<span>A tiger looks so much different as an adult than it did as a single fertilized egg because it developed through different stages from being a zygote (fertilized egg), to becoming an embryo (where it experiences intense cellular changes), to becoming a fetus (where it gains a great measure of cell specialization, and develops distinct tissues and organ systems). After birth, the tiger still undergoes further growth and development into adulthood. This is largely regulated by the expression of different genes at different times and also by environmental factors.</span>
A tiger looks differently from the way it looked as a single cell because the cells split and make new cells, causing the life form to grow in size. Along with these cells come more genes, each varying due to purpose. To think, that a fully grown tiger started as a single cell, and is now much larger.
If they didn't adapt, they couldn't survive in the changed environment. Because abiotic factors determine the kind of organisms that are able to live in certain conditions.
