Origin and Evolution of Life
1. Origin of Life
1.1 What is a Living Being?
– All living things are organized around something called a cell.
– In human beings, there are six main chemical elements: C, H2O, N2, P, S.
– The organic molecules are:
- Carbohydrates (containing C, H2, and O)
- Lipids (containing C, H2, and O)
- Proteins (C, H2, O, N2, S)
- Nucleic acids (C, H2, O, N2, P)
1.2 The Germinal Theory
Spontaneous Generation Theory: Human beings may appear from inanimate matter.
Pasteur (1822-1895): He demonstrated that living organisms could not arise from inert matter.
2. How Life Appeared
2.1 Life on Earth
– The atmosphere had no oxygen; gases present were water vapor, ammonia, hydrogen, and methane.
– Haldane (1892-1964) introduced the concept of prebiotic soup to refer to the first organic compounds dissolved in water.
– Miller: A mix of the prebiotic soup molecules trapped within micelles called coacervates.
– Miller: In this mixture of molecules, there were some strands of RNA called ribozymes.
2.2 Life from Space
– This theory is called Panspermia.
3. Classification of Life
– Linnaeus established four levels of classification: class, order, genus, and species. He named species using the binomial system (genus and species). Ex: Canis lupus.
3.1 The Current Classification of Living Beings
– Individuals are organized into groups called taxa.
– A taxon is a group of organisms with known characteristics that differentiate it from others.
– Different taxa form a taxonomic category.
– There are different encyclopedic categories, which group individuals according to more or less general characteristics.
– The categories are: Kingdom, Phylum, Class, Order, Family, Genus, Species.
– All living beings are classified into five kingdoms: Monera (bacteria), Protoctista (protozoa), Fungi, Plants, and Animals.
– The taxonomic species category is the basic unit of classification. A species is formed by very similar individuals, which can reproduce among themselves, giving fertile offspring.
Hybrid: A mix of organisms that have characteristics of both species. When two species can produce a hybrid, it generally does not survive or is sterile. If the hybrid is fertile, its offspring are sterile.
4. The Appearance of Species
Speciation: Two or more species emerge from a common ancestor because of biological barriers that limit the reproduction of populations of this common ancestor. It can be:
a) Allopatric speciation: Due to the physical separation of two populations.
b) Parapatric speciation: Two separate populations evolve differently (a factor affects one but not the other).
c) Sympatric speciation: A population of individuals undergoes modifications that allow them to perform a different function in the ecosystem.
Biological barriers: A set of mechanisms that prevent different species from reproducing. They can be:
a) Prezygotic (prevent the appearance of hybrids):
– The two species are fertile at different times.
– The two species live in different habitats.
– The two species cannot mate.
– Mating occurs, but male and female gametes are not compatible, or the male cannot fertilize the female.
b) Postzygotic (reduce survival or fertility of hybrids):
– The hybrid does not develop or dies after birth.
– The hybrid develops but is sterile.
– The hybrid develops and is fertile, but its offspring are sterile.
5. Evolution
– The appearance of different life forms from existing ones. It is the direct result of the processes of speciation. It has enabled various organisms to adapt to different environments and colonize the planet.
– The science that studies how organisms have evolved over time is called phylogeny.
5.1 Is Evolution Real?
– Currently, it is accepted that there is evidence demonstrating the existence of evolutionary processes. The most common evidence is:
a) Anatomical:
– Comparing the anatomy of different organisms reveals how the morphology of a species could change over time.
– When comparing the organs of different species, two types are found: analogous (with a different origin but performing the same function. These organs do not imply any close relationship between organisms) and homologous (have a common origin and structure and can perform different functions. These organs are used to determine the proximity between species).
b) Paleontological: Fossils can show how living things have evolved.
c) Biogeographical: Observing different organisms on the planet, we can see similarities between distant organisms and verify that speciation has occurred over a long time.
d) Molecular:
– All organisms have a molecular structure based on the same elements. The greater or lesser proximity between two species is reflected in the amount of similar genetic information.
e) Embryological: Coincidences observed in the embryonic development (ontogeny) of phylogenetically close species.