Evolution Study Notes
Evolution
Introduction to Biological Diversity
Earth boasts millions of organisms that exhibit a vast range of shapes, sizes, and habitats.
Questions that arise include:
How did all these different organisms arise?
How are they interrelated?
Understanding Species
There are over 8 million species currently living on Earth.
A species is defined as a group of individuals that share similar characteristics and whose members are capable of producing fertile offspring in their natural environment.
Example: The blue-striped snapper is classified as a species of fish.
Related Species
Certain species exhibit close relationships.
To be considered related implies a shared ancestry.
Similar to how two individuals sharing a common ancestor are recognized as being related.
Common Ancestors
Charles Darwin’s observations of various finch species in the Galapagos Islands led him to conceive that these finches shared common ancestors.
A common ancestor is defined as an ancestral species that lived in the past, related to two or more modern species.
Evidence for Common Ancestors
Evidence that supports the relatedness of species and confirms the existence of common ancestor species includes:
Similar Development
Homologous Structures
Vestigial Structures
Fossils
1. Similar Development
Related animals undergo similar developmental processes.
Example: Pharyngeal slits observed in diverse species such as pond turtles, chickens, domestic cats, and humans.
2. Homologous Structures
Homologous structures are anatomical features in related species that arise from a common ancestry but serve different functions.
Components include:
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Example: Structures in humans, cats, whales, and bats demonstrate these homologous relationships.
3. Vestigial Structures
Vestigial structures refer to anatomical features present in modern organisms that have lost their original function.
Example: Vestigial pelvic bones in whales imply that their ancestors once had hind legs.
4. Fossils
Fossil remains of extinct species provide insight into what the ancestors of modern species might have looked like.
Example: The extinct species Indohyus, believed to be a common ancestor to both whales and hippos, existed around 50 million years ago (mya).
Origins of New Species
Inquiry into how a single common ancestor evolves into two or more distinct species is crucial.
Speciation is defined as the emergence of new species.
It is hypothesized that speciation occurs when two groups of the same species become physically isolated in different habitats.
Such habitats may feature diverse food sources, climates, and predator species.
Evolution Defined
Evolution refers to the process of change that takes place over long periods of time.
Microevolution addresses small changes in a species that transpire over a few generations.
Macroevolution occurs when groups from the same species are separated for an extended time, often leading to speciation.
Mechanisms of Speciation
The gradual process of speciation is influenced by evolution and time.
Founder species exemplify species that initiate populations in new environments, leading to speciation.
Example: The Amakihi and the Nihoa finch are instances of gradual speciation within birds.
Speciation in Birds of Paradise
This concept serves as an illustrative example of the speciation process.
Evidence from Fossils
Recent findings of fossils that document the evolutionary journey of whales from terrestrial ancestors.
Notable examples include Pakicetus and Ambulocetus, which indicate transitional features adapted for both aquatic and terrestrial environments.
Ambulocetus: suggests capability of swimming in shallow water as well as walking on land.
Pakicetus: represents one of the earliest known ancestors that lived primarily on land.
Rodhocetus: characterized by short hind limbs, likely not able to support weight, indicating a more aquatic lifestyle.
Basilosaurus: marked by a streamlined body and reduced hind limbs, adapted for a fully aquatic life.
Modern whales possess vestigial pelvic bones that bear historical significance.
Mechanisms of Evolution
How Does Evolution Occur?
The process by which species adapt and change over time is intricate.
Lamarck’s Theory of Evolution
Jean-Baptiste Lamarck, a notable 18th-19th century naturalist, studied biological diversity and proposed that organisms could gain or lose characteristics through use or disuse.
His example, often referred to as Lamarck's Giraffe Idea, suggested:
An original short-necked ancestor stretches its neck to reach leaves higher up in trees.
Over generations, this behavior leads to progressively longer necks.
This idea has since been discredited as incorrect.
Key Elements of Evolution
Variation
Refers to differences among individuals within the same species.
Variation exists naturally across all populations and is caused by small changes in an organism’s DNA.
Example: Members of the same species, such as ladybugs (Harmonia axyridis), exhibit observable variations.
Mutations
Small changes in an organism’s DNA that occur at random.
While many mutations may be detrimental or neutral, occasional mutations may confer beneficial traits.
Example: Albinism typically results from mutations in OCA genes.
Fitness
Defined as the probability of an individual surviving and reproducing successfully within its environment.
An individual may be considered fit in one particular environment but not in another.
Black Peppered Moths: Individuals with darker coloration may be more likely seen and predated by birds as opposed to lighter-colored (white) moths.
Adaptations
Characteristics that enhance an organism's fitness are termed adaptations.
Natural Selection
The evolutionary process by which certain traits become more common within a population due to their contributions to improved survival and reproduction rates.
Steps of Natural Selection:
Variation exists in every population.
Some variations contribute to enhanced fitness.
The fittest individuals are more likely to survive and reproduce.
Conversely, less fit individuals are less likely to reproduce and survive.
Sexual Selection
A subset of natural selection where certain traits promote increased mating success.
Organisms possessing these desirable attributes tend to have more offspring that inherit these traits.
Artificial Selection
A form of selection that parallels natural selection but is driven by human intervention.
Humans decide which individuals within a species will reproduce.
This practice leads to the development of numerous cultivated varieties, such as fruits and vegetables, and diverse dog breeds.
Examples of Evolutionary Practices
Modern Corn Production: Resulted from artificial selection from its wild ancestor, teosinte.
Dog Breeding: Various dog breeds have been created through selective breeding from the common ancestor, the gray wolf, across different regions globally.
Phylogenetic Trees
Phylogenetic Tree: A diagrammatic representation illustrating the evolutionary relationships and history among groups of organisms or species.
Key Components of a Phylogenetic Tree:
Nodes: Indicate common ancestors where lineages diverge.
Branches: Represent connections between nodes and endpoints, chronicling evolutionary paths.
Tips: Represent existing species or groups at the end of branches.
Root: Represents a single common ancestor for all species depicted in the tree.