed but was easily spotted by predators. As industrial pollution blackened the trees with soot, the light-colored moths became more visible, while the dark-colored moths were better camouflaged. This led to an increase in the survival and reproduction of the dark moths, and their population became more common in industrial areas. This is a classic example of natural selection in action.

Human Ancestors