Ethan Walker 
An animal species is usually understood as a distinct evolutionary lineage: a population, or connected set of populations, that is evolving separately from other such lineages. Scientists test that idea with evidence from reproduction, genes, anatomy, behavior, ecology, and geographic history. No single test works for every animal. That is why the familiar rule that … Read more
Species, genus, family, and order are taxonomic ranks used to organize animals into nested groups. A species is usually the most specific standard rank, a genus contains one or more closely related species, a family contains related genera, and an order contains related families. Moving upward through the hierarchy creates broader groups that include more … Read more
Warm-blooded animals produce and retain much of the heat needed to keep their bodies within a useful temperature range. Cold-blooded animals depend more heavily on heat moving between their bodies and the environment. Biologists usually call these strategies endothermy and ectothermy, because the familiar labels can be misleading. An ectothermic lizard basking on a rock … Read more
Mammals, birds, reptiles, amphibians, and fish are all vertebrates, but they solve the challenges of breathing, temperature control, reproduction, movement, and water balance in very different ways. Mammals have hair and produce milk. Birds have feathers and lay hard-shelled eggs. Nonavian reptiles have keratinized scales and amniotic development. Amphibians usually have permeable skin and life … Read more
The simplest difference between vertebrates and invertebrates is that vertebrates belong to the animal lineage with a vertebral column, while invertebrates are animals outside that lineage. A dog, eagle, frog, salmon, and snake are vertebrates. A butterfly, earthworm, octopus, sea star, coral, and sponge are invertebrates. That quick rule is useful, but it does not … Read more
Scientists classify animals by comparing many kinds of evidence, not by choosing one obvious feature such as size, habitat, color, or whether an animal can fly. They examine body structures, development, behavior, ecology, fossils, proteins, and DNA. They then test which grouping best explains the pattern of shared traits and common ancestry. Modern animal classification … Read more
The animal kingdom includes organisms as different as sponges, beetles, sea stars, sharks, frogs, eagles, and humans. Scientists place them together in Kingdom Animalia because they share a deep evolutionary origin and a broad set of biological features. Animals are multicellular eukaryotes, meaning their bodies are made of many cells with nuclei. They obtain energy … Read more
Animal memory is the ability to retain information from experience and use it later. It allows a chickadee to relocate hidden seeds, a dolphin to recognize a former companion’s whistle, a fish to repeat a learned choice, and a predator to avoid prey that was difficult or dangerous to capture. Memory is not one single … Read more
Crows are highly capable problem solvers, social learners, and long-term observers of their surroundings. Some can recognize individual people, learn which situations are risky, remember useful locations, and adjust their behavior when familiar strategies stop working. New Caledonian crows go further in a specialized domain: they manufacture hooked tools and can solve carefully designed multi-step … Read more
Dolphins are highly capable learners with strong social memory, flexible communication, sophisticated cooperation, and several locally learned foraging traditions. Those findings make them important subjects in the study of animal minds. They do not, however, provide a scientific basis for assigning dolphins a human IQ score or saying that a dolphin thinks like a child … Read more
