I have to say, at the moment I’m feeling a bit like this chap:
Mainly because we are currently ‘between’ registrars & so I don’t seem to have a life! But I shall press on – with a question from the 2006 paper on human evolution.
The question provided a hominin phylogenetic tree (something like this, perhaps) & followed this with the following information:
Although there are differences in interpretation of the evidence, it is generally accepted that human biological evolution has not been a linear progression from one species to the next. In fact, there are now thought to have been between 5 and 7 hominin genera, and at several points there have been 2 or more species and/or genera in existence at the same time.
Significant factors involved in the biological evolution of humans include:
Using selected named hominins, discuss how each of these three factors has contributed to the biological evolutionof humans.
I rather like this question. First, because it’s one of those lovely ‘big picture’ questions (like all Schol Bio questions, in fact), applying evolutionary concepts to our own family line in a more in-depth way than the L3 examiner can. And second, because it makes it clear that natural selection isn’t the only player in evolutionary change: genetic drift can (& often does) play a significant role. (Darwin, of course, with his lack of knowledge of how heredity works, could have no concept of genetic drift. Yet another example of how science moves on as new information comes to hand.)
Anyway, what was the examiner after?
Well, you need to show that you know what these terms mean. And because there are 3 terms needing definitions, you could really split the essay into three main sections & deal with each in turn. First up, genetic drift: what is it, how is it relevant in a named hominin, and how might it have contributed to human evolution? It would be a really good idea to set these points – & any related ideas – out in an essay plan before you get started on your actual answer.
Genetic drift is where you get changes in allele frequencies in a population due to chance events (e.g. all the mice carrying a dominant allele giving them long fur shelter under a tree during a storm – to keep dry, of course. Anyway, lightning strikes the tree, it falls on the mice, & behold – the long-hair allele is removed from the population…) It’s often the result of a population bottleneck event: if a small group of individuals leaves a parent population (or is all that’s left after some catastrophe – like the mice in my example), those migrants are unlikely to be representative of the parent population’s gene pool, simply by chance. Homo floresiensis was isolated on a small island & probably had a fairly small population, so genetic drift could well have played a role in this species’ evolution. The same could be said for populations of H.sapiens migrating out of Africa, & could possibly have have influenced the distribution of A/B/O blood groups around the world.
Natural selection – you can probably give a good definition of this. The examples you could use to demonstrate how this affected named hominins could include: changing environmental factors & their possible impact on the evolution of bipedalism, or the effect of climate on body form. This last one’s quite well known, & in fact has a couple of ‘rules’ describing how it works. Allen’s rule (or law) states that warm-blooded animals in a cold environment will tend to have shorter protruding body parts (including limbs & digits) than members of the same species in a warmer region. The corollary, Bergmann’s rule, says that a species population in a cold area will have a larger body (greater mass) than a population from a warm place. Both are adaptations that reduce heat loss through a reduced surface area: volume ratio. For human evolution – the shorter, squat Neandertal physique may well have been the result of selection pressure from the harsh, cold climate of Europe 300,000 years ago.
And cultural evolution? It involves the transition of learned behaviours from one generation to the next, and cumulative change in these behaviours. You could choose from a range of cultural innovations to explain the relevance of cultural evolution in our own lineage. Tools, for example: the development of tools by Homo habilis offered the possibiity of processing food more efficiently, & perhaps of accessing new food sources. After all, with their relatively small teeth, habilis individuals wouldn’t have had much luck getting the meat off any carcase that they managed to scavenge. But even very simple stone tools would allow them to cut or scrape meat from the bones, thus providing a whole new source of protein. And the greater nutrition (in terms of both energy & nutrients) would have been quite an advantage & could well have underpinned changes in brain size, for example. (Which in turn could lead to more complex tool technologies, greater processing ability… you get the picture.)