Evolution of Life and Animal Characteristics

• Life on Earth began approximately 4.5 billion years ago.
• Early life consisted of single-celled organisms.
• Fossil records help scientists to link and date the evolution of life.
• A single-celled organism, or unicellular organism, is composed of only one cell that performs all necessary life processes.

Characteristics of Animals

• Animals belong to the Kingdom Animalia and are multicellular eukaryotes.
• The eight characteristics used to classify animals are:
  • Eukaryotic cells: nucleus-centered cells
  • Multicellular: having more than one cell
  • Heterotrophic: they cannot produce their own food
  • Ability to move: they can move freely on land or through water
  • Symmetry- being the same on both sides divided by an axis, which can be bilateral or radial
  • Body cavity: contain and protect vital organs, usually surrounded by fluids
  • Tissue: grouping of cells to provide one function
  • Vertebral Column: spine of an animal which begins at the base of the neck and extends to the tailbone
• Multicellular organisms have specialized cells for specific functions.
• Eukaryotes have cells with a nucleus and membrane-bound organelles.
• Animal cells differ from plant cells, as plant cells have chloroplasts for photosynthesis, cell walls, and large vacuoles.
• Animal reproduction can be sexual or asexual.
• Sexual reproduction requires gametes from two parents.
• Development occurs through cell production and division, fueled by food intake.

How Animals Evolved

• Evolution is the change in a species' characteristics over generations.
• Evolution can be caused by:
  • Mutation: genetic material change
  • Migration: relocation to a different area
  • Natural selection: survival and procreation of the fittest
  • Genetic drift: change in allele frequency
  • Non-random mating: mate selection based on specific traits
• Cells are the basis of life and can be prokaryotic or eukaryotic.
• The five kingdoms of life are Animalia, Plantae, Fungi, Protista, and Monera.
• Single-celled organisms, made of prokaryotic cells, were the first to inhabit Earth.
• Prokaryotic means before-nucleus.
• Monera kingdom contains Eubacteria and Archaebacteria.
• All other organisms are multi-cellular and make up the remaining four kingdoms of life.
• Animals evolved from prokaryotic organisms around 2.5-1 billion years ago.
• Both plant and animal cells use aerobic respiration with mitochondria for energy.
• Scientists believe mitochondria evolved from single-celled bacteria.
• Animal cell structures are categorized for having a nucleus.

The Evolution of Animals

• Modern animals evolved from aquatic species starting around 2.5 billion years ago.
• The oldest known ancestors of animals are the metazoans, similar to worms.
• Second, came the Ediacaran animals which were a similar mix of jellyfish with tougher outer walls
• During the Cambrian period, ancestors of modern animals like insects and jellyfish emerged.
• Amphibians bridged the gap between water and land.
• Mammal-like reptiles formed around the same time as dinosaurs.
• The extinction of dinosaurs allowed mammals and vertebrates to flourish.
• Vertebrates possess a spinal column and a notochord.
• Invertebrates lack a backbone and make up most of the animal kingdom.

Evolution of Invertebrates

• Invertebrates are among the first life forms and predate vertebrates.
• Invertebrates can range from simple to highly specialized.
• Specialization caused tissues to perform specialized functions.
• Three main traits formed during the evolution of invertebrates:
  • Specialization
  • Symmetry
  • Cephalization
• Cephalization is the formation of a head.
• The creation of a head allowed organisms to have sight, smell, and have a specific cavity for the development of a brain.
• Symmetry allows for specific bodily functions.
• Bilateral symmetry features identical sides, while radial symmetry has identical sides radiating from a central point.
• Examples of invertebrates include jellyfish, butterflies, snails, starfish, and sponges.
• Invertebrates are animals with no backbone, some examples include jellyfish, flies, leeches, and squids.

Evolution of Vertebrates

• Vertebrates possess a backbone and mostly exhibit bilateral symmetry.
• Less than 5% of animal species are vertebrates.
• All vertebrates originated from jawless fish.
• Development of cartilage and bones in fish led to the evolution of amphibians.
• Amphibians facilitated the transition from sea to land.
• Reptiles, birds, and mammals evolved from amphibians.
• This speciation took around 250 million years to develop.
• Examples of vertebrates include birds, mice, humans, snakes, and sharks.
• Vertebrates are animals with backbones, some examples include snakes, sharks, frogs, mice, birds, and humans.

Stages of Evolution of Animals

• The four eras of Earth's history are:
  • Archeozoic
  • Paleozoic
  • Mesozoic
  • Cenozoic
• The Archeozoic era spanned from Earth's formation to about 550 million years ago.
• The first life forms arose during the Archeozoic era.
• Organisms that evolved during this time include bacteria, invertebrates, amoeba, and sponges.
• The Paleozoic era lasted from around 550 to 248 million years ago, and includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.
• Organisms that evolved during this time include gastropods, fish, sharks, plants, insects, reptiles, amphibians, and some mammals.
• The Mesozoic era lasted from around 248 to 65 million years ago and includes the Triassic, Jurassic, and Cretaceous periods.
• The Mesozoic era is known as the age of the dinosaurs.
• Organisms that evolved during this time include birds and relatives of modern animals.
• The Cenozoic era began around 65 million years ago and continues to the present.
• The Cenozoic era includes the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene epochs.
• Mammals diversified and humans evolved during the Cenozoic era.
• A major diversification of animal species occurred during the Cambrian explosion.

Examples of Evolution in Animals

• Adaptations include the development of lungs, appendages, loss of hair, formation of the spinal column.
• Adaptations in animals result from speciation and environmental changes.
• Human evolution began in Africa around 8 million years ago from a common apelike ancestor.
• Modern humans evolved from Australopithecus ramidus over approximately 6 million years.
• As humans evolved, they lost body hair, began walking on two legs, became taller, and developed speech.
• Modern humans are known as Homo sapiens.

An overview of the early origins of life on Earth, starting from single-celled organisms. The lesson highlights the key features that define animals, like being eukaryotic, multicellular, heterotrophic, and motile. It also covers symmetry, body cavities, tissues and vertebral columns.