Biology Chapter: Animal Diversity and Adaptability

Biology and Society: Evolving Adaptability

• Human success is largely due to brainpower.
• Human brain volume to body mass ratio is 2.5 times greater than chimpanzees.
• Human's capacity for problem-solving, language, and understanding others is highly developed.
• Brain size has increased by about 40% in humans over 1.5 million years.
• Humans can adapt and modify their behavior.
• There are approximately 1.3 million animal species.
• Animal diversity evolved through natural selection adapting to diverse environments.

The Origins of Animal Diversity: What Is an Animal?

• Animal life began in Precambrian seas with multicellular creatures consuming other organisms.
• Animals are eukaryotic, multicellular, heterotrophic organisms absorbing nutrients from food, capable of digestion.
• Animal cells lack cell walls unlike plants and fungi.
• Most animals possess muscle and nerve cells controlling movement.
• Most animals reproduce sexually.
• Sea star larvae undergo a notable metamorphosis into adult forms.
• Oldest animal fossils are roughly 560 million years old.
• Animal diversification significantly increased during the Cambrian explosion (525-535 million years ago).
• Increased atmospheric oxygen and complex predator-prey relationships are possible factors triggering the Cambrian explosion.

Identifying Major Themes

• The ability to build complex bodies depended on "master control" genes already existing before rapid body diversification.
• Structure and function are interrelated.
• Information flow is essential in biological systems.
• Transformations of energy and matter through biological pathways are key.
• Biological interactions occur within systems.
• Evolution occurs due to interactions within biological systems.
• Certain body features have specific functions.
• Bees and flies pollinate crops and facilitate crop and human health interactions.
• Insects are carriers of diseases impacting human health and directly compete with humans for food.
• Interactions impact the surrounding biological systems.

Major Invertebrate Phyla: Sponges

• 95% of animal kingdom is composed of invertebrates (animals without backbones).
• Sponges (phylum Porifera) are stationary animals without true tissues, likely evolving early from colonial protists.
• Sponge bodies are sac-like with holes, allowing water to flow through for feeding and respiration.
• Cnidarians (phylum Cnidaria) possess tissues, radial symmetry, and stinging cells (cnidocytes) for defense and feeding.
• Cnidarians have sacs with a central digestive compartment for digestion.
• Cnidarians include stationary polyps and floating medusa forms.
• Cnidarian body types vary with different species and environment.

Major Invertebrate Phyla: Molluscs, Flatworms, Annelids, Roundworms

• Molluscs (phylum Mollusca) – soft-bodied animals with a shell.
• Flatworms (phylum Platyhelminthes) – simple animals with bilateral symmetry.
• Annelids (phylum Annelida) – segmented worms.
• Roundworms (phylum Nematoda) – cylindrical body, important decomposers and parasites.
• Arthropods have jointed appendages, exhibit adaptability to various habitats.
• Arachnids - mainly terrestrial, have 4 pairs of legs.
• Crustaceans - mostly aquatic, have various appendages.
• Millipedes – eat decaying plant matter, two pairs of legs per body segment.
• Centipedes – carnivores, one pair of legs per segment.
• Insects – characterized by three body parts (head, thorax, and abdomen), adaptable to diverse environments.

Echinoderms and Vertebrate Evolution

• Echinoderms (phylum Echinodermata) - spiny skin, radial symmetry, and a water vascular system.
• Echinoderms are closely related to chordates (including vertebrates) on evolutionary trees.
• Vertebrates are characterized by a dorsal, hollow nerve cord, a notochord, pharyngeal slits, and a post-anal tail during development.
• Early vertebrates lacked jaws, later vertebrates developed bony or cartilaginous skeletons, and then fins and swim bladders.

Fishes, Amphibians, and Reptiles

• Fishes – cartilaginous and bony fishes with a lateral line system.
• Amphibians – amphibians are tied to water for reproduction and have 2 life stages, and exhibit aquatic and terrestrial adaptations.
• Reptiles – ectothermic (cold-blooded), have scaled skin, and lay amniotic eggs.

Birds and Mammals

• Birds – endothermic (warm-blooded), have feathers and wings, and lay amniotic eggs.
• Mammals – endothermic, have mammary glands and hair, and are characterized by diverse groups.

The Human Ancestry

• Primates emerged from insect-eating mammals about 65 million years ago.
• Arboreal adaptations shaped early primates: limber shoulders, forward-facing eyes, and excellent hand-eye coordination.
• Humans belong to a group of primates called Anthropoids.
• Humans and chimpanzees share a common ancestor, but humans are not evolved from chimpanzees.
• Neanderthals are an extinct human species who interbred with modern humans.
• Modern humans (Homo sapiens) emerged in Africa and migrated globally.

Evolution Connection: Are We Still Evolving?

• Humans’ traits have adapted to specific environmental needs.
• Adaptive changes can also include skin color as a response to UV radiation.
• Genetic adaptations for disease resistance have occurred in different human populations.
• Populations eating dairy products have developed lactose tolerance.