Darwin's theory of evolution states that evolution happens by natural selection. According to the evolutionary theory, the genes that allow a species to thrive are passed down from parent to offspring. Individuals of a particular species often have a wide range of variation and this variation occurs because of a difference in genes. Any individuals that possess the characteristics that will help the species thrive and survive in a particular environment will be the ones to reproduce.
Only the strongest survive long enough to reproduce. Over the years, those species that reproduce will continue to evolve, while those that are poorly adapted to their environment will eventually go extinct.
Humans survived to get to where they are today thanks to the ability to adapt and evolve to their environment. Since the first hominids appeared on the planet three million years ago, the species has continued evolving and eventually became the humans of today. Homo sapiens have only been around for about 200,000 years and they change and evolve with every new generation. According to Darwin's theory of evolution, any species that cannot deal with things like climate change will not survive.