Understanding Biological Evolution: Fixism, Natural Selection, and Paleontology

Fixism: A Rejected Theory

Fixism is a belief that maintains existing species have remained unchanged since their creation. It is rejected as an explanation for the origin of species because it cannot answer questions such as:

• The existence of huge variability among individuals of the same species.
• The existence of fossils.
• The presence of vestigial organs.
• The similarities in internal organs of species that are very different.
• The fact that an individual's ontogeny reflects its phylogeny.

Natural and Artificial Selection

Natural selection states that descendants survive whose changes pose an advantage in adapting to the environment, and they may transmit those changes to their descendants. Artificial selection is a process where humans select different individuals of a plant or animal species for reproductive use based on desired characteristics.

The main difference is that natural selection is not planned by humans, but is imposed by environmental conditions.

Biological Evolution and Culture

Biological evolution refers to the physical and mental changes that occurred in the ancestors of humans until they became what they are today. Cultural evolution refers to what humans have created to build societies.

Paleontology: Studying Past Life

Paleontology studies the remains of living beings that inhabited past times. To explain their existence, the diluvian theory was used, according to which the remains belonged to animals now extinct as a result of a universal geological flood. The development of geology from the eighteenth century permitted relative dating from fossil sequences in stratigraphic layers. The diluvian theory was replaced by the theory of catastrophes, which states that since the creation of the world, catastrophes have occurred that eliminated ancient species and led to new, more perfect ones.

Comparative Anatomy and Classification

Comparative anatomy enabled the establishment of a greater or lesser degree of relatedness between species based on the similarity in their bodies and their functioning. It classifies all living things into three great domains: Bacteria, Archaea, and Eukaryotes. Bacteria and Archaea have no nucleus, while Eukaryotes consist of beings whose cells have nuclei. Eukaryotes are further divided into four kingdoms: Animals, Plants, Fungi, and Protists.