Darwinian Evolution Review Flashcards

7.1 Evolution: Genetic changes in a population over time

The theory of evolution posits that species change over time in response to environmental conditions. This concept dates back hundreds of years and serves as the foundation for understanding how species adapt to their surroundings.

7.1 Charles Darwin and Natural Selection

In 1859, Charles Darwin published his seminal work, On the Origin of Species by Means of Natural Selection, where he introduced the theory of evolution through natural selection. His ideas were influenced by earlier geologists and naturalists:

• Charles Lyell: Proposed that geological features gradually change, impacting ecosystems.

• Jean-Baptiste Lamarck: Suggested that species might change over time, hinting at evolving characteristics.

• Georges Cuvier: Documented fossils showing extinction events.

• Georges Buffon: Claimed the Earth is much older than previously understood, allowing time for gradual evolution.

Darwin's observations during his travels on the HMS Beagle from 1831 to 1836 provided him with varied examples of species and their adaptations across different environments, which played a crucial role in shaping his theory.

7.2 The Logic of Natural Selection

Darwin's observations led to four crucial conclusions about natural selection:

1. Overproduction: More individuals are born than can be sustained by the environment.

2. Limited Resources: Resources such as food and shelter remain relatively constant.

   • Conclusion: This creates competition since not all individuals can survive.

3. Variation: Individuals differ in their capabilities to utilize resources, introducing variability.

4. Heritability: Traits influencing survivability can be passed from parents to offspring.

Overall, Darwin concluded that natural selection favors individuals with advantageous traits, leading to their increased survival and reproduction, thus propagating these traits within a population.

7.2 Example of Natural Selection: Antibiotic Resistance

Natural selection can be observed in populations of bacteria developing resistance to antibiotics. This example illustrates how a random mutation can give rise to an advantageous trait:

1. Variation exists in a bacterial population.

2. Introducing antibiotics changes the environment.

3. Bacteria lacking resistance are eliminated.

4. Resistant bacteria reproduce, shifting allele frequencies in the population toward resistance.

7.3 Important Points about Evolution

• Individuals do not evolve: Natural selection acts on individuals, but evolution is observed at the population level.

• Evolution is not goal-oriented: Changes occur due to local environmental pressures and not predetermined pathways.

7.4 Evidence of Evolution

Fossils provide essential evidence of evolution, illustrating how species have changed over different geological ages. Fossils can be dated through geological position or radiometric dating, revealing simple organism structures in older rock layers.

7.4 Biogeography

The geographic distribution of species supports evolutionary theory. For example, marsupials originated in South America and later appeared in Australia due to continental drift. Specific species exhibit analogous traits adapted to similar environmental challenges, demonstrating convergent evolution.

7.5 Comparative Anatomy

Similar anatomical structures across species suggest common ancestry. For example, vertebrate forelimbs have similar bone structures, adapted for different functions. Additionally, embryological similarities in development further support this hypothesis.

7.6 Molecular Evidence

All organisms utilize DNA as their genetic material. Closely related species share similarities in their DNA sequences. Bioinformatics aids in analyzing genetic data to reveal evolutionary relationships.

7.7 Mechanisms of Evolutionary Change

Several mechanisms drive evolutionary change:

• Mutation: The source of all genetic variation, can be spontaneous or induced.

• Gene Flow: The exchange of genes between populations, often reducing genetic differences.

• Genetic Drift: Random changes impacting allele frequencies, especially in small populations.

  • Bottleneck Effect: A significant reduction in population size due to environmental events can lead to decreased genetic diversity.

  • Founder Effect: Establishment of new populations by a small number of individuals can result in a limited gene pool.

7.7 Effects of Population Bottlenecks and Founder Effects

An illustrative case of founder effect is that of Pingelap Island, where a typhoon culminated in the survival of only a few individuals, resulting in a high prevalence of colorblindness among descendants. Similarly, a bottleneck can lead to a drastic loss of genetic variability.

Conclusion

Understanding these mechanisms of evolution provides insight into how species adapt and evolve over time in response to changing environmental pressures. The synthesis of evidence from various fields solidifies Darwin's foundational theory of evolution by natural selection, establishing it as a central element in biological sciences.