Biological Evolution and the Diversity of Life

Posted on Dec 11, 2024 in Biology

Evolution and Natural Selection

Evolution is the gradual and continuous accumulation of heritable changes in populations that give rise to new species.

Fixism

This theory holds that species remain fixed and immutable from the beginning to the present day. Fixist theories are strongly influenced by myths and religious beliefs.

Main Fixists

  • Linnaeus grouped organisms according to their degree of similarity.
  • Cuvier, a French anatomist, was a defender of fixist theories. To explain the existence of fossils, he proposed the theory of catastrophism (the existence of different fossils compared to modern species), which posits that Earth’s geological history is marked by great catastrophes or cataclysms.

Precursors of Evolutionism

Aristotle observed affinities between organisms that led him to establish the scale of nature, ordered in which living beings range from the very simple to the more complex. Naturalists of the 18th and 19th centuries laid the foundation of evolutionary thinking, among whom Buffon and Erasmus Darwin are notable.

Charles Lyell’s current theory argues that events of the distant past were caused by the action of forces identical to those operating at present and explains the geological changes of the Earth as a slow, gradual, and continuous process that continues to act in the present.

Lamarck’s Transformism

  • In principle, there is in organisms a vital force that pushes them to change over time and acquire more complexity and perfection.
  • Spontaneous generation is the mechanism of occurrence of life forms, evolving from simpler to more complex organisms.
  • Evolution is a gradual process that leads to the adaptation of organisms to their environment by changes in their behavior.
  • These changes in dietary habits cause the use of a limb or organ that develops, and disuse leads to the atrophy of others, with a subsequent phase (the function creates the organ).
  • New characters acquired by use and disuse are transmitted to the following generation (inheritance of acquired characters).

Darwin’s Postulates

  • The world is not static but evolves.
  • The process of change is gradual and continuous, without discontinuous jumps.
  • Similar organisms are related.
  • Evolutionary change is the result of natural selection.

Natural Selection

  • Variability: In any population, individuals are randomly produced variations.
  • Struggle for existence: The number of individuals in a population remains constant over time; more individuals are born than can survive. Among the organisms of a population, a struggle for existence is generated because of limited resources.
  • Differential reproduction: Individuals with favorable variations survive and reproduce successfully. This is the result of adaptation.

Speciation

Speciation is the mechanism of the appearance of new species that causes a species to split into two or more new ones. There are sympatric and allopatric types.

Saltationism

Saltationism argues that macroevolution is not performed through small incremental changes and suggests that the fossil record is not incomplete but reflects the reality of the evolutionary process.

Evidences of Evolution

  • Paleontological: Phylogenetic series are sets of fossils sorted from oldest to most recent. Bridge forms or links are remains of organisms with intermediate characteristics of two groups of living things.
  • Comparative Anatomy:
    • Homologous organisms perform different functions but have the same basic structure and the same type of embryonic development.
    • Analogous organisms perform the same function but have a different evolutionary origin and a different basic structure.
  • Biochemical:
    • Great uniformity in the molecular components of all organisms.
    • The genetic code for translating genetic information from DNA.
    • Basic metabolic processes in all forms of life.

Adaptation

Adaptation refers to heritable changes that allow for the suitability of living conditions to the environment, enabling survival.

  • Adaptations to moisture: Camels and dromedaries.
  • Cactus: Adaptations to temperature.
  • Ectothermic animals.

Biodiversity

Biodiversity is the variety of species and their relative abundance in an ecosystem.

Causes of Biodiversity Loss

  • Overexploitation due to deforestation, overgrazing, etc.
  • Destruction and alteration of ecosystems due to pollution, forest fires, etc.
  • Fragmentation of natural habitats due to the construction of public works.
  • Introduction of non-native species that displace native species.

Protection of Biodiversity

  • Protected areas.
  • UN.
  • International agreements and seed/gene banks.
  • Sustainable use of natural resources.

Taxonomy

Linnaean Binomial Nomenclature

Linnaean binomial nomenclature assigns each species a scientific name with universal value. The name of each species is composed of two Latin words: the first is the name of the genus, and the second is the specific epithet.

Monera

Nutrition

  • Autotrophs:
    • Photoautotrophs, such as cyanobacteria.
    • Chemoautotrophs, such as nitrifying bacteria.
  • Heterotrophs:
    • Saprophytic, decomposing dead organic matter or organic debris.
    • Symbiotic, if obtained from other living beings, to those they benefit.
    • Parasitic, causing some change, more or less serious, to the host.

Relationship

Monera are able to detect changes in the environment and carry out appropriate cellular responses.

Reproduction

They reproduce asexually by binary fission.

Groups

  • Archaebacteria: Monera are the most primitive living beings, found in extreme environmental conditions. There are three types:
    • Halophilic, those living in hypersaline waters.
    • Methanogens, those living in anaerobic environments and producing methane from CO2.
    • Thermoacidophilic, those living in hot springs.
  • Eubacteria: All others are classified as:
    • Bacteria with cell wall (the majority):
      • Gram-positive, stain blue-violet with Gram stain and form endospores.
      • Gram-negative, stain red and include pathogenic bacteria like those causing the plague.
    • Mycoplasma: Smaller than the other groups, they have no cell wall, are Gram-negative, and most are pathogens.

Protoctista

Protoctista includes eukaryotes that are neither plants, animals, nor fungi. They can reproduce asexually or sexually.

Groups

  • Unicellular protozoa: Microscopic and lacking a cell wall.
    • Zoomastigina have one or several flagella used for locomotion.
    • Rhizopods emit pseudopods to move and capture food.
    • Ciliates move and capture food by cilia.
    • Sporozoa lack locomotive structures; all are parasites.
  • Fungus-like protoctists:
    • Myxomycetes: Cells are unicellular amoeboid forms without cell walls and with multiple nuclei inside.
    • Oomycetes: They have a body structure called mycelium, composed of filaments or hyphae, similar in structure to that of fungi.
  • Algae: Photoautotrophic protoctists that can be unicellular or multicellular, microscopic or macroscopic. Main groups include:
    • Euglenophytes
    • Bacillariophytes (diatoms)
    • Chlorophytes (green algae)
    • Phaeophytes (brown algae)
    • Rhodophytes (red algae)

Fungi

Fungi are heterotrophic eukaryotes whose cells have glycogen as a storage substance and a cell wall made of chitin. They can be unicellular or multicellular. Asexual reproduction occurs by fragmentation, regeneration, or asexual spores formed by mitosis. Sexual reproduction can also occur, involving the fusion of cells from different individuals, producing sexual spores.

Classification

Fungi were loosely classified with plants. They comprise five groups: zygomycetes, deuteromycetes, ascomycetes, basidiomycetes, and lichens.

Plants

  • Vascular: Ferns.
  • Non-vascular: Bryophytes.

Animals

  • Metazoa: Animals lacking tissue and symmetry (Parazoa, sponges).
  • Cnidaria: Polyps and jellyfish.
  • Eumetazoa: Animals with tissues and symmetry.
    • With radial symmetry.