Adaptation: any trait that helps an organism survive and reproduce. Structural adaptations: physical features of an organism designed to increase reproduction and survival. (ex. bill on a bird, or fur on a bear) Behavioral adaptations: things that organisms do to survive. (ex. Physiological adaptations: permit the organisms to perform special functions (ex. making venom) and more general functions such as growth and development and homeostasis. Suggested that species are not fixed, but change over time. If the organ is used it is enlarged, if not it decreases, and is passed on. Wrote the origin of species after 23 years of research. Suggested that the main mechanism of adaptation is natural selection. Natural selection: the process by which the individuals in a population that have the characteristics best suited to the environment survive and reproduce better than the others. Adaptation: competition: theory that population has the ability to increase rate. Reality: increases, then plateaus, because resources are limited.