Life’s Journey: Origins, Evolution, and Human Development
Theories on the Origin of Life
Panspermia: Life from Outer Space
Panspermia states that life emerged from outer space to colonize our planet. It suggests that life, in the form of very simple organisms, moves throughout the universe and colonizes planets.
Abiogenesis: Life’s Terrestrial Beginning
Abiogenesis proposes that life appeared on Earth 3.5 billion years ago, when the necessary prebiotic conditions for life began. It suggests this was a unique and unrepeatable fact.
The Process of Obtaining Life
The process of obtaining life involved:
- Concentration of molecules from inert matter.
- Chemical conversion reactions of protected amino acids.
- Formation of lipid layers.
- Gathering energy.
- Formation of DNA and RNA.
Stromatolites: Earth’s First Organisms
Stromatolites are considered the first living organisms on Earth. Some believe these emerged in bubbles within the warm waters of the primitive Earth, while others believe the first life forms appeared associated with dirt and clay particles. The first living things emerged away from ultraviolet rays.
Understanding Species Change
Fixity: Unchanging Forms of Life
The theory of Fixity holds that both nature and living species are an ultimate, finished reality. Living things are considered unchanged forms, existing today as they were designed from the beginning.
Evolution: Continuous Transformation of Species
Evolution, specifically biological evolution, admits a continuous process of transformation of species through genetic changes in successive generations of a population.
Darwinian Evolution and Modern Synthesis
Charles Darwin’s Revolutionary Ideas
Charles Darwin noted that life is evolution and that some species originate from others through Darwinian selection. His four assumptions were:
- Life Forms: Life forms on Earth are not static but evolve.
- Gradual Process: The process of evolution is gradual and slow.
- Common Ancestry: Similar organisms are related and descend from a common ancestor.
- Natural Selection: This involves the production of variability (changes in individuals) and survival in the struggle for life (the fittest individuals).
Points 2 and 4 are controversial and nuanced by genetics, while points 1 and 3 are currently accepted.
The Current Explanation of Darwin’s Theory
In the twentieth century, Darwin’s theory was reformulated. The distinction between somatic and germ cells highlights that acquired changes are not inherited unless they affect germ cells. The explanation of natural selection now includes:
- The sudden appearance of new variants in the process of reproduction is due to the production of genetic mutations.
- Carriers of a more favorable genetic endowment to address ecological pressure have a higher chance of survival than the rest, which makes possible the emergence of new species.
Mutations and other factors mean there are many different ways to consider Darwinism today.
Human Evolution: Key Features and Timeline
Defining Features of Hominins
The four defining features of hominins are:
- Terrestriality: Descending from trees and living on the soil.
- Bipedalism: Walking with two legs.
- Culture: Mastery of fire, construction of tools, clothing.
- Encephalization: Increase in brain size in relation to the body.
Humans are intelligent because they are the only living beings that change their environment to suit their needs.
Hominid Chronological Timeline
Under the term hominid (or more precisely, hominin), we group all humans and their ancestors who have walked upright on two limbs. The known hominin timeline includes:
- Australopithecus: 4 to 2 million years ago.
- Homo habilis: 2.4 million years ago.
- Homo ergaster: 2 million years ago.
- Homo antecessor: 800,000 years ago.
- Homo erectus: 400,000 years ago.
- Neanderthals: 200,000 to 35,000 years ago (became extinct 35,000 years ago).
- Homo sapiens: 100,000 years ago to present (modern Homo sapiens technologicus).