Over the long period of time that life has existed on Earth, there have been a number of important or significant innovations including (but not limited to) endosymbiosis to create mitochondria and chloroplasts; multicellularity; adaptation to land by plants and animals; development of exoskeletons in arthropods, shells in molluscs, and notochords followed by vertebral columns in chordates and vertebrates; and bipedalism in the ancestry of humans. All of these had to come about by natural selection in response to changing environmental forces.
Pick one of these significant innovations and describe:
How the innovation appears to have happened
What environmental challenges were met and overcome by this innovation, and
What opportunities were opened for the organism that made this innovation.