The History of Man by L.F.
A detailed History of our Incomplete Fossil lineage and why the Out of Africa Hypothesis is Flawed
“Light will be thrown on the origin of man and his history” are the notable words of Charles Darwin in the introduction of The Decent of Man (1871). Evolution arose as a controversial topic initially during the 19th Century. Much of the controversy derived from conflicts between religious or spiritual beliefs in creationism and naturalism and contentions were wagered against the ideas involved in the new theory that undermined those beliefs in some capacity. Even those who accepted the theory as it applied to flora and fauna kingdoms refused the idea that humans may have descended from ape-like ancestors. Thomas Henry Huxley, a colleague and friend of Darwin, addressed the topic of the ancestral origins of man in Man’s Place in Nature (1863) while Darwin developed his ideas about the origin of humans in The Decent of Man (1871) shortly thereafter. He effectively predicted that our human ancestors would be found in Africa as this was the place that our closest living relatives could be found in more modern times. (Lyons)
In time, the theory was accepted by the general population and the previously challenged notion of common descent or that we evolved from ape-like creatures was thought plausible. This acceptance led to new questions of how this could be possible and when and where this occurred. Initially, much of the evidence in support of the origin of man came from the clues offered by the fossil record. Some fossil specimens seemed to have features that did not reflect as similar to modern man for instance, several specimens appeared to have smaller brains. In contrast, characteristics in the latter forms of fossil specimens bore more apparent similarities to those observed in modern man.
It would make sense that the more derived forms came after the earlier, more primitive forms however, for the fossils that are dated to around similar times, we can also make comparisons between their derived characteristics and observed how they link to another. This is how we come to understand which fossils specimens are our human relatives. The incompleteness of the fossil record had posed challenges wherein intermediary species are missing, and this is why, with new fossil discoveries, the human lineage is sometime redefined. We also have incomplete or partial specimens which sometimes tells us only a limited bit of information about the progeny. For instance if we find teeth, we may be able to determine by looking at characteristics of shape, size and thickness, how much the specimen relates to the other forms in the fossil record. What we do see in the human family tree, is that most of the earliest forms appeared on the African continent.
To start off by discussing some of the key fossils that have contributed to our understanding of human evolution, beginning with Australopithecine and progressing to the rise of anatomically modern humans encompasses the consideration of several factors. Some of the factors primarily include the primitive and derived characteristics of each fossil species where we have come to understand features by comparison to past, intermediary and more modern species. From there, we have deduced further information about behaviors, habitats, and relative geography. We can also understand migration patterns by observing location as well as dating specimens. This dually helps us to make comparisons between earlier forms and contemporaries, or later forms. It is important to be cognizant of the fact that the hominin fossil record is incomplete, especially as we go back further and further in time. This poses specific challenges to identifying certain pieces of information about characteristic traits, behaviors, habitats and relationships.
Most recently, a specimen has been revealed as possibly the oldest link to our human lineage. This specimen is very unique in comparison to other specimens and living lemurs, prosimian lineage and anthropoids that encompass monkeys, apes and humans. A private collector had found the specimen several years ago and finally sold it to a Norwegian anthropologist to then be studied by a team of renown scientists from around the world. The fossil, Ida, is hypothesized to be a missing link in primate divergence between prosimians and anthropoids. While it was unclear if Ida was an intermediate form of a prosimian to anthropoid species, morphological evidence points to a transitional species. I was surprised to learn that Ida was found in Germany, near Frankfurt, in a crater created by a volcanic explosion during the eocene period nearly 47 million years ago. Even more astonishing is the fact that Ida is 95% intact. Ida was so well preserved because she had fallen into a water filled crater where she was preserved in the cold muddy sediments at the 800 foot deep basin known as Messel pit. Whereas much of our confirmed hominin fossil line is fragmentary, we are able to look at many of Ida’s morphological characteristics, as the fossil is primarily intact, to determine what she was, how she behaved, how she lived and more. I was also puzzled by the location in which Ida was found because most of our early fossil evidence of this kind has been found in East Africa, including “Lucy” in a region that is collectively referenced to as the “Cradle of Civilization.” This evidence challenges the “Out of Africa Hypothesis.” One of the most questionable hominin specimens appearing in this region much later without an apparent link to Africa would be H. neanderthalensis. Perhaps Ida is a link to this form? If we look at a common geographical characteristic in the Cradle of Civilization, we see that water sources were pinnacle to the evolution of life. In Germany, the Messel pit had been filled with water during the Eocene period which would also be conducive to the development of life. Even as we go back to the Eocene period, and we see that many forms of prosimian or mammalian life began to flourish and diverge from the earlier life-forms, we have never come across evidence of a link to a anthropoid type creature. The eight primate specimens collected at the Messel site are fragmentary at best. This is yet another reason why Ida, as a nearly complete specimen, is such a compelling find. She is so complete that we can even observe through Computer Assisted Tomography that her last meal was made up of seeds, leaves and fruits. In order to rule out a link to the prosimian animals, lemurs, morphology needed to be studied. Ida had some primitive features of cranial and post-cranial anatomy found in lemurs but some of the derived or specialized characteristics that lemurs possessed during the time and into the present were missing in Ida such as a grooming claw and a tooth comb. The opposable thumbs, fingernails and tarsus bone in her ankle is shaped like that of a primate while her small baby teeth indicate a commonality between other placental animals. Her leg structure also indicated that she stood erect. For reasons such as these, Ida has been called the holy grail of human evolution and regarded as our newest find yet oldest link in the story of our human origins.
The hominin-like Sahelanthropus tchadensis was unearthed from strata in Chad, a region in Central Africa and found to be about seven to six million years old based on biostratigraphy analysis. This was an unusual and sort of isolated incidence where most other hominin fossils originated in regions closer to water on the African continent, as water is a life-giving resource. We know a bit about some of the primitive characteristics of this taxon based on the pieces of cranial bones found. For example, we know that the features such as the size of the cranium correlates to the volume capacity of the brain that it may have protected. In this case, Sahelanthropus tchadensis had a small brain similar to that of the African ape. A possible derived feature is a small canine tooth, which leads some scientists to speculate a relationship to hominin lineage. We do not have many other fossil fragments other then the skull structure to evaluate for other primitive and derived characteristics, which leaves a classification as a hominin, speculative. However, from there, we still have enough to make the assumption about this variants locomotion abilities by examining the foramen magnum, which is the opening in the base of the skill where the cervical vertebrae would be connected. In this case, there is evidence to say that Sahelanthropus tchadensis had an erect posture but not enough to discern any early indication of bipedality.
In the East African region, Kenya, fossil fragments from Orrorin tugenesis were excavated from four sites that include, Cheboit, Kapsomin, Kapcheberek and Argai. Radioisotopic analysis methods identify the levels of carbon atoms in sedimentary strata and were used to date the specimens in the temporal range of 6.1 to 5.8 million years ago. Both primitive and derived characteristics were observed. Some of these characteristics have indicated plausible evolutionary relationships of Orrorin tugenesis to the more contemporary forms, Ardipithecus ramidus and Kenyanthropus platyops. One such common feature of dentition is the smaller size of the molar teeth. The specialized thickness of dental enamel is also similar to that of Kenyanthropus platyops and Australopithecus afarenis. Depending on how a comparison is made to other fossil forms, these traits may be considered primitive or derived. The most significant thing we would look for in fossil specimens when placing them taxonomically in line with hominin ancestry would be morphological features that indicate obligate locomotion. Computed tomography imaging of the proximal femur indicated a variation in thickness inferiorly and superiorly which might mean O. tugenensis was bipedal but other specialization’s indicated arboreal locomotion which is the ability to move in trees. Fossils of other animals found in the similar location were more complete and gave better clues about the environment in which O. tugenensis inhabited, by comparison. It is suspected that the environment was wooded with lakes and streams. This may point to the geographical features theorized to coincide with the development of bipedality if not obligate locomotion. I also think that the water resource points to an element of the landscape conducive to survival, and may be one reason why other fossil specimens have been found relatively nearby this region in Africa.
Several other hominid-like specimens have turned up on the African Continent, and we collectively refer to them as hominin types. Hominins have primitive and derived features that may link them to hominid lineage but in several cases, there is not enough fossil evidence to distinguish relationships, especially between intermediate forms. Two hominin forms, Ardipithecus kadabba and Ardipithecus ramidus were discovered in the Middle Awash Valley of Ethiopia, in Northeastern Africa. The catch here is that temporal range in which Ardipithecus kadabba may have inhabited the Middle Awash Valley is 5.7 to 5.2 million years ago while it was found that Ardipithecus ramidus lived there between 4.5 to 4.2 million years ago based on paleomagnetic studies which evaluated periodic reversals in the Earths geomagnetic field and radioisotopic dating records which measured the decay rate of radioisotopes like carbon atoms isolated in strata. There is a significant time difference involved between the emergence of each form. The latter form, Ardipithecus ramidus is more indicated to be of hominin relation while Ardipithecus kadabba is only speculated to be. Study of the crania and post-crania structures, as fragmented fossils, points to bipedalism as a derived trait. Most indicative of this reference toward obligate locomotion, or at least bipedality, the feature we are looking for as a clue to hominin relation, is upward orientation in the joint connecting to the fourth toe. A similar morphology has been identified in the hominin species, Australopithecus afarensis and even the most modern hominids, Homo sapiens. A problem here is the fact that the toe bone was found at a distance away from the other fossil specimens and was dated to several hundred thousand years earlier. Perhaps, this fragment points to the existence of and intermediate or earlier form? There is really not enough evidence to say. If more fossil fragments were discovered, then perhaps scientists could discern more distinct conclusions. In contrast, we know much more about Ardipithecus ramidus. Ar. ramidus did not evolve obligate bipedality but perhaps had functional bipedality which is the ability to walk upright for periods of time, for a momentary or brief purpose. We see functional bipedality in chimpanzee populations. Cranial structure and dentition indicate some homo characteristics. Locomotive behavior is suspected based on the size and shape of the ischium as related to muscle development and primary movement on all four limbs. Ar. ramidus specimens were not only found in the closed woodland region of Middle Awash Valley but also in Gona, a region that also had grasslands.
So when did hominids begin to walk upright as their primary form of ambulation? Perhaps around 4.1 to 3.9 million years ago, according to radioisotopic dating of volcanic sediments that encased and preserved Australopithecus anamensis fossils. Australopithecus anamensis is said to be the first of the Australopithecus and early homo genus with obligate bipedality. Around 3.5 to 3.2 million years ago came Kenyanthropus platyops, discovered sometime after Australopithecus anamensis in a relatively close part of Kenya. Kenyanthropus platyops fossils indicate more primitive features complimented by derived traits which has made it difficult to distinguish the exact relationship to other hominins. It features a partially flat face similarly observed of Homo rudolfensis as well as Australopithecus afarensis but it is possible that this feature is a result of skeletal wear or damage, and K. platyops may just be a variant of Au. afarensis especially as the temporal range of Au. afarensis which is 3.9 to 2.9 million years ago, coincides with that of K. platyops and both linages were discovered in Kenya. Au. afarensis, dubbed “Lucy” is a near complete skeleton which means that we know a lot about this fossil, and can make comparisons to some incomplete Au. afarensis specimens that include consideration of sexual dimorphism’s and age differences. The scientist, Mary Leakey and her team discovered fossilized footprints from Au. afarensis. This clearly points to obligate bipedality which is an adaption that would also eventually allow for species to migrate further distances. Population expansion and isolation greatly influenced the evolutionary progress of early hominids. In addition, Au. afarensis was present for almost one million years which must mean that the population expanded in terms of variants. When populations grow it increases competitive pressures and warrants expansion. It is also a precursor to the necessity of greater interdependence as a benefit to survival and in competition. Interactions between others and communication would have likely developed to some degree and this may have led to learned behaviors. Evidence of learned behavior may be that tools, that were not necessarily constructed but derived from natural elements, were used to accomplish specific tasks, such as scrapping the marrow from animal bones.
According to biochronological dating methods, Australopithecus africanus is one of the oldest hominids to be discovered in south Africa, around 3 to 2 million years ago. As time has passed many Australopithecus africanus fossil fragments, both cranial and post-cranial, have been unearthed, allowing scientists to call Australopithecus africanus, a true hominid. Australopithecus africanus is considered a distinct link between modern man and our ape-like ancestors. Prior to this, the piltdown man, “discovered” in England was thought to be the closest link between man and ape until the multi-specimen was exposed as a fake. Au. africanus and A. afarensis are quite similar in certain ways, in terms of an evolutionary relationship in that they were both small-bodied in comparison to earlier forms. Their pelvis, leg and foot structures such as the phalanges were adapted to allow for primary bipedality. Some derived characteristics in Au. africanus also found in other Homo species are a taller frontal bone and a longer flattened orientation of the occipital structures. Australopithecus garhi is said to have inhabited Ethiopia 2.5 million years ago, just as A. afarensis had earlier. Features for dentition in Australopithecus garhi were divergent from the more primitive traits observed in robust australopiths. Australopithecus garhi species made stone tools which likely indicates a higher level of cognition then some number of their possible predecessors. The ability to develop technologies would not only be linked to neurobiological advances in evolution but also morphological distinctions perhaps those even adapted ensuit to bipedality. The relationship is not so much the indication of a nature to nurture relationship but a nature to nurture relation. Very generally, I want to reference the fact that walking upright freed the hands, to create and use tools. The longer femora of Australopithecus garhi are distinctly different from the femora of Au. afarensis and more like that of Homo sapiens. Derived post-cranial features indicate bipedality which suggests the link between Au. garhi to the genus Homo. There are also some primitive characteristics apparent in Australopithecus garhi. Around the same epoch, 2.7 to 2.5 million years ago, Paranthropus aethiopicus may have appeared as an intermediate species between Au. afarensis, Australopithecus garhi and both, earlier hominin and contemporary forms but scientists are not really sure how this species, if distinct from another and not a variant, fits into the hominin phylogeny. Paranthropus aethiopicus, was discovered in Kenya in 1985 by Richard Leakey (the son of Mary Leakey) and has also been identified as originating in Ethiopia. Morphological evidence points to the function of the temporomandibular joints as similar to Au. afarensis. We see that there are some features in common with Paranthropus robustus, a hominin said to have emerged in south Africa 2 to 1.2 million years ago. Another robust australopith, Paranthropus boisei emerged in a very close timeframe to that of Paranthropus robustus, just 2.3 to 1.4 million years ago. Both species of australopiths had cranial features different from most all other hominins, such as megadont cheek teeth. It is suspected that there are no descendants of either species.
1.95 to 1.75 million years ago another Australopith, Au. Sediba appeared in South Africa. Au. Sediba, like most all hominins that emerged prior to homo sapiens, has some primitive and derived features. Au. Sediba shares many features with other Australopiths with the exception of Au. africanus. The shape of the pelvis is distinct to structural features observed in Homo erectus. Husband and wife team, Mary and Louis Leakey turned up Homo habilis in Kenya. Homo habilis is one of the first species of the homo genus, that lived 2.5 to 1.6 million years ago. Finally, we are following the fossil evidence closer to homo sapiens emergence. Cranial morphology was similar to that of Australopiths but the cranial capacity was larger. Both primitive and derived traits appear such as thick and curved phalanges that point to an ape-like ancestor and palms similar to homo sapiens.
Homo erectus emerges 1.8 to 50 thousand years ago in Indonesia, China, and northern, eastern and southern Africa. It is clear that Homo erectus had migrated to different areas based on the fact that land-bridges were formed during this time by expanded glacial covering which also retreated at different times, and led to isolated populations. It is the first known species to have moved out of Africa. It is very possible that differences emerging between the Asian and African phylogeny of Homo erectus as a species was greatly influenced by different geographical niches. For example, some of these differences in the environment may have been different dietary resources which led to distinct adaptions in features of dentition. Also, similar cranial and post-cranial features as well as time and displacement of the Homo erectus lineage has directly linked the hominid to that of Homo habilis. A possible predecessor of Homo habilis was Homo rudolfensis.
Recently, the fossil Homo floresiensis was discovered in Indonesia and is dated back to 100,000 to 12,000 years ago. A timeline that coincides or partially overlaps with that of Homo neanderthalensis and Homo sapiens. Homo floresiensis was quite distinct in that it had a significantly smaller body size then other hominins observed to have lived during that time, as well as by comparison to some earlier forms. There are some cranial features present that correlate with those observed in Homo erectus but also divergent post-cranial features that resembled those found in Australopiths. So with several primitive features present, what linked Homo floresiensis with Homo sapiens? Derived characteristics appearing as morphologies in dentition such as tooth enamel thickness, size and shape of molars and of the mandibles, were similar to Homo erectus and Homo sapiens but of a smaller scale. Homo floresiensis is a hobbit, standing about a meter tall. It is suspected to be a dwarf form of the Asian line of Homo erectus. While conflicting and more recent theories regard H. floresiensis as a later form of H. habilis. If this is so, then there are some challenges posed to what was previously determined about the dates and possibly the migratory patterns of early Homo species in that the idea intends that H. floresiensis left Africa before the evolution of H. erectus. Due to the smaller stature of this line, it’s cranial size was dwarfed which coincides with a smaller brain size similar to that observed in much earlier periods. Skeletal structure indicates obligate bipedalism which had also been assumed based on the similar ability being found in multiple common ancestors. Other clues such as tools were found, dating back to 840,000 years ago appearing as stones that were reconstructed and used for survival purposes. Dwarfing may be a result of environmental conditions such as limited food supply and isolation which is conducive to the conditions of their reconstructed environment as shifting between glacial and interglacial cycles. No larger forms of Homo floresiensis have ever been discovered which raises the speculation that they arrived on the Island of Flores in a variant form of similar stature. Other Scientists believe that this fossil form was a variant of the Homo sapien but suffered a disease which would account for its petite size. There were problems with this idea though because there has never really been a disease that would consequentially impact size, but perhaps development and most of these conditions are arising in genetic mutations. This may explain why there were several small statured variants appearing but the hypothesis is negated by the fact that if it were so there still would have likely been larger that appeared as well.
Homo heidelbergensis appears to have lived in Germany 800 to 350 thousand years ago. Homo heidelbergensis possessed primitive traits seen in Homo erectus such as a projecting face and brow ridge and many more derived traits found in Homo sapiens such as a large cranial capacity. Homo heidelbergensis crafted and used tools in a manner that precursors the technological developments of homo sapiens.
Homo neanderthalensis lived 200 to 28 thousand years ago and for some of the time, along side Homo sapiens which emerged 125 thousand years ago and survived as a species, into the present form of modern man. Homo neanderthalensis is found throughout Europe and western Asia and suspected to have lived in caves. They were quite skilled in hunting and gathering. Some of their behaviors were similar to that of Homo Sapiens but they were morphologically different in some ways. There is no concrete evidence that points to the intermarriage of Homo neanderthalensis and Homo sapiens despite their similarities and coexistence for a period of time. It is suspected that their cranial capacity did not compare to that of Homo sapiens and for this reason, adaptive changes in behavior to the rapidly changing conditions of the global climate during ice ages could have been more of a challenge. Here, cranial capacity is not necessarily indicated by cranium size, but perhaps structure. Homo neanderthalensis actually had a much larger skull them Homo sapiens as well as a larger post-cranial build. This information tells us that the Homo sapien brain as a glandular organ, was larger then ever before observed in the Homo lineage. It is said that Homo sapiens were more cognitively able to adapt their behaviors to environmental changes in comparison to Homo neanderthalensis which may have led Homo sapiens to out compete Homo neanderthalensis to extinction. It seems as though Homo neanderthalensis as a fossil specimen receives a significant deal of attention from scientists and the public alike. I think this is because there is a strong connection between this species and homo sapiens whereby temporal range overlaps, regional habitation or even regional co-habitation is indicated and further there are not only some common characteristics but great differences which drive many questions about where exactly Homo neanderthalensis falls in the lineage of hominins. Also, the reason for the extinction of Homo neanderthalensis seems unclear while the extinction of earlier forms seems a to be explained by intermarriage, expansion, environmental factors and other pieces of evidence such as the identification of fossil specimens as intermediate forms and molecular evidence that places such progenitor species in the homo linage with more certainty. To note, there is no proof alluding to intermarriage between Homo neanderthalensis and Homo sapiens, but in the context of evolutionary theory, the question has been raised. In that context, it is possible that one species evolved to a more derived modified form while the other is replaced by that form. In some cases, animal hybrids have had an advantage over progenitor forms because they inherited traits from both parents which may have given them advantages that both the earlier forms possessed apart from one another. In addition, Homo neanderthalensis lived along side Homo sapiens but Homo sapiens did not become extinct. So what were the differences of factors that drove Homo neanderthalensis to extinction and not Homo sapiens? Scientists have been able to make many hypotheses to try to answer this question. Some cite environmental factors however, if those environmental factors left populations volatile during that time, how come the same impact was not observed in the Homo sapien population? Were there physical differences that allowed for Homo sapiens to better adapt to rapid shifts in the climate such as temperature? The drying or drought periods combined with periods of flooding were experienced around the globe due to glacial recession and expansion. It is possible that food sources were depleted as a result, both plant and animal alike. Here we may consider that Homo sapiens possessed some cognitive advantage as one possible trait that allowed them a survival advantage over Homo neanderthalensis. This advantage may even implicate a struggle for existence as competition between each progeny. Darwin tells us that “It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change.” Indeed, I agree but I think a higher ability toward cognition could have created an advantage in this case while I also think there may have been some other physical differences. In consideration of an entirely different probable cause, I wonder if some disease effected the Homo neanderthalensis population and not Homo sapiens based on genetic differences. We see that certain viruses only effect certain animal species and not others so there is some supporting research on this sort of occurrence. Now along this line, there has also been DNA analysis for Homo neanderthalensis that indicates a lack of diversity in mtDNA sequences. Why is this? Did they evolve from a extended yet related tangent of the Homonin line, where the predecessors of their population did not expand as much as those ancestral links more directly associated to the Homo sapien line had? If so, this could account for the lack of diversity in mtDNA and a correlated under exposure to certain pathogens. In this case, we can infer that Homo sapiens may have had the advantage. It is not unheard of that disease could spread at pandemic rates and relate to high mortality rates in certain populations; We have historic record of this. So if it happened at a later time, perhaps it had happened at an earlier time in the history of man. What we do know for sure is that the line connecting Homo neanderthalensis with Homo sapiens diverged some 500,000 years ago. Finally, there is more to discuss about Homo sapiens, because that’s us! Homo sapiens are the genus of modern man. As mentioned above, H. sapiens emerged around 175,000-160,00 thousand years ago in East Africa. In an earlier comparison between Homo neanderthalensis and Homo sapiens, I mentioned that Homo sapiens may have had a cognitive advantage. This postulation has been backed up by fossil evidence as great differences in cranial and post-cranial anatomy have been discovered. Larger cranial size relates to the structural capacity to house a larger brain. We can also make reasonable predictions or assumptions about the stasis and features of the environment for the time and place based upon where the location of Homo sapien fossils were found. We know that changes took place and a more tropical environment developed. One of the ways we can determine this is by also studying the fossils of other fauna and specifically flora located around the same regions and dated to the similar time. The presence of Homo sapien fossils in such a time and space thereafter environmental changes suggests that the population adapted. This has multiple implications which include the idea of a larger cognitive capacity and structuralisation of the brain anatomy and physiology. Anatomical changes like this would mean that behavioral changes and adaptions were possible, thus, an advanced cognitive capacity may have benefitted survival in many ways. Some of these behavioral changes are measurable by the comparison of relic evidence such as symbolism in cave drawings, advanced tools, and a related subsistence strategy such as using those tools to procure sources of nourishment through agricultural and hunting applications. Advancements in sustenance strategies may have even led to the extinction of other animal species as several populations were outhunted, especially when resources were scarce. Resources would be particularly scarce based on a shifting climate theory, making populations more vulnerable to factors that influenced their declining numbers and extinction. In addition, sustenance strategies may have aided the survival of animal populations as it increased agricultural byproducts. New evidence suggests that farming began 23,000 years ago. Seed gathering by stone age people was taking place around 10,000 years ago. Cro magnonensis was modern man, one of the most early forms of homo sapiens. Homo sapien Cromagnonensis was a stone age population that existed 10,000 to 40,000 years ago. This is supportive of the fact that Homo sapien Cromagnonensis developed some forms of systems which they also did socially as hunter-gather societies where gender specialization and social stratification were implemented.1
Homo sapiens were gracile and of a more petite build in a general deliberation to earlier forms including H. neanderthalensis and H. heidelbergensis. The smaller size of Homo sapiens may have also given the species its own unique advantages. The smaller structure was an advantage to maintaining body temperature in tropical warm climates. In some recent studies this morphological advantage of heat stabilization is linked to advancement in cognitive ability. To study these advantages is important for our past and present understanding of human evolution. There are morphological differences in dentition and cranial features such as the smaller size of the mandible, which tells us that the way in which they consumed food and what types of food they ate may have been different from earlier forms or related species. Perhaps they were able to chew foods better and in turn derive more nutritional elements out of products for consumption? Their technological advancements allowed them to fish and hunt a wide variety of prey, and this undoubtably exposed them to new nutritional elements as common elements in their diet. The new forms of tools and their general tool arsenal must have been developed gradually over time. I think if we can assume this, we could also assume that the secrets of their trade were communicated between one generation to the next. These tools may have given Homo sapiens a survival advantage over H. neanderthalensis who perhaps lacked the instinctiveness combined with cognitive capacity to develop the more advanced tools on their own. This is assumed for the sake of contemplation alone and not to imply as an absolute, that each population did not have common instincts or even some similar cognitive abilities because we see even into the present that many animal species have similar instincts derived based on similar survival needs and that this capacity has a indication toward neurobiological processing. Even if H. neanderthalensis could learn how to develop such tools by example it is very likely communication barriers and defensive instincts segregated the populations, where learned skills were non-commutative. In fact, recently the evolution of prejudice has been explored in rhesus monkeys in isolated natural populations and it was observed that one group would demonstrate discriminatory behavior in response to facial misrecognition of outsiders. One reason for this behavior was because outsiders may have posed a threat. So even if Homo sapiens could communicate somehow with H. neanderthalensis, it may be unlikely that they would teach them techniques that would allow them to outhunt the other kind.2 It seems very unclear as to whether or not H. neanderthalensis crafted tools on their own despite more significant findings that they have have used naturally occurring materials, as is, for tools. Perhaps the ongoing excavations of territories once inhabited by H. neanderthalensis will unveil greater evidence of tool making in the future.
Another reason why Homo sapiens may have developed better and better tools is based on their values for expansion. Expanding over greater areas, toward and to the European and Asian continent would have allowed them to obtain more diverse natural materials to use in their technological innovations. Expansion is often driven by a desire to escape competitive pressures in the evolutionary context. Even if one animal population was not experiencing such competitive pressures and another animal population that they preyed upon was, their prey may migrate and therefore some populations that relied on that food source followed. Migration alone likely became a demographic advantage because different portions of the collective population would have been exposed to different environmental factors such as different resources, different pressures, different diseases, different climates and isolation. Isolation may have occurred as a result of settling in certain areas for certain times by preference but also as glacial melting dissolved land-bridges that connected early geological and geographical expanses, during times when the super continent Pangea was being broken down. Tectonic motion resulted in earthquakes and volcanic activity which caused separation of landmass as well as the development of new land-masses. As populations expanded under these conditions they would have adapted derived characteristics through the criteria for evolution by natural selection. Their populations would become more diverse and such diversity would likely be in more ways favorable to survival. H. neanderthalensis had a stockier build that was indicative of habitation of a colder environment. This may have been a disadvantage in expansion as they may not have regulated thermal stasis within their bodies as easily as Homo sapiens, who were adept to warmer climates but also could develop methods of keeping warm in colder climates, such as developing shelters or clothing. Here we see that it is not even just a physical adaption but the application of cognition to innovation and material creations that could also play a part in how species interacted with features of their environment. Where each species may or may not have been able to develop adaptive mechanisms to thermal regulation, biochemically, if some number of variants were able to acquire traits or characteristics for the regulation of body, some may have survived to reproduce in greater numbers and the adaptive mechanism may have become dominant. H. neanderthalensis as a species, originated in Europe and Asia. We know this based on the fact that these are the only regions where their fossil remains have ever turned up. As Homo sapiens expanded there appears in the fossil record to be a systematic displacement of H. neanderthalensis by Homo sapiens. Maybe they didn’t just out compete the other in terms of resources but also in violent combat. I am not sure that there is direct evidence. Perhaps wound markings on fossils could give us some clues but even if we found wound marks on fossil specimens it would be difficult to say where they came from, if not from a predator, or their own kind or outsider populations? It could be possible to evaluate the type of wound and see if it came from a weapon that Homo sapiens used or the teeth of a predator, but I suppose the findings would not be definitive with certainty. Violent behavior as a territorial defense mechanism and as a resulting form of competition, is observed in many animal populations. Even if we can infer the likelihood of this sort of fight between species, could we know who started it? We’d have to observe very delineated circumstances, such as the nature of the species. Were they passive or aggressive. Would they move on if another population came to compete for their land or would they fight for the territory? These are the sort of questions we need to answer to at least determine what happened to H. neanderthalensis.
Many of the Homo sapien behaviors I have mentioned did not evolve all at once, but at slightly different times and regions in Africa, while research suggests the behaviors did evolve more uniformly on the European continent. This is probably because the expansion of Homo sapiens out of Africa did not take place for several thousands of years and those behaviors were likely to be adapted in Africa and carried with the species to Europe. As a matter of fact, it was probably not just traits like bipedality that allowed for expansion but also the development of tools and behavioral adaptions that allowed them the versatility to survive in different environments and during the survey of great distances. There is also evidence that both H. neanderthalensis and H. sapien populations used fire. Some paleolithic people wore hides and may have even woven garments; Homo sapiens crafted beads and pendents from shells and bone and even carved figurines, like venus figures, that perhaps represented a value for fertility.
Advancements in technologies that allow for the analysis of genetic evidence has pushed our understanding of our human lineage further. We no longer have to rely only on the clues of fossil evidence or applications of environmental analysis alone but we can now look at factors such as changes in single-nucleotide polymorphism’s in those fossils, or the displacement as time and space variables, for the frequency and rate of change in mtDNA sequences and y-chromosomal patterns. We can not only observed these values from fossil specimens but also in modern man into the present. What we find is most profound in the search for our human origin. We’ve learned by genetic testing that there is greater diversity present in modern African populations then other populations around the world. We have also learned from this, that that population is much older then other populations. This means that evolution occurred for a longer period of time in Africa then anywhere else in the world. This is confirmed in the fossil record also as most early hominin forms are found on the continent. As for our origins, it seems clear that our common ancestor(s) came from Africa. This is called the Out of Africa hypothesis. Before I talk more about this idea at length, I want to mention its implications on the relationship between H. neanderthalensis and H. sapiens. It had been determined to some significant degree through genetic analysis that neither species interbred which would rule out any gene flow hypothesis about their relationship while other genomic studies suggest it occurred rarely. H. neanderthalensis may just been a separate, distinct species in terms of genetic distinction apart from H. sapiens. In light of the recent findings, some scholars still maintain the multi-regional model. Genetic or genomic comparison between H. sapiens and earlier forms dating back to almost 4 million years ago has given many more indications about where each form comes in line to the next, where it may have been unclear in some cases. While, “researchers continue to unearth fossils from all over the globe, and add branches to the evolutionary human tree, enriching, but at the same time complicating, the story of our origins,” molecular evidence advances our understanding which leads us to take a closer look at the, Out of Africa Hypothesis. Lyons, Bones of Contention: The Fossil Evidence (2011)
The Out of Africa Hypothesis
The Out of Africa Hypothesis a.k.a The Human Replacement Hypothesis is the postulation that every Homo sapien, or human on earth is directly descendant from a small group of hominids originating on the African continent. One tangent of the theory is supported by y-chromosomal DNA analysis that suggests that a small group migrated out of Africa around 50-60,000 years ago and expanded to become a global population. There is also a conjunctive theory called the “Eve Hypothesis” which links the human lineage with a most common recent ancestor as a matrilineal female hominid that lived in East Africa around 200,000 years ago.
The “Eve Hypothesis” is based upon the idea that we are all living decedents of a mitochondrial eve. There is mitochondrial DNA (mtDNA) evidence that has been uncovered through genetic and genomic analysis especially as endeavored by The Human Genographic Project, in support of these theories. Female mtDNA is trackable because it does not undergo rapid mutations. Analysis of mtDNA can be traced back as patterns in matrilineal heritage while patterns in y-chromosomal inheritance allows scientists to trace back the origin of man to an “Adam” or common patrilineal ancestry. While I have no doubt there are in fact both a male and female common and recent ancestor to all of humanity at large, the question here for me was how could our common matrilineal link have appeared so much further into the past then our patrilineal link? Was this because there were separate migration lines that converged these two genetic “amalgams”? The answers are unclear to me but I think one explanation may lie in the fact that we are tracing back a molecular fossil record, of two distinct origins, which is mtDNA and y-chromosomes.
We know that the male sex determining chromosomes in the genus Homo are XY while the female combination is XX. For this reason, males always inherit their y-chromosome from their paternal parent and only inherit one X-chromosome from the maternal parent which is the partial reason as to why males do not pass along an mtDNA sequences that are traceable to a matrilineal ancestor including a most recent common ancestor. It is also why we can trace the y-chromosomal frequencies and patterns back to a patrilineal common ancestor. In addition, it may account for the different temporal ranges for each point of origination, that of “Adam” and that of “Eve.”
There seems to be distinct problems in tracing such roots which I think is why we see different patterns of decendency unveiled by The Human Genographic Project. Before I talk about those patterns and their implications, I want to address what I believe to be the probable cause of the divergence between the adam and mitochondrial eve lines as well as why the studies on the topic are limited.
While we can collect wide samples from current Homo sapien populations around the world, we have a limited fossil record which makes for a limited sample comparison on at least one end. We also have several controversies arising out of conflicting views having to do with the incompleteness of the fossil record. For example, we have several ancestral groupings popping up in different locations at different times, and also co-evolving. With molecular evidence we can sort of bypass some of the indirect leaves on our evolutionary tree and focus more on the branches in order to propose a mitochondrial eve or in that, an adam; collectively our most recent common ancestors. We may have to consider that mitochondrial eve was either the only matrilineal progeny in existence at the time of origination, that did in fact reproduce and(or) there were others but none of their children survived. More so, I do not think the argument ends there in fact, I have thought of another idea based in theory which suggests that mitochondria was acquired in our human DNA several millions of years ago and passed on through female oocytes. Paying attention to those details I also recalled that mitochondrial DNA (mtDNA) is located in organelles, called mitochondria and in eukaryotic organisms convert food sources into energy. Note, that the ability for earlier hominins to conserve energy could have had great evolutionary implications, such as the ability to retain energy when escaping predation. Here I want to focus on what this may have meant for reproduction and how it shapes the line that we draw back to a common matrilineal ancestor.
The Endosymbiotic Theory proposes that energy-producing eubacteria may have been engulfed by a larger primitive cell and come to reside within it, eventually evolving into what we now know as mitochondria. Based on what I know, and what I have recently studied about the origins of mammalian evolution as it relates to captured genes from viral genomes, there is evidence that mammalian DNA that is similar to viral or even bacterial DNA, and the mechanisms of transcription, may by default admit the DNA of an invading pathogen within it’s own DNA by the capture and reinsertion of genes from the invading organism, where that genetic material may have been reinserted back into the mammalian genome. This is considered anti-apoptotic cellular behavior and may indicate the ability of pathogens to integrate within the human genome whereby a cellular memory is forged. We see this occur even into the present with the pathogenesis of oncoviruses. What I am suggesting is that there are several factors in support of the hypothesis. However debatable the origin of mtDNA may be, we know that all humans carry mtDNA within their cells and scientists can trace that information back to mitochondrial eve. From that, one may wonder if there were in fact earlier forms, or a mother to our mitochondrial Eve that did not come to acquire mtDNA in her cells and therefore we really would have no way of tracing a common matrilineal ancestor beyond 200,000 years ago through this type of analysis, if there was in fact one.
Along the same line, and assuming or accepting that symbiosis plays a role in evolution, I want to mention that the captured retroviral envelope protein, syncytin, appears to have integrated in placental animals and our primate ancestors several million years ago. HERV proteins, syncitin-1 and syncitin-2 are passed on in mtDNA. These genes allowed for more vital births and this may be why we see a population expansion in terms of numbers following the lineage of mitochondrial eve.
Dr. T. Heidmann and colleagues (Placental syncytins: Genetic disjunction between the fusogenic and immunosuppressive activity of retroviral envelope proteins. Proc Natl Acad Sci U S A 2007; 104: 20534-20539.) suggested in the results of their work involving Placental syncytins, that the protein that exists in viruses, called syncytin, originated in an evolutionary context, as a surface protein on retroviruses that fused to cells, and became essential for human birth because it is expressed in the placenta. Dr. Heidmann and colleagues determined this by knock-out studies and experimentation, where the gene was disabled in mice and the placentas became deformed leading to embryo death. Syncytin, as a captured gene in humans, is expressed by the foetal side of the placental membrane and allows for vital nutrient transfer from mothers their embryos through the the syncytium. It also helps cells from both the mother and child to not enter one another’s blood stream and effectively prohibits any immunological attack on either organism. It is a benefit to survival but there is more; Genetic material in viruses is also present in human DNA so does this conclusively mean that most proteins are acquired in a similar capacity? This makes for an alarming hypothesis (should it be taken as conclusive) in that some 40 million years ago the borna virus infected our monkey-like ancestors. Presently, viruses are found in about 5-8% of the genome of every person on earth, according to the reference for the article, Hunting Fossil Viruses in Human DNA (Carl Zimmer), that is, Endogenous non-retroviral RNA virus elements in mammalian genomes. Nature 463, 84-87 (7 January 2010) The results of this work suggest that a measurable 8% of the human genome is traced back namely, to retrovirus infections. “To put that number in perspective, that’s seven times more DNA than is found in all the 20,000 protein-coding genes in the human genome.” Hunting Fossils Viruses in Human DNA (Carl Zimmer, 2010)
With regard to the above from an evolutionary standpoint, it is important to point out that the generational effects of captive virus are going to take place only in the surviving descendants of populations that had been infected where integration of pathogenic material is effectively inserted within the human genome. This idea is even true to the requirements of evolution, in specific relevance to Darwin’s three criteria for natural selection where: 1) a trait producing variation for some characteristic (whether known or unknown) exists, 2) is at least partially heritable and 3) variants survive to reproduce at higher rates (herein, germ cells carry the viral information). Germ cells are spermatozoa and oocytes. An oocyte that carries mtDNA is a germ cell. When effected germ cells existent in progenitor species come together during gametogenesis, the viral information is often distributed in the genomic structure (i.e. chromosomes) of filial generations. The genome of the offspring is impressed by the provirus, that is the latent or hidden derivative of the virus that has successfully integrated within the genomic structure. This integration had and(or) continues to take place where reverse transcriptase activity occurs or is coded in Long interspersed repetitive elements or Long interspersed nuclear elements (LINE). I suspect this could mechanize a sort of epigenetic effect within some locus of expression, causing a sort of fossil remnant in human DNA.
The big point that all the above leads up to comes in the suggestion that mtDNA may have in fact come into our human genome through some process of endosymbiosis and pathogenesis. If this happened at some point in time, 200,000 years ago, then the theoretical eve may not be the most recent common human ancestor but she may come in line before or even after the time in which our current model tells us. That is, a true eve apart from one that we trace through mitochondrial evidence.
The story of the origin of the origin of man must hold the evolutionary precept that over time, forms tend to become more complex through the acquisition of specialization’s primarily through the process of natural selection. This is why the point of origin would really go much further, beyond the emergence of primates, beyond the divergence of prosimians from anthropoids, to explore what I believe would be very simple molecular compounds that developed more complex life-forms through symbiotic relationships. Those compound would likely have been subject to decomposition based on their purely organic nature that a record of such singular cellular compounds would only be observable in a more complex fossilized form which had integrated them into their genome. This does not make the search for our roots obsolete but it in fact fortifies it because what we are doing here, especially in the case of mitochondrial eve, is tracing back molecular evolution in living ancestral organisms. So this begs that question, when we theorize about mitochondrial eve, are we taking about the point in which a common matrilineal ancestor evolved or are we talking about the point that the derived specialization of mitochondrial expression in our DNA was acquired, such as we would point out the time in which morphological specialization’s allowed for bipedality? In essence, we are tracing the mitochondrial pattern in the x-chromosome of eve but if the endosymbiotic hypothesis is true, then we really may just be pointing out a time of a common specialization in a common matrilineal ancestor, where she may too have a matrilineal line leading up to her, that is not trackable by the same process. In other words, I think mitochondrial eve is a point of common ancestry but I do not know if she was the most recent common ancestor or if there is some other specialized trait that can be traced back further, apart from mtDNA analysis. Now is this such the case for our patrilineal adam?
I think we can say our adam is a bit different, because there we are tracking something entirely different which is the pattern and frequency of the male sex-determining characteristics, for the y sex chromosome (haplotypes) groups in an XY chromosomal combination. If we could trace male mtDNA back to a common patrilineal ancestor perhaps we would see the theoretical emergence of this take place around the same times as it has with mitochondrial eve, 200,000 years ago but since male mitochondrial cells are selectively destroyed during the process of meiosis and mitosis in fertilization, we cannot trace patrilineal ancestry through mtDNA analysis. This could be one reason as to why we see the emergence of Adam as our most common recent patrilineal ancestor appearing 50-60,000 years ago and mitochondrial Eve emerging much further in the past, some 200,000 years ago.
It is important to understand that when we consider common ancestry, we are considering a point of intersection, of convergence, not divergence. Thereafter we can observe divergence from that point and that is the focus of the Human Genographic Project. To understand the point of origination for a matrilineal and patrilineal line, we have to consider that we are tracing back the origin of two distinct groups. One reason we know this is because our adam is emerging about 50,000 years ago, while he surely had a matrilineal line, it is not traced to this timeframe. Matrilineal heritage, and our common recent ancestor mitochondrial eve is traced back much further probably because our most recent common ancestors were from separate families. I think that mitochondria Eve as a most common recent ancestor would have had to be the standalone female where the females around her did not survive to reproduce, adam could have reproduced with several females, producing several lines. Well, this is really not an entirely correct assumption. Earlier on I had discussed that mitochondrial eve as a most recent common human ancestor may had been the only human to survive and reproduce the mtDNA sequence observed in all females on earth into the present but that may not be the case. This is because comparative estimates of nuclear DNA studies place mitochondrial eve as living in a time when the number of variants in a population was at least in the tens of thousands and some of those numbers must have been female. So, what must have happened was that somewhere along the line, there was a single male that reproduced female offspring forging a mitochondrial line and mitochondrial eve is the matron of such line. Also, the most recent common ancestor (MRCA) is a distinction that refers to the most recent common ancestor of all homo sapiens, revealed by The Human Genographic Project to have emerged only 5,000 years ago in what is referred to as the identical ancestor point (IAP) or last common ancestor (LCA). If we should only explore this point then it would not reveal as much about our early human origins as tracing separate paternal and maternal lineages has which tells us about our MRCA.
We can recount the advancements in technology that allowed for the processes that have led to the Out-of-Africa hypothesis, to appreciate the theories further. While none of the milestones involved in the journey toward the development and applications of such genetic analysis are in anyway obsolete, I could only recount some of these landmarks here as the historical advances are so great. I could start with the discovery of the transformation principle was made up of Deoxyribonucleic acid (DNA) by Avery, MacLeod and McCarthy in 1944 and the discovery of the form of DNA as a double helical structure by James Crick and Francis Watson as a revelation that eventually enabled us to understand it’s function in inheritance and other capacities but I would be recounting innumerable steps. So, I want to skip ahead for the purpose of understanding how the Human Genographic Project started. In 1967, Allan Wilson and Vincent Sarich followed ensuit to one of the founding fathers of molecular evolution, Emile Zuckerandl. Emile Zuckerandl worked with his colleague Linus Pauling at The California Institute of Technology (Caltech) to develop the idea that time or displacement variables could be determined from molecular analysis. He studied the link between hemoglobin proteins and phylogenetic distances in human populations which culminated in his work, Evolutionary Divergence and Convergence in Proteins (1964). This work initially proposed the Molecular Clock Hypothesis and offered some evidence of an evolutionary clock with hands that pointed toward patterns in genetic sequences as indicators of what would become the working basis for the Out-of-African hypothesis. (History of Recent Science and Technology. Interview with Zuckerkandl. Caltech. <http://authors.library.caltech.edu/5456/1/hrst.mit.edu/hrs/evolution/public/clock/zuckerkandl.html>) In 1967, in collaboration with Vincent Sarich, Wilson, following the work of Emile Zuckerandl, argued that molecular clocks could reveal much about the early history of the human race. In the 1980s Wilson sought to challenge the paleontologists once more, this time on the issue of the emergence of modern humans. While anthropologists favored a date of 1 million years, Wilson’s work suggested a time no later than 200,000 years ago. (Allan Wilson<http://www.answers.com/topic/allan-wilson>) Wilson studied mitochondria and postulated that all mtDNA must have been present in a common female ancestor. This led to a study of mitochondrial DNA in individuals from several continents and races where phylogenic trees were constructed, where two branches that were distinguished and linked to a common female ancestor emerging on the African continent.
The Human Genographic Project uses the results of the analysis of people and groups from around the worlds DNA sequences to trace the migratory patterns of our Human lineage out of Africa and around the world. Humans ventured out of Africa about 60,000 years ago, leaving behind genetic footprints of their journey. Mapping the appearance and frequency of genetic markers in modern populations we can see the pattern of expansion in ancient peoples. From this, our hominid lineage is illuminated and so, the “Out-of-Africa” or “Eve” hypothesis seems clear in terms of geographic origin.
The Human Genographic Project
History of Recent Science and Technology. Interview with Zuckerlandl. Caltech. <http://authors.library.caltech.edu/5456/1/hrst.mit.edu/hrs/evolution/public/clock/zuckerkandl.html
When did Farming Start? <http://varnam.org/blog/2004/06/when_did_farming_start/>
The Evolution of Prejudice <http://www.scientificamerican.com/article.cfm?id=evolution-of-prejudice>
Becoming Human <http://www.becominghuman.org/node/human-lineage-through-time>
The Link: < http://www.historyinternational.com/schedule>