Classification and Diversity of Life Notes

Characteristics of Life

• Organisms respond to diverse stimuli, e.g., plants bending toward light.

• All organisms use energy for metabolic activities.

• All organisms reproduce to increase their numbers.

• All organisms are made of cells.

• Organisms are highly organized structures consisting of one or more cells.

Why the Diversity of Life Happened

• As a result of evolution or adaptive radiation.

• Adaptive radiation: An evolutionary pattern over a short time where a single species rapidly diversifies into closely related species to adapt to specific environmental changes.

Origin of Life: Chemical and Biological Evolution

• Chemical evolution: the process by which simple chemical compounds in the oceans gradually combined to form more complex organic molecules, a key step in the development of life.

• Biological evolution led to the formation of life and complex organisms.

Domains of Life

• Living things have evolved into three large clusters called domains:

  • Bacteria

  • Archaea

  • Eukaryota (Eukarya)

• Eukaryota is Eukaryotic.

• Order of appearance:

  • Bacteria evolved first.

  • Gave rise to Archaea.

  • Eukaryota evolved recently.

Domains of Life Details

• Bacteria:

  • Prokaryotes with cell walls containing peptidoglycan.

  • Wide variety of lifestyles, including many that can produce their food.

• Archaea:

  • Prokaryotes without peptidoglycan, but with similarities to Eukaryotes in genome organization.

  • Usually live in extreme conditions (high salt, high temperatures, etc.).

• Eukaryota (or Eukarya):

  • Eukaryotic.

Domains and Kingdoms

• Three Domains:

  • Bacteria

  • Archaea

  • Eukarya

• Six Kingdoms:

  • Bacteria

  • Archaea

  • Protists

  • Plants

  • Fungi

  • Animals

How Was the Diversity of Life Identified?

• Systematics is the study of different organisms and how they are related to each other.

• Systematics considers:

  • Taxonomy: Naming and grouping organisms into logical categories.

  • Phylogeny: Exploring the evolutionary relationships among organisms.

What is Taxonomy?

• Taxonomy is the scientific study of naming, identifying, and classifying biological organisms based on shared characteristics.

• The current taxonomic system has eight levels in its hierarchy.

• Taxonomic hierarchy: organizes living things into levels, ranging from broad categories like kingdom down to more specific ones like species.

• Organisms are grouped into taxa (singular: taxon) and given a taxonomic rank.

Taxonomic Hierarchy

• Domain is the highest (most general) rank.

• Taxonomic ranks (from general to specific):

  • Domain (e.g., Eukarya)

  • Kingdom (e.g., Animalia)

  • Phylum (e.g., Chordata)

  • Class (e.g., Mammalia)

  • Order (e.g., Carnivora)

  • Family (e.g., Canidae)

  • Genus (e.g., Canis)

  • Species (e.g., Canis latrans - Coyote, Canis lupus - Gray wolf)

Development of Taxonomy

• Introduced by Carolus Linnaeus.

• Developed a system based on physical and structural similarities.

• Used binomial system of nomenclature to classify organisms.

• Each species is assigned a unique two-part name: Genus & Species.

  • Genus: A group of closely related organisms ranking below family and including more than one species.

  • Species: A closely related group of organisms with similar characteristics.

Rules: Binomial Nomenclature

• Equus is the genus name for horses and their close relatives.

  • Equus burchellii, the Zebra

  • Equus africanus, the Donkey

• Binomial names are either italicized or underlined.

• The first letter of the genus is capitalized; the specific species is NOT capitalized.

Phylogeny

• Phylogeny is the study of evolutionary relationships among different groups of organisms.

• Phylogeny is based on derived characteristics:

  • Fossils

  • Comparative anatomy studies

  • Life cycle information

  • Biochemical and molecular studies

Fossil Record

• A fossil is the preserved remains of a dead organism from millions of years ago in sediments.

• Fossils are found in rocks and can take many forms:

  • Body Fossils: Preserved physical remains of an organism (bones, teeth, shells, leaves).

  • Trace Fossils: Indirect evidence of an organism's activity (footprints, burrows, nests).

  • Chemical Fossils: Molecular traces of life (organic molecules that remain after decomposition).

Comparative Anatomy

• Comparative anatomy is the study of similarities and differences in the anatomy of different species.

• Different animals' hands have the same basic pattern of bones.

• They inherited this pattern from a common ancestor.

• Their forelimbs now have different functions.

Life Cycle Information

• Life cycles show how animals grow and reproduce.

• Example:

  • Butterfly: Egg → caterpillar → pupa (chrysalis) → adult butterfly.

  • Frogs: Eggs → tadpoles → adult frogs.

• These stages help animals adapt and survive in different environments.

Biochemical and Molecular Studies

• Initially assumed humans were most closely related to chimpanzees.

• DNA sequence analysis reveals humans and chimpanzees share about 98% of their DNA, with non-functional genes; the remaining 2% provides major differences.

Phylogenetic Tree or Phylogram

• Phylogenetic tree (phylogram): A diagram showing relationships among different groups of organisms.

• Branches represent evolutionary distance between groups.

• Branch length indicates differences in DNA.

Cladistics: Cladogram and Clade

• Cladistics: Method to evaluate the degree of relatedness among organisms based on shared characters and similarity of species derived from ONE ancestor.

• Cladistics involves a diagram known as a Cladogram.

• Each Cladogram Contains several Clades.

• Clade: A group of organisms that consists of a common ancestor and descendant species with shared Characteristics or Traits.

Cladistics Based on Molecular Data

• The length of the branches indicates the differences between the DNA.

• DNA shows that humans and chimpanzees diverged from a common ancestor species that lived between 8 and 6 million years ago.

• Derived shared trait: Tail Loss

• Unique Trait: Bipedal

Difference Between Cladistics and Phylogeny

• Cladistics:

  • Often used to trace a very common ancestor of one species and study their characteristics.

  • All branches in a cladogram are of equal length as they do not represent any evolutionary distance.

• Phylogeny:

  • The study of the relationships and evolutionary history between groups of organisms.

  • All branches in a phylogram represent any evolutionary distance between different groups.

How Did We Become Such a Powerful Species So Quickly?

• Strong opposable thumbs

• Walk upright

• Intelligence

Macroevolution vs. Microevolution

• Microevolution:

  • Within species

  • Small changes

  • Few generations

• Macroevolution:

  • Complete different species

  • Large changes

  • Longer period of time

Macroevolution vs. Microevolution Details

• Microevolution:

  • Involves minor differences in genes between populations of the same species.

  • Happens on a smaller scale from generation to generation.

  • Involves small changes to DNA, producing small changes to phenotype (e.g., green to brown color).

• Macroevolution:

  • Large scale, major biological changes over millions of years.

  • Involves origin of new species from a common ancestor, from one species into two.

  • Involves extinction of species.

  • Involves evolution of new features (e.g., backbone, wings).

How Evolution Occurs

• Four basic ways:

  • Mutation

  • Gene Flow (Migration)

  • Genetic Drift

  • Natural Selection

Mutation and Gene Flow (Migration)

• Mutation:

  • Changes in the base sequence of DNA.

  • Source of new genes/alleles, thus increases diversity.

  • Example: Some “green genes” randomly mutated to “brown genes.”

• Gene Flow (Migration):

  • Movement of individuals into and out of populations, resulting in genes being added or removed.

  • Shuffles genes between populations; thus prevents speciation and diversity.

  • Example: brown beetles join green beetle population and make gene for brown coloration more frequent.

Genetic Drift

• Significant change in gene frequency that is NOT a result of natural selection.

• Results from random or chance events (natural disaster or indiscriminate human hunting).

• Occurs when the population size is limited or small.

• Decrease in Diversity (Especially in Small Populations)

• Example: green beetles killed when someone stepped on them, so by random chance more brown beetles reproduced.

Natural Selection

• Nature’s way of