Finally, we come back to the beginning: climate change. Climate change 2 million years ago enabled human development. Our ancestors had a long time until natural selection produced the prototype Homo sapiens. A special feature of human development was the ability to adapt to almost all climate zones.We have had just over 200 years of artificial climate change to date. This time is hardly enough for a possible adapted phenotype (heat tolerance, humidity, ozone, etc.) to be already subject to natural selection. The effects of climate change on human health are manifold and range from previously unknown tropical diseases and hygiene problems to an increasing scarcity of food. Heat directly affects our brain and will increase processes there that, in turn, favor the development of dementia. The high mortality rate among older people during the heat wave of 2003 in Europe is a further challenge not only for care but for everyone. Are we moving back in the direction from which we came? Observations that the human brain is losing volume indicate this, although no hard evidence exists.