Depending on the scope and therefore the source, the Neanderthal is housed in the genus Homo and species sapiens.The modern man is called Homo sapiens sapiens (the second sapiens covers the subspecies).The Neanderthal becomes then Homo sapiens neanderthalensis.
A different object is that Homo sapiens and Homo neanderthalensis are separate species.The fact that they are both of the same sex (and in the previous case also species) increases the likelihood of hybrisions. This would be evidenced by recent genetic research in the modern man where Neanderthal DNA was found.
Back to the essence of the question.Considering we cannot return in time these are common speculations.
From Wikipedia :
In Byzovaja in the Komi Republic , a team of scientists led by Ludovic Slimak found the most recent site of the Neanderthal.
Neanderthals must have lived in this region until about 26,000-20,000 years ago.It is not only the youngest, but also the northernmost habitat of the Neanderthal. Byzovaja is located at the same latitude as Iceland.
In Europe The Neanderthal disappeared about 32,000-34,000 years ago.At the southern edges of the Iberian Peninsula, including Gibraltar, the Neanderthal has been able to maintain several thousand years longer. 91
The last Neanderthals in Europe, so far known, lived in Gibraltar at least 39,000 years ago.
However, that Gibraltar was the last place in Europe where Neanderthals could maintain itself is doubted by other archaeologists.They suspect that the findings are rather the result of the very intensive archaeological research carried out by the English on such a small surface.
The question is why the Neanderthals, despite their great brains, their ability to hunt down large and dangerous prey animals and survive at least two glacials, eventually become extinct.
Perhaps this has to do with a slight reproductive drift, which could have an impact on so-called population bottlenecks.These were not uncommon in the history of mankind, and may also have influenced the Neanderthals.
Modern man was rather sexually mature and had more offspring.
Researchers estimate that a female Neanderthal woman gave birth to a child only once each four years.This was possibly one of the reasons why perhaps no more than a few thousand Neanderthals have lived at the same time. Statistical population models show that small percentage differences in birth and mortality are enough to allow a small group to extinction in a few thousand years.
In 2009, an international team of researchers from the Max Planck Institute for Anthropology published a genetic comparison study of Neanderthals.It was previously assumed that 30,000 years ago about 50,000 Neanderthals lived in Europe, now it is assumed that there were only about 10,000. Such a small population can easily be wiped out by disease or food shortages.
In addition, his choice of food may have been a cause.As a meat eater he mainly ate meat from large prey animals. By the end of the last ice age, however, many species of animals died, including, for example, the woolly mammoth, woolly rhinoceros, giant stag and cave Bear.
Another model relates to volcanic eruptions that took place around 40,000 years ago.An investigation conducted by Lyubov Vitaljeva Golovanova and Vladimir Borisovich Doronitsjev of the ANO Laboratory of Prehistory in St. Petersburgsuggests that the Neanderthal is partly due to a volcanic eruption Extinct.
The effects of these volcanic eruptions on the ecology of large parts of Europe were destructive.
The earth layers in which the axis was found contain evidence of sudden and potentially devastating climate change.Compared to surrounding layers, the sediment samples of the two layers contain strongly decreased pollen concentrations. That is indicative of a sudden shift to a cooler and/or drier climate.
The second of the two eruptions seems to mean the end of the Neanderthal presence in the Cave of Mezmaj (Northern Caucasus).Numerous Neanderthal bones, stone tools and bones of prey are found in the earth layers beneath the second ash layer, but not above. The ash layers are chronologically similar to what is known as the Neapolitan ignimbrite superburst (The Neapolitan ignimbrite is a huge caldera called Campi Flegrei, or the Flegrean fields) , which took place about 40,000 years ago in contemporary Italy, and a smaller eruption happened around the same time in the Caucasus Mountains.The researchers argue that these eruptions caused a “volcanic winter” when ash clouds dared the sun for years. The climatic shift disrupted the regional ecosystems, causing prey, predators and hominids to perished massively.
The idea that the Neanderthal man died because he had a lower life expectancy compared to modern humans was disproved by the anthropologist Erik Trinkaus .
In His studies he shows that the Neanderthal and modern man were about the same age.In both human species, almost no individuals are found that are older than 40.
Between the anatomic modern man and the Neanderthal, there was perhaps a direct competition for space and resources.
In addition, the anatomically modern man had a strong competitive advantage over the Neanderthals: he was able to use a demonstrably more complex technology and organization.This competitive pressure may have been due to the strong increase in the population of modern human beings, which, according to a study by Paul Mellars and his colleagues, occurred some 40,000 years ago.
This increase in population contributed to the penetration of Neanderthals.Modern man would have brought diseases against which the Neanderthal had no resistance. Conversely, Neanderthal genes gave resistance to certain diseases.
A research team of geneticists, paleontologists and statisticians established in 2011 that modern man did not play the leading role in the extinction of Neanderthal people.
When modern man pulled from the Middle East to Europe from 50,000 to 40,000 years ago, he met a Neanderthal population who was already disappearing.This finding is derived from the comparative study of the mtDNA of Neanderthal bones of 13 people from all over Europe. The mtDNA is inherited by the mother. This is to reconstruct the family tree in the motherly line. While the 55,000 year-old Neanderthal bones indicate that there was a large variety of genetic ancestors, the bones of younger date show that there has been a genetic impoverishment. A phenomenon that occurs when a species is extinct. The researchers point out that the Neanderthals have been decimated by climate change during the last ice age. The low birth rate apparently also played a role in extinction.
For the references: please consult the page on Wikipedia .