Evolution Theories: Punctuated Equilibrium and Evidence for Natural Selection
Neodarwinism
Neodarwinism is a school of thought that emerged in the 20th century, associated with Wright, Dobzhansky, Mayr, and Weismann. Starting from Darwin's work, it held that natural selection was the main mechanism of organic change and the exclusive explanation of evolutionary processes. Its defenders were known as neodarwinists.
Punctuated Equilibrium
Punctuated equilibrium is a theory proposed by Eldredge and Gould that challenged the gradualist view of biological evolution. According to this theory, during most of the time a species exists, it remains stable or undergoes only minor changes (known as stasis). Evolutionary change occurs mainly during brief periods of rapid speciation, in which a new species arises, often from small isolated populations.
Evidence for Evolution
Living beings with the same or similar internal structure may be adapted to very different functions. For example, the wings of birds and the arms of humans are homologous organs.
Analogous bodies have the same function but different structures. For example, the wings of flies and the wings of doves are analogous structures. Such organisms are classified separately because their similarity arises from function rather than common ancestry.
1. Paleontological Test
The fossil record demonstrates the existence of evolutionary change through the presence of extinct flora and fauna and their distribution in rock strata.
2. Comparative Anatomy Test
Different species have body parts constructed under the same structural pattern, supporting the existence of homologous organs and suggesting a common origin during an ancestral period.
3. Biochemical Comparison Test
Biochemical homologies are found in all living beings, which are notable characteristics of the evolutionary scale.
4. Embryological Test
All species show similar characteristics during early embryonic development, and these ancestral traits disappear as development proceeds.
5. Adaptation and Mimicry Test
In 1848, a mutated white butterfly with dark color was discovered in England, adapted to the industrial pollution that darkened the trees of the region. These butterflies, originally white, rested on tree trunks with extended wings, making them easily detected by birds. The scientist Bernard Kettlewell was able to verify this in 1955: after releasing butterflies marked with light and dark colors, he recovered more dark ones in polluted areas and more light ones in clean areas. The birds acted as agents performing natural selection.
Mimicry follows a mechanism similar to adaptation: certain animals become difficult to distinguish from their surroundings by adopting shapes, temporary behaviors, or skin color changes that match the environment.
6. Biogeographic Distribution Test
The existence of a uniform set of species in a region shows that geographic barriers or dispersal mechanisms prevented circulation to places where suitable habitats already existed.
7. Domestication Test
Domestication is a clear example of evolutionary change caused by human intervention. Through agricultural and livestock activities, humans have experimented with and selected plants and animals, producing great variability from ancestral specimens.
Artificial selection is a process in which breeders choose reproductive individuals of a plant or animal species according to their desired characteristics. Carried out over several generations, this produces reasonably stable varieties that are later used in agriculture and livestock farming.
Evolutionary Series and Intermediate Forms
An evolutionary series is a set of phases through which an initial ecosystem passes, from simple organisms to those of greater complexity.
Intermediate forms display characteristics of two different living groups, and both are considered to share a common ancestor. For example, intermediate characteristics between reptiles and birds would include scales, tails, and forelimbs with feathers.