Mechanisms of Evolution and Principles of Genetics

Natural Selection and Evolutionary Theory

The British naturalist Charles Darwin proposed a mechanism to explain evolution: natural selection based on the survival of the fittest.

Jean-Baptiste de Lamarck proposed that varied species acquire new body traits to address new needs or adaptation requirements. Lamarck believed that snakes evolved from lizards that preferred to crawl rather than walk; over time, their legs became futile. One key to Lamarckism is the idea that acquired traits are inheritable, which we now know is false.

Darwinism and Genetics

What Darwin did not understand was why some offspring were more resistant than others. Subsequently, the mechanism of inheritance of paternal and maternal characteristics and how these are mixed in sexual reproduction was described. Today, we call these determinants of heredity genes, and the science that studies them is genetics.

The Origin of Human Beings

Eight million years ago, mantle convection currents that move the continents began to break Africa into two unequal parts. Thus was born the so-called Rift Valley, a large crack in the east of the continent. Groups of apes lived in the jungle—great apes, the forefathers of the hominid family, to which humans belong.

Mendel's Conclusion: Heredity and Genes

The conclusion reached by Gregor Mendel was that the reappearance of parental characters in the grandchildren (which were lost in the first generation) showed that the "mixed character" idea was false. It supported the hypothesis that hereditary factors maintained their individuality throughout generations. Besides, these characters were transmitted independently of each other.

For each character, there are two versions of the gene: one from the father and one from the mother. One version of a gene that controls a trait, such as color, can be dominant over the other.

In 1909, that hereditary factor was named a gene by Wilhelm Johannsen. The gene is a unit of hereditary information that controls a certain character:

• Phenotype: The expressed character (e.g., plant height, color of pea).
• Genotype: The hereditary factors that are received from the parents.

Fertilization and Genetic Endowment

In 1902, Walter Sutton noted that the sex cells of grasshoppers appeared with a single set of chromosomes, whereas they appeared in pairs in the remaining cells. That is, human cells have 23 pairs of chromosomes; all except sex cells, which have 23 individual chromosomes.