In 2002 Gerard Gierlinski, a Polish Geological Institute paleontologist, was enjoying a holiday on the Greek Mediterranean island of Crete. While he was there, Gierlinski decided to explore the village of Trachilos, on the coast near the town of Kissamos. And during that visit, he stumbled across a mysterious set of some 50 footprints imprinted on the rocky beach. At the time, he categorized the footprints simply as mammalian. But subsequent studies of them led to conclusions that in scientific terms are incendiary.
It was 2010 before Gierlinski and a colleague returned to Trachilos to further examine the footprints, in fact. And several more years passed before they published a paper outlining what they’d learned. One important finding that the 2017 paper included was the age of the footprints – a staggering 5.7 million years.
The age of the footprints had been established by analyzing tiny fossils in the rocks called foraminifera. These tests can provide an accurate dating of sedimentary layers of rock. And those particular footprints lay just below a layer created 5.6 million years ago, when the Mediterranean Sea completely disappeared for a time.
Although remarkable, the age of the prints was uncontroversial. But what did prove to be extremely contentious were the conclusions that the paper made about what animal had made the footprints. The scientists reported that there were two tracks – and that they had been made by a creature that walked on two legs and stood vertically.
And this information led the scientists to make the controversial claim that the animals that had walked on these sediments 5.7 million years ago were hominins. This is the modern term that scientists use to describe all types of humans and their immediate ancestors, including those that are now extinct. Neanderthals, for example, are classed as hominins.
But why is this identification of 5.7 million-year-old hominin footprints on a Cretan beach so controversial? Well, the answer to that lies in the overwhelming consensus about the emergence of Homo sapiens that has held sway for decades in the world of paleoanthropology.
The accepted scientific theory of human evolution is that we evolved in Africa and spread out from there across Europe, Asia and ultimately the rest of the world. Ever since quarry workers in South Africa discovered a fossilized skull with humanoid features in 1924, it’s been believed that all modern humans can ultimately trace their lineage back to Africa. And these early pre-humans are known as Australopithecus africanus.
Subsequent discoveries of other hominin fossils, especially in East Africa, added to the scientific evidence supporting the out-of-Africa theory. The Laetoli site in Tanzania, for example, yielded footprints of a hominin which was dated to 3.6 million years ago. These footprints closely resemble those of modern humans. This is the earliest instance of bipedal hominins so far found.
Other fossil discoveries were made at Hadar in Ethiopia, and the early human-type species there and at Laetoli have been given the name Australopithecus afarensis. Some 300 specimens of this species have now been found in Africa, and they lived between three and four million years ago. In fact, they were around for at least 900,000 years – a lot longer than Homo sapiens has been.
The footprints found on that Trachilos beach have been dated to 5.7 million years ago, however. And therein lies the controversy. Previously, it has been believed that hominins first left Africa much later than that. But if that is the case, then how did these footprints appear on the Cretan coast?
In fact, accepted scientific theory puts the time of the first migration by our human ancestors from Africa at some two million years ago. For instance, a hominin species called Homo ergaster was in Eurasia by about 1.7 million years ago. At around the same time, Homo erectus had settled in South-East Asia. But that, of course, is nearly four million years later than the Trachilos footprints found by Gierlinski in 2002.
Even if we accept that the dating is correct, which with modern techniques seems likely to be the case, how do we know that these footprints were made by early ancestors of the human race? Well, the evidence lies in the shape of the prints.
The first sign that these Cretan prints could belong to our hominin ancestors is that the creatures that made them clearly walked on the soles of their feet rather than on their toes. Moreover, the impressions of the toes in the sedimentary rocks also hold vital clues.
There are clearly five toes in the footprints, and one of those is more developed than the others, just like the big toe that modern humans have. As well as that, there is no sign of claw marks, which indicates that these creatures had toenails rather than claws.
However, the shape of the footprints does not necessarily provide conclusive evidence that the animals who made them were hominins. An alternative view of the prints posits that they could belong to an ape, not one of the hominins related to us. This theory suggests that the creatures perhaps walked upright only occasionally.
And there is a wealth of archaeological evidence showing that there were apes living in Europe around the same time as the footprints were created in Crete. In fact, the fossil record for great apes stretches back 13 million years, to an extinct species called Pierolapithecus. The bones of this species, which were discovered in Spain, show that it may have been able to walk upright.
In an article in The Conversation, Matthew Robert Bennett and Per Ahlberg, two of the team that published the Trachilos paper, wrote, “If – and for many it is a big if – the tracks of Trachilos were indeed made by an early human ancestor, then the biogeographical range of our early ancestors would increase to encompass the eastern Mediterranean.”
And Bennett and Ahlberg went on to point out that earlier in 2017, another paper described possible hominin fossil teeth discovered in Greece and Bulgaria that were said to be seven million years old. These teeth, it was suggested, could show that humans started to evolve in Europe hundreds of millennia before they did in Africa.
Bennett and Ahlberg say they are skeptical of this claim, however, which would turn current human evolutionary theory on its head. But the two scientists do believe that all of this evidence could be an example of the well-documented phenomenon of divergent evolution. They describe this as “two unrelated animals developing similar anatomical features as adaptations to a particular lifestyle.” In other words, the teeth and feet may belong to animals not actually part of the human lineage.
So, these European discoveries suggest a possible hominin presence earlier than that so far found in Africa. Nonetheless, the evidence has certainly not convinced most scientists that we need to re-write our text books just yet, and perhaps it never will. That won’t stop it from being talked about, however. As Professor Ahlberg told Sci News, “This discovery challenges the established narrative of early human evolution head-on and is likely to generate a lot of debate.”