Evidence for Evolution
📌 Direct observation of evolution is possible, notably with drug-resistant strains of bacteria, which demonstrates natural selection acting upon random mutations.
🧬 Homology across species, such as similar bone structures in human arms, whale flippers, and bat wings, strongly supports the concept of common ancestry.
🦴 Vestigial structures, like pelvis bones in snakes or remnants of eyes in cave fish, are anatomical relics of ancestral features.
🗺️ Biogeography (the global distribution of species) provides evidence, with predictions about fossil locations successfully made based on continental drift patterns over millions of years.

Mechanisms of Genetic Change and Variation
🔬 Novel traits originate from alterations in the DNA sequence, leading to microevolutionary changes.
🧬 Harmful new alleles are typically removed by natural selection, while recessive, harmful alleles may persist in the population.
⏳ Neutral variation (benign mutations) accumulates over time because there is no selective pressure to eliminate these differences.
🔄 The gene pool represents all alleles in a population; for evolution to occur significantly, external factors must act on this variation, which is quantified using the Hardy-Weinberg equation.

Hardy-Weinberg Equilibrium and Deviation
🧮 The equilibrium assumes no mutation, random mating, no selection, large population size, and no gene flow; under these conditions, allele frequencies ($p+q=1$) and genotype frequencies ($p^2 + 2pq + q^2 = 1$) remain constant.
📉 Deviation from the expected frequencies of $p$ (dominant allele) or $q$ (recessive allele) indicates that the population is evolving.

Forces Driving Evolution Beyond Natural Selection
🎲 Genetic drift causes random changes in allele frequencies, often magnified in small populations through the founder effect or the bottleneck effect (caused by catastrophic events like floods or fires).
🚶 Gene flow results from the movement of fertile organisms between populations (e.g., migration), transferring alleles into or out of the gene pool.
💞 Sexual selection, a non-random component of natural selection, drives sexual dimorphism through processes like intersexual selection (mate choice based on trait indicators of health) and intrasexual selection (competition between members of the same sex).

Limitations of Natural Selection
🏗️ Nature is blind and can only modify existing structures; evolution does not create features from scratch but gradually modifies what is present over generations.
🦒 Imperfections in biological design, such as the illogical laryngeal nerve pathway in the giraffe's neck or flaws in the human eye, illustrate that natural selection builds upon prior, workable but imperfect structures.

Key Points & Insights
➡️ Evolution is observable directly through phenomena like rapid antibiotic resistance in pathogens.
➡️ Homologous structures across diverse mammals provide strong evidence for a single tree of life stemming from common ancestors.
➡️ Genetic drift is a significant driver of random allele frequency change, especially when populations are small (founder or bottleneck effects).
➡️ Natural selection, while a guiding force, is constrained by historical contingency, meaning adaptations arise through incremental modification of existing traits.

📸 Video summarized with SummaryTube.com on Nov 04, 2025, 21:13 UTC