The story of the study of human evolution, if you will, has always been about finding features that seem to set us apart from other animals, right? Our large brains. Our tool-making behaviour. The fact we walk on two legs. The fact that we have very small upper canines. These are features that are distinctive for us compared to other humans and apes, and other animals. And so generally, without a fossil record, it’s easy to think that that package of features evolved together. That somehow they’re all interrelated. And yet the fossil record has continuously shown us that it’s not the case. Many of these features evolved independently at different times and places.
And it’s just in more recent evolutionary times that they’ve come together in the package that we recognise in us. So for instance, we see hominid bipeds that are three million years old and have essentially been bipedal for several million years, and yet they still retain small brain sizes. We see hominins with small brains making and using tools very early. And so tool use actually comes well before the expansion of the brain as well. Backwards to how paleo anthropologists predicted it 100 years ago before having a fossil record.
So Homo floresiensis underscores that again because it shows us that even though we had built up this model of how some of these features evolved and ultimately led to us, we see that in another sister lineage, if you will, those changes didn’t occur. And they weren’t necessary for their survival on Flores for likely as long as a million years. And that’s really remarkable because it expands our view of what does it really mean to be human? We have our view, but it’s a very Homo sapiens view.
And yet we have to now recognise that there were other humans living on this planet that overlapped with our species that were actually human in a very different way, in a very foreign way compared to what we conceptualise as what that means. With this one partial skeleton, we see it all in one package. And there’s an amazing amount of information that’s preserved in the anatomy. So for instance, within the cranium, again we can see that the canines are small, is a hominin characteristic. We also see the foramen magnum is tucked– this is the area for the spinal cord. It’s tucked underneath the skull, not positioned more posterior like it is in a quadruped.
So even from the cranium itself here we can see that this is unequivocally a hominin, meaning it’s more closely related to us than to chimps and gorillas. The brain is remarkably small we still see some constriction behind the orbits where the cranium is narrowed. Modern humans, we don’t have that. Essentially the sides of our cranium come on the sides of our orbits. You can also see from the back of the skull that it’s widest at its base, and it’s much narrower up top. This is where we and Neanderthals differ. Where the upper part of our cranium has become expanded.
So it’s really the frontal part and the top part of our brain that’s really expanded and the shape of our brain case shows that. The mandible of Homo floresiensis is very interesting. We can see we have a full set of adult dentition including all three permanent molars. So this isn’t a child. It is an adult. We can see it’s very robust, particularly in the symphysis region where the two halves of the mandible come together. This is very distinctive of earlier hominins. In fact, in our species, in Homo sapiens, we’re the only hominin that has what is called a bony chin. Where this part of the mandible actually projects more forward, and has very particular markings.
And is much more gracile in this region. It’s much thinner, and not as supported on the inside. And so Neanderthals don’t have a bony chin. All other hominins don’t have a bony chin, except us. And Homo floresiensis also shows this more archaic or more ancestral characteristic of our lineage. Overall the stature of the type specimen is estimated to be roughly around 106 centimetres. So around a metre. And a lot of people will focus on that, saying, oh, they’re so small, are they like other modern human populations that are small bodied? And the answer to that is actually no. Although they’re small, the proportions within their bodies is very different than it is in us.
So for instance, if we look at the femur, which is the thigh bone, we can see that if I just compare it to me. Right where my knee–you can see it’s extremely short compared to my femur. But if I look at its upper arm bone, the humerus. You can see that it’s almost– it’s much closer to the length of what my humerus would be. These are called humeral-femoral proportions. And in earlier hominins this is the general morphology, where we actually see that the arms and legs are more similar in overall length. This is also similar with living apes today. We might go to the zoo and see chimpanzees, for instance, and say, oh look how long their arms are.
But actually if you look closely, you realise that it’s actually that their legs are just short, so their arms appear long. And in us we’re the opposite. So during human evolution, certain hominins evolved a much longer proportionate– a proportionally longer lower limb changing the body proportions. We need to focus less on the overall size, and actually look at what the anatomy is telling us in terms of the body proportions. So this is really interesting because, for example, the partial skeleton of Lucy, of Australopithecus afarensis that’s around three million years old from East Africa, has essentially the same body proportions as what we see in Homo floresiensis.
In fact, from the neck down many of the bones in the anatomy is very similar to what we see in afarensis. So again, that doesn’t mean that Homo floresiensis is a direct descendant from afarensis. It just means that probably in the lineage that led to Homo floresiensis they’ve retained this ancestral morphology. There hasn’t been as much evolutionary change to their skeleton as there has been in the lineage that led to us. So we can also see similarities there in the hip bones. OK so this is the left pelvis pelvic bone. Now, they have what we call a laterally flaring pelvis where the upper part of the pelvis flares out to the side.
This is, again, similar to what we see in earlier hominins, but not the morphology that is typical in us where our pelvic bones are more curved and sort of wrap around the upper pelvis. Again these modifications are usually interpreted in us as additional adaptations to terrestrial bipedality. It’s not that these features are also adaptations to bipedality, but we’ve seen additional sort of tweaking in the skeletons of us. Here we have a number of small wrist bones from the left hand of Homo floresiensis And these are also very interesting because the shapes of these bones are more similar to what we see in earlier hominins and African apes, and unlike the wrist bones that we see in us and modern humans.
So again, the signals here show us that Homo floresiensis, its lineage has departed from our common ancestor earlier, before some of the evolutionary changes to the wrist occurred in the common ancestor that led to humans and Neanderthals. Each part of the body tells its own evolutionary story because none of these features are really evolving together at the same time. So it’s almost like the skeleton acts like a time machine, and different parts of the body give us information about different periods of earlier human evolution. Similarly the feet, the hobbit feet, if you will, are really interesting because they in fact are proportionately long. So hobbits do have large feet. But again, this is partly in terms of the proportion.
Because the lower limb bones are so short, proportionally short, the foot appears proportionately longer. But in essence, in us, generally and in humans, and it doesn’t matter if they’re small body modern humans or NBA basketball players. Typically our feet are roughly about half the length of our femur. In Homo floresiensis’ case, looking at almost 70% or to almost to 3/4 the length. Now this is really interesting because it means that there would have been some ramifications for moving bipedally quickly. So when we think of walking, sure it’s no problem. But for Homo floresiensis to run, or especially sprint like we can.
It probably posed some difficulties, because it would be like if you try to put on shoes that were too big. You’re going to start to trip over– the foot can’t clear quick enough. As well, the proportions within the foot are the opposite in comparison to us. So we have very, very short toes compared to our metatarsals and our metatarsals are shorter compared to our tarsus and in our ankle bones. And in Homo floresiensis it’s the opposite. Each segment is proportionately longer. So in essence, their toes would look a little bit more like mini fingers compared to our toes, which are so short and stubby we can’t do anything with them.
But we can certainly go up on our tippy toes and put lots of pressure on it and sprint. And so there’s likely some biomechanical and functional differences in terms of how Homo floresiensis may have been able to run. But likely out with this anatomy in terms of moving around and climbing and moving up and down trees, Homo floresiensis would certainly have big advantages compared to us, because with the lower hindlimb able to get the centre of gravity of the body closer to the substrate, and basically use less energy to move around in an arboreal environment.
So from the head all the way through the body to the tips of the toes, there is a tremendous amount of information within the skeleton that tells us a lot about Homo floresiensis and gives us clues in terms of how we’re related to it.