Animal Behavior: Proximate vs. Ultimate Causes

Sea Turtle Behavioral Puzzle

• Observation: Newly hatched sea turtles emerge from sandy nests and execute a frantic dash toward the ocean.
• Later in life, adult females return to the same beach to lay eggs, completing a surprisingly precise life cycle.
• Scientific fascination: How do turtles locate the natal beach decades later? Which parts of the behavior are inborn vs. acquired through experience?
• Overarching questions raised:
  • What drives this and similar animal behaviors?
  • Are these actions hard-wired instincts (innate) or are they shaped by learning/experience?
  • What purpose (adaptive value) do these behaviors serve in the first place?

Innate (Hard-Wired) vs. Learned Behaviors

• Innate / hard-wired: Behaviors encoded genetically; they appear in full functional form the first time they are performed.
  • Example from transcript: The immediate dash to the ocean is likely innate—hatchlings have no prior experience.
• Learned / experience-dependent: Require practice or environmental input; can be modified by individual life history.
  • Open question: Do turtles learn magnetic or chemical cues that help them return?
• The module will compare roles, mechanisms, and adaptive consequences of each category.

Defining “Behavior”

• Working definition: “What an animal does and how it does it.”
  • Includes observable actions (e.g., running, vocalizing) and internal processes leading to those actions (e.g., hormone release, neural activation).
• Emphasis on process (not merely the end result).

Tinbergen’s Framework for Studying Behavior

Dutch ethologist Niko (Nico) Tinbergen created a systematic way to break down the overarching question “Why does an animal do X?”

Tinbergen’s Four Questions (Grouped in Two Dimensions)

1. Proximate (mechanistic / “how”):
   • Immediate stimuli that elicit the behavior (e.g., light, temperature, predator presence).
   • Physiological mechanisms: hormones, neural circuits, sensory organs.
   • Developmental processes: genes, maturation, early learning contributing to the behavior’s expression.
2. Ultimate (evolutionary / “why”):
   • Adaptive value: How the behavior increases survival or reproductive success (fitness).
   • Phylogenetic history: When and in which ancestral lineages the behavior evolved; comparative method among related species.

Transcript emphasizes the broad split between proximate causes (the immediate how) and ultimate causes (the evolutionary why).

Proximate Causes (Detailed)

• Ask: “What events in the environment or inside the organism trigger the behavior right now?”
• Could involve:
  • Sensory reception (visual, auditory, chemical): e.g., hatchling sees the brighter horizon over the ocean.
  • Neural processing and motor output.
  • Hormone levels or circadian rhythms.

Ultimate Causes (Detailed)

• Ask: “Why has natural selection favored this behavior?”
• Framed in terms of fitness: probability that an individual’s genes reach the next generation.
  • Conceptual formula: w = \frac{\text{offspring produced by individual}}{\text{average offspring in population}}
• For turtles:
  • Dash increases odds of reaching water quickly → reduces predation risk.
  • Natal philopatry (returning to birth beach) may align females with environmental conditions suited to their own embryonic development, thereby enhancing hatchling survival.

Survival, Fitness, and Evolutionary Significance

• Fitness links behavior to Darwinian natural selection.
  • Behaviors that improve survival to reproductive age or boost reproductive output tend to persist.
• Ultimate explanations always circle back to this criterion.

Key Takeaways & Concept Map

• Behavior = action + mechanism.
• Two fundamental explanatory tiers:
  1. Proximate (“How?”) → Immediate triggers and mechanisms.
  2. Ultimate (“Why?”) → Evolutionary rationale and fitness benefits.
• Behaviors are variously innate or learned; many contain both components.
• Tinbergen’s questions provide a structured roadmap for dissecting animal actions—from sea-turtle navigation to any organism’s behavioral repertoire.