Evolution
Learning Objectives
TAXONOMY: the ordering of life into categories based on similarities and differences.
Life on Earth is divided into:
Kingdom Phylum Class Order Family Genus Species
Each division is more specific than the next. For example, the classification of humans is:
Kingdom: Animals
Phylum: Chordates
Class: Mammals
Order: Primates
Family: Hominid
Genus: Homo
Species: Sapiens
There are five kingdoms of Life:
Monera: simple organisms, prokaryotic (cell has no nucleus) example: bacteria
Protists: unicellular eukaryotic (cell has a nucleus), many different types
Fungi: undergo external digestion
Plants: autotrophic multicellular organisms
Animals: multicellular heterotrophic organisms
Organic Evolution: the idea that all life on Earth descended from other life and therefore all life is linked by a pattern of ancestry and descent.
Natural Selection: Darwin suggested that all individuals are unique and that within a population some organisms are better able to adapt to a particular environment. Organisms that are better suited for an environment survive to produce offspring and the offspring inherit traits that enable them to survive in that environment. THE ENVIRONMENT SELECTS organisms that survive, the pressures in a given environment favor survival of some organisms in a population over others. Darwin did not suggest why certain organisms were better suited than others just that they were.
Inheritance: Mendel experimented with pea plants and discovered that inheritance from parent to offspring was predictable. He stated that heredity was determined by "factors" (we know these as genes) that divide and recombine in sexual reproduction to pass traits from parent to offspring.
Later experimentation discovered that genes are composed of DNA and are located on chromosomes. During the production of gametes (sex cells), a process called meiosis, crossing over occurs. Crossing over (gene recombination) is a mixing of genetic material between chromosomes to produce gametes that are unique. This is why offspring from the same parents are not all identical. During gene combination mutations can occur. Mutations are mistakes in the genetic code on a chromosome. Many times these mistakes are benign, they have no obvious effect on the organism. Sometimes the mistakes cause disease or are so severe that they are fatal. BUT in very rare instances mutations are believed to be beneficial to an organism.
Meiosis Tutorial: if you want more information on meiosis
Modern evolutionary theory states:
Organic evolution is a slow change in a population overtime as the result of genetic mutations, gene recombinations and natural selection.
Evidence that supports the theory of evolution:
- The branching structure of life (Biologic Succession): each group of organisms is more specialized than the one before. For example, humans are hominids, are primates, are mammals ect.
- Homologous structures: organs built from the same basic parts but with very different functions. Forelimbs are grasping hands in humans, wings in birds, swimming flippers in dolphins and strong supports in a horse.
- Vestigial structures: organs or structures that an organism possesses that have no apparent function presently but may have in the past. Humans have a set of muscles for moving their ears. They must have been able at one time to move their ears like a dog. Whales have a pelvis bone that serves no purpose but did when ancestral whales were land animals.
- Comparative embryology: during the early stages of fetal development embryos from very diverse organisms resemble one another.
Patterns of evolution:
- Divergent Evolution: rapid speciation from one parent. Population changes rapidly to adapt to new environments, evolving into many species from one original parent.
- Convergent Evolution: two or more unrelated lineages develop similar traits to adapt to a similar environment. Marsupial and placental mammals are two distinct lineages yet similar animals have evolved.
Placental Mammal Marsupial Mammal
Wolf Tasmanian wolf
Flying Squirrel Flying Phalanger
Ground Hog Wombat
Mouse Marsupial Mouse
- Iterative Evolution: evolution of similar form more than once from the same lineage.
Modes of Evolution:
- Phyletic Gradualism: slow gradual change through time. The fossil record of the horse supports phyletic gradualism. Changes in the foot, teeth and face show a slow steady change over time.
- Punctuated Equillibrium: little evolution for a long period interrupted by short periods of rapid evolutionary change. This is supported in the fossil record by mass extinctions.
