Evolution Theories: Lamarck, Darwin, and the Modern Synthesis
Lamarck’s Theory of Evolution
Inheritance of Acquired Characteristics: This theory posits that modifications acquired by parents during their lifetime are passed on to their offspring.
Lamarck observed that fossils in deeper strata represented simpler life forms, while surface strata contained more complex organisms, suggesting a progression from simple to complex life.
He argued for the existence of a biological evolution process where primitive forms gave rise to better-organized life forms.
Lamarck’s theory included two main concepts:
- The Universal Creative Principle: Species are guided by a higher power to evolve into more complex forms.
- The Inheritance of Acquired Characters: Changes in a species occur through environmental influences.
Living beings develop certain organs through use, while disuse leads to atrophy. These acquired traits are then inherited by offspring.
Darwin’s Theory of Evolution
Darwin investigated the diversity of animal and plant species.
He proposed that ancestors of animals gave rise to diverse groups, each adapted to its specific environment.
Natural Selection: Environmental pressures and resistance determine which individuals survive and reproduce.
Organisms with more suitable features are more likely to survive than those less adapted.
An organism may be born with a new trait not present in its ancestors or other members of the population.
Change: Changes occur in living beings compared to their parents, due to processes within cells (later understood as DNA).
Speciation: Over extended periods, substantial changes accumulate, leading to distinct groups. These groups do not mix features, and each follows a different evolutionary path, with unique variations emerging.
Synthetic Theory of Evolution
Following the publication of “The Origin of Species,” significant discoveries explained objections to evolutionary theory. Gregor Mendel’s work on inheritance mechanisms, initially ignored, became crucial.
Inheritable traits are passed down through independent factors (genes).
The discovery of chromosomes as hereditary material, along with mutations, led to the synthetic theory of evolution, which states:
- Populations: Evolution acts on populations, not individuals.
- Genes: Individual characteristics are determined by genes. Differences among individuals in a population arise from variations in these genes.
- Mutations: Genetic information in DNA can be altered by random mutations, which can be beneficial, harmful, or neutral.
- Natural Selection: Individuals with gene combinations (genotypes) that provide an adaptive advantage have a better chance of survival and passing on their genes.
Phylogenetic Tree
Darwin aimed to organize living species systematically. Recognizing that species evolve, he created a family tree.
Organisms are placed within specific species, showing relationships between ancestors and descendants. For example, apes evolved larger brains, leading to humans.
Species are grouped based on their evolutionary history, illustrating how primitive prosimians branched into species that evolved into humans. The path to humans took 60 million years, with stages characterized by:
- Radiation of early mammals.
- Dominance of flowering plants.
- Emergence of modern mammal and invertebrate groups.
- Proliferation of bony fishes.
- Dominance of mammals and birds.
- Appearance of humans.