Evolutionary Biology: Darwin, Wallace, and Evidence of Evolution
Evolution and Natural Selection
Evolution occurs through mutations. Individuals do not change; they pass changes to their offspring, leading to population change.
Alfred Russell Wallace and Darwin’s Contemporary
Alfred Russell Wallace was a naturalist who independently conceived the theory of natural selection, similar to Darwin’s. Although they corresponded by letters, they never met in person. Wallace’s contributions were not as widely recognized as Darwin’s for several reasons. Wallace mistakenly believed that God created the human soul and brain. Additionally, he had fewer proofs than Darwin and published his ideas later.
Charles Darwin and the Theory of Natural Selection
Charles Darwin developed the theory of natural selection (building upon the existing concept of evolution). During a five-year voyage to the Galapagos Islands as a naturalist, he studied finches. Years later, he published his book on natural selection, explaining that organisms that successfully adapt to their environment thrive and reproduce, while others die off. Prior to Darwin, prevailing ideas included:
- Fixism: The belief that evolution never occurs.
- Creationism: The belief that all nature was created by God.
Transformist Thinkers
Buffon
Buffon proposed that organisms degenerate from their original form created by God, suggesting that organisms change over time.
Lamarck
Lamarck developed “transformisme,” the idea that traits acquired during an organism’s lifetime are passed down to offspring. He also believed that evolution was progressive, moving from simple to complex organisms, in contrast to Buffon’s view.
George Cuvier
George Cuvier, a naturalist, defended fixism. He proposed that fossils came from living things that became extinct due to catastrophes, a concept known as Catastrophism.
Carl Linnaeus
Carl Linnaeus created the binomial system, still used today for classifying species. The first name indicates a general characteristic, and the second name specifies a particular trait. To classify a new animal, one first determines its kingdom, then its class.
Evidence of Evolution
Anatomical and Morphological Evidence
- Homologous Structures: Structures with different functions but a shared origin, demonstrating divergent evolution (e.g., bat wings and human arms).
- Analogous Structures: Structures with the same function but different origins, demonstrating convergent evolution (e.g., bat wings and butterfly wings).
- Vestigial Structures: Structures that tend to disappear because they are no longer useful (e.g., a pelvis bone in a snake).
Fossil Evidence
Paleontology is the science that studies fossils, which are the remains of ancient organisms or their activities. Most fossil remains are incomplete because soft tissues decompose, and hard parts can break and be moved.
Fossilization Steps:
- Soft tissues decay, leaving behind hard parts.
- Hard parts may be transported and broken.
- Hard tissues become buried and altered.
Fossils indicate that millions of dinosaurs once lived on Earth. They prove that living things have changed over time. Fossils show organisms that existed in the past and differ from present-day organisms, demonstrating species change. Fossils of organisms intermediate between major groups confirm the evolutionary link between them.
Embryological Evidence
Similarities in embryos of different species suggest an evolutionary relationship. Protostomes are primitive invertebrates, while deuterostomes include chordates and echinoderms. In protostomes, the blastopore develops into a mouth, while in deuterostomes, it develops into an anal opening.
Biogeographical Evidence
Over time, isolated groups of animals evolved differently, creating new species.
- Divergent Evolution: Closely related species adapt to different environments.
- Convergent Evolution: Unrelated species may resemble each other if they live in similar environments.
Molecular Evidence
The greater the molecular similarities between two groups of organisms, the closer their evolutionary relationship. Examples include:
- Chlorophyll: Found in all green plants.
- Hemoglobin: Found in vertebrate blood.