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The Human Fossil Record, Part 9: Out of Africa (The First Time)

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April 12, 2012 Tags: Human Origins

Today's entry was written by James Kidder. Please note the views expressed here are those of the author, not necessarily of The BioLogos Foundation. You can read more about what we believe here.

The Human Fossil Record, Part 9: Out of Africa (The First Time)
Image source: Wikipedia commons: "Homo Georgicus” as displayed at Lausanne Natural History Museum

Note: Today, James Kidder continues to tell the story of the evolution of creatures on our own small branch of the primate family tree, the hominins. Kidder’s previous post in the series looked at fossil evidence suggesting that the appearance of Homo ergaster in East Africa about 1.8 million years ago was a significant step towards hominins with fully modern proportions and stature. But more importantly, that more modern body (including a larger brain) seems to have come at the same time as new kinds, uses and sources of stone tools. This combination of evidence leads some researchers to surmise that these hominins were exhibiting anticipatory cognition: the ability to plan ahead for future goals, including travel over great distances to find food and other raw materials. This capability may have set the stage for additional cultural development, but also begs the question, “When did our ancestors first start exploring beyond the African continent?” This post discusses archaeological discoveries from the last 30 years that allow anthropologists to answer that question with more precision than ever before, and to fill in details of the story of how hominins developed in and outside of Africa.

Out of Africa

One of the persistent questions involving paleoanthropological research is the timing of that first migration out of Africa. Work by several researchers beginning in the 1890s had uncovered remains of hominins in both East and Southeast Asia, but because of problems understanding exactly how remains decayed or were preserved in those environments, very few concrete dates could be determined. In Europe and the Near East prior to the 1980s, there were no early hominin remains that could be dated older than 500 thousand years.

Transitional species?

Beginning in the summer of 1999, however, the remains of six individuals—including two remarkable partial skulls, or crania—were recovered from a hilly location at the site of Dmanisi in the Republic of Georgia (see map, below). One surprising characteristic of the skulls was their primitive appearance (Figure 2). Their small cranial size of 800cc put them squarely within the early Homo range (modern humans skulls range between 1350 and 1500 cubic centimeters). Also notable was that from the back, the widest part of the head was quite low, just above the ear. In modern humans, the widest part is three-quarters of the way up from the cranial base. These characteristics, plus the shape of the eye sockets and cheeks strongly suggested an affinity to Homo ergaster (Gabunia et al., 2000).

Two characteristics were different from Homo ergaster, however. First, the skull bones were very thick, and second, they displayed a ridge of bone not found on Homo ergaster or any of its African contemporaries. This ridge, called the angular torus, is a defining characteristic of Homo erectus, the hominin that follows Homo ergaster. These characteristics strongly suggest that the Dmanisi hominins occupy a transitional status between these two forms.

In direct association with these hominins were stone tools of what is known as the Oldowan mode: scrapers, choppers and flakes (Figure 3). This tool kit was more primitive than what was associated with African specimens of African Homo ergaster and closer to what has been found at earlier Homo habilis sites. Based on Paleomagnetism and 40Ar/39Ar dating, the hominin remains at Dmanisi are estimated to be between 1.5 and 1.8 million years old, putting them within the historical range of African Homo ergaster. This suggests that the Dmanisi hominins may represent an earlier branching of the H. ergaster line, and that each line had its own independent evolutionary trajectory.

The appearance of this hominin this far north and at such an early date is striking because it suggests that an early form of Homo had learned to migrate long distances. It should be pointed out that this migration involved more of a change in location than a change in scenery. The environmental conditions at Dmanisi were dramatically different 1.5 million years ago than they are today, and analysis of the ancient climate for the hominin layers there indicates that it was a temperate savanna with small trees and brush (Palmqvist, Gröcke, Arribas, & Fariña, 2003).

Rapid Expansion

Apart from the Georgian Caucasus, it appears that there was also a rapid expansion out of Africa into other areas of the Old World (defined as all continental areas except North and South America and the polar regions). This began shortly after the appearance of Homo ergaster. As Figure 4 indicates, hominins first appeared in Europe, the Near East, and Asia between 1.5 and 1.8 million years ago.

Southwest Asia (The Near East)

Because of its rich religious history, southwest Asia has always been an emotionally charged region for archaeological research. Yet it is here that scientists have found evidence of early non-African Homo. Two sites have been proposed as the earliest habitation locales in the Near East: Yiron and Erq el Ahmar, both in the Jordan Valley region of Israel. However, despite yielding primitive tools, they have not produced reliable dates.

At the site of Ubeidiya, also in Israel, several levels of habitation have been unearthed that suggest a long-term occupation between 1.5 to around 1.0 million years ago. Stone tools found at Ubeidiya range in complexity from Oldowan (such as those made by late H. habilis) to Acheulean (typically associated with H. ergaster). This indicates the presence of more advanced (and slightly later) hominins than those found in Dmanisi. Unfortunately, no human remains have been discovered at this site (Bar-Yosef & Belfer-Cohen, 2001).

Another notable site is Gesher Benot Ya’aqov, which has been recently re-dated to approximately 780,000 years ago (Goren-Inbar et al., 2000). The archaeological layers there are quite rich with thousands of tools, all of which are Acheulean in nature: hand axes and cleavers along with flake tools. The material at Gesher Benot Ya’aqov reflects a much greater complexity in behavior than at earlier sites, as well, yielding evidence of a remarkable advancement: the continual, purposeful use of fire. By examining the pattern of burned artifacts, Alperson-Afil has concluded that the small-stone waste pattern at the site reflects a controlled fire-source. The author argues that, while there are places where burned and unburned artifacts overlap, there are also clusters of burned artifacts alone. Here, he suggests “that an anthropogenic [that is, man-made] fire is the agent responsible” (Alperson-Afil, 2008, p. 1735). This conclusion has been supported by Goren-Inbar et al (2004).

This innovation would have been tremendously important. Control of fire would have allowed the migration of hominins into less temperate climes, giving them access to vastly different fauna to be hunted. Fire also extends the working hours of the day by providing heat and light, and could have allowed for additional planning or continued social bonding. Another considerable advantage of having controlled fire was protection, as wild animals rarely approach an open fire. Being able to protect one’s group as well as one’s food source would have increased home range and cut down on population loss due to predators. Since fire is portable, it may have allowed early hominins to become more adventurous as they moved around.

Western Europe:

Spain:

In addition to the Near East corridor, there is ample evidence that early Homo made the trek across North Africa and crossed the straits of Gibraltar. In Spain, the partial remains of a hominin jaw (Figure 5) and a lower premolar were found at the site of Sima del Elefante, near the town of Atapuerca.

This location will figure prominently into the discussion of the appearance of archaic Homo sapiens. These remains are clearly of hominin origin and share similarities to the remains from Dmanisi, but their fragmentary nature precludes a detailed exploration of how they relate to those at other sites. In addition to the hominin fossil remains, stone tools of a pre-Acheulean variety were found. These consist of flakes and scrapers and show little complexity beyond that found at Dmanisi (Carbonell et al., 2008). Paleomagnetism, cosmogenic nuclide dating, and the presence of distinctive fauna put the date of these remains and artifacts at between 1.1 and 1.2 million years ago.

At the site of Orce, in southern Spain, tools were discovered similar to those at Sima del Elefante and Dmanisi, but none of them were Acheulean. Following Gilbert and colleagues’ (Gibert et al., 1998) analysis of tools and other evidence, we know that humans were present in the area around 1.5 to 1.6 million years ago, but we do not know who they were.

Italy:

Evidence for the earliest settlements in Italy has also been discovered in the last decade. At the site of Pirro Nord, a small collection of flakes and scrapers was found at a karst level dated between 1.3 and 1.7 million years ago by biostratigraphy and palaeomagnetism (Arzarello et al., 2007) (Figure 6). As with the Dmanisi site, from the kind and numbers of animals and plants found at the archaeological levels, the environment was open and dry. Once again, we know hominins were there, we just don’t know what they looked like.

The trek to the north of Europe appears to have taken more time, and the earliest archaeological material in Germany—an almost-intact lower jaw discovered in a sandpit—is dated between 0.7 and 0.5 million years ago. Travel to this area of Europe may have been hindered by the presence of ice. Northern Europe was often impassable during much of the Pleistocene because of glacial advances and there may simply have been no way to get there until the Donau-Günz interglacial, beginning around 700,000 years ago. That first discovery representing early Homo occurred at the site of Mauer, in Heidelberg, and is dated to approximately 500,000 years ago. When found in 1908 it was given the name Homo heidelbergensis, but it has since been reclassified as Homo erectus, a form that we will discuss in detail in the next post.

Who Were These People?

One of the frustrating things about fossil hominin studies in Europe is that we have only small amount of human remains to work with. Any reconstruction requires some guesswork based on what we uncover. But from skeletal material in the Russian Republic of Georgia, at the Dmanisi site, it is clear that these hominins had evolved beyond the basic Homo habilis form. Though we do not know exactly what they looked like, we have a wealth of evidence about their migration patterns. Hominins similar to these dwelled within Spain between three and five hundred thousand years later, and they were also found in the Near East. These discoveries come not just from limited skeletal material but also from abundant archaeological material of other kinds.

It is unfortunate that we do not have more material to work with, but the discoveries of the past thirty years have greatly advanced our understanding of pre-human history. As we shall see in the next post, the story of early Homo in Europe and the Middle East reflects only part of the hominin journey; for in addition to migrating north and west, they also traveled east.

Further Reading

Alperson-Afil, N. (2008). Continual fire-making by Hominins at Gesher Benot Ya‘aqov, Israel. Quaternary Science Reviews, 27(17–18), 1733-1739.

Arzarello, M., Marcolini, F., Pavia, G., Pavia, M., Petronio, C., Petrucci, M., et al. (2007). Evidence of earliest human occurrence in Europe: the site of Pirro Nord (Southern Italy). Naturwissenschaften, 94(2), 107-112.

Bar-Yosef, O., & Belfer-Cohen, A. (2001). From Africa to Eurasia--early dispersals. Quaternary International, 75(1), 19-28.

Carbonell, E., Bermudez de Castro, J. M., Pares, J. M., Perez-Gonzalez, A., Cuenca-Bescos, G., Olle, A., et al. (2008). The first hominin of Europe. Nature, 452(7186), 465-469.

Gabunia, L., Vekua, A., Lordkipanidze, D., Swisher, C. C., Ferring, R., Justus, A., et al. (2000). Earliest Pleistocene Hominid Cranial Remains from Dmanisi, Republic of Georgia: Taxonomy, Geological Setting, and Age. Science, 288(5468), 1019-1025.

Gibert, J., Campillo, D., Arqués, J. M., Garcia-Olivares, E., Borja, C., & Lowenstein, J. (1998). Hominid Status of the Orce Cranial Fragment Reasserted. Journal of human evolution, 34(2), 203-217.

Goren-Inbar, N., Alperson, N., Kislev, M. E., Simchoni, O., Melamed, Y., Ben-Nun, A., et al. (2004). Evidence of Hominin Control of Fire at Gesher Benot Ya`aqov, Israel. Science, 304(5671), 725-727.

Goren-Inbar, N., Feibel, C. S., Verosub, K. L., Melamed, Y., Kislev, M. E., Tchernov, E., et al. (2000). Pleistocene Milestones on the Out-of-Africa Corridor at Gesher Benot Ya'aqov, Israel. Science, 289(5481), 944-947.

Palmqvist, P., Gröcke, D. R., Arribas, A., & Fariña, R. A. (2003). Paleoecological reconstruction of a lower Pleistocene large mammal community using biogeochemical (δ13C, δ15N, δ18O, Sr:Zn) and ecomorphological approaches. Paleobiology, 29(2), 205-229.


James Kidder holds a Ph.D. in Biological Anthropology from the University of Tennessee (UT). He currently employed as an instructor at UT, and as a science research librarian at Oak Ridge National Laboratory. He has been involved in the Veritas Forum at UT and runs the blog "Science and Religion: A View from an Evolutionary Creationist/Theistic Evolutionist."

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HornSpiel - #69299

April 13th 2012

James,

Thank you for your consistently informative posts.

I am wondering why, in your  discussion of the importance of fire (Sec. Soutwest Asia, p.4), you do not mention cooking. My understanding is that the development of cooking, espcially meat, allowed hominins to digest food more easily. This in turn resulted in a smaller gut and other physiological changes—things that wiould be observable in the fossil record as well as in hominin artifacts.

I am wondering if you would care to comment on that.


Jimpithecus - #69304

April 13th 2012

While it looks like archaic Homo sapiens may have cooked food, there is no evidece that Homo erectus or ergaster did.  Where you really see the physiological changes occuring is in the teeth, when the chin appears because the teeth are getting smaller.  This is a likely result of cooking food, which, as you say, makes it softer. 


GJDS - #69326

April 16th 2012

” ...., but because of problems understanding exactly how remains decayed or were preserved in those environments, very few concrete dates could be determined.”

I have tried to understand what is central to evolution or Darwinism: Mutations and changes are proposed to give rise to new forms of species (or simply other life forms) and this is random to an extent. Natural selection steps in and those fit to survive do so, and I presume the rest are eliminated.

On this basis, I understand that the many are not selected, and a few are - and this is given a progression of changes leading to the present life forms. I am puzzled, as this central tennet of Darwinism should easily be supported by fossil records which would contain a vastly greater number of those that failed to survive (by virtue of the large number of unselected mutations) and a small number of those that survived.

If the fossils of the unselected exist and can be shown to conform to this notion, can someone point them out to me so that I can study them to better understand Dawinism. If they do not exist, can someone explain to me how Darwinism can be suppoted by scientists; failure to obtain this data that is so central to the entire theory is beyond belief or disbelief.

If preservation of life forms is a problem (as stated in the article), we are still faced with the probability that some of the more numerous rejects are more likely to have formed fossils, while the fewer survivors would have undergone decay and are more likley to have dissappeared.

Either way, I see a difficulty that needs to be addressed. 


HornSpiel - #69327

April 16th 2012

fossil records which would contain a vastly greater number of those that failed to survive (by virtue of the large number of unselected mutations) and a small number of those that survived.

The fossil record does not contain a record of any that survived! The mortality reate fro the fit and unfit is the same: 100%.

All things being equal, it will contain a record of the offspring of those most likely to have reproduced, thus chilren of the fittest individuals in Darwinian terms. Rejects will not have reproduced so there will be little or no record of their kind.


Jimpithecus - #69329

April 16th 2012

GJDS writes: “On this basis, I understand that the many are not selected, and a few are - and this is given a progression of changes leading to the present life forms. I am puzzled, as this central tennet of Darwinism should easily be supported by fossil records which would contain a vastly greater number of those that failed to survive (by virtue of the large number of unselected mutations) and a small number of those that survived.”

Evolution doesn’t work like that.  There is very little in the way of “nature red in tooth and claw.”  What happens is the same thing that happens now.  Most people reproduce, not just a few, and some have traits that are differentially more adaptively successful than others.  Over the long haul, those traits begin to predominate in a given environment.  For example, when the cold ice sheets began to recede in northern Europe during the Wurm interglacial, there was a relaxation for the very constitutionally expensive cold adaptation in the Neandertals.  Consequently, in the later Neandertals, you see the teeth get a tad smaller and rudimentary chins appear.  The heads are not quite as long and the faces not quite as puffed out.  That is just a change in gene frequencies for those traits over time due to relaxed selection.  It all ramped up when you had interaction and (as the genetics now shows) interbreeding with southern populations that were much more gracile than they were. 


GJDS - #69331

April 17th 2012

“Evolution does not work like that” ... I hope you do not take my comments as aggressive, but that is how evolution is reported to work, beginning from “The Origin of the Species”, in which Darwin draws the analogy betwee selective breeding (as by a farmer for example) and natural selection. You must, surely by definition, have species that proved to be unfit, and furthermore, from these be able to show why they failed the test of selection. Random mutations as I read from your literature, by definition, are random, so why would mutations focus on preventing reproduction only? In any event, there must have been non-selected species, and even if they were statistically as likely as selected ones, this means there should be a similar fossil record as from those that were selected.

If we are relying on present day observations of present day species, why would we accept speculation concerning events that are to have occurred millions of years ago; unless you can draw a strong link with these past events, which you say cannot be found in the fossils (or are not as available as for the selected species). Again, I am not questioning peoples credibility; in my view, these questions are ones that any person, whatever the background, is entitled to ask.

If you think fossil records cannot be found, this means you do not have data to support an ascertian.

In any event, I thank you for your response.


Jimpithecus - #69404

April 19th 2012

I did not say they could not be found.  The problem is that we don’t have all of the pieces of the jigsaw puzzle.  If a species is stressed beyond its ability to recover from an environmental change or is outcompeted, as a whole, it will go extinct.  But it does so animal by animal.  There was an interesting story about the Tasmanian Tiger, which went extinct in 1936.  It did so because it did not have enough genetic variability in its population.  In most species, for every generation, thousands of new mutations are present.  Some work, some don’t but they are all part of the variation present in the species.  if there is a stress on the species, those with novel mutations that are suited to that change will leave more offpspring, on average.  This is very time consuming but, over time, a change in the morphology of the species occurs.


GJDS - #69405

April 19th 2012

I understand you comment on the lack of all of the pieces of a jigsaw. I do not know which Tasmanian Tiger your are refering to (although I am not disputing your statement). The past few years have shown the Tasmanian Devil almost went extinct, but this was because of an illness that seemed to be transmitted in that species, and a great deal of effort has gone into trying to prevent their extinction. If this is your point, regarding the Tiger, I am not sure that it is valid. Just to make my point, the use of selection seems to me to be more of an assumption. We are shown nowadays that if conditions are changed sufficiently, species are made extinct; in cases that I see in public discussions, the cause for this is mostly human activity. Is it argued that this may be a form of natural selection?


Jimpithecus - #69408

April 19th 2012

Over 90% of all species that have ever lived have gone extinct because of changing environmental conditions.  There have been at least three major die-offs, the last of which was the at the K-T (Cretaceous-Tertiary) boundary when everything with a body size of more than 50 pounds went under.  Humans were still 50 million years in the future. 

Yes, it is true that humans have made life very hard for a number of species, not the least of which are the non-human primates, but selection has worked wonders in the past without our help. 


GJDS - #69409

April 20th 2012

You seem to have spent much more time on this topic than I have, so I am not trying to dispute your comments. I guess I use the same criteria for other areas of science that I use for my own research and that of my peers - in that I begin with ‘I do not know’ and see how close I can come to ‘knowing’. Within this context, I accept that this area of research has established the earth has been around for a long time, and somehow life began (without going into theistic arguments). Over this long time span, numerous events have occured and for some we have information that is sketchy. I still cannot see how this provides the foundation for a coherent, proven scientific theory, that I am informed is evolution (or Darwinsm) whatever Dawkins may say about the evils of religion. I guess I will go back to my usual position of saying ‘I do not know’ but the scientific method, if I apply it correctly, will enable me (and us) to achieve some reliable knowledge.

Thank you for your response.


melanogaster - #69418

April 20th 2012

Jim:
“In most species, for every generation, thousands of new mutations are present.”

Jim, this is just wrong. The reality is that we have many ALLELES present. You can call it by its proper name, polymorphism, but you have no idea whether they are “new mutations.” Polymorphisms are maintained during speciation, for crying out loud!

GJDS:
“The past few years have shown the Tasmanian Devil almost went extinct, but this was because of an illness that seemed to be transmitted in that species,…”

And why were all of the individuals susceptible, GJDS? What’s the most polymorphic locus in your genome?

“…If this is your point, regarding the Tiger, I am not sure that it is valid.”

Your uncertainty is refreshing!

“Just to make my point, the use of selection seems to me to be more of an assumption.”

That’s not refreshing. It only seems that way because you ignore the evidence and desperately try to pretend that all both sides offer is rhetoric.


Jimpithecus - #69436

April 21st 2012

Motoo Kimura, in the early 1970s, argued that there were many new mutations in each generation but that most of them are neutral.  Some new mutations take hold, most don’t.  A polymorphism is simply where there is more than one allele at a locus maintained in a population.  The presence of a new allele in the population only rises to the level of polymorphism when it reaches 5%.  The Sickle cell mutation was new at one point but, because, in the presence of malaria, the heterozygote was positively selected and it rose to the level of more than 5% in the population. 


melanogaster - #69437

April 21st 2012

Kimura argued? In the ‘70s? Are you kidding, Jim?

The human mutation rate is an uncontested fact that is routinely measured. Why would you employ a creationist rhetorical construction like “X argued”?

Do you not see that when many new mutations occur every generation and those mutations are neutral with respect to fitness, that the vast majority of differences between people are the result of OLD mutations?

Do you not see why I objected to your use of “mutations”?

If you don’t, here’s why. People are genetically different—that’s a fact.

Those genetic differences are subject to selection even if God stopped all mutations from occurring, and since He won’t, it’s imperative to point out that the number of existing differences dwarfs the number of new ones.

Your misrepresentation, on the other hand, feeds beautifully into denialist “reasoning,” in which mutation = random = bad and atheistic.

Do you really not understand that selection doesn’t need new mutations at all? Do you really not understand that polymorphism is an important concept not subject to an arbitrary 5% threshold?


Jimpithecus - #69442

April 22nd 2012

I am not suggesting that the differences aren’t the result of Old mutations.  I do not have any idea where you got that idea.  Of course they are. I am stating that in any given new generation, there are many new mutations.  That is all.  The differences that we see in all organisms, human or otherwise are the result of mutation, drift and selection.  There is absolutely NOTHING creationist in ANYTHING that I wrote. 


melanogaster - #69445

April 22nd 2012

“I am not suggesting that the differences aren’t the result of Old mutations.”

Where did you mention the existing differences? It’s not very wise to call them “old mutations.”

“I do not have any idea where you got that idea. Of course they are.”

Perhaps you shouldn’t go on and on about new mutations, then?

“I am stating that in any given new generation, there are many new mutations. That is all.”

It’s irrelevant to what you were discussing, as it is insufficient to create sufficient polymorphism in many bottlenecks.

“The differences that we see in all organisms, human or otherwise are the result of mutation, drift and selection.”

My point, which you’re not getting, is that when dealing with denialists there is no need to invoke mutation as the origin of heritable variation. Polymorphism is a simple, observable fact, regardless of its origin, and it is sufficient to drive and explain evolution.

“There is absolutely NOTHING creationist in ANYTHING that I wrote.”

Your TOTAL emphasis on new mutations and failure to mention extant polymorphism was a TOTALLY creationist framing. I’m trying to explain to you why it doesn’t work!


Jimpithecus - #69450

April 22nd 2012

I didn’t make a total emphasis on new mutations.  Most human genetic loci are polymorphic and changes in gene frequencies for these alleles accounts for the variation that we see in human populations.  But human evolution is a complex process of mutation, drift and selection.  Polymorphisms form as a result of mutations that are incorporated into the genome of a population.  Selection and drift act on those.  This likely explains the differences between the Neandertals, early modern humans and Denisovans (which have twice the number of genetic substitution differences from the modern humans as the Neandertals do).  But you cannot get genetic substitutions by drift.  And, no, nothing I wrote was creationist. 


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