Natural Selection and Evolution: Darwin’s Legacy
Natural Selection
Darwin’s Challenges
In The Origin of Species, Darwin addressed two key challenges: demonstrating that modern species descended from earlier species and explaining the mechanism behind this process. The concept of natural selection emerged from prior discussions, notably influenced by Thomas Malthus’ Essay on the Principle of Population (1798).
Malthus’ Influence
Malthus argued that population growth exceeding food supply leads to competition for survival. Since reproduction occurs geometrically while food production increases arithmetically, populations inevitably outgrow resources. Consequently, not all organisms reproduce, leading to the potential extinction of species. Darwin expanded on this idea by introducing two crucial aspects:
- Variation and Advantage: When resource limitations hinder population growth, any variations among individuals that provide an advantage significantly increase their chances of reproduction.
- Inheritance: If offspring inherit traits from their parents, even small advantages accumulate over generations, creating significant evolutionary trends.
These principles suggest that future generations become better adapted to resource limitations compared to their predecessors. This is the core of Darwin’s theory: evolution by natural selection.
Evolution by Natural Selection
Darwin and Wallace’s Contribution
In 1858, Charles Darwin and Alfred Russel Wallace published their groundbreaking work on evolution by natural selection. Darwin’s The Origin of Species (1859) refuted arguments for divine design, proposing a mechanism for the emergence of complex adaptations without a designer.
The Core Idea
Darwin’s central idea is that all living beings reproduce, creating copies of themselves with minor variations. Limited resources lead to competition, where individuals with advantageous variations are more likely to survive and reproduce. Over long periods, these advantageous variations spread throughout the population, resulting in adaptations that appear as if designed by an engineer.
Reactions and Implications
Immediate Impact and Opposition
Darwin’s work sparked immediate controversy. In 1925, Tennessee attempted to ban the teaching of evolution, reflecting the clash between scientific and religious perspectives. Today, some groups advocate for “intelligent design,” attempting to equate evolution with creationism.
Early Evidence and Universal Principles
Two centuries before Darwin, Nicolaus Steno identified fossilized shark teeth, and in 1856, Johann Carl Fuhlrott classified Neanderthal remains, providing early evidence for human evolution. The theory of evolution implies a common origin for all life, suggesting universal biological principles. Three essential properties of life are:
- Selective Exchange: The ability to exchange materials with the environment through membranes composed of fats, a feature shared by all living organisms.
- Metabolic Processes: Chemical reactions that convert materials into essential components. Central metabolism, the interconnected set of reactions involving organic molecules, is universal.
- Replication: The ability to make copies based on the DNA double helix, the universal genetic material considered the database of self-replicating organisms.