Understanding Fixism and Evolutionary Concepts

Fixism (Cuvier) or fijista theory is a belief that holds that existing species have remained essentially unchanged since they were created, therefore, immutable. The fossil remains of animals would be killed in the biblical flood or by the vagaries of nature (as theories such as vis plastica).
Now become (Lamarck 1809): Progression from simple organisms to complex plants and animals, ultimately reaching humans. "Existence impulse towards perfection" - Cap. of the organisms for adaptability to environmental changes - Principle of use and disuse of organs - Inheritance of acquired characteristics.
Compression Fossils and Printing: This occurs when an organism is caught or parts of it are covered by sediments without decomposing, resulting in completely unsalvageable debris.
Petrifaction: This happens when solid parts such as bones and shells are replaced by minerals like calcium carbonate or silica.
Molds: These are obtained when the material encompasses a dead organism, solidifies, and the tissues are drained and filled with minerals that harden to form an exact copy of the structure of the external organism.
Living Fossils: There are species of plants and animals that have retained the same anatomy for millions of years, such as the Nautilus, Coelacanth, and Ginkgo Biloba.
Its Counterparts: They have the same origin but different functions (distinct traits in species) which is divergent evolution from a common ancestor.
Like Organisms: These perform the same function but are of different origins. This is known as convergent evolution, where several ancestors originate with one specific function.
Vestigial Organs: Some organs that once served a purpose are now useless and may disappear one day or have already done so.
Adaptations to Terrestrial Environments:
Plants: Vascularization - Xylem: Transports water and salts from roots to the upper parts of the plant.
Phloem: Distributes the sap drawn from the rest of the plant.
Selection Types:
Stabilizing: It favors the average phenotype, disadvantaging extreme phenotypes.
Directional: Reproductive selection favors one of the extreme phenotypes.
Disruptive: Reproductive selection is favored by lowering the average phenotype.