Biological Foundations: Life, Origins, and Evolution

Living Beings

Living organisms are defined by their complex structures and their ability to perform the three vital functions.

Key Features

• Spontaneity and Intent: They act with purpose to fulfill vital functions.
• Complex Composition: Composed of organic matter (C, H, O, N) and inorganic matter (minerals, H2O).
• Cellular Structure: Organized into cellular units.
• Biological Information: Structure and functional information are stored in nucleic acids.
• Homeostasis: The ability to maintain a relatively stable internal environment.

Theories on the Origin of Life

Spontaneous Generation

Historically, it was believed that life could originate from inert material, a theory supported by Aristotle and Van Helmont. However, Francesco Redi disproved this using meat and flies. Later, Louis Pasteur definitively proved spontaneous generation false, demonstrating that microbes and fungal spores present in the air cause the decomposition of organic matter.

Oparin's Hypothesis of Coacervates

A. Oparin proposed that life emerged from chemical evolution. He suggested that the primitive Earth's atmosphere (hydrogen, water, ammonia, hydrocarbons) created organic molecules in a "primitive broth," which combined to form coacervates.

Experimental Synthesis

• Miller-Urey Experiment: S. Miller confirmed Oparin's hypothesis by simulating primitive atmospheric conditions with electrical discharges, resulting in the formation of sugars, fatty acids, and amino acids.
• Artificial Synthesis: S. Fox demonstrated that applying heat to volcanic springs could produce proteinaceous microspheres.

Current Hypotheses on the Origin of Life

A protobiont is considered the first autonomous unit of life.

• Revised Oparin Hypothesis: Suggests the primitive atmosphere contained oxygen, as evidenced by carbonates. Protobionts evolved through membrane components, coacervates, proteins, enzymes, and eventually genes.
• RNA World Hypothesis: Proposes that RNA acted as both genetic material and enzymes, eventually leading to the formation of the plasma membrane.
• Clay Crystal Hypothesis: Suggests that clay mineral crystals acted as templates for the organization of RNA genes and enzymes.

The First Organisms

The First Eukaryotic Cell

• Autogenous Hypothesis (Taylor and Dobson): Proposes that eukaryotic organelles formed through the compartmentalization of prokaryotic cell membranes.
• Serial Endosymbiosis Hypothesis (Lynn Margulis): Suggests that an ancestral anaerobic eukaryotic cell engulfed prokaryotic cells, establishing a symbiotic relationship where each became a specialized cellular organelle.

Evolution of Multicellularity and Metabolism

Multicellular Organisms: Evolved from unicellular eukaryotes that formed temporary colonies; when they lost the ability to separate, they gave rise to specialized tissues.

Metabolic Evolution: Progressed from prokaryotic heterotrophic fermentation to the development of photosynthesis.