Finally..

Homo sapiens have been incredibly successful; our resourcefulness and intelligence coupled with frequent interbreeding with other hominids (including Neanderthals and Denisovians) has attained us the place as top monkey on the block. As time wore on all other species of Homo died out, whether through competition with us or succumbing to climate change, we have become the sole survivors of our genus. Though still a youthful species (200,000 years old compared to H.erectus 1.5 million years ago) we have changed our planet beyond recognition, so much so that scientists have introduced a new geological epoch - the Anthropocene. From humble beginnings we have come a long way.

Through the last 3 (and a bit) months I have taken you on a whistle stop tour of human development and dispersal, through origins just finding our feet to our eventual conquest of the entire planet.  However all good things must come to an end, and sadly this is true for this blog. On the bright side I've learnt loads from the research of this blog, it really gave me a great excuse to further my knowledge in a subject area I have always had a particular interest in. I hope you feel like you have gained some insight into our history too. 


I'll leave you with an answer to a question I know you are all wondering 'who would in in a fight between a Neanderthal and a human?'

Thanks for reading.

The importance of language

As I think I've said before, I am a big promoter of TED Lectures, there are a fantastic way of learning about current research and theories and are delivered in a was that is easy to understand even if you have no previous knowledge of an issue. With that being said I have included a lecture by Mark Pagel on how language has transofmed humanity. Language is one of the corner stones of what makes us different from the rest of the animal kingdom, its development is argued to be a key as the development of bipedalism (a topic I covered in an earlier post) and the control of fire.

The lecturer in the video above explains that the development of social learning, through copying, imitating and observing, allows us to develop on others' ideas. Other advanced species, including Homo erectus and even perhaps Neanderthals were unable to do this. He calls this cumulative cultural adaptation, it allows ideas to develop and enables people to 'stand on the shoulders of giants'.

However social learning leads to visual theft - your neighbour can copy your best ideas and perhaps do them even better. The way we overcame this is through developing language, allowing us to strike deals with one another and cooperate effectively.

I tend to agree with Mark Pagel's ideas, without language and the cooperation it brings, large complex social groups would be very difficult and living in cities would be impossible.

Aussie Crossing

Apologies for last week's blogging silence, Christmas took me away from my computer, however I am back and here with another installment.

Regardless of whether the original Australians came from Africa in an early wave 75,000 years ago or a later split from an Asian population, they still had to undertake an epic journey across Indonesia and a sea voyage to reach this new home. Looking at a map of Australasia today it is difficult to imagine a group travelling such vast distances using only fairly primitive rafts for transport. However as always seems to be the case with human migration, climate seems to have played a role in enabling this spread south into Australia. The world 55-65,000 ya was experiencing a glacial period, because of this large quantities of water were locked away in the polar regions, the consequence of this was that sea levels in the Australasian area were as much as 200m lower. This meant that instead of chains of islands between Australia and Asia there were land bridges - the Sunda and Sahul shelves, allowing the migrating humans to cross an extensive area by land.

                                                                   

Figure 1 - Migration route of humans in blue

Despite much of their journey being across land there was still Wallacea to contend with. As you can see in Figure 1, Wallacea is an area consisting of small islands separated by deep channels of water, the most extensive section of open water would have been 50 miles, across the Java trench. The most likely method of travel across this expanse was using bamboo rafts, whether this journey was possible at such an early time was a debated topic, however the prominent anthropologist Alan Thorne recreated the journey, constructing a raft from materials which would have been available to the ancient population, and using no modern navigational gadgets, the raft lasted the 50 miles of the journey, illustrating that this transportation was a possible mode for the new colonisers .

The video below is taken from 'The Incredible Human Journey', it shows what travel by bamboo raft would have been like and the difficulties that can be encountered in open water. It also suggests that the discovery of Australia would have occurred by accident, mainly because it was over the horizon and would have therefore been into the unknown.

Native American origin - A review

You might be surprised to learn that the peopling of the Americas (just in case you get confused I'm talking about North and South America throughout this post) occurred extremely late in the day compared to other continents. It wasn't until around 17,000 years ago that the first pioneers arrived, compared to Australia 50,000 ya and Europe 40,000 ya. The reason for this colonisation being so late in our history is due to the prior isolation of North and South America to the rest of the world. This isolation allowed many extraordinary species to evolve which are not found anywhere else including the megafaunal giant ground sloth, the saber tooth cat Smilodon and short faced bears, however it prevented Homo sapiens from entering.

Figure 1 Species endemic to the Amerias - Short faced bear, Smilodon and Giant ground sloths  

The theory generally accepted these days is that the entry route into the Americas was via the Bering Strait land bridge. This bridge was originally created during the last glacial maximum 26,000-19,000 ya a time when ice sheets were at their most extensive, but the bridge lasted right up until 11,000 ya. Over the course of many generations hunters would have migrated across the land bridge following herds of caribou from Siberia into Alaska, from here they followed the coast down the west of North America and eventually into South America, this route can be traced by an increasing decline in genetic diversity displayed by native populations as you travel south.

Figure 2 - humans migrated from Siberia into Alaska

Other theories which have been dismissed include entry to the Americas by South Asia and Polynesia on multiple occasions by means of the sea and by land. The land bridge theory was finally accepted as the most likely in 1997 thanks to genetic evidence linking the Siberian and Alaskan populations. However although the location of migration was agreed upon, the number of migrations which took place were still open for debate. The original 1997 study proposed that the whole population of the Americas stem from a single migration from East Asia.

A new paper coordinated by Professor Andres Ruiz-Linares of UCL and published in Nature in August of this year may shed some light into what really happened. Through more extensive evaluation of the genetics of both North American populations and Siberians they concluded that the migration actually occurred in three waves of migration. Although the first wave of migration did populate the majority of the two continents, some Arctic populations trace their heritage back to a second and third migration occurring later in history. The study also highlights how complex dispersal patterns can be; some Central American populations are equally related to both North and South American populations, suggesting that some back migration would have occurred (people travelling from South to North America). This kind of migration pattern can muddy the waters and make it confusing to see the real picture.

Figure 3 - The new three wave migration route

For the time being the new 2012 paper seems to be accepted by the scientific community as the most likely scenario,  however it should be remembered that studies such as these contain limitations. In this case it is a lack in genetic data, due in part to a reluctance among native populations to partake in the study but also to uncertainty whether skeletal remains are ancestors of tribes or not. I think it will be interesting to see whether scientists manage to obtain more data in future and if so what new evidence may emerge on the settling of the Americas, there may have been many more migrations yet to be discovered.

Out of Africa 2 - Homo sapien dispersal - a review

We've now learnt that all human beings today can trace their origin back to Africa, so now I bet you're wondering about how this second Out of Africa dispersal played out.

Today we have wind back 200,000 years ago (ya), our location is East Africa. Over a million years have past since Homo erectus successfully migrated, and they have now set up home throughout Asia and Europe. The earliest known remains of H. sapien are found in Ethiopia 160,000ya. From this singular east African origin, three lines diverged, one travelling to southern Africa, one to Central and West Africa, and the last line traveled North. It is this last lineage we are interested as this small group are the ancestors of every non African person in the World. 

Figure 1 The range of other Hominid groups and our dispersal route.
1 = H. sapien
2 = Neanderthal
3 = H. erectus

The most widely supported route these early H. sapiens took is strikingly similar to the H. erectus dispersal I described in Out of Africa 1 - Homo erectus dispersal - climate induced changes in sea level enabled a crossing of the red sea and into the Arabian peninsular.  Ericksson's 2011 paper lends support to the importance of climate in facilitating the migration, he explains that '60-70kya (thousand years ago) the global colonisation of humans ancestral to modern populations was prevented by the arid climate in Northern Africa and much of the Arabian peninsular.' Long after spreading throughout Asia they traveled North into Europe, following game migrations and favorable climates. 

Upon reaching the China region 70,000ya there was a divergence. It seems one group island hopped through Indonesia, eventually entering Australia 50,000ya; whilst another group dispersed Northwards, crossing into the Americas 15,000ya. 

An opposing view is presented in  Rasmussen et al.  2011 paper. They used DNA analysis of an aborigine’s lock of hair and discovered a greater similarity to African DNA compared to Asian and European. These findings go against the idea that a single migration occurred and that the Australian population diverged from the Asian one. Instead it suggests that the ancestors of the Australian population left Africa first 75,000ya, travelling along the South Asian coast and interbreeding with the Denisovian population before arriving in Australia. The evidence of these travels would then have been swallowed up by rising sea levels; the Asian and Europeans would then have emerged from Africa separately at a later date around 25,000-38-000ya. The main archaeological evidence to back up this theory comes from the 'Mungo man'a 50,000ya skeleton found in Australia. the path this early migration may have taken has not preserved and so there is minimal physical evidence however new technique of matching DNA to powerful computer models is reputed to make up for this; however the research is still very new and it will be interesting to see if it stands up to academic scrutiny over the coming years. 

Alternative dispersal routes

A bit of fun...

Hey folks, here's some light relief with a human evolution game. Let's see if my blog has taught you a few things. All topics the game covers are mentioned in the 'Walking with Cavemen' series that I linked you a few weeks ago.

Enjoy.

Timings - a review

I'm sure many of you reading this are aware of the magazine New Scientist. It covers stories which are newly emerging and occasionally controversial; in last weeks issue (24th November) they ran a story which suggested that we have been miscalculating the age of our split with the last common ancestor of chimpanzees; a result which would mean the re-writing of textbooks and a shift in the way we view our evolution. Pretty revolutionary stuff right? That's what I thought; lets take a look at the evidence.

The way we have always been told in schools and lectures is that the timing of the split between us and chimpanzess was 5 million years ago. This age was a fork in the evolutionary road, along one branch an ancestor evolved into modern day chimpanzee, along another the ancestor became us. The technique of working out this date lies in our DNA; with each generation new mutations appear, these occur randomly and many do not cause any significant changes affecting our likelihood to survive, they just sit there hanging out and can be picked up upon DNA analysis. The rate these mutations accumulate remains relatively stable through the generations and was thought to be 75 per generation, this allows us to calculate how many generations there have been since our ancestors split with the chimp's ancestors, all we have to do is add up the mutations.

Sounds pretty simple, however a recent study by Kong et al. proves that this method needs some corrections. His study was focused on mutations observed between human parents and offspring, after analysing the genetics of 78 'parent offspring trios' (child with both parents) they found that each child had on average 36 mutations which  were new and not shared with either parent. This is clearly half what we have always thought; the mutations accumulate much more slowly Now if we add up all the mutations it appears that the acutal age of split between us and chimps is more like 7-13 million years.

Figure 1 Old 5my split versus the newer estimates of 7-13my

If this more ancient split is to be believed then Australopithicus afarensis may not be the oldest ancestor we can identify as hominin, other species may have to be brought into the family such as Sahelanthropus tchadensis at 6-7mya and Orrorin tugenensis at 6mya .Other ramifications include an older Homo sapien migration out of Africa date at around 90,000-130,000 years ago (a topic I haven't covered yet but when I do I will try to give a scenario based on both dates).

All of this is enough to get very excited, Kong's paper was published in August of this year (2012) in Nature, a journal which undergoes heavy peer reviewing, something which helps with the reliability of a paper. However some anthropologists in the field such as Matt Skinner from UCL, suggest caution should be used when reading such revolutionary claims. Public interest is focused on the more sensationalist stories and scientists are therefore pressured into making claims they themselves would rather not make in order to get their articles to be published. Whether or not this is the case with this story is up for debate and I'd be interested in hearing your opinions.