Theories of Life’s Origin and Evolution: A Comprehensive Study

Posted on Dec 28, 2024 in Biology

Theories About the Origin of Life

  • Theory of Spontaneous Generation (Aristotle)
    • Formerly, it was believed that decomposing organic matter produced living beings spontaneously.
  • Theory of Prebiotic Synthesis (Alexander Oparin, John Haldane)
    • Life arose from inorganic matter.
  • Panspermia Theory
    • Proposed by Svante Arrhenius.
    • Suggests that life came to Earth from another planet.
    • It does not solve the question posed by the origin of the first living being.
  • Present-Day Hypothesis
    • Possible appearance of living beings in deep-sea hydrothermal vents.

Theories of Evolution

  • Lamarckism or Transformism
    • Proposed by Jean-Baptiste de Monet, Chevalier de Lamarck, in 1809.
    • It is the theory of inheritance of acquired traits.
    • Principles:
      • Environmental conditions vary over time.
      • Changes create new needs (the need creates the organ).
      • New habits emerge.
      • Modifications are passed on to offspring.
  • Darwinism
    • Proposed by Charles Darwin and Alfred Russell Wallace in 1859.
    • Theory of evolution by natural selection.
    • Principles:
      • There are small variations in individuals of the same species.
      • There is a struggle for survival in the habitat where they live.
      • Some variations are more successful (natural selection).
      • The species changes.
  • Neo-Darwinism or Synthetic Theory
    • It arises as a result of genetic research produced in the 20th century.
    • Changes in species occur by:
      • Mutations: changes in the genetic sequence of DNA, harmful or neutral.
      • Sexual reproduction: combinations of genes different from those of the parents.
      • Genetic recombination: new combinations of genes in meiosis and in the fertilization of sexual reproduction.
  • Neutralism
    • Created by Motoo Kimura.
    • Living beings evolve by mutations.
    • Defends that there is no natural selection.
  • Theory of Punctuated Equilibrium
    • Proposed by Niles Eldredge and Stephen Jay Gould.
    • Evolution is not slow and always gradual; instead, in many cases, new species are formed rapidly.
  • Endosymbiosis
    • Proposed by Lynn Margulis.
    • Explains the evolution of the eukaryotic cell from prokaryotic cells.
    • Primordial protoeukaryote: digested prokaryotes.
      • Among the survivors, there would be two types:
        • Effective in respiration: originated the mitochondria.
        • Effective in photosynthesis: they originated chloroplasts.
  • Evolutionary Developmental Biology
    • Some body changes in species are due to mutations in a small group of Hox genes.

Evidence of Evolution

  • Anatomical and Morphological Evidence
    • Homologous organs.
    • Analogous organs.
    • Vestigial organs.
  • Fossil Evidence
    • Fossils show that many different organisms existed on Earth.
    • Evolutionary series show gradual changes in species.
  • Embryological Evidence
    • Embryonic development (ontogeny) is a summary of evolution (phylogeny).
  • Biogeographical Evidence
    • Organisms with a common origin evolve into different species if they are geographically separated.
  • Molecular Evidence
    • The more similar the biomolecules of various living things are, the closer their evolutionary relationship.
    • Example: chlorophyll.
  • Other Evidence
    • Coevolution between species:
      • Mutualism.
      • Parasitism.
      • Mimesis.
      • Domestication.
    • Temporal sequence of the stratum.

Process of Hominization

The Hominization process consists of the evolutionary transformation of hominoids into hominids. It is a process that has occurred in the hominoid line since its divergence from the last common hominoid ancestor shared with any living ape.

  • Human Evolution
    • The hominization process has spanned 6 million years.
    • Australopithecus:
      • Australopithecus afarensis.
      • Australopithecus africanus.
    • Homo:
      • Homo habilis.
      • Homo erectus.
      • Homo sapiens neanderthalensis.
      • Homo sapiens sapiens.

Environmental Factors

  • Characteristics of the environment that affect living beings.
  • Types of factors:
    • Abiotic: biotope.
    • Biotic: biocoenosis.

Limiting Abiotic Factors

  • Part of the biotope.
  • They define the living conditions.
  • Types of factors:
    • Terrestrial environment: temperature, humidity, relief, availability of water, light, nutrients.
    • Aquatic environment: depth, light, pressure, water movement, oxygen concentration, temperature, salinity.
  • Ecological valence:
    • Range of values of abiotic factors in which a species can live.
    • Optimal: ideal environmental conditions for a species.
    • Adaptations: allow a species to adapt to the environment.
    • Euryoic species: large tolerance ranges. Example: eurytherm.
    • Stenoic species: small tolerance ranges. Example: stenohaline.

Concepts of Adaptation, Limiting Factor, and Tolerance Limit

Adaptation is a process that allows a species to adapt to the environment. Adaptations produce changes in populations over time: they are the engine of evolution. Thanks to adaptations, species survive. Adaptations can be anatomical (morphological), physiological, or ethological (behavioral).

Limiting factor: Part of the biotope that defines the living conditions, which can be:

  • Terrestrial environment: temperature, humidity, relief, availability of water, light, nutrients.
  • Aquatic environment: depth, light, pressure, water movement, oxygen concentration, temperature, salinity.

Tolerance limits consist of the upper and lower limits of a particular environmental condition which allows a certain species to survive. Environmental conditions can include the amount of water, temperature, light, or the availability of other resources.

Population

Group of organisms of the same species that live in the same territory and can reproduce with each other.

Ecotone

Transition between two communities of an ecosystem.

Community or Biocoenosis

Living things that make up an ecosystem. It includes the populations of all species in an ecosystem.

Intraspecific Relationships

  • Between individuals of the same species:
    • Colony: Organisms attached to a substrate, attached to each other.
    • Family: Individuals with a high degree of kinship.
    • Social: Many individuals live in large groups and divide the work to benefit the whole.
    • Gregarious: Individuals united for defense, mobility, etc.

Interspecific Relationships

  • Neutral.
  • Beneficial: Mutualism, Symbiosis, Commensalism.
  • Detrimental: Predation, Herbivory, Parasitism.
  • Competition, Amensalism.