Homo erectus migrated from out of Africa via the Levantine corridor and Horn of Africa to Eurasia during the Early Pleistocene, possibly as a result of the operation of the Saharan pump, around 1.9 million years ago, and dispersed throughout most of the Old World, reaching as far as Southeast Asia. The Sahara pump theory is a hypothesis that explains how flora and fauna migrated between Eurasia and Africa via a land bridge in the Levant region. It posits that extended periods of abundant rainfall lasting many thousands of years (pluvial periods) in Africa are associated with a "wet-Sahara" phase, during which larger lakes and more rivers existed.[1] This caused changes in the flora and fauna found in the area. Migration along the river corridor was halted when, during a desert phase 1.8–0.8 million years ago (mya), the Nile ceased to flow completely[2] and possibly flowed only temporarily in other periods[3] due to the geologic uplift (Nubian Swell) of the Nile River region. https://www.google.com/url?sa=t&rct...-6GgAQ&usg=AFQjCNHBcr1xwuQmAzRy77gV2_03QgohNg
Actually, that may have been the reason. Dr. Cavalli-Sforza (and other anthropologists) place the first successful migration out of Africa around 60,000 years ago. At that time an ice age was in progress, which means that much of the planet's water was trapped in the polar caps and in the glaciers on the taller mountain ranges like the Andes, Rockies and Himalayas--even the Alps. With less water evaporating into the sky, rainfall was lower than normal, resulting in fewer plants growing, and then obviously fewer animals for the humans to eat. Cavalli-Sforza sees evidence that members of the San tribe (who lived in northeastern Africa in those days but today are down in the southeast) crossed over the Red Sea (which, of course, was much narrower than it is today because the water level was much lower) into Asia. They found the weather to be not much different from what they left at home, so they kept walking. Eventually they found their way to Australia (again, the distances between the islands that make up the East Indies were much narrower because of the low water level, so the primitive boats they were able to build could safely carry them from one island to another). Due to the vagaries of weather patterns, Australia turned out to be a paradise with plenty of food. The genetic link between today's Native Australians and today's San tribe is clear. Moreover, Cavalli-Sforza found a few people living on the southern coast of India who are closely related to the Australians, indicating that a few of their ancestors decided to make homes along the way instead of making the long trek. About ten thousand years later, another group of members of the San tribe crossed the Red Sea again. This time bad weather was not the reason, they were just adventurous. They settled in southwestern Asia, and very slowly their descendants spread out to cover the globe. (All non-Australian, non-African humans have clear genetic markers showing that we are descendants of that second group of adventurers. And as I noted earlier, the San still exist, although many people refer to them as the "Bushmen.") Scientists in other disciplines see reasons why the first successful migration out of Africa occurred when it did. Anthropologists see convincing evidence that the technology of spoken language had been invented by 60KYA. At that time humans were engaging in complex, coordinated activities that could not possibly have been performed by people who, at the same time, were using their hands to communicate in gestures. So, there are two answers to your question: 1. Because people were starving and hoped to find food on other continents. 2. Because they had developed the ability to speak, which made it easier for them to successfully perform highly complicated tasks.
"That's a good question" (my least favorite answer from professors at the universities) Let's break it down "man" is ill defined and little understood. It seems that every year we are presented with new knowledge that dispels current "knowledge". If we are to assume that we are "man" and that we carry dna from various populations of previous "man" and that we are a mixture of dna from those predecessors, then drawing the line delineating us from them becomes problematic. If a "man" who carries much neanderthal dna marries a woman with much denisovan dna, are their children who carry both more or less "man". Why do we have both denisovan and neanderthal "hotspots"(where there is a higher percentage of those DNAs) in south america. Did the precursors migrate to the americas, then interbreed with later arivals? or did the recent migrants coming from different populations carry different percentages of those precursor DNAs? Confused enough? Ok let us address timing: It seems that there may have been a genetic bottleneck for our species circa 70,000 years ago(currently attributed to Toba's eruption and a potential thousand year volcanic winter) which is shortly before the majority of the prognostications attributed to the migrations. Another likely hypothesis is that our ancestors population decreased steadily with the advent of the last glacial cycle, perhaps to a low of below 10,000 individuals. This long and slow bottleneck may have lasted for 100,000 years until populations expanded rapidly during the late stone age. This expansion is largely derived from a marked increase in the diversity of artifacts, which may or may not translate well into absolute population numbers. If we accept that modern humans are believed to have emerged about 195,000 years ago in Africa, then we must wonder if there were migrations during the much warmer eemian between 130,000 and 115,000 years ago. We have yet to grasp estimates of population numbers of/for heidelbergensis, neanderthalensis, of denisovans. Which begs the question of just how important were these supposed interbreedings and sharing of dna to the psyche of current "man". Let us assume that they also evolved in Africa and migrated out first. Did they carry a wanderer gene? Did we get it from them? Does it predate them but just lay dormant in us for over 100,000 years? It seems that "climate change" must surely have played a roll in the migrations, but just what roll remains in doubt. So, good question unfortunately, we have no definitive answers, just many hypotheses, and very little evidence.
There's no evidence of humans in the Western Hemisphere prior to the colonization by H. sapiens. The reason that the Native Americans have bits of DNA from Neanderthals and other pre-sapiens species is the same reason that people on the other continents (possibly excluding Australia--I haven't looked into it) have those bits: the older species were still extant when our ancestors were colonizing the planet. The Europeans in particular have a few percent of Neanderthal DNA, because the Neanderthals were all over Europe when the ice age began to end, allowing the sapiens to thrive in the continent's new climate. But on other continents, similar encounters took place with the Denisovans and other species of genus Homo. As I noted above, all of this seems to correlate with a technology paradigm shift. The materials had been around forever, but rather suddenly our distant ancestors developed techniques for leveraging their value. Many anthropologists suspect that the catalyst was the development of spoken language. A tantalizing question which will probably never be answered, since we don't have any heidelbergensis or Denisovans to talk to. Cavalli-Sforza says that famine was the problem and wandering was the solution. Our ancestors migrated out of Africa because they needed to find a place with more food. Cavalli-Sforza says that the first migration out of Africa did indeed correlate with an ice age. We don't really know what percentage of the population who stayed in Africa survived; only that it was enough to keep the continent populated. The second migration, on the other hand, has no easy explanation. The restored African climate provided adequate food, and the higher sea level made the Red Sea crossing a much greater challenge than it had been for the first migrants. Your hypothesis of a "wandering" gene is as good as any, although as the Head Linguist on this website, I suggest that since the technology of language had been invented several hundred generations ago, the new generation of Africans had heard legends of ancestors who had already made the trip. After all, some of those San emigrant communities probably had a few members who wanted to go back to Africa and tell the folks what they had found. Humans love to brag. Please Register or Log in to view the hidden image!
Cavalli-Sforza asserts that Europeans are, in their ancestry, about two-thirds Asian and one-third African. Accurate?
I have a better one, based on the evolution of the ability to perceive in real time. (with out the neural delays, which can be up to 0.25 seconds). I.e. continuous* sensory data can be projected ahead to compensate for these delays, in a parietal simulation of the external environment. - That gives the first tribe to do that a huge battle advantage: Try ducking a thrown rock or spear if you only perceive it as where it was 0.1 seconds earlier. A real-time simulation would have great survival value. Perhaps the Neanderthals still experienced slightly delayed “emerging transforms” of retinal data when our smaller brained and weaker ancestors perfected a real-time simulation of their environment. (Ecological pressure from the larger and stronger Neanderthals would have accelerated the rate of evolution in our ancestors.) Likewise, the “Out of Africa” mystery, (Why one branch of hominoids, expanded and dominated all others approximately 50,000 years ago.), which is often assumed to be related to the acquisition of “autonomous language” (no gestures required - hands free and education facilitated), might better be explained by the development of the real-time simulation of the environment. The post from which the above paragraph is copied is a the end. There also are many reasons why the accepted view about perception is simply wrong. Perception does not "emerge" after many stages of neural processing. One quick proof of this is "phantom limbs." They are as perceptually real and in same full detail as physically existing limbs, yet there is no detailed sensory input. Another is the visual perceptions of dreams in dark room with eyes closed. Not only is the accepted POV wrong, - It conflicts with many facts. Also it is just "hand waving" with zero explanatory power and makes no prediction, like my Real Time Simulation, RTS, model of perception does. For example the RTS predicts / requires many retrograde connections from the parietal lobes to the visual cortex. They not only exist, but are more numerous than those coming from the eyes (via the LGN). This fact is such an unexplainable embarrassment to cognitive scientists' accepted "emergent" POV that they never mention it - a fact found only in anatomy texts. If perception were with neural processing delays, and after perception of object's location, motor action neuron delays, you could not hit a fast baseball or play Ping-Pong. * Non continuous changes in the environment, (exploding fire crackers, etc.) can not be projected ahead. The require revision of the RTS. If major it is "paused" for this. When it restarts, there is an observable spike in the EEG, often called the "startle spike" but more formally called "P300" as it is positive going and occurs about 300 ms after the unexpected "startle event." That spike is strongest over the parietal lobes - as predicted for a RTS in the parietal lobes. (The RTS is placed there because major parietal stroke abolished the victims perception of half the world. Smaller ones only cause "unilateral neglect." (Eat only the food on one side of the plate, etc.) More evidence on why we surviving humanoids perceive all continuously changing events in real time at: http://www.sciforums.com/threads/is-free-will-inherent-in-life-is-it-an-illusion.49127/page-4#post-905778
He did an exhaustive analysis of human DNA from all over the planet several years ago. PBS did a ten-part series on his work, which is available on YouTube. At that time, he found that all modern humans outside of Africa were clearly descended from the San tribe. The differences in DNA between two modern humans from widely separated locations (e.g., Borneo and Norway) were so slight as to make the concept of "races" laughable. In fact, when his assistant was in Arizona (Cavalli-Sforza is in his 90s and wasn't up to the rigors of making a TV series), he met a Navajo chief who insisted that his people were created right there in the Four Corners area and are unrelated to other humans. Meanwhile, the chief's son was looking through the photos taken in other places, and when he saw a member of the Yenisei tribe in Siberia, he shouted, "Dad! This guy looks just like Uncle Ernie!" The chief looked at the photo for quite some time, then he straightened himself, stared directly into the camera, and said, "Then I guess what you white men have been trying to tell us is true: We really are all brothers." There was no mention in the series of significant infusions of DNA from other human species. The only non-sapiens genes covered were the Neanderthals of Europe. If you've found references to significant concentrations of DNA from other Homo species, then perhaps he has published more recently. That would require a major revision of his life's work. To imply that more than half of our DNA is not sapiens turns it upside down. Which Asian species are you referring to? Traces of Homo habilis, ergaster and other closely related species do indeed show up in our DNA, but not in a high enough concentration to rewrite our history.
The confusion many people have is connected to the biological cataloging of animals, compared to humans. This is not consistent. I can find two humans, who look entirely different in 1-10 gauges of appearance and they are called one species. But if we have two birds that have the same amount of difference, each is a different species. Should the dual standard be eliminated so humans are cataloged like animals and/or animals like humans? If one species of birds suddenly gets a red spot on the tail and is unique to a location, this may be called an example of evolution. But if a humans gets such a marking, we bend over backwards to say nothing to see here. Does politics have anything to do with the dual standard?
YOUR confusion is due to your ignorance of the definition of "species." The two humans can mate and produce fertile off springs. - Ergo are the same specie. The two birds that can not produce fertile off springs are different species, even if with essentially identical appearances.
What do you think about the citation fro wiki. Female mules have been known, on rare occasions, to produce offspring when mated to a horse or donkey, though this is extremely uncommon. Since 1527 there have been more than sixty documented cases of foals born to female mules around the world.[citation needed] In contrast, according to the ADMS, there is only one known case of a female hinny doing so. In China in 1981, a hinny mare proved fertile with a donkey sire. When the Chinese hinny was bred to a jack, she produced "Dragon Foal," which resembled a donkey with mule-like features.[2] In Morocco in 2002, a mule mare bred to a donkey sire produced a male foal.[3] DNA testing revealed the foal has a mixed karyotype hybrid like the Chinese hinny offspring, Dragon Foal.
They look "entirely different" to you because you have been associating closely with humans for your entire life. You must have the ability to distinguish one of us from the others in order to socialize with us. We look a lot more similar to animals whose only interest in us is as food. That's not categorically true. As an aviculturist I can assure you that, while many species of birds do indeed have almost identical coloration, there are other species in which individuals differ enormously. An important reason for this was discovered only recently: Many birds have more than the three color receptors that humans have. In particular, quite a few of them have a fourth receptor that is sensitive to ultraviolet, a color that's completely out of our visible range. It turns out that this is how many species can distinguish males from females. Ultraviolet markings let them know which ones to court. No. What needs to happen is for humans to learn a lot more about biology. Where do you get this stuff? Did you go to school in some place like Texas where the textbooks are written by Southern Baptist preachers? The "marking" that is most closely allied with racism in our species is skin color. Once we began to understand both genetics and the migrations of our distant ancestors, the reason why some people have very dark skin and others have very light skin was explained. People who live close to the equator receive a lot more sunshine than those who live closer to the poles. In order to avoid an epidemic of skin cancer that would wipe out the population in ten generations, their skin needs to have a lot more sunlight-blocking melanin--which manifests as dark skin. People who live closer to the poles have the opposite problem: in order for their metabolism to generate enough Vitamin D to keep them healthy, their skin needs to receive as much sunlight as possible, so they have very little melanin and their skin looks almost white. The very light-skinned Lithuanians and the very dark-skinned Bengalis are very closely related--their languages are even members of the same branch of the Indo-European family. Their ancestors lived together on the Pontic Steppe, but after 3 or 4 millennia of migrating in opposite directions, one community evolved very light skin while the skin of the others is very dark.
Actually, it is not uncommon for two animals of different species within the same genus to be able to produce viable offspring. Wolves and coyotes, cattle and bison, the two species of chimpanzee, even lions and tigers in captivity, and in the past when their habitats overlapped in Asia, there are accounts of this occurring in the wild. It's arguably even more common among birds. In captivity, aviculturists have created a rainbow of multi-generation hybrid parrots. There are wild hybrid conures (one family of parrots) in South America, and in the USA the black-headed grosbeak and the rose-breasted grosbeak established a thriving hybrid population once the boundary between their territories (the thick forest that used to run along both sides of the Mississippi River) was replaced with farmland bearing fruit that both species love to eat.
The custom is to call the offspring of a male horse and a female donkey a "hinny," while the offspring of a female horse and a male donkey is a "mule." Mules are much more common because it's apparently more difficult for a jack (male) donkey to reproduce with a mare (female) horse. This isn't my field of expertise so I can't say whether this is a genetic problem, or simply the reluctance of a jackass and a mare to be interested in each other.
I don't think people intentionally migrated. What you have is a settled area and someone decided to live just a bit farther away. In thousands of years this results in people living all over the place.
