1. Overproduction: Within a population more offspring are born than can possibly survive.
2. Competition: Since the number of individuals in a population tends to remain constant from generation to generation due to limited resources, a struggle for survival occurs.
3. Survival of the Fittest: The individuals who survive are the ones best adapted to exist in their environment due to the possession of variations that best suit them to their environment. This genetic variability within a species is chiefly due to mutation and genetic recombination.The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions.
4. Reproduction: Variations assist or hinder individuals in their struggle for survival. The best adapted individuals survive and reproduce, passing on the favorable variations to their offspring.
5. Speciation: As time and generations continue, adaptations are passed on and new species may evolve from a common ancestor. Small differences between parents and offspring can accumulate in successive generations so that descendants become very different from their ancestors.
An adaptation is a variation which assists an organism or species in its survival. Biological adaptations include include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.
Some characteristics give individuals an advantage over others in surviving and reproducing, and the advantaged offspring, in turn, are more likely than others to survive and reproduce. The proportion of individuals that have advantageous characteristics will increase.
Behaviors have evolved through natural selection. The broad patterns of behavior exhibited by organisms have evolved to ensure reproductive success.