If you do uncertain things like smelling markers, it can kill your brain cells, your organs,cells, and your other cells. Stem cells are cells in the body that have the potentials turn into anything. Cells form tissues, tissues for organs, organs form systems, and the systems work together to keep us alive! We have all adapted to earth's climate. Aliens would most likely not look like us because their environment would likely be very different. What changes would likely need to happen on humans if gravity was 4 times stronger? More air. What changes would likely need to happen on humans if oxygen was 5 times more scarce? Probably our world would have to be bigger.I think that they had to adapt to the world by being able to breathe and eat.