The enamel on our teeth isn’t the first place you’d think to look for hints about evolution. Yet, surprisingly, it reveals a lot about how our ancient ancestors and relatives are connected.
In a recent study published in the Journal of Human Evolution, we take a closer look at enamel, particularly its absence.
It turns out that the tiny, shallow pits found in fossilized teeth might not indicate something like malnutrition or illness. Instead, they could hold unexpected evolutionary significance.
You might ask why this is important. For researchers piecing together human evolution and our ancestors’ relationships, teeth are crucial. Identifying a new marker on fossilized teeth could help us better construct our family tree.
Consistent, shallow pitting
These specific pits were first noticed in Paranthropus robustus, a close relative of our own genus, Homo. They are quite remarkable for their uniform, circular, and shallow appearance.
Initially, we thought only P. robustus had these pits. However, our recent findings revealed similar pitting in other Paranthropus species across eastern Africa, and even in some Australopithecus individuals, which might have been ancestors to both Homo and Paranthropus.
People typically assumed these enamel pits were defects from stressors like illness or malnutrition during childhood. But the consistent patterns across species and time suggest that these pits might be more than just defects.
The pitting appears subtle and organized, usually clustered in certain areas of the tooth. Importantly, it presents without any other signs of damage or irregularity.
Tracing over two million years
We examined fossil teeth from hominins in the Omo Valley of Ethiopia, providing insight into over two million years of human evolution. We also compared these with teeth from various southern African sites such as Drimolen, Swartkrans, and Kromdraai.
The Omo collection features teeth attributed to Paranthropus, Australopithecus, and Homo, allowing us to track these notable pits across different branches of our evolutionary tree.
What we discovered was unexpected. The uniform pitting is frequently found in Paranthropus from both eastern and southern Africa and can also be traced back to the early Australopithecus teeth from about three million years ago. Yet, this pitting is conspicuously absent in southern African Australopithecus and our own genus, Homo.
Traits or defects?
If these uniform pits were indeed caused by stress or disease, we would anticipate a correlation with factors like tooth size and enamel thickness, affecting both front and back teeth. But that’s not the case.
Furthermore, stress-related defects typically form horizontal bands and impact all teeth developing during the stress. However, that isn’t reflected in this pitting.
We suspect this pitting most likely arises from developmental and genetic factors, possibly linked to changes in enamel formation. It could even serve an unknown function. Essentially, we’re proposing that these uniform pits should be recognized as a trait rather than a defect.
Modern-day comparisons
Supporting this idea is a rare condition in today’s humans known as amelogenesis imperfecta, which impacts enamel formation.
This condition affects about one in every 1,000 people, whereas we observe uniform pitting in up to half of the Paranthropus individuals. It seems too frequent to classify as a harmful disorder, especially since it persisted for millions of years.
A potential evolutionary marker
If this pitting does have a genetic basis, we might use it to trace evolutionary relationships.
We currently utilize various tooth features for identifying species, like enamel thickness and cusp shape. This uniform pitting might serve as another identifier.
For example, our findings suggest that Paranthropus forms a “monophyletic group,” indicating all its species evolved from a relatively recent common ancestor instead of developing separately from different Australopithecus taxa.
Interestingly, we did not find this pitting in the southern African species Australopithecus africanus, despite examining over 500 teeth. However, it does appear in the earliest specimens from Omo.
This could suggest the pitting might help identify where Paranthropus diverged on its evolutionary journey.
A fascinating example
A particularly captivating case is Homo floresiensis, the “hobbit” species from Indonesia. Images suggest their teeth may also exhibit similar pitting.
If that turns out to be true, it could indicate a closer evolutionary relationship with earlier Australopithecus species than with Homo. Still, it’s vital to conduct more research due to potential skeletal and dental conditions seen in H. floresiensis.
There’s plenty to investigate to clearly understand the mechanisms behind the uniform pitting before we can incorporate it into taxonomic work. However, our findings point to it likely being a heritable trait, not observed in any modern primates studied, nor in our own Homo genus, aside from rare cases of amelogenesis imperfecta.
So, in short, it presents an exciting new avenue for exploring evolutionary ties among ancient hominins.
