Evolution Scales and Darwinian Fitness

Comparing Evolution Scales

• Microevolution involves small-scale changes within a population over time, often involving allele frequency changes due to natural selection, genetic drift, mutation, and gene flow.
• An example of microevolution is changes in the fur color of mice in response to their environment, with darker colors more common in areas with dark soil.
• Macroevolution encompasses larger-scale evolutionary changes over longer periods, leading to speciation, major evolutionary novelties, and changes in biodiversity.
• Examples of macroevolution include the evolution of mammals from reptilian ancestors and birds from theropod dinosaurs.
• Microevolution and macroevolution are interconnected, with microevolutionary changes accumulating to produce macroevolutionary outcomes.

Describing Darwinian Fitness

• Darwinian fitness, or simply "fitness," measures an organism's ability to survive and reproduce in a specific environment.
• It's not just about strength or health, but reproductive success.
• Survival is crucial; organisms must overcome environmental challenges (predation, competition, disease) to reproduce.
• Reproductive success considers the number of offspring produced and their likelihood of surviving and reproducing.
• Fitness is relative; it's compared to the reproductive output of other individuals within the population. A more successful organism in producing offspring will have higher fitness.

Outlining Artificial Selection

• Artificial selection is the intentional breeding of organisms with desired traits by humans.
• Human preferences drive changes in traits, unlike natural selection where environmental pressures do.
• Examples include domestic dogs (developed from wolves) and crop plants (bred for enhanced yield or disease resistance).
• While artificial selection can rapidly alter traits, it can also reduce genetic diversity and lead to health problems in populations with extreme phenotypes.

Natural Selection and Speciation

• Natural selection can drive speciation through mechanisms like geographic isolation, where separated populations adapt differently to differing environments and develop distinct traits.
• Genetic drift in small populations can significantly alter allele frequencies, combined with natural selection influencing divergence.
• Adaptive radiation is when a single ancestral species rapidly diversifies into multiple distinct species adapted to various ecological niches.
• Reproductive isolation can occur through behavioral, temporal, or mechanical isolation mechanisms, preventing interbreeding even if species return to the same environment.

Evidence for Relationships Between Species

• Morphological evidence: Comparative anatomy reveals homologous structures (similar structures with common ancestry, but different functions) like human, whale, or bat forelimbs.
• Molecular evidence: DNA and RNA sequencing reveal genetic similarities, indicating evolutionary relationships and common ancestry.
• Fossil records provide a chronological record of past life forms, showing transitional fossils that document gradual changes in characteristics.
• Biogeography: Geographical distribution of species reflects evolutionary connections and historical migrations.

Comparing Divergent and Convergent Evolution

• Divergent evolution occurs when related species become more dissimilar over time due to varying environmental pressures or niches.
• Convergent evolution refers to the development of similar adaptations in unrelated species in response to similar environmental challenges and selection pressures.
• Examples include the development of wings in bats and birds, despite divergent evolutionary paths.

Comparing Homologous and Analogous Structures

• Homologous structures share a common ancestry, similar structure, but may have different functions.
• Analogous structures perform similar functions but have different evolutionary origins.
• Understanding these structural distinctions highlights the mechanisms of evolution and the diversity of life. Homologous structures show common ancestry, while analogous prove convergence driven by similar environmental pressures.