Evolution

Evolution and Diversity of Life

  • Quote by Theodosius Dobzhansky: "Nothing in biology makes sense EXCEPT in the light of evolution."

  • Image of Charles Darwin at 72 years old (1881).

Darwin's Evolutionary Theory

Natural Selection

  • Definition: Natural selection is the process by which individuals that have certain physical or behavioral traits that better suit their environment are more likely to survive and reproduce than those without such traits.

    • Commonly summarized as "Survival of the fittest!"

    • It acts on a range of phenotypes within a population, not on individuals.

    • Population: All members of a species that live in a specific area.

Understanding Evolution

What is Evolution?

  • Definition: Evolution is the change in the genetic composition of a population over time, leading to the emergence of new phenotypes.

  • Inquiry about how changes occur in populations.

Impact of Allelic Changes

  • If individuals with a red allele do not survive:

    • The allele is removed from the population.

    • The allele is not passed to future offspring, resulting in a change in the population's genetic makeup.

Causes of Genetic Changes

  1. Mutations: spontaneous changes in DNA.

  2. Environmental Changes: altering habitats and survival checks.

  3. Genetic Drift: random changes in allelic frequencies, often in small populations.

  4. Gene Flow: the transfer of genes between populations.

  5. Reproductive Isolation: populations cannot breed due to geographic barriers.

  6. Gradualism: slow environmental changes leading to speciation.

Adaptation

What is Adaptation?

  • Definition: An adaptation is an inherited characteristic that enhances an organism’s chance for survival.

    • Adaptations can manifest as behaviors, physical traits, or appearances.

  • The degree of adaptation in a population corresponds with how prevalent the adaptation is.

Types of Adaptation

Physical Adaptations

  • Examples: Speed, camouflage, claws, quills, etc.

Behavioral Adaptations

  • Examples: Solitary living, social groups (herds, packs), nocturnal behavior.

  • Notably, individuals do not choose adaptations; they are inherent traits within a population. If beneficial, they become predominant.

Specific Adaptation Examples

Mimicry

  • Definition: When one species resembles another.

    • Particularly, a harmless species mimicking something harmful.

Camouflage

  • Definition: Resembling the surroundings to avoid predators or gain a predatory advantage.

  • Commonly observed in fish, crabs, bugs, snakes, frogs, etc.

  • Inquiry prompt for identifying camouflaged animals in images.

Natural Selection Mechanism

  • If a species cannot adapt, it risks extinction. Individual capacity for change is limited to genetic mutations in sex cells that can be transmitted to offspring.

  • Natural selection neither provides what organisms need; it undergoes a lengthy process favoring certain variations, leading to the elimination of less favorable traits.

  • Driving mechanism of natural selection: Genetic variation, where natural selection prioritizes phenotypic traits.

Summary of Natural Selection

  • Natural selection encompasses the survival and reproduction of individuals with advantageous traits, passing those traits to subsequent generations.

  • Illustrated as a gradual process through generations.

Types of Natural Selection

Directional Selection: Favors one extreme phenotype over other

Disruptive Selection: Favors extreme traits while rejecting intermediate traits.

Stabilizing Selection: Favors intermediate traits, reducing prevalence of extreme traits.

Natural Variation and Artificial Selection

Natural Variation

  • Differences in traits within a species.

Artificial Selection

  • Selective breeding to enhance desired traits among livestock or crops

Misconceptions about Evolution

  • Darwin did not suggest humans directly evolved from apes but that they, alongside apes, share a common ancestor.

Evolutionary Model Representation

  • Evolution resembles a branching tree rather than a simple lineage.

  • Darwin observed notable relations in generations and species due to common ancestry and extinction between different species.

Common Descent with Modification

  • Darwin's hypothesis asserted all organisms descend from common ancestors, leading to divergence over time and resulting in new species.

Deeper Understanding of Descent with Modification

  • Progresses over extensive periods, observable through anatomical changes, diversification into ecological niches, and variations in behavior.

Evidence of Evolution

Fossil Record

  • Compiles all information about past life forms, aiding our understanding of evolutionary history.

  • Despite being incomplete, it highlights that over 99% of species that ever existed are now extinct.

Microevolution and Observations

  • Refers to observable evolutionary changes within a brief time frame.

  • Notable examples include changes seen in peppered moth populations under varying environmental conditions (light and dark winged variations).

Drug Resistance in Evolution

Pesticide Resistance

  • Genetic adaptations lead to pesticide resistance within insect populations through selective pressures.

HIV Evolution

  • Examples of drug-resistant variants demonstrating evolutionary mechanisms under treatment pressures.

Biological Molecules and Genetics

  • Closely related organisms share significant similarities in their DNA, lending credence to evolutionary theory (example: human and chimpanzee amino acid similarity).

Homologous Body Structures

  • Structures inherited from common ancestors that take diverse forms. Evidence supporting common descent among vertebrates, visible through bone structure similarities across species.

Vestigial Structures

  • Physical remnants in organisms that no longer serve a significant function (e.g., human appendix, snake legs, whale pelvic bones).

Comparative Embryology

  • Similarities in embryonic development among species suggest common evolutionary pathways, evidenced by shared structures during early vertebrate stages.