In January of 2007 assemblages had been found that showed evidence that Neanderthal people and humans had been mixing their genetic material for quite sometime about 28,000 years ago.
Please floow this link to an old article within National Geographic.
https://www.google.com/imgres?imgurl=https://s.ngeo.com/wpf/media-live/photos/000/199/cache/neanderthals-interbreeding-humans_19941_600x450.jpg&imgrefurl=https://news.nationalgeographic.com/news/2010/05/100506-science-neanderthals-humans-mated-interbred-dna-gene/&usg=__wg0ens0VAw3lEJHGLW1YBdNyQl8=&h=450&w=583&sz=36&hl=en&start=20&itbs=1&tbnid=vFPR-xCFUTktBM:&tbnh=103&tbnw=134&prev=/images%3Fq%3Dneanderthals%2Bpictures%26hl%3Den%26gbv%3D2%26tbs%3Disch:1
If you enlarge and study the image of the skull on the Geographic site you will see that the eyebrows of the assemblage is quite robust. Now take a look at the molars in the skull. They too are quite larger than normal.
It has been said that humans who looked the way we are now, alled Cromagnon, came up out of Africa and settled for a time in Turkey where they "regressed" by mating with the older species known as Neanderthal.
That theory might be very off because no one has ever thought that the Neanderthal might have been much younger than we were at the time as a species.
Neanderthal left behind burials that had been dusted and sprinkled with mineral colors. The people who had buried their loved ones also left behind flowers, much like we do today during a funeral. They also took the time to bury their beloved tribal member with their tools. If you really think about it, Neanderthal people were quite compassionate beings and they might not have been so "regressed" or primitive as we make them out to be. They cooperated with one another to bring down large game just like Cromagnon did. This means that they had a social order going for them as well as a tribal mode of life.
Within the old word of mouth stories within the American Indian tribes there is recalled a time before when the ice covered the plains, rivers and mountains. The indifenous people worked hunted and lived during the time of the great ice age. This is something that we can't dismiss. The law passed by the united nations states that we all have to respect and honor tribal history that has been passed from person to person by word of mouth. People who lived during the last ice age were already a mixture of Neanderthal and Cromagnon.
Nature as we know it is a benevolent being. There are unspoken rules within it that we all have to follow so that we may survive in what has been called by civilized men and women as a hostile environment.  It has also been discovered that inbreeding amongst animals and humans is detrimental to a particular species when they are isolated within a specific environment. It seems that nature has laid out a healthy genetic plan that includes geneatic variation so that a species will survive within any given environment. So logically diversity is the key word here.
When we look at Neanderthal people we call to mind a well built human being that was able to bring down large game. Musk ox, elephants and wild horses. The climate as well as the atmosphere were conducive to animals that had evolved to be very large in their stature it would make sense that Neanderthal people would also evolve to become very robust and strong like their prey were. The protein and bone marrow they eventually consumed worked to enhance the material in their brains so that their reaoning and logic would be well adapted to their harsh environs.
Their tool making was quite advanced and it was on the level of being sophisticated enough to be compared to sculpture, When working a piece of stone, marble, quartz or flint one has to take into consideration the faults within that stone while fracturing and working it into a tool. The thought processes involved have to be very keen and not brutish.
As genetic material of Cromagnon and Neanderthal mixed one can assumed that our autonomic evolutionary processes worked to derive and keep the best of both species of people in place so that the species that would arise from that genetic mixing would become better and finer than the older species it had been born from. As the climate changed so did humanity so they could adapt to their new abode. Nature shrugged and tugged at herself to make the necessary adjustments when the ice age fell away from the planet. Creatures over the planet became smaller and smarter so they could survive and adapt. Those species that were old never really died off like we all assume. They, like the Neanderthal were absorbed into the genes of the new species.
You see, nature never wastes anything. Everything is recycled within her domain. Its a lesson that we all still have to learn.