B5 - Developing Theories to Explain Change

B5 - Developing Theories to Explain Change

• The learning objective is to discuss the importance of sexual reproduction, compare Lamarckian and Darwinian explanations of evolutionary change, and use evidence to explain evolution from ancestral forms.

Developing Theories to Explain Change

• A scientific hypothesis offers a possible answer to a question or suggests explanations for an observation.
• It needs testing to validate its accuracy (truth).
• Successful hypotheses, consistently leading to accurate predictions and explanations, can be combined into broader statements called scientific theories. These theories explain a range of observations.

Historical Theory

• Early Greek philosophers, like Plato and Aristotle, believed life on Earth was perfect and unchanging.
• Before the 18th century, the prevailing view was that living things were fixed and didn't change over time.
• In the late 18th century, scientists began to speculate about evolution.

Developing Theory of Natural Selection

• Evolutionary theory developed over many centuries.
• The influence of the Roman Catholic Church in Europe hindered the development of evolutionary theories during the 1700s.

Georges-Louis Leclerc (Comte du Buffon) (1749)

• Noted similarities between humans and apes, suggesting a common ancestor.
• Proposed that the Earth is much older than 6000 years (a common belief at the time).

Georges Cuvier (1813)

• Published an essay on the Earth's theory, studying ancient life through fossils.
• Found that different groups of fossils are found in distinct rock layers, and older layers contain more dissimilar species from modern life.
• Provided evidence of species appearing and disappearing over time.
• Hypothesized that natural disasters like floods and volcanic eruptions caused species extinction.

Charles Lyell (1830)

• Rejected the idea of evolution by natural disasters.
• Proposed that geological processes are slow and gradual, suggesting the Earth is very old.
• Theorized that slow, subtle processes over long periods can cause substantial changes in the Earth.

Jean Baptiste Lamarck (early 1800s)

• Proposed that characteristics acquired during an organism's lifetime could be passed to offspring ("Inheritance of Acquired Characteristics").
• Example: Giraffes stretching their necks to reach higher leaves resulted in their offspring inheriting longer necks.
• His theory was eventually rejected.

Charles Darwin

• In 1831, Darwin travelled on the HMS Beagle to survey the coast of South America.
• Made significant observations of organisms during the voyage.
• Named "Father of Evolutionary Theory".

Darwin's Observations

• Observed fossils in South America that resembled giant versions of modern sloths and armadillos.
• Noted that South American species differed from African species, even in similar environments.
• Observed 13 species of finches in the Galapagos Islands, closely resembling species from the South American coast.
• Questioned if these similar, but different species, evolved from a single species that migrated from South America.

Alfred Russel Wallace

• Conducted research in South America and Malaysia concurrently with Darwin, making similar observations.

Theory of Evolution by Natural Selection

• Darwin and Wallace were influenced by Malthus’s "Essay on the Principle of Population," which noted that populations produce more offspring than the environment can sustain.
• This leads to competition for resources.
• Individuals with favorable traits (traits improving survival and reproduction) are more likely to survive and reproduce.
• Over time, these favorable traits become more common in the population.
• This process is called natural selection.

Evolution

• Environmental pressures can drive populations of the same species to become so genetically different that they can no longer interbreed.
• This leads to the formation of new species – a process known as evolution.
• Natural selection is the mechanism driving evolution.

Natural Selection and Evolution - Intersection

• Natural selection acts on individuals, favoring traits better suited to the environment.
• Evolution acts on the population, resulting in changes to populations over time.
• Changes over time in gene frequencies within a population are a result of evolution in populations.

Further Evidence for Evolution

• Fossils
• Patterns of distribution
• Comparative anatomy
• Embryology
• Molecular biology
• Genetics

Fossils

• Fossils found in rock layers near the surface are often more closely related to modern species.
• Fossils in deeper layers are more dissimilar, demonstrating species change over time.
• Transitional fossils link different species and fill gaps in the fossil record.

Patterns of Distribution

• Biogeography: Studies the past and present geographical distribution of organisms.
• Closely related species are usually found in similar environments.
• Species in similar environments on different continents often resemble species in those same environments on the nearby mainland.
• Similar fossil evidence exists on coasts of neighboring continents.

Comparative Anatomy

• Many related organisms have homologous structures (same origin, different function) pointing toward a common ancestor.
• Analogous structures (similar function, different origin) do not provide evidence of common ancestry.

Embryology

• Embryos of different species often exhibit similar early stages of development.
• This similarity suggests a common origin.

Molecular Biology

• Modern techniques identify DNA and proteins.
• DNA and protein analysis provide evidence for common ancestry and provide explanations for evolution through natural selection.
• All cells have membranes, genetic material, proteins, and lipids/carbohydrates.
• Enzymes control chemical reactions in cells.

Genetics

• Darwin, when developing his theory, had limited understanding of inheritance and genetics.
• Genetic evidence demonstrates species pass on traits through genetic material.
• Genetic materials can mutate, creating variation in traits.

DNA Analysis and Human Movement

• DNA analysis is used to trace the movement of the human species across the globe. Dates are included for evidence.

Explore the theories of evolution in this quiz, focusing on sexual reproduction and the comparison between Lamarckian and Darwinian explanations of change. Understand the transition from early beliefs in the unchanging nature of life to the development of modern scientific theories. Test your knowledge on the historical context and scientific hypothesis formation.