Lecture 4: Adaptation vs Exaptation Vs Novelty Flashcards
Adaptation
- Definition: Adaptation refers to features that arise to increase an organism’s fitness (survival and reproduction) through natural selection
. - Key Points: Adaptations enhance the functionality of traits specifically shaped by environmental pressures and genetic advantage.
Evolutionary Novelty
Definition: Novelty refers to the development of entirely new traits that provide new evolutionary possibilities for a lineage.
Explanation: Often a result of developmental changes that lead to traits previously unseen in the ancestral lineage, which may allow the species to explore new ecological niches.
Exaptation
Definition: Exaptation is the repurposing of an ancestral trait for a new function that differs from its original role.
Example: Feathers may have originally evolved for temperature regulation but were later co-opted for flight in birds.
Theories of Jaw Development
1) Serial Theory: Suggests a repeated pattern in structures (like gills) that later diversified into jaw elements.
2) Composite Theory: Proposes that jaws formed from a fusion of different embryonic elements.
Evolution of the Splanchnocranium in Gnathostomes
1) Gnathostome Splanchnocranium: This part of the skull supports the gills and other cranial structures in jawed vertebrates.
2) Spiracle & Stapes Evolution: The spiracle in fish is an opening behind the eye that, through evolution, led to structures like the stapes in tetrapods (early ear bone aiding in sound transmission).
Mammalian Ear and Jaw Evolution
1) Stem Mammal Evolution: Primitive ancestors, including Dimetrodon, Gorgonopsia, and Thrinaxodon, illustrate the transition from jaw structures to the mammalian ear.
2) Mammalian Middle Ear: Evolved from jawbones like the quadrate and articular into the three bones of the mammalian ear (incus, malleus, stapes), allowing efficient sound amplification.
Diagnosis of Mammaliao
Defined by the dentary-squamosal jaw joint, which marks a distinctive mammalian trait.
Human Ear Bones
Incus and Malleus: These bones work as levers to amplify sound, significantly enhancing hearing by up to 120 times compared to simpler bones like a single stapes.
Mammalian Teeth Complexity
Dentary-Squamosal Joint: This stable jaw joint enables precise tooth occlusion (alignment of upper and lower teeth), facilitating the evolution of specialized teeth for different functions.
Adaptions in the Fossil Record
1) Hard to distinguish because some traits are reused or repurposed from prior adaptations, complicating interpretation.
2) Fossil evidence often lacks the detail needed to confirm whether a feature arose as an adaptation or exaptation.
What is the summary of the concepts talked about in this lecture?
1) Adaptation: Traits increasing fitness via natural selection.
2) Exaptation: Derived use of ancestral traits for new functions.
3) Novelty: Development of completely new traits, leading to evolutionary opportunities.
4) Evolutionary Challenges: Identifying these changes in the fossil record can be difficult due to lack of evidence and the gradual repurposing of traits.
