The diverse organisms on Earth have gradually changed over long periods of time. This is called evolution, and evidence of it can be understood from fossils and body structures.
Basic Knowledge
Evolution: the process by which the structure and characteristics of organisms change over successive generations.
Evidence of evolution:
① Fossils: remains or traces of organisms from the past, found in strata.
・Archaeopteryx: intermediate between reptiles and birds; had feathers, teeth, and a tailbone; lived about 150 million years ago.
・Ichthyostega: intermediate between fish and amphibians; lived during the Devonian Period of the Paleozoic Era.
② Homologous organs: organs with the same origin but different forms and functions.
Examples: human arms, bat wings, and whale flippers—their skeletal structures are the same. This is evidence that they evolved from a common ancestor.
③ Analogous organs: organs with different origins but similar appearances or functions (such as butterfly wings and bird wings).
④ Vestigial organs: organs that have degenerated because they are no longer used (the human appendix and whale hind-leg bones).
Darwin proposed the theory of natural selection in On the Origin of Species in 1859.
Evolution (the process by which organisms change over generations)
Fossil (the body or traces of activity of an ancient organism preserved in strata)
Archaeopteryx (an intermediate fossil showing evolution from reptiles to birds)
Homologous organs (organs with the same origin but different forms or functions; evidence of evolution)
Vestigial organs (organs that degenerated during evolution)
Darwin (the British naturalist who proposed the theory of natural selection)
Further Study (Background and Significance)
Tracing the history of life, the first life appeared in the ocean about 3.8 billion years ago, fish appeared about 500 million years ago, and amphibians moved onto land about 370 million years ago. Later, reptiles, mammals, and birds diverged, leading to the present day.
Archaeopteryx was discovered in Germany in 1861. It had feathers and wings (bird characteristics), as well as teeth, clawed fingers, and a long tailbone (reptile characteristics), so it was considered decisive evidence that “reptiles evolved into birds.”
Homologous organs (human arms, bat wings, whale flippers, and horse forelegs) look completely different, but their number and arrangement of bones are almost the same. This shows that the ancestors of different animals were the same.
Darwin observed that the beaks of finches (small birds) differed from island to island in the Galápagos Islands and proposed natural selection: individuals suited to their environment survive and leave descendants.
- Evolution=organisms change over successive generations
- Evidence of evolution=fossils, homologous organs, and vestigial organs
- Archaeopteryx=intermediate fossil between reptiles and birds
- Homologous organs=human arms, bat wings, and whale flippers (same skeletal structure)
- Vestigial organs=human appendix and whale hind-leg bones
- Darwin's On the Origin of Species (1859)=theory of natural selection
- History of life: ocean→fish→amphibians→move onto land
Points of Caution (Easily Confused)
① Distinguish homologous organs (same origin, different forms) from analogous organs (different origins, similar forms). ② Archaeopteryx was not a “type of bird,” but an intermediate between reptiles and birds. ③ Evolution does not mean that an individual changes; it means that a population changes over generations. ④ Vestigial organs are structures on the way to disappearing completely.
Practice
- Name the fossil with intermediate characteristics of reptiles and birds.
- What are organs such as human arms, bat wings, and whale flippers, which have the same origin, called?
- Who published On the Origin of Species in 1859?