Evolution is the process by which this occurs and it is spread out over many generations. Thus, the short minimal definition of biological evolution is, Evolution is a process that results in heritable changes in a population spread over many generations. This is a good working scientific definition of evolution; one that can be used to distinguish between evolution and similar changes that are not evolution.
Bone, cartilage, or dentine is used in the Ostracoderm fish and turtles. Chitin forms the exoskeleton in arthropods including insects, arachnids such as spiders, crustaceans such as crabs and lobsters (see arthropod exoskeleton), and in some fungi and bacteria. Calcium carbonates constitute the shells of molluscs (see Mollusc shell), brachiopods, and some tube-building polychaete worms.
1 chitin Hard and tough natural material made from glucose molecules joined together. 2  Chitin is found in cell walls of fungi and in the exoskeletons of arthropods. 3  chloroplast Contains the green pigment chlorophyll; the site of photosynthesis. cell Basic unit of life. 2  Unicellular organisms only have one cell. 3  Multicellular organisms have many cells. 4  chitin Hard and tough natural material made from glucose molecules joined together. 5  Chitin is found in cell walls of fungi and in the exoskeletons of arthropods.