Evolution and Diversity of Life: From Creationism to Natural Selection

Posted on Nov 22, 2024 in Biology

Explanations of Life’s Origin and Diversity

Creationism and Fixity:

The creationist view holds that living things were created by a supernatural being. Fixity suggests that species remain unchanged over time.

However, these theories lack credibility due to fossil evidence showing changes in organisms over time, supporting the idea of evolution.

Aristotle held creationist ideas and classified animals:

• With red blood (vertebrates)
  1. Viviparous quadrupeds (mammals, except the oviparous platypus)
  2. Oviparous quadrupeds (reptiles and amphibians)
  3. Birds
  4. Fish (though whales are mammals)
• Without red blood (invertebrates)
  1. Cephalopods (octopus, squid)
  2. Shelled animals (snails, clams, oysters)
  3. Insects
  4. Animal-plants (sea anemones)

Linnaeus and Classification

Who was Linnaeus and what did he invent?

Linnaeus, a Swedish biologist, accepted divine creation but developed a system for classifying organisms.

He began by describing species, grouping similar ones into genera, then families, orders, and classes based on shared characteristics, creating a more accurate system.

Although he believed in the fixity of species, his classification system aided evolutionary theory by highlighting similarities between groups.

Example:

Theories of Evolution

Inheritance of Acquired Characteristics

Lamarck proposed that organisms change their bodies through use or disuse, and these changes are inherited. A classic example is the giraffe’s long neck, supposedly acquired through stretching to reach higher leaves.

However, this theory is refuted by examples like tail docking in dogs, where offspring still inherit tails.

Natural Selection

Darwin’s theory of natural selection states that organisms with advantageous traits are more likely to survive and reproduce. He argued that the Earth is old, species share similarities, and organisms descend from extinct ancestors. His evidence came from a five-year voyage around the world.

Malthus’s Influence

Malthus, an economist, predicted that population growth would outstrip food supply, leading to a struggle for existence. Darwin applied this idea to nature, realizing that not all offspring survive, leading to the survival of the fittest.

Conclusions on Natural Selection

Struggle for Existence: Competition for resources means many individuals die young or produce few offspring.

Survival of the Fittest: Individuals best adapted to their environment produce more offspring.

Natural Selection: The environment favors individuals with advantageous traits, leading to their increased prevalence over time.

Recent Evidence of Evolution

Before the industrial revolution, light-colored moths were camouflaged on lichen-covered trees near London. Industrial pollution darkened the trees, favoring darker moths, demonstrating natural selection in action.

Evidence for Evolution

• The fossil record
• Comparative anatomy and physiology
• Comparative embryology
• Geographical distribution
• Artificial selection
• Biochemical and genetic evidence

Fossils are preserved remains or traces of past organisms. Fossilization involves the replacement of organic material with minerals.

Evolution of the Horse

Early horses were smaller, lived in forests, had multiple toes, and ate soft vegetation. Over time, they adapted to grasslands, developing single hooves for speed and larger teeth for grazing on tougher grasses.

Comparative Anatomy

• Homologous Structures: Same embryonic origin, different function (e.g., human arm, bird wing).
• Analogous Structures: Different embryonic origin, same function (e.g., bird wing, insect wing).
• Vestigial Structures: Remnants of structures that no longer serve a function (e.g., appendix).

Embryonic Evidence

Similarities in embryos of different species suggest a common ancestor. The more similar the embryos, the closer the relationship (e.g., amphibians, fish, reptiles, birds, mammals).

Artificial Selection

Humans selectively breed organisms for desired traits, demonstrating how traits can change over time.