Evolution, Primates & Behavioural Ecology – Comprehensive Lecture Notes
Types of Homology and Evolutionary Thought
Developmental Homology
- Gill slits / gill pouches, post-anal tail, vertebral column appear in the embryonic stage of distantly related species (e.g. a0chick, human, cat).
- Indicates common developmental pathways; answer to the sample MCQ.
Genetic Homology
- Similarities in DNA/RNA sequences across species; measured directly with molecular techniques.
Structural (Morphological) Homology
- Similar bone layouts used for different functions (human arm, whale fin, bat wing).
Lamarcks "Inheritance of Acquired Characteristics" (Disproven Mechanism)
- Traits strengthened by use (e.g. a0giraffe neck) supposedly passed on; replaced by Darwinian natural selection in which the environment filters heritable variation.
Mass vs. Background Extinction
- Mass Extinction 539 Rapid, global loss of a large proportion of taxa.
- Five recognized events; key ones covered: Permian ("Great Dying") and Late Cretaceous (non-avian dinosaurs lost).
- Background Extinction 539 Normal, lower a0rate of species loss due to ordinary ecological/ evolutionary processes.
Meteor-Impact Evidence for the Late Cretaceous Event
- Thin global sediment layer enriched in iridium (rare on Earth, common in meteorites) 4A5 correct answer to MCQ.
- NOT: U-238 layers, complete dinosaur extinction per se, or CO₂ in glacial ice.
Core Behavioural-Ecology Terms
| Concept | "How? / Why?" | Key Example(s) |
|---|---|---|
| Proximate causation | Mechanism (how a behaviour occurs) | Lobsters detect Earths magnetic field to navigate home at night. |
| Ultimate causation | Evolutionary reason (why it exists) | Navigation increases survival by returning safely to shelter. |
| Habituation | Decreased response after repeated benign stimulus | Nestling birds stop ducking after many overhead shadows. |
| Operant conditioning | Behaviour linked to reward/punishment | Skinner box: lever ⟶ food pellet or mild shock. |
| Fixed Action Pattern (FAP) | Innate, stereotyped, nearly unstoppable once triggered | Host yellow bird feeds oversized cuckoo chick that killed its own brood. |
| Reciprocal Altruism | Exchange of fitness benefits separated in time | Vampire bats regurgitate blood meals to unrelated group members. |
| Kin Altruism | Help directed toward relatives; modelled with Hamiltons rule | Cooperative breeding, alloparental care. |
Hamiltons Rule: rB > C
(Help is favoured when the coefficient of relatedness r times the benefit B to the recipient exceeds the cost C to the actor.)
Study Strategy Highlighted
- Use MCQ stems not only to pick the right letter but to rehearse definitions, contrasts, and underlying principles.
Hybrid Case Study: The Pizzly (Grolar) Bear
- Hybrid of polar bear (Ursus maritimus) 2B grizzly bear (U. a0arctos).
- ~8 verified individuals in the wild; fertile.
- Likely arises where shrinking sea-ice pushes polar bears south and warming climate allows grizzlies north ⟶ range overlap.
- Currently no self-sustaining pisley population; all hybrids traced to one female polar bear × two male grizzlies.
Adaptive Radiation of Mammals After Dinosaur Extinction
- Non-avian dinosaurs vanish ext{≈}65\text{ Mya}.
- Vacant niches ⟶ rapid diversification (adaptive radiation) of mammals.
Earliest Primate-Like Mammals (Plesiadapiforms)
- Time: just post-Cretaceous.
- Traits: small brain, long muzzle, rodent-like incisors, claws (not nails), lateral eyes (poor depth perception), excellent smell, arboreal but non-leaping, low-crowned herbivorous teeth.
Primate Overview: Shared Synapomorphies
- Grasping hands/feet with opposable thumbs.
- Nails (not claws).
- Forward-facing eyes enclosed in a post-orbital bar.
- Hind-limb dominated locomotion.
- Relatively large brain-to-body ratio.
- Generalised heterodont dentition (incisors, canines, premolars, molars).
Major Primate Branches
Prosimians ("before monkeys")
- Lemurs, bush babies, lorises.
- Often nocturnal; huge eyes.
- Endemic/isolated (e.g. a0Madagascar) ⟶ unique evolutionary paths.
New World Monkeys (Platyrrhines)
- Geography: Central & South America.
- Small–medium; broad lateral nostrils; prehensile tail; no buttocks pads/cheek pouches.
- Examples: squirrel monkey, golden lion tamarin.
Old World Monkeys (Cercopithecoids)
- Geography: Africa & Asia.
- Larger; downward nostrils; longer hind-limbs; flat nails; sitting pads; non-prehensile tails.
- Examples: macaques, baboons.
Apes
- Shared trait with Old World monkeys: closely spaced nostrils.
- Lesser Apes – gibbons; extreme brachiation.
- Great Apes (Hominidae) – orangutans, gorillas, humans, chimpanzees, bonobos.
- No tail, long arms, short legs, broad chest & shoulders, large brain-body ratio.
Molecular Evidence of Human–Chimp Relationship
- DNA double helix melts at 95^\circ\text{C} when perfectly matched.
- King & Wilson (1975) created human–chimp hybrid DNA; melted at 94^\circ\text{C} ⟶ ~1 % sequence divergence.
- Full genomes: Human (2003), Chimpanzee (2005) confirm \approx99\% similarity; divergence 5\text{–}7\text{ Mya}.
Hominins: Definition & Earliest Member
- Hominins = modern humans (Homo sapiens) + all extinct, bipedal ancestors; excludes chimpanzees & bonobos.
- Earliest specimen: Sahelanthropus tchadensis (discovered 2002).
- Age: 6\text{–}7\text{ Mya}.
- Chimp-sized brain, prominent brow ridge.
Skeletal Adaptations for Habitual Bipedalism
- Foramen Magnum Position – hole for spinal cord under centre of skull keeps head balanced over body.
- S-shaped Vertebral Column – weight centred above pelvis.
- Short, Broad Pelvis – supports internal organs; aligns femurs.
- Long Legs / Valgus Knee – stride efficiency; knees angled inward to keep feet under centre of gravity.
- Arched Foot & Non-Opposable Big Toe (not detailed in transcript but integral) – spring & shock absorption.
Modern slump (hunched over laptops) counteracts evolved posture – periodic movement recommended!
Fossil Teeth as Evolutionary Clues
- Teeth & enamel fossilise readily (hard tissues).
- Wear patterns, crown height, and micro-damage reveal diet and habitat.
- Aid in placing extinct taxa on phylogenetic trees.
Key Numerical / Statistical Points
- Iridium layer dating late Cretaceous: \sim65\text{ Mya}.
- Background extinction rate ≪ mass-extinction pulse.
- Human–chimp DNA difference: \sim1\% (melting temp 1 °C lower).
- Earliest hominin: 6\text{–}7\text{ Mya}.
- Number of verified pizzlies: \text{≈}8.
Timeline Snapshot
- 65\text{ Mya} – Asteroid impact ⟶ dinosaur extinction ⟶ mammal radiation.
- \sim60\text{–}50\text{ Mya} – Plesiadapiforms (primate-like).
- \sim40\text{–}30\text{ Mya} – Split of New vs. a0Old World monkeys.
- \sim20\text{ Mya} – Early apes diversify.
- 6\text{–}7\text{ Mya} – First hominins.
- 2003 – Human genome.
- 2005 – Chimp genome.
Quick Glossary
- Agnostic (in quiz) – merely a distractor; not used in behavioural ecology.
- Iridium – extraterrestrial metal marking impact layer.
- Prehensile – capable of grasping.
- Brachiation – arm-over-arm tree locomotion (gibbons).
- Monophyletic Group – clade containing ancestor & all descendants.
- Synapomorphy – shared, derived trait defining a clade.