Final answer:
Neanderthals disappeared due to a combination of factors including climate change, competition with Homo sapiens, low genetic diversity, and interbreeding which led to the absorption of Neanderthal genes into the modern human gene pool. Their smaller, scattered groups and inability to adapt as efficiently as Homo sapiens contributed to their decline.
Step-by-step explanation:
According to the PBS video, the Neanderthals disappeared because they faced various challenges such as climate change, competition for resources with modern humans (Homo sapiens), the spread of diseases, and potential conflicts. Modern humans were better at adapting to environmental changes with more complex technology and language skills; they also tended to live in larger groups than Neanderthals, who had low genetic diversity and lived in small, scattered groups which could have been a disadvantage. Additionally, there was interbreeding between Homo sapiens and Neanderthals as early humans spread out from Africa, which may have led to the gradual absorption of Neanderthal genes into the modern human gene pool. The Neanderthal population dwindled due to these factors, weakening their presence until they vanished around 40,000 years ago.
Climate change in Europe may have introduced variations that were especially challenging for the Neanderthal population. However, it is widely acknowledged that no single theory can account for their disappearance entirely. It is more likely that a combination of factors contributed to the decline and eventual extinction of Neanderthals.