Human Ancestry: A Timeline of Key Species and Discoveries
Human Evolution: From Australopithecus to Homo Sapiens
Key Hominid Species
- Australopithecus: 4.5 – 1.5 million years ago (Ma). The first species with clearly human characteristics.
- Homo habilis: 2.5 – 1.5 Ma. The first tool builders.
- Homo erectus: 1.8 – 0.2 Ma. The first hominids to leave Africa and use fire.
- Homo heidelbergensis: 0.5 Ma – 50,000 years ago.
- Homo neanderthalensis: 0.2 Ma – 25,000 years ago. A European species that lived alongside Homo sapiens.
- Homo sapiens: Appeared about 150,000 – 200,000 years ago. Currently, the only Homo species on Earth.
Characteristics of Human Evolution
Bipedalism, hands-free for manual skills, a larger field of vision, cranial development, social complexity, and symbolic thought.
Paleontology and Dating Methods
Paleontology is the science that studies fossils. Dating methods enable us to know the age of fossil remains.
- Radioactive dating: Measures the radioactivity of a sample to determine its age.
- Carbon-14 dating: Measures the decay ratio between C14 and C12.
Evolutionary Theories
Classical evolutionism proposes gradual evolution through many small, continuous changes.
Modern evolutionism suggests leaps in evolution, with large changes followed by periods of stability. In any habitat, there are a variety of conditions, and within each species, there is a variety of individuals. Individuals often live in environments where there is not enough food for all, or where they must protect themselves from predators. Only the strongest, best-trained, in short, the most-adapted, survive. Those who can survive, i.e., the best-equipped, transmit their characteristics to their offspring. Over time, species become better prepared for existence.
Lamarck (1744-1829) proposed that when there are changes in the environment, individuals vary their habits and adapt their anatomy. These changes are transmitted to offspring. So, with time, species are transformed and perfected.
Alternative Theories of the Origin of Life
Panspermia: According to this theory, there would be an indefinite number of germs or spermatia throughout the universe that have given rise to all life, which then developed on Earth.
Life from biochemical evolution: In the early atmosphere, it is thought that the first life forms appeared under the following conditions: methane, water vapor, and ammonia. Amino acids are simple organic molecules that are the basic constituents of proteins. Combining amino acids can form proteins.
Spontaneous generation: Some living things arose spontaneously from certain substrates through a kind of vegetative force emanating from the matter itself. Looking through a microscope, tiny beings were seen in drops of water that had not been there before. After boiling broth in a flask, it remained sterile for a long time.
The Definition of Life
A living being is any body capable of carrying out the three vital functions: nutrition, interaction, and reproduction. All living cells are formed by cells that create copies of themselves and transmit their information from generation to generation.
Elements Necessary for Life
Oxygen, carbon, nitrogen, sulfur, phosphorus, calcium, magnesium, iron, and others. High temperatures and high-energy radiation were also present in early Earth.
Earth’s Structure
Static Model: Crust, upper mantle, transition zone, lower mantle, outer core, inner core.
Dynamic Model: Lithosphere, asthenosphere, mesosphere, endosphere, inner core.