Scientific Revolutions and Diversity Models

Scientific Revolutions

• The Scientific Revolution of the 16th and 17th centuries challenged the dominant Greek view of nature.
• The Darwinian Revolution in the 19th century overturned ideas about how nature works.

Models of Diversity of Life

• Plato proposed the idea of typological thinking, where species are unchanging and represent perfect essences created by God. This ignored variations among animals.
• Aristotle introduced the Scala naturae, a hierarchy of organisms from simple to complex forms, arranged by "perfection."
• Jean-Baptiste Lamarck proposed the theory of use and disuse, where organisms develop features through repeated use and lose them through disuse. However, he also proposed the inheritance of acquired traits, a concept later refuted by Darwin.
• Comte de Buffon rejected the idea of species evolving into other species.
• George Cuvier introduced fossils into biological study and proposed the theory of catastrophism, where extinction events are caused by natural cataclysms, followed by the emergence of new species.
• Charles Darwin developed the theory of evolution by natural selection, based on observations like variations in Galapagos finches and tortoise species, and the concept of speciation.
• Alfred Russel Wallace also formulated the theory of evolution by natural selection, independently of Darwin.

Evidence of Evolution in Living Species

• Soapberry bugs show beak length evolution in response to variations in their food source.
• Vestigial organs are useless or rudimentary body parts present in some species but functional in their ancestors, suggesting evolutionary descent. Examples include flightless birds (vestigial wings), snakes with tiny hind limbs, and the human coccyx (tailbone).
• The arrector pili muscle in humans is a vestigial trait used for predator defense in animals.
• The absence of CMAH enzyme in humans is a result of a 92-base-pair deletion, causing a deficiency that has been linked to increased brain growth and improved immune self-recognition.
• Three-spined sticklebacks demonstrate adaptation to freshwater environments, with reduced armor compared to their marine ancestors.

Evidence of Evolution from the Fossil Record

• The geologic time scale charts the evolution of life forms through geological events, with the fossil record providing evidence.
• Fossils are traces of past organisms.
• Radiometric dating (decay of isotopes) and relative age dating (comparison of fossils) are used to determine fossil age, while Carbon dating is not suitable for evolutionary events.
• The Ediacaran epoch (Proterozoic Eon) marks the appearance of Aspidella, one of the oldest eukaryotic organisms and among the first multicellular organisms.

Paleozoic Era

• The Cambrian period witnessed the Cambrian explosion, a sudden diversification of multicellular forms.
• The Ordovician period saw the rise of marine filter feeders and small plants like bryophytes, but also a mass extinction event linked to glaciation.
• The Silurian period saw continental aggregation and the first appearance of arthropods and vascular plants.
• The Devonian period saw the evolution of all major fish groups, including cartilaginous and bony fish. On land, the first insects and amphibians emerged, along with forests rich in clubmosses and ferns.
• The Carboniferous period saw the formation of large coal deposits from fossilized tree ferns. The first reptiles evolved from amphibians, along with winged insects.
• The Permian period saw the formation of the supercontinent Pangaea, with reptiles becoming the dominant land vertebrates. The period also saw a major extinction event caused by climate warming, ocean acidification, and volcanic activity.

Mesozoic Era

• The Triassic period saw the dominance of C plants and conifers in terrestrial vegetation, with reptiles remaining dominant. A mass extinction event (Triassic extinction) occurred due to volcanic eruption and increased carbon dioxide.
• The Jurassic period witnessed the radiation of dinosaurs, some transitioning from quadrupedal to bipedal locomotion. The first mammals appeared, with bony fish dominating marine and freshwater environments.
• The Cretaceous period marked the complete separation of continents, with the rise of flowering plants (angiosperms). Dinosaurs continued to dominate, but the period ended with a mass extinction event caused by a meteorite impact, leading to the extinction of dinosaurs.

Cenozoic Era

• The Tertiary period saw continents drift towards their present positions, with a cooler and drier climate leading to extensive grassland formation. Mammals diversified extensively, and the extinction of dinosaurs allowed for the evolution of other vertebrates.
• The Quaternary period saw the emergence of humans, alongside numerous extinctions of large birds and mammals.
• This era further divided into epochs: Paleogene (Paleocene, Eocene, Oligocene), Neogene (Miocene, Pliocene), and Quaternary (Pleistocene, Holocene).

Observations from the Fossil Record

• Cuvier's extensive study of fossils established the reality of extinction, identifying 23 extinct species.
• Fossils revealed a pattern of increasing differences between extinct species and modern organisms as the depth of fossil discovery increased, suggesting evolutionary change.
• Fossils like mammoths and Irish elk supported the concept of common ancestry, descent with modification, and extinction.
• Darwin used the fossil record to challenge the special creation view, proposing extinct species as relatives of modern species.

Explore the key concepts and figures from the Scientific Revolution and theories of life's diversity. Delve into the contributions of Plato, Aristotle, Lamarck, Buffon, and Cuvier, and understand how these ideas shaped modern biological thought. Test your knowledge on how these historical perspectives influence our understanding of evolution today.