Lesson 3

1️⃣ Geographic diversity & similarities between nearby species

2️⃣ Differential species distribution (flightless birds)

3️⃣ Fossil record (gradual change)

4️⃣ Vestigial or non-functional traits

They are morphological remnants of structures that once had a function in ancestors (e.g., whale pelvic bones, human appendix).

1️⃣ Variation

2️⃣ Heritability

3️⃣ Adaptation

4️⃣ Selection

5️⃣ Speciation

Individuals in a population differ in morphological, physiological, or behavioral traits that are not caused by the environment.

Many variations are inherited — offspring resemble their parents more than unrelated individuals.

Individuals whose traits suit their environment are more likely to survive and reproduce, increasing those traits in the population.

Favorable variations increase reproductive success and become more common over generations.

Over time, accumulated inherited changes transform one species into another; the process can lead to reproductive isolation.

The modern integration of natural selection with genetics, paleontology, and systematics

• — explaining evolution via gene-frequency changes in populations.

• Gene: DNA segment coding for a trait

• Locus: gene’s position on a chromosome

• Allele: alternative form of a gene

• Fitness: ability to pass genes to offspring

Population: individuals of the same species living in the same time & place•

Gene pool: total set of genes & alleles within that population

1️⃣ Mutation

2️⃣ Migration (gene flow)

3️⃣ Genetic drift

4️⃣ Sexual selection (non-random mating)

5️⃣ Natural selection

A random or induced change in DNA that introduces new genetic variation.

Movement of individuals or gametes between populations, introducing or changing allele frequencies and maintaining homogeneity.

Random change in gene frequencies, especially in small populations (e.g., founder effect or bottleneck effect).

• few individuals from a large population migrate or become isolated and form a new population.

• large population is suddenly reduced (e.g., by disease, natural disaster, hunting).

Non-random mating where certain traits (e.g., color, size) increase attractiveness, altering gene frequencies.

• Anagenesis: slow, linear transformation of one species into another

• Cladogenesis: one species splits into two or more (branching evolution)

Rapid diversification of one lineage into many species adapted to different ecological niches (e.g., Cambrian explosion, mammal radiation).

Long-term evolutionary stability with little morphological change (e.g., coelacanth, crocodile).

• Allopatric: due to geographic isolation

• Sympatric: within the same area (without physical barriers)

1️⃣ Geographic isolation

2️⃣ Local adaptation through natural selection

3️⃣ Establishment of reproductive isolation mechanisms

Biological barriers preventing gene flow between species; they can be prezygotic or postzygotic.

• Temporal (different mating seasons)

• Ecological (different niches)

• Ethological (behavioral differences)

• Mechanical (incompatible organs)

• Gametic (incompatible sex cells)

• Hybrid mortality

• Hybrid sterility (e.g., mule)

• Hybrid degradation (unviable offspring in later generations)

When populations lose genetic variability or face extreme environmental changes they cannot adapt to

; often worsened by habitat destruction.

1️⃣ Divergent evolution

2️⃣ Convergent evolution

3️⃣ Parallel evolution

Related species become increasingly different due to adaptation to distinct environments

• (e.g., polar bear vs. brown bear).

Unrelated species evolve similar traits due to similar environments and selective pressures (e.g., shark vs. dolphin).

Closely related lineages evolve similarly because they adapt to comparable ecological niches (e.g., marsupials vs. placental mammals).

Traits with similar functions but different evolutionary origins

• products of convergent evolution (e.g., wings of birds and insects).

Traits inherited from a common ancestor, possibly with different functions today (e.g., forelimbs of vertebrates).

Yes — structures can be anatomically homologous but serve different functions (e.g., human hand vs. whale flipper).

Similar behaviors in unrelated species due to similar ecological pressures

• (e.g., colony structure of ants and naked mole rats).

Shared behaviors in closely related species due to common ancestry

(e.g., smiling/laughter in primates).

• Ancestral: earlier traits seen in fossils and relatives (e.g., five fingers)

• Derived: newer traits that evolved later (e.g., no tail in apes)

Derived traits help determine relatedness between species; ancestral traits are less informative for modern classification.

• 3.8 BYA – first prokaryotes• 2.5 BYA – eukaryotes• 1 BYA – sexual reproduction• 750 MYA – multicellular organisms & neurons→ Origin of nervous system and complex behavior.

Ratio between brain size and body size — higher in mammals and associated with complex behavior and cognition.

Primate traits (grasping hands, binocular vision) evolved as adaptations for living in trees.

Binocular vision and hand-eye coordination evolved to catch prey (insects), not just for arboreal life.

Increasing group size and social complexity drove the evolution of larger, more complex brains in primates.

• Strepsirhini (lemurs, lorises)

• Tarsiiformes (tarsiers)

• Haplorhini → Platyrrhines (New World monkeys) & Catarrhines (Old World monkeys + apes)