Question

Use the 9 steps of evolution by natural selection to explain how the body type of Homo erectus & heidelbergensis (both had very similar bodies) could then change to a Homo neanderthalensis body.

Begin with a specific morphological change in the body of a Homo heidelbergensis, combined with the relevant selection pressures and adaptive benefits, to work your way through each of the nine steps to explain the evolution of Neandertals.

Answer 1

The most well-known late archaic humans were the Neandertals . More Neandertal skeletons have been found than any other ancient human species. They lived in Europe and Southwest Asia from at least 130,000 years ago until around 28,000 years ago. This is in the late Pleistocene Epoch. It is likely that the Neandertals evolved from Homo heidelbergensis in Southern Europe. Neandertal-like skull characteristics have been found in 400,000 year old fossils from Spain. The Neandertals adapted physically and culturally to the ice age conditions that prevailed during much of their time.

No other ancient people have aroused more controversy and confusion over the last century and a half than have the Neandertals. There is an on-going debate as to whether they should be considered Homo sapiens. If they were members of our species, they were a different variety or race (Homo sapiens neanderthalensis). On the other hand, if they were dissimilar enough to be a distinct species, they should be called Homo neanderthalensis

The first discovery of Neandertal bones may have been during the late 1820's in Western Europe. Subsequently, other, better documented Neandertals were found and stored in museums without being recognized as early forms of humans. In 1839, for instance, a portion of a child's skeleton was found in Engis, Belgium. In 1848, an adult female skull was found at Gibraltar, at the southern tip of Spain.

In 1856 a discovery was made in Germany that finally sparked the recognition that these were, in fact, not just strange looking modern people. This was the discovery of a skull and a number of other bones from a limestone cave deposit in the small Neander River Valley near Dïüsseldorf. Thinking that they were from a bear, the quarrymen gave them to a local school teacher and amateur naturalist, Johan Karl Fuhlrott . He recognized them as being human but somewhat different from those of modern Europeans. When several leading paleontologists and medical pathologists in Germany became aware of the fossils, a disagreement developed about who the "Neandertal Man" might have been. It was suggested that he had been an old Roman, a Dutchman, and even a Central Asian soldier in the service of the Russian czar during the Napoleonic wars of the early 19th century. The reality that these bones were from an earlier variety or species of human was not yet conceivable to most of the scientific world in the 1850's.

What finally convinced the scientific community that Neandertals were very ancient Europeans was a combination of additional fossil discoveries and new perspectives that largely began with the publication of Charles Darwin's On the Origin of Species in 1859. This seminal work in biology popularized the idea that species of living things evolve over time as a result of natural selection. Subsequently, it was not a major leap in understanding to realize that humans also must have evolved from earlier forms. In fact, Darwin proposed just that in his 1871 influential publication The Descent of Man, and Selection in Relation to Sex. For enlightened Victorians, the Neandertals ultimately came to be seen as important human ancestors. They were given the name "Neandertal Man" in 1864 by William King, an Irish anatomist. He named them after the Neander River Valley (or Tal, in German).

In 1886, two Neandertal skeletons were found in a Belgium cave site named Spy. These specimens were physically associated with stone tools and food refuse bones from extinct ice age animals. This evidence once and for all demonstrated that Neandertals were not modern people. As a result, the majority of European paleontologists in the late 1880's finally accepted them for what they really were.

The Neandertals were physically diverse, but in general they were larger boned and more heavily muscled than most modern humans. This was particularly true of the European Neandertals, like the La Chapelle-aux-Saints man. Some of the Southwest Asian Neandertals were less robust in appearance and somewhat more like modern humans. The Neandertals were relatively short and stocky compared to some other archaic humans and modern Europeans. Adult male Neandertals averaged 5 feet 5 inches tall (164 cm.) and 143 pounds (65 kg). Females averaged 5 feet 1 inch tall (155 cm) and 119 pounds (54 kg). They probably stood as erect as we do and were fully bipedal. They were not only strong but apparently quite flexible. The thickness and high density of their leg bones suggest that they did a great deal of walking and running. Their lower arm and leg bones were short compared to modern humans. These traits were likely adaptations to an aggressive hunting and gathering way of life as well as to the cold climates in which most Neandertals lived. The fact that adult Neandertal skeletons frequently have multiple healed bone fractures suggests that these people had rough lives. Some researchers believe that many of the broken bones were the result of hunting large game animals up close with jabbing spears--a dangerous enterprise.

It is likely that at least some Neandertals had pale skin color and red hair. This is based on the discovery of a variant of the MC1R gene associated with these traits in the bones of two European Neandertals dated to around 50,000 years ago. This was very likely an adaptation that helped their bodies produce more Vitamin D and subsequently absorb more calcium from their food in ice age Europe.

Neandertal heads were long (from front to back) compared to ours. This resulted in relatively low, sloping foreheads. At the back of their skulls, they had a prominent bulge or projection called an occipital bun . They had large faces (especially in the middle part) with big noses and prominent brow ridges that extended between the eyes.  They lacked the pointed chin that is common in modern Homo sapiens. These traits give the Neandertal face and head an appearance more reminiscent of late Homo erectus and Homo heidelbergensis than of modern people.  

Most researchers agree that modern humans and Neanderthals interbred, though many believe that sex between the two species occurred rarely.

These matings introduced a small amount of Neanderthal DNA into the human gene pool. Today, most people living outside of Africa have trace amounts of Neanderthal DNA in their genomes.

People of European and Asian descent have an estimated 2 percent Neanderthal DNA. Indigenous Africans may have little or no Neanderthal DNA. That’s because the two species did not meet—and mate—until after modern humans had migrated out of Africa.

Some of the Neanderthal genes that persist in humans today may influence traits having to do with sun exposure. These include hair color, skin tone and sleeping patterns.

Neanderthals had been living in Europe and Asia for hundreds of thousands of years when modern humans arrived. Neanderthals were already adapted to the climate of Eurasia, and some experts think Neanderthal DNA may have conveyed some advantage to modern humans as they exited Africa and colonized points north.

Neanderthals went extinct in Europe around 40,000 years ago, roughly 5,000 to 10,000 years after first meeting Homo sapiens. There are several theories for their extinction.

Around 40,000 years ago, the climate grew colder, transforming much of Europe and Asia into a vast, treeless steppe. Fossil evidence shows that Neanderthal prey, including wooly mammoths, may have shifted their range further south, leaving Neanderthals without their preferred foods.

Humans, who had a more diverse diet than Neanderthals and long-distance trade networks, may have been better suited to find food and survive the harsh, new climate.

Some scientists believe that Neanderthals gradually disappeared through interbreeding with humans. Over many generations of interbreeding, Neanderthals—and small amounts of their DNA—may have been absorbed into the human race.

Other theories suggest that modern humans brought some kind of disease with them from Africa for which Neanderthals had no immunity—or, modern humans violently exterminated Neanderthals when they crossed paths, though there’s no archeological evidence that humans killed off Neanderthals.