The Genesis of Life and Human Ancestry

Posted on Sep 9, 2025 in Geology

The Origin of Life: Hypotheses and Theories

Alien Hypothesis

This hypothesis suggests that life emerged in outer space, then colonized our planet. It proposes that life came to Earth in the form of spores brought by meteorites. While the existence of a vast arsenal of organic compounds in space has been confirmed, there is no evidence yet of life outside Earth.

Terrestrial Hypothesis

This theory states that life began under specific prebiotic conditions, from chemical elements and physical conditions, defending the appearance of the earliest forms of life from non-living matter.

Fixist Theory

The Fixist Theory states that the world is static and living things are immutable since their creation. Several sub-theories exist:

  • The Diluvian Theory: Defends that fossils are remains of animals that survived the flood.
  • The Catastrophe Theory: Proposed by Cuvier, it explains that successive episodes of extinction were followed by immediate new creations.

Evolutionary Theory

Evolutionary Theory is characterized by:

  • Naturalist expeditions in the 18th and 19th centuries.
  • Advances in the scientific method, which increased the estimated age of the Earth.
  • Lamarck’s Theory of the Inheritance of Acquired Characters: Based on two principles: the function creates the organ, and characters acquired during an individual’s life are inherited.

Darwinism: The Theory of Evolution

After his travels around the world, Darwin identified three distinct principles:

  • Variation in Descent: Offspring differ from each other and their parents in some characteristics.
  • Natural Selection: Individuals in a population that are better adapted to the environment survive more easily and transmit these traits to the next generation.
  • Gradualism: Individuals carrying adaptive traits will increase in the population.

Neo-Darwinism

This theory is based on Mendel’s Laws and the discovery of genetic mutations. It explains that:

  • Character changes in an individual are produced by mutations, which are modifications of DNA.
  • Mutations occur randomly.
  • Mutations are classified as:
    • Favorable: Individuals with these mutations are better adapted to the environment, and natural selection tends to consolidate them compared to those without the mutation.
    • Harmful: Detrimental to the individual and can even cause death.
    • Indifferent: Changes some characters but neither favors nor harms adaptation to the environment.

Human Evolution: The Hominid Lineage

Australopithecus

The oldest known hominid fossils. The first individuals barely exceeded one meter in height, had long, ape-like arms, and were bipedal. Bipedalism involves:

  • Arms and hands are free while walking, allowing them to be used for other tasks.
  • Reduced solar radiation exposure.
  • Expanded field of view in open areas.

Homo habilis

Appeared with an appearance similar to Australopithecus but had the ability to create tools. The consistent increase in brain size along the evolutionary path is significant, as the brain is an organ that requires much energy. Homo habilis is characterized by:

  • A larger brain.
  • The manufacture of simple, carved stone tools.
  • Being an opportunistic scavenger, eating bone marrow.

Homo erectus

Lived for 1.8 million years, coexisting with our species. It is characterized by:

  • Making useful, more elaborate stone tools, carved on both sides.
  • The invention of the first spear and bowl, both made of wood.
  • Most importantly, the control of fire, vital for mankind.
  • Being the first hominid to leave Africa, with remains found in Africa, Asia, the island of Java, and Europe.
  • Hunting large animals, which required communication skills, organization, and planning.

Homo antecessor

Findings from Atapuerca led to its naming as Homo antecessor, believed to be the ancestor of both Neanderthals and modern humans. Its characteristics include:

  • Remains of all individuals show signs of cannibalism.
  • Bones of the face suggest a flattened, more modern facial structure.

Homo neanderthalensis

Key features are:

  • A very robust skeleton.
  • A skull that slopes backward and forward, with a larger cranial capacity than ours, and a prominent face.
  • They buried their dead and likely crafted specialized tools.