Evolution and Origin of Species: Key Theories

Creationism

The origin of each species was due to a specific act of creation.

Fixism

Species remain unchanged over time.

Catastrophism

During the course of Earth's history, catastrophes happened, causing the extinction of certain species.

Biological Evolution

The process of transformation from one species into another by the accumulation of differences that appear between one generation and the next.

Lamarckism

Lamarck argued that God creates nature and this gives rise to species because of its tendency toward complexity and adaptations caused by environmental variations.

Darwinism

• High reproductive capacity: Since food resources are limited, it does not increase indefinitely.
• Variation in offspring: The descendants of sexually reproducing organisms are adapted to the improved environment.
• Natural Selection: If environmental conditions are adverse, only individuals that can adapt to them survive, and only these individuals can reproduce and transmit their characteristics to their descendants. Through natural selection, the species are transformed.

Taxonomic Evidence

Consists of classifying living things based on criteria of similarity in morphology and genetics. All such species would be in the same genre, this in one family... Each taxonomic category includes elements similar to each other.

Biogeographical Tests

The further apart two areas are, the more different their flora and fauna will be. These tests are based on the geographical distribution of species.

Paleontological Evidence

From the first simple organisms, others more complex can arise. The study of fossils reveals an increase in the complexity of organisms and the diversity of species.

Anatomical Evidence

Based on a comparison of organs between different species. We can distinguish:

• Homologous Organs: They have the same embryological origin.
• Analogous Organs: They perform the same function, but their internal structure is different.
• Vestigial Organs: They perform no function and are approved with respect to ancestral organs.

Embryological Evidence

In the study of embryos of different animals, we see some similarities in their development. For example, a heart with only two chambers in the human embryo, like in a hen.

Biochemical Tests

These are based on the comparative study of the molecules of organisms of different species.

Neo-Darwinism or Synthetic Theory

• Variation in offspring: It is due to mutations, which give rise to new genes and genetic recombination.
• Natural Selection: Eliminates the least fit individuals and allows the best suited to reproduce.
• Variation of gene frequencies: Populations evolve as their gene frequencies vary. Individuals always have the same genes. Factors that cause a variation in gene frequencies are mutations, genetic drift, natural selection, and migration.

The Neutral Theory

According to Kimura, at the molecular level, most mutations are neither good nor bad, but are neutral mutations. They are not affected by natural selection.

The Theory of Punctuated Equilibrium

It was presented by Eldredge and Gould to give answers to questions not explained in Neo-Darwinism. According to this theory, during evolution, there may be long periods of equilibrium in which species do not change significantly, followed by short stints of discontinuity in which rapid development takes place. Neo-Darwinism explains the evolution of shells by phyletic gradualism, but fossil sequences are not graded; jumps occur in the absence of intermediate forms. Here, the model of phyletic gradualism does not provide an explanation of these jumps.

Hominids

These are the families of bipedal primates. The type of power is a factor due to the shape of the jaw and teeth. For its age, bipedalism would be the first hominid, Orrorin tugenensis. Until 1980, only two genera were distinguished: Australopithecus and Homo, which differ in cranial capacity, and Homo manufactured stone tools.

Hominization Process

• Acquisition of bipedalism:
  • Adjustment to life in a savanna.
  • Release of the hands.
• Strengthening the sexual bond:
  • Ability to copulate throughout the year.
  • Instinct of possession.
  • Altruistic behavior.
• Establishment of social groups:
  • Care of children.
  • Period of learning.
• Food and development:
  • Richer protein foods.
  • Development of the brain.
  • Development of the skeleton of the skull and face.
  • Development of language and intelligence.