Evolutionary Biology: Lamarck, Natural Selection, and Genetics

1. Lamarck and Early Evolutionary Thought

Jean-Baptiste Lamarck was the first to express the idea that biological species are not unchanged. He proposed that organisms adapt to emerging needs.

The Primary Error in Lamarckism

Lamarck's biggest mistake was the claim that acquired characteristics are heritable. We now know this statement is false. For example, Lamarck hypothesized that snakes evolved from lizards that preferred to crawl rather than walk, eventually losing their legs over time.

Natural Selection: The Case of the Giraffe

In a population of giraffe ancestors, those with longer necks and legs had better access to food in higher branches. These individuals were more likely to survive and produce offspring. Over many generations, this trait became an advantage, demonstrating how natural selection acts on populations.

2. Fundamental Genetic Concepts

• Gene: A DNA fragment encoding information for the synthesis of a protein, which determines a specific function or character, such as eye color.
• Allele: Each of the alternative forms a gene can take, differing in sequence and potentially modifying the gene's function.
• Homozygous: An individual who possesses the same type of allele for a given gene on each counterpart chromosome.
• Heterozygous: A condition where one allele is dominant over another. The dominant allele manifests, while the recessive one does not.

Types of Inheritance

• Dominant Inheritance: One allele dominates over another.
• Intermediate Inheritance: There is no dominance between alleles; the expressed trait is a mixture of both.

3. Evidence for Evolution

Evolution is the process of transformation from one species into another through continuous change.

Scientific Proof

• Paleontology: The study of fossils demonstrates the presence of less evolved life forms. By studying geological strata, we know that deeper layers contain the oldest fossils.
• Vestigial Organs: Organs that belong to a species but no longer serve a primary function. Examples include wisdom teeth, which reveal our granivorous ancestors, and the coccyx at the end of the spinal column, which indicates the presence of a tail in our ancestors.