Part Four: Hominid Evolution and Fossil Collecting
Humans are in a world of their own. There are many common questions now of the sociological implications of the old humanoids, how did they interact and split duties? What was the early evolution of them like? What did they eat? How did they interact with the environment? When did they begin to influence it? I do not have the answers to any of these questions, but here is a very brief note on their evolution, with respect to climate change and speciation.
The fact that human evolution happened at the same time as major climatic deterioration through glaciations and global cooling has prompted questions on the extent that the two events are causally related, including the driving forces in hominid evolution. An issue that needs to be taken into account (not including the complexity of climatic interactions with life) is that of the fossil record, the reliability of dating methods and major tendency for the whole human evolutionary story to shift and change with every new find. Therefore, it is important to remember that correlations mean associations between factors and not necessarily causality. In addition if there is a lack of correlation it does not mean that there is no inter linking of associations. What is important is not only whether climate and hominid evolution are related but the nature of the mechanisms involved.
The lower the minimum or modal temperature, the higher probability of hominid extinction. Therefore, there is a distinct correlation between extinction and climate but not with speciation and climate, so that other primary factors control the first appearance of taxa. It has been found that species diversity varies somewhat with climate, but not in a robust manner. There is a difference in Homo to Australopithecus, where Homo vary positively (more) with low temperature and the latter negatively (less), so that the Australopithecus are more temperature sensitive than Homo. However it may also be the case that species diversity is a measure that shows how ecological changes determine the way in which speciation and extinction interact. When speciation is measured in relation to climatic stability a number of relationships can be observed. It was found that, unsurprisingly, the more stable the climate, the more hominid species. When split into groups of Homo and Australopithecus, it was found that Australopithecus were good with stable climates, but that Homo showed less speciation. There was not a very strong relationship between climatic stability and extinction with hominids, showing the more stable the climate the less extinction.
Climate is likely to be an important element in any model of evolutionary change, that goes hand in hand with competition. When climatic change occurs, it means that it operates through competition. The change will alter the nature, abundance and distribution of environments and resources within the areas initiating changes in the competitive relationships between species. It is these altered competitive relationships that are likely to lead to evolutionary consequences. The consequences might be extinction, speciation rising from reduced intra-community competition or the opening of new ecological opportunities. However, even with this interpretation of the effects of climate change, it is clear that this is not sufficient to describe the changes in speciation, diversity and extinction of taxa. So, it is probable that these effects are locally important effects of competition, but not from climate change as a global effect.
To finish with a flourish, as I promised at the beginning of this four part blog series, I will attempt to reel the palaeo-madness back in towards a more ‘cultural heritage’ alignment. Prehistoric Fossil Collectors by Ken McNamara, details the fascination that we, as species of hominids have had with fossils. Specifically, with the common sea urchin. When alive, the sea urchin can be beautiful, and their shells when washed up on the beach and non-fossilised are beautiful enough to see. However, it seems that the five pointed star that holds so much symbolism in many human cultures for hundreds (maybe thousands) of years can be traced back all the way to the Ordovician, 450 million years ago.
The earliest evidence we have of Homo collecting these trinkets is 400,000 years ago with Homo heidelbergensis where a hand axe has a fossil echinoid displayed on the side. Other usages of the fossils have been placement in graves, as necklaces with holes drilled through the middle, adorning windows and doors or homes and churches and many others.
It could be that in some cases these stars were thought to have some sort of spiritual significance, a trinket to ward off the Devil or to help them in the afterlife. Personally, I think that alongside these possibilities may be the fact that they were pretty, and formed a simple way to adorn the grave of a loved one much as we may do today, without any specific meaning having to be attached to the fossils. In many ways, we are pre-disposed to enjoy beautiful items, especially those with symmetry, which has many connotations for our own bodies, the legs, arms and neck/head symbolised in the five points.
What interests me is the idea that 400,000 years ago our ancestors picked up fossils and cherished them in some way. The practice could go back further, and I think would undoubtedly extend to other fossils. We find even as children that we are drawn to these objects without understanding what they are or have been, but maybe there is something in all of us that wants to understand how we got here. I love the fact that fossils and fossil collecting have been important for so long, and hope that we continue to understand the value of looking at rocks and understanding them in the future.
Foley, R A, (1994), Speciation, extinction and climate change in hominid evolution, Journal of Human Evolution, 26, Available online: http://www.human-evol.cam.ac.uk/Members/Foley/pubs/94jhe-26(275-289).pdf