Lamarck vs. Darwin: Evolution, Natural Selection, and Adaptation
Lamarck’s Incorrect Ideas on Adaptation
a) Web-Footed Legs in Ducks
Lamarck’s flawed explanation:
- Ducks developed webbed feet by constantly swimming.
- Living things strive for perfection.
- Useful features are developed through effort.
- Acquired traits are passed to offspring.
b) Reduced Eyes in Moles
Lamarck’s flawed explanation:
- Moles reduced their eyes by not using them.
- Living things strive for perfection.
- Useful features are developed through effort.
- Acquired traits are passed to offspring.
- Unused features are lost.
- Moles’ eyes became small due to living in the dark.
Evolutionary Processes Explained
The legs of ducks: Duck ancestors had diverse feet, some with slight webbing due to random mutations. Natural selection favored ducks with more webbing, as they swam faster and got more food. These ducks reproduced more, passing on the trait. Over time, the population evolved to have fully webbed feet.
Eyes of moles: Mole ancestors had diverse eye sizes due to random mutations. Natural selection favored moles with smaller eyes, as they were better suited for underground life (less infection risk, less energy use). These moles reproduced more, passing on the trait. Over time, the population evolved to have very small eyes.
Rebutting Lamarck: Acquired Traits and Inheritance
An acquired trait, like losing a limb, doesn’t alter the DNA in gametes (sperm and egg cells). Gametes are responsible for passing on inherited traits. Therefore, a person who loses a leg will still have children with normal legs.
Natural Selection in Action
A study shows that environmental conditions favored birds with a specific beak thickness (characteristic K). These birds reproduced more, leading to a population with that trait. This is a case of natural selection.
Beak Thickness and Environmental Demands
Increased beak thickness is a result of environmental demands and the existing diversity in bird populations. Natural selection favors the most suitable traits.
Homologous Organs
Bird beaks with different functions are homologous organs, sharing a common origin and structure.
Darwin and Natural Selection
Darwin’s concept of natural selection is present in this text. Natural selection is the mechanism of evolution, where a phenotype has advantages in a specific habitat. For example, insects with better camouflage are less visible to predators and reproduce more.
Diversity Within Species
Origin of Variability
Genes determine traits, and evolution acts on them. Mutations and recombination are sources of variability.
Role of Variability in Adaptation
Natural selection favors individuals best adapted to the environment, who leave more offspring.
Example: Biston Betularia
The Biston betularia moth in England had gray and white forms. Industrialization caused the white moth population to decline, while the gray moth population increased due to better camouflage on soot-covered trees.
Lamarck vs. Darwin: A Specific Trait
Lamarck’s View: Long Snout
Lamarck would argue that some individuals stretched their snouts to reach food, passing this acquired trait to offspring. The internal drive towards perfection and the function of the organ would lead to adaptation.
Darwin’s View: Long Snout
Darwin would argue that there was initial variability in snout length. Natural selection favored longer snouts, as they were better for feeding. These animals reproduced more, passing on the trait.
Contributions to Darwin’s Ideas
The synthetic theory explains the origin of intraspecific diversity through mutations and recombination during meiosis. It also explains the inheritance of traits through genes on chromosomes, which are passed to offspring via gametes.
Evolutionary Concepts
a) Evolutionary Convergence
Similar traits in separate species are due to evolutionary convergence. Similar nutritional habits favored similar traits (long snouts, tongues, and strong nails) in both species.
b) Natural Selection and Offspring
Natural selection implies that individuals better adapted to an environment leave more offspring, who inherit their traits. These offspring are also well-adapted, and this process continues as environmental conditions change.