The species most widely regarded as the direct ancestor of Neanderthals is Homo heidelbergensis, a large-brained hominin that lived in Africa and Europe roughly 700,000 to 300,000 years ago. Neanderthals didn’t appear suddenly. They evolved gradually over hundreds of thousands of years as populations of these earlier humans became isolated in Europe and shaped by repeated ice ages.
Homo heidelbergensis: The Leading Candidate
Homo heidelbergensis was first identified in 1908 after the discovery of a distinctive jawbone near Mauer, Germany, now dated to roughly 609,000 years ago. The prevailing model holds that around 700,000 years ago, a population of these hominins dispersed from Africa into Europe. Once established on the European continent, that branch gradually evolved into Neanderthals, while the African branch eventually gave rise to modern humans. This makes Homo heidelbergensis a shared ancestor of both lineages.
Mitochondrial DNA comparisons place the last common ancestor of Neanderthals and modern humans between 550,000 and 690,000 years ago, which aligns well with the fossil evidence for Homo heidelbergensis. Fossil and genetic evidence together suggest Neanderthals and our species diverged from this common ancestor somewhere between 700,000 and 300,000 years ago, a wide window that reflects genuine scientific uncertainty about exactly when the split became permanent.
Homo heidelbergensis isn’t the only candidate, though. At least five species have been proposed as the last common ancestor, including Homo erectus (a much older and more widespread species), Homo antecessor (known from 1.2-million-year-old fossils in Spain), and several African species. But Homo heidelbergensis has become the focus of most modern debates because its anatomy, geography, and timing fit the evolutionary story most neatly.
What the Fossils Actually Show
One of the most important windows into this transition comes from a cave site in northern Spain called Sima de los Huesos, or “Pit of Bones.” The site contains remains of at least 28 individuals dating to around 430,000 years ago, placing them squarely in the period when Homo heidelbergensis populations were becoming more Neanderthal-like. These skulls show a striking mix of features: primitive traits that later Neanderthals had already lost (especially in the braincase), transitional features in the back of the skull, and characteristics that look fully Neanderthal, like heavy brow ridges and a face that juts forward in the middle.
This mosaic pattern is exactly what scientists would expect if Neanderthal features accumulated piece by piece over many generations rather than appearing all at once. The Sima de los Huesos fossils represent a population caught mid-transition, not yet Neanderthal but no longer quite Homo heidelbergensis either. The earliest fossils classified as Homo neanderthalensis date to about 400,000 years ago, and the species persisted until roughly 40,000 years ago.
How Europe’s Ice Ages Shaped Neanderthals
The transformation from Homo heidelbergensis into Neanderthals wasn’t driven by time alone. It was pushed along by Europe’s increasingly extreme climate. Around 600,000 years ago, a shift scientists call the “Middle Pleistocene Revolution” dramatically increased both the intensity and duration of glacial and interglacial cycles. Ice sheets expanded farther south, permafrost spread, and sea levels dropped enough to reshape coastlines and expose continental shelves.
During the worst cold periods, large portions of Europe became uninhabitable, forcing hominin populations into shrinking southern refuges in Iberia, Italy, and the Balkans. When the ice retreated, survivors recolonized the emptied landscapes. This cycle of isolation, population crashes, and recolonization created genetic bottlenecks that accelerated evolutionary change. Small, isolated groups are far more susceptible to genetic drift, where random changes become fixed in a population simply because there aren’t enough individuals to dilute them. Over many cycles, this process drove the European population further and further from their African relatives.
Neanderthals’ stocky builds, broad ribcages, and shorter limbs are often interpreted as adaptations to cold stress. The fossil record suggests the cold episodes that triggered these distinctive features likely predate 400,000 years ago, with some researchers proposing that the severe glaciation known as OIS 6 (around 190,000 to 130,000 years ago) was catalytic in producing “classic” Neanderthal anatomy. But skull fossils from slightly before that period already show most Neanderthal braincase features in place, meaning the process started considerably earlier.
Neanderthals and Denisovans: Sister Species
Neanderthals weren’t the only species to branch off from this ancestor. Genetic sequencing of Y chromosomes from both Denisovans and Neanderthals reveals that the Denisovan lineage split off around 700,000 years ago from a lineage that Neanderthals and modern humans still shared. The Neanderthal and modern human Y chromosomes then diverged from each other around 370,000 years ago. This means Denisovans, the mysterious hominins known mainly from a few bones found in a Siberian cave, were essentially Neanderthals’ sister species, both descending from the same ancestral population but taking different evolutionary paths in different parts of Asia and Europe.
How Early Humans Reached Europe
Before Homo heidelbergensis could evolve into Neanderthals in Europe, earlier hominins had to get there first. The oldest securely dated evidence of human presence in Europe comes from Korolevo in western Ukraine, dated to 1.4 million years ago. This site bridges a gap between the earliest known hominin sites in the Caucasus region (around 1.85 to 1.78 million years ago) and southwestern Europe (around 1.2 to 1.1 million years ago), supporting the idea that Europe was colonized from the east.
These early colonizers exploited warm interglacial periods to push into higher latitudes. They were likely Homo erectus or a closely related species, and they represent the deep backstory that eventually led, hundreds of thousands of years later, to the arrival of Homo heidelbergensis and the slow emergence of Neanderthals. A major new wave of migration from Africa around 600,000 years ago, coinciding with enhanced glacial and interglacial cycles, likely established the populations that became the direct ancestors of Neanderthals.
Fire and Tools Before Neanderthals
The ancestors of Neanderthals were not simple creatures waiting for evolution to refine them. Evidence of controlled fire use stretches back surprisingly far. Sites in Kenya dating to around 1.5 million years ago preserve burnt sediments and heat-altered stone tools. By around 1 million years ago, sites like Wonderwerk Cave in South Africa show vegetation and bone deliberately burned deep inside a cave, far from where natural wildfires could reach. The important site of Gesher Benot Ya’aqov in Israel, dating to about 700,000 years ago, preserves burnt materials at numerous levels across a 30-meter sequence, with clusters of burnt flint marking out the footprints of ancient hearths.
By the time Homo heidelbergensis was established in Europe, fire use was likely a regular part of life. The site of Zhoukoudian near Beijing, associated with Homo erectus activity between 400,000 and 700,000 years ago, preserves burnt bone alongside more than 100,000 stone tools. These weren’t one-off events. The repeated associations across multiple sites and time periods point to populations that understood and relied on fire, a skill they would pass down to their Neanderthal descendants.