Key Theories of Life's Origin and Evolution

Theories on the Origin of Life

Panspermia Hypothesis

Life originated from spores traveling through space from one planetary system to another.

Prebiotic Synthesis Hypothesis

Life emerged from organic molecules on Earth, which in turn formed from inorganic matter.

Oparin-Haldane Hypothesis (Prebiotic Synthesis)

In 1923, Oparin and Haldane proposed that simple organic molecules could form from gases present in the early atmosphere. This hypothesis is based on several key points:

• Millions of years ago, the planet had an atmosphere without oxygen.
• When the Earth's temperature decreased, water vapor condensed into clouds, resulting in rain and the formation of oceans.
• The energy from the sun and electric discharges caused inorganic compounds present in the atmosphere to interact and form organic compounds.

Biological Evolution: Core Concepts

Defining Evolution

Biological evolution is the transformation process of species over time.

Fixism vs. Evolution

• Fixism: Species have remained unchanged since their creation.
• Evolution: Species can change and become other species.

Creationism

Creationism explained the origin of species as creations of God, which remained unchanged over time. It often claimed the Earth was approximately 6,000 years old.

Pioneers of Evolutionary Thought

Carolus Linnaeus: Binomial Classification

Linnaeus introduced binomial classification, a system to denote each species with two Latin terms:

• The first term describes the genus and is capitalized.
• The second term describes the species and is lowercase.

Georges Cuvier: Catastrophism Theory

Cuvier proposed the catastrophism theory to explain the existence and disappearance of species. According to his theory, in the past, different beings existed from current ones, which suddenly became extinct due to catastrophic events.

Jean-Baptiste Lamarck: Theory of Acquired Characteristics

Lamarck's theory proposed several principles:

• Organisms show a tendency towards complexity.
• Repeated use of an organ leads to its development (use and disuse).
• Acquired characteristics are inherited by offspring.

Charles Darwin: Natural Selection

Darwinism is centered on the concept of natural selection:

• There is a struggle among organisms for survival.
• Among individuals within a population, variability exists.
• The environment selects better-adapted organisms, leading to their increased survival and reproduction.

Genetic Variation and Evolutionary Mechanisms

Mutations: Genetic Alterations

Mutations are random alterations that occur in genes, which affect gametes and can be transmitted to offspring.

• Deleterious Mutations: Give disadvantages to an individual's survival or cause death. These mutations tend to be eliminated by natural selection.
• Favorable Mutations: Proportionately improve individuals' survival and reproductive capacity.
• Neutral Mutations: Are neither advantageous nor harmful. Natural selection does not eliminate or favor them, unless the environment changes.

Analogous Organs

These are structures that perform the same function in different organisms but have different evolutionary origins.

Vestigial Organs

These are organs whose function is gradually lost over the course of evolution.

Modern Synthesis of Evolution (Neo-Darwinism)

The Modern Synthesis integrates Darwinian natural selection with Mendelian genetics:

• It rejects Lamarckism.
• Genetic variation arises from two processes: mutation and recombination.
• Natural selection acts on genetic variation.
• Natural selection leads to changes in the frequency of alleles in a population.
• Populations evolve, not individuals.
• Evolution generally occurs gradually.

Punctuated Equilibrium

This theory proposes that species exhibit long periods of stasis (little or no change) interrupted by rapid bursts of speciation.

• Transformation occurs in rapid leaps, alternating stasis with periods of speciation.
• Transformation into a new species is often produced from a small, isolated population.

Speciation

Speciation refers to the processes leading to the formation of a new species from existing ones.

Human Evolution: Acquisition of Bipedalism

The acquisition of bipedalism involved several significant anatomical changes:

• Lengthening of the lower limbs relative to the upper limbs and trunk.
• Shortening and widening of the pelvis, positioning it lower.
• The spine, which bears the body's weight, acquires an S-shape with four curves.
• The foramen magnum (the opening at the base of the skull) is located in an inferior position on the skull.
• Elongation of the big toe, which becomes oriented parallel to the other toes, losing its grasping ability.