Australopithecus sediba is one of the most significant additions to the human family. They lived around the time our genus - ; hence our name Homo sapiens- was evolving. However, their strange anatomy indicates they clearly weren't part of our group. In other words, they prove our early ancestors had evolutionary company. Now, they're back in the news for a less glamorous reason: Australopithecus sediba has been found to have the oldest case of cancer ever found in a member of the human family.
Fortunately for one of my favourite hominins, their tumour seems to have been benign. However, researchers have also found another case of cancer on hominin fossils from the nearby site of Swartkrans. This fossil seems to be slightly younger than Au. sediba (a mere 200,000 years difference between them) but is afflicted with a more malignant form of the disease.
Too bad for fans of the palaeodiet. Turns out eating like a caveman won't save you from disease and misery.
Teenage Au. sediba
The afflicted Australopithecus sediba isn't just any old hominin. It is the type (i.e. defining) fossil for the species. Called MH1 (because scientists ran out of fun nicknames after Lucy) this fossil is a relatively complete male; with good chunks of the skull, torso, hips, and limbs preserved. But what's most interesting in this case is his spine. Or more specifically, his sixth thoracic vertebra.
When this bone was discovered it was noted that it had a lesion on the "spine" of the vertebra (puns very much intended). Further analysis - including a CT scan - revealed that this growth extended quite far into the bone; even changing the angle of the bone slightly (although not enough to cause problems).
Now, growth in a bone doesn't exactly sound healthy, but it can be caused by a myriad of different conditions. Including a fracture which didn't quite heal right. Such a find would be particularly interesting given the young age of the fossil. Whilst the bones themselves may be ~2 million years old; when MH1 died he was only 13-14. Evidence of such trauma (and it healing) in such a young individual would offer a fascinating, albeit enigmatic, insight into the rough and tumble life of Au. sediba.
However, as I already spoiled in the title and introduction of this article; that isn't the case. An in-depth analysis of the bone revealed its most likely osteoid osteoma. This is a benign sort of bone tumour that grows to around 2cm in size and typically afflicts younger individuals. The growth in the fossil was only ~1/4 of this maximum size, suggesting it might have been a recent development in his life. Luckily - all things considered - it doesn't seem to have impacted him too much and unlikely contributed to his death.
Suffering at Swartkrans
So MH1 can join the ranks of hominins shown to have cancer. And the oldest example at that! Although it isn't a particularly long list, so it doesn't take much to climb to the top. You could probably count confirmed cases of the disease in our ancestors on one hand. Most of these - including MH1 - seem to have been benign growths.
However, another fossil from South Africa (also reported in the same journal issue as the Au. sediba discovery) had a less than positive diagnosis. Hailing from the site of Swartkrans, a foot bone was discovered with a fairly major growth on it. Ultimately this increased the bones thickness by an extra third; which is not something you really want going on in your foot.
This list of harmful effects such a major displacement would have is long and would likely have hampered the gait of this individual. As if that wasn't bad enough, a CT scan of the bone revealed that this growth was malignant in nature. This would have made things very tough for our hominin, perhaps even leading to his ultimate demise either by ruining his gait, which sucks; or by just being cancer, which also sucks.
Unfortunately, we can't tell much else about this individual as all we have is the toe bone. Hardly the most diagnostic feature of a human. However, the cancer was identified as osteosarcoma; which - like MH1's affliction - typically occurs in younger individuals. We might well be dealing with another youngster here.
Why is cancer so rare in hominins?
These two papers about cancer in hominins might seem like a veritable landslide of discovery. However, it still only adds up to two more cases of cancer in our ancient family; almost doubling the total known cases. Given that it's now one of the leading causes of death in humans, is such rarity unusual? Not really.
There several factors at play here. Perhaps the most important one is that age is a significant risk factor for developing the condition, and hominins don't seem to have had long lives. Although we don't exactly have birth records to plot the demography of our ancestors, hunter-gatherers don't really paint a rosy picture of their odds of survival. More than half of all children born won't make it to age 15. In other words, most of our ancestors simply didn't live long enough to start suffering from many of these conditions. Hence why both of the fossils discussed above seem to be afflicted with a condition that primarily occurs in young people. Most simply aren't going to live long enough to get anything else.
The other key issue is when you consider the material we're dealing with. Only bones are preserved this long, and bone cancer is relatively rare. And bone cancer occurring in the bits of fossil that survive is often even rarer. Going back to the malignant tumour seen in the toe; that sort of cancer occurs in <1% of the population. Of the incidences of that cancer, <1% occurs in the metatarsals. In other words, they represent 0.0001% of the population. It makes looking for a needle in a haystack look like easy.
Cancer was rare in our ancestors, but that's because they were all busy dying at age 15.
Summary
Two fossils have been found suffering from cancer, pushing back the earliest incidence of the disease in our ancestors to 2 million years ago.
References
DeSilva, J.M., Holt, K.G., Churchill, S.E., Carlson, K.J., Walker, C.S., Zipfel, B. and Berger, L.R., 2013. The lower limb and mechanics of walking in Australopithecus sediba. Science, 340(6129), p.1232999.
Edward J. Odes et al. 2016. Earliest hominin cancer: 1.7-million-year-old osteosarcoma from Swartkrans Cave, South Africa, South African Journal of Science
Gurven, M. and Kaplan, H., 2007. Longevity among hunter‐gatherers: a cross‐cultural examination. Population and Development review, 33(2), pp.321-365.
Patrick S. Randolph-Quinney et al. 2016. Osteogenic tumour in Australopithecus sediba: Earliest hominin evidence for neoplastic disease, South African Journal of Science
