Class 10

Systematics (Definition)

The study of biodiversity and the evolutionary relationships among organisms.

Goal of Modern Taxonomy

To assign taxonomic names that are consistent with our present understanding of evolutionary relationships.

Carolus Linneaus's Contributions (2)

1. He introduced Binomial nomenclature. 2. He developed a hierarchical system of classification.

Taxon (Definition)

A single named taxonomic unit at any level in the hierarchy (e.g., Family, Species).

Hierarchical Classification Order (From Broadest to Narrowest)

Kingdom Phylum (Phyla) Class (Classes) Order (Orders) Family (Families) Genus (Genera) Species (Species).

Purpose of Biological Classification

To provide a name when referring to shared information on an organism (e.g., scientific literature, conservation assessments). This gives classification predictive power and allows for the interpretation of origins and evolutionary history.

Phylogenies (What they show)

They show the evolutionary histories of species by illustrating lines of descent that persist across generations, how populations are aggregates of genetic lineages, and how species split to give rise to multiple species.

Nodes

Represent historical lineage splitting events where one lineage splits into two.

Branches

Represent single ancestor-descendant lineages. All branches are connected by nodes.

Tips (Terminal Branches)

Represent the most recent/modern individuals, species, or clades. They do not have descendants represented in the diagram.

Internal vs. External Branches

External branches (terminal branches) connect a tip to a node. Internal branches connect two nodes.

Root (Definition)

A node representing the earliest time point in the diagram, often represented by an unlabeled branch.

Most Recent Common Ancestor (MRCA)

The youngest node that is ancestral to all lineages in a given group of taxa (i.e., the common ancestor of the ingroup taxa).

Sister Groups (Sister Taxa)

Those taxa that are the immediate descendants of the same ancestor.

Monophyly

Describes a group made up of an ancestor and ALL its descendants (e.g., amphibians).

Paraphyly

Describes a group made up of an ancestor and SOME of its descendants (e.g., reptiles).

Polyphyly

Describes a group that doesn't contain the most recent common ancestor of all its members.

Ingroup vs. Outgroup

The Ingroup is the focal species in a phylogenetic study, all related to one common ancestor. The Outgroup is the common ancestor of the ingroup taxa.

Ancestral Trait

A trait that was inherited in its present form from the MRCA of the clade.

Derived Trait

A trait that originated from a descendant of the MRCA within the clade.

Trait Ambiguity (Important Detail)

The same trait can be classified as ancestral for a particular clade but derived within a larger clade.

Synapomorphy

A shared, derived trait for a clade. It is a trait shared by all species in the clade that evolved on the branch leading to that clade.

Homology

When structures observed in different taxa/species can be traced to a single structure present in a shared evolutionary ancestor.

Homoplasy (Definition & Consequence)

When a characteristic arises more than once on a phylogenetic tree (e.g., same structure but different function). It is not indicative of a common ancestor and can mislead phylogenetic inference.

Reconstructing Phylogenies (Modern Method)

Modern methods fit models of evolution to observed trait data. Trait data can be genetic or phenotypic. Phylogenetic relatedness is inferred from homologous traits.

Practical Applications of Phylogenetics (3 Examples)

1. Determining where and when parasites spread. 2. Identifying the most successful flu strain in a given year. 3. Identifying the driver mutations as viruses like SARS-COV-2 evolve.

Two Principal Sources of Macroevolutionary Insights

1. Paleontology: Provides a direct record of past evolutionary change (strongest inference for groups that fossilize well). 2. Phylogenetics: Provides an indirect record of past evolutionary change (strongest inference for groups with living representatives).

Mass Extinction (Definition)

The extinction of >75% of Earth's species in a geologically short period. Mass extinctions periodically restructure life on Earth.

Fossil Record Contribution to Extinction Knowledge

Provides the only evidence for completely extinct clades. It documents long-term patterns of global biodiversity and provides evidence for catastrophic extinctions.

Phylogenetics Contribution to Post-Extinction Knowledge

Provides evidence for explosive diversification following mass extinctions.

Diversification Rate Formula

Diversification rate = Speciation rate minus Extinction rate.

Features Associated with Increased Diversification (5 examples)

1. Herbivory. 2. Species with more sexual selection. 3. Animal pollination in plants. 4. Increased dispersal. 5. Increased range size