Lecture 11: Physical & Historical Constraints

Question 1

Material Properties of Biology

Answer 1

1) Bone Microstructure: Bone is optimized for strength and flexibility, balancing lightness with durability. Bone has a unique microstructure that allows it to bear weight and resist stress, key for animals with larger bodies.

2) Square-Cube Law: This principle states that as an object grows, its volume increases faster than its surface area. Larger animals must contend with this, as they need structural support to handle their mass—hence, different scaling adaptations arise in larger animals like Brachiosaurus.

Question 2

Semicircular Canals

Answer 2

The semicircular canals are small, fluid-filled structures in the inner ear that help with balance. Their size affects an animal’s ability to detect motion, which is critical for coordination and stability. Miniaturization affects these organs in tiny animals, requiring adaptations to maintain function within limited space.

Question 3

Functional Constraints

Answer 3

• Examples of Convergent Evolution: Bats, birds, and pterosaurs (prehistoric flying reptiles) each developed wings independently, showing similar functional solutions to the need for flight. Different evolutionary paths led to similar results due to the same physical demands of flight.
• Locomotor Evolution: Adaptations like limb orientation change over time. Early tetrapods had a sprawling gait, while mammals developed an upright posture and efficient locomotion like galloping. Evolutionary innovations here allow organisms to exploit new modes of movement.

Question 4

Transfer Constraints

Answer 4

1) Diffusion Limitations: Transfer of gases or nutrients is limited by factors like surface area, concentration gradients, and distance. For example, the efficiency of gas exchange through tissues depends on these constraints. The equation

–> describes the rate of diffusion, showing how animals must adapt in structure (e.g., respiratory systems) to optimize transfer.

2) Metabolic Scaling: The ¾ power rule describes how metabolic rates scale with body size across many species. This principle could be linked to how transfer systems (like blood vessels or xylem in plants) scale with organism size.

Question 5

Historical Constraints

Answer 5

Evolution isn’t always a clean slate; some anatomical features are inherited from distant ancestors. For example, Pikaia (an ancient chordate) exhibits features that became constraints, like lateral undulation in swimming. Descendants, such as modern fish, carry forward these ancestral patterns in movement and skeletal structure.

Question 6

Locomotion and Evolutionary Adaptations

Answer 6

1) Shark Swimming: Sharks swim using lateral undulation, aided by a lightweight cartilage skeleton and a liver filled with oil to help maintain buoyancy. In contrast, bony fish developed a swim bladder, allowing them to regulate buoyancy and freeing them to explore new body shapes and habitats.

2) Lung Ventilation and Posture: Early tetrapods sprawled, which limited their lung capacity during movement. Mammals evolved upright limbs, which allowed simultaneous lung ventilation and motion, and some evolved galloping, an efficient terrestrial locomotion strategy.

3) Aquatic Reversions: Some land-dwelling ancestors of marine mammals (e.g., early whales) evolved back to a fully aquatic life. Despite adapting to water, they still retain characteristics of their land-dwelling ancestors.

Question 7

Summarize this lecture and what it is about! Constraints and Evolution!

Answer 7

1) Form Predicts Function: Many biological forms are optimized for their function due to physical and functional constraints. For example, the streamlined bodies of aquatic animals reduce drag in water, while bird and bat wings are optimized for flight.

2) Stasis and Rapid Change: Constraints can lead to long-term stability in form (morphological stasis) until a new adaptation or environmental shift allows for rapid changes.

3) Overcoming Historical Constraints: Evolutionary novelties, like the mammalian gallop or swim bladders in bony fish, can open up new niches and lead to diversification by breaking free from ancestral limitations.