Neo-Darwinism, Consanguinity, and Precambrian Era: Key Concepts
Neo-Darwinism
Although Darwin made significant contributions to evolutionary thought, his theory could not fully explain how hereditary traits are passed from generation to generation, nor the cause of variability within populations upon which natural selection acts. Evolution is a phenomenon of populations, not individuals. It is the population that evolves, as this is where genetic variability is present, allowing selection to act.
It wasn’t until the 20th century that the synthesis of Darwin’s theory of natural selection, Mendelian genetics, and the chromosome theory of heredity was achieved, giving rise to population genetics. Thus, Neo-Darwinism, or the synthetic theory of evolution, was born.
Consanguinity
Consanguinity refers to the degree of kinship between two individuals who share a common ancestor. If this ancestor carried a pathological recessive mutation, it is likely that the mutation has been transmitted to more immediate descendants, making them at least carriers. The problem with inbreeding, for example, between first cousins (who share a common set of grandparents and therefore share one-eighth of their genes), is that it increases the risk of having children affected by an anomaly that manifests when a child inherits the mutated allele in a homozygous recessive state.
Crosses and Phenotype Analysis
In experimental crosses, it’s important to count the number of offspring at each crossing and apply mathematical calculations to analyze the data. Observed frequencies of each phenotype should be calculated for comparison with the expected frequencies and theoretical probabilities. The results derived from the cross above are true in all cases dealing with the transmission of a character governed by a gene with two allelic forms and dominant inheritance.
The Precambrian Eon
The Precambrian Eon begins with the formation of the Earth (approximately 4.55 billion years ago) and is the least understood. During this time, the first continental nuclei and primitive oceans formed. Abiotic chemical evolution preceded the first forms of life, which were prokaryotic cells.
The Archean Eon started about 3.8 billion years ago and also marks the beginning of tectonic activity on Earth. The emergence of life was immediate, with the primitive prokaryotic LUCA (Last Universal Common Ancestor) giving rise to the domains Bacteria and Archaea. Anaerobic bacteria appeared first, followed by photosynthetic cyanobacteria and subsequently aerobic bacteria.
The long, solitary existence of bacteria lasted about 2 billion years, until the mid-Proterozoic Eon, around 1.8 billion years ago, when the first eukaryotic representatives of the kingdom Plantae (algae and protozoa) appeared after a process of symbiotic evolution. The activity of photosynthetic organisms (cyanobacteria and algae) caused a gradual increase in atmospheric oxygen and a decrease in carbon dioxide.
In the late Proterozoic, about 610 million years ago, the concentration of atmospheric carbon dioxide, removed by photosynthetic organisms, reached extraordinarily low levels. This caused a reduction in greenhouse gases, and the Earth’s climate cooled significantly. The sharp thermal drop almost completely froze the globe, leading to the so-called “snowball Earth” effect, as much of the Earth’s surface was frozen, leaving only a narrow fringe unfrozen in Ecuador. This environmental disaster was a major environmental stress for eukaryotic organisms, leading to extinctions and the accumulation of many mutations caused by extreme environmental conditions, generating gene diversity.
In the late Precambrian, about 580 million years ago, the groundwork had been laid for the appearance, after the great glaciation, of the early members of the Kingdom Animalia, represented by the fossils of the Ediacara fauna. These are invertebrate animals with soft bodies, such as Charniodiscus, which looks like a lush leaf, and Spriggina, with its flattened body. Later, animals with shells appeared, subdivided into the Tommotian fauna, such as Anabarites, with its tubular appearance. Most of these organisms gradually disappeared in the late Precambrian.