The Modern Synthesis and Proofs of Evolution

Neo-Darwinism: Principles of Variation and Selection

Variability of Offspring

Organisms exhibit reproducibility. Asexual reproduction relies solely on mutations. In sexually reproducing organisms, variation is primarily generated by sexual recombination, which occurs during meiosis.

Mutations arise randomly and can be favorable, unfavorable, or neutral. They are preadaptive, meaning they occur before selection acts upon them. This inherent variability is the raw material upon which natural selection operates.

Core Tenets of Neo-Darwinism (The Modern Synthesis)

1. The evolutionary process is based on the Darwinian principles of variation in offspring and natural selection.
2. Offspring variability is due to genetic mutation and recombination. Mutations create new alleles (genes), while recombination creates new combinations of existing genes.
3. Evolution occurs in populations, not individuals. Populations persist and change, while individuals eventually die.
4. Factors driving changes in gene frequencies within a population are: natural selection, mutations, genetic drift, and gene flow (migrations).
5. For a population to generate a different species, it must become reproductively isolated from other populations.

Compelling Evidence for Biological Evolution

The nature of scientific observation permits the discovery of realities that explain and support the evolution of species. These observations are often referred to as the tests of evolution.

Taxonomic Evidence

Biological classification is based on criteria of similarity (homology). All similar species are grouped within the same genus, genera into similar families, and so on. According to evolutionary theory, these similarities exist because related species share a common ancestor.

Example: The platypus exhibits characteristics of both reptiles and mammals. This is better explained by an evolutionary process transitioning from reptiles to mammals than by the independent creation of two separate groups.

Biogeographical Evidence

This evidence is based on the distribution of species. Geographically distant areas often show greater differences in flora and fauna. This pattern is best explained if species have colonized new areas and subsequently diversified.

Example: The existence of many different species of finches across the Galápagos Islands is understood if they descended from a single ancestral species that colonized the archipelago. Isolation on different islands led to diversification based on local food sources, a process known as Adaptive Radiation.

Paleontological Evidence

Based on the study of fossils, the paleontological record shows an increase in species diversity and increased structural complexity of organisms over geological time.

Anatomical Evidence

Anatomical evidence is based on the comparison of organs between different species. We distinguish two main types:

1. Homologous Organs: They share the same embryological origin and internal structure, but may have different functions and forms. Example: The forelimbs of a bat and a human share the same internal bone structure (one long bone, followed by two long bones, then smaller bones). This similarity is only logical if all species come from a common ancestor that has undergone biological evolution. Thus, homologous structures suggest a kinship with common ancestors.
2. Analogous Organs: They have a different embryological origin and internal structure but perform the same function. Example: The wings of an insect and the wings of a bird. This is explained by convergent evolution, where unrelated species evolve similar traits to perform the same function (flying).

Organs that serve as further evolutionary tests are vestigial organs, which have lost their specific function. Their removal does not significantly decrease the ability of the individual. Examples: The human vermiform appendix, and the coccyx (formed by fused tail bones).

Embryological and Cellular Evidence

This evidence is based on the comparative study of embryonic development in animals. Following the concept of ontogeny, the Biogenetic Law suggests that embryological development is a short recapitulation of the phylogeny (evolutionary sequence) of ancestral species.

Biochemical and Serological Evidence

Biochemical Tests: These are based on the comparative study of molecules in different organisms. A key finding is that the more similar the morphology between two organisms, the greater the molecular match.

Methods currently used to compare organisms include sequencing nucleotides of nuclear DNA, mitochondrial DNA, ribosomal RNA, and sequencing amino acids in various proteins.

Serological Tests: A comparative study based on agglutination reactions of the blood in different organisms. Example: Biochemical studies demonstrate the high genetic similarity between humans and the great apes.