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主题：【原创】【讨论】【文摘】你们相信我们中国人的祖先真的是从东非来的吗？ -- 你知道我是谁
你说的“人”这个概念在定义上的问题，以前也听方是民在他的文章里讲过。
呵呵，不是怕和欧洲人同源，是因为我原来觉得“多起源说”听起来更合情理，可后来看到的不少“证据”好像对他并不有利，可能倒是单起源说更有可能似的，所以挺想弄明白的。
嗯，我突然有点明白你的意思了，这个问题本身意义就不大，因为那都是十几万年前的事了，对吧？
前面说了如何从序列推出祖先，现在再说说序列的改变是如何从一个人推广到全人类的。哈哈，这个题目够吓人的吧。
前面我们说过假定一个序列原来如下，sanfengzi is a dangerous lady.那么所有的人都是这个序列。可是某一天，我们的共同祖先砰的一声，出了个变化。sanfengzi is an dangerous lady。要想让这个变化传遍全人类，需要多长时间。
假定只有这一个男的，那么很简单，一代就够了，因为下一代的Y染色体都从这位身上出，那么Y染色体上的这个变化成了唯一选项。
如果有两个男的，假定是自由交配，那么，所有的后代里面，将会有一半的男性是这个序列（概率么）。那么再下一代呢？这就要看这个变化对于男性的生存有没有影响了。如果sanfengzi 是大神，一看犯了这么个低级错误，那么一时高兴，把所有的正确的版本都给消灭了，那么一代就可以了。要是大神无动于衷，不管，但是，那个时候的妞就是喜欢出错误的，比不出错误的要喜欢10%（这个怎么算出来的，嘿嘿，就不告诉你，因为我也不知道）那么，第二代将有50% X (1+10%)=55%的男性有这么个序列。第三代将有50% X （1+10%）（1+10%)=60.5% 第n代将有50% 乘以 （1+10%）的N次方。那么究竟有多少代就可以了呢，你查查对数表不就出来了么，大概是不用十代人就可以了。
但是如果，大神无所谓，妞也无所谓呢。那可就惨了，每代都是50%的可能性，要把这50%给提高，只有偶然事件发生的时候才产生影响，要想提高到100%，那就真是mission of impossible了。
所以，我们回过头来看1万2千个中国人的样本中有11311个样本在M89的位点上发生突变意味着什么？因为这些位点对于生存和生殖，几乎没有影响，也就是说，没有外来的基因导入的话，其组成将几乎不变。这也意味着94。25%的样品中的M89位点，是遗传下来的。而5。75%的所谓非突变位点，是外来基因掺杂进来的。
至于那个处于遗传主导位置的M89是怎么来的，唯一的一个可能性就是由一大家子逐步发展出来的。而其他的家族很不走运，都统统死翘翘了，没有留下后人来。
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对于一般人来说，这个问题根本没有讨论的意义。
除非你是搞遗传的，或者对于人类的谱系特别的感兴趣。至于单起源和多起源，是属于很纯粹的遗传学范畴了。即使有足够的试验证据，在逻辑上也很难分清楚，因为早期人类的种群太小了，一个随机事件就可以改变整个进化过程。比方说，假定多起源是对的，但是除了非洲之外，其他的地方因为各种原因，Y染色体都没有流传下来，线粒体也没有流传下来。举一个极端的例子，假定中国原来的祖先因为某种原因，男性全部死光光，（Y染色体全部丢失）只好接受外来的受精，然后产生的全部是男性，（线粒体又丢光了）。但是，他们征服了全人类，把所有的男人都杀光，把所有的后代都变成自己的。那么，人类的基因组中，至少有一半是中国制造，但是，无论在线粒体还是，Y染色体中，都完全没有表现出来。这么说来，以前的关于这些方面的研究就是一张废纸。
光是十几万年的时间就足以使一个物种分布到全世界吗
还不要说 在这个时间里 还要把全世界其他的近亲全都消灭掉
这可能吗
Homo Erectus200万年前就存在了，Homo Sapiens起源于二十万年前的非洲
我记错了，多谢更正。
彻底分解是生成二氧化碳和水。另外，葡萄糖的氧化过程有许多的中间步骤，不是一下子就变成二氧化碳和水。
你这个嘉宾不发言，还在这里敲我砖头。是写的仓促了点，好多错误。
New York Times
May 13, 2005
DNA Study Yields Clues on Early Humans' First Migration
By NICHOLAS WADE
By studying the DNA of an ancient people in Malaysia, a team of geneticists says it has illuminated many aspects of how modern humans migrated from Africa.
The geneticists say there was only one migration of modern humans out of Africa; that it took a southern route to India, Southeast Asia and Australia; and that it consisted of a single band of hunter-gatherers, probably just a few hundred people strong.
Because these events occurred in the last Ice Age, when Europe was at first too cold for human habitation, the researchers say, it was populated only later, not directly from Africa but as an offshoot of the southern migration. The people of this offshoot would presumably have trekked back through the lands that are now India and Iran to reach the Near East and Europe.
The findings depend on analysis of mitochondrial DNA, a type of genetic material inherited solely through the female line. They are reported today in Science by a team of geneticists led by Dr. Vincent Macaulay of the University of Glasgow.
Everyone in the world can be placed on a single family tree, in terms of their mitochondrial DNA, because everyone has inherited that piece of DNA from a single woman, the mitochondrial Eve, who lived some 200,000 years ago.
There were, of course, many other women in that ancient population. But over the generations, one mitochondrial DNA replaced all the others through the process known as genetic drift.
With the help of mutations that have built up on the one surviving copy, geneticists can arrange people in lineages and estimate the time of origin of each lineage.
With this approach, Dr. Macaulay's team calculates that the emigration from Africa occurred 65,000 years ago, pushed along the coasts of India and Southeast Asia and reached Australia by 50,000 years ago, the date of the earliest known archaeological site there.
The Malaysian people whom the geneticists studied are the Orang Asli. The term means "original men" in Malay.
They are probably descended from this first migration, because they have several ancient mitochondrial DNA lineages that are found nowhere else.
These lineages are 42,000 to 63,000 years old, the geneticists say. Subgroups of the Orang Asli, like the Semang, have probably been able to remain intact because they adapted to the harsh existence of living in forests, said Dr. Stephen Oppenheimer, the member of the geneticists' team who collected blood samples in Malaysia.
Some archaeologists theorize that Europe was colonized by a second migration that traveled north out of Africa. This fits with the earliest known modern human sites, dating from 45,000 years ago in the Levant and 40,000 years ago in Europe.
Dr. Macaulay's team says there could have been just one migration, not two, because the mitochondrial lineages of everyone outside Africa converge at the same time to the same common ancestors. Therefore, people from the southern migration, probably in India, must have struck inland to reach the Levant and, later, Europe, the geneticists say.
Dr. Macaulay said it was not clear why just one group succeeded in leaving Africa. One possibility is that because the migration occurred by continuous population expansion, leaving people in place at each site, the first emigrants may have blocked others from leaving. Another is that the terrain was so difficult for hunter-gatherers, who carry all their belongings with them, that only one group succeeded in the exodus.
Although there is general but not complete agreement that modern humans emigrated from Africa in recent times, there is still a difference between geneticists and archaeologists about its a timing. Archaeologists tend to view the genetic data as providing invaluable information about the interrelationship between groups, but they place less confidence in the dates derived from genetic family trees.
There is no evidence of modern humans outside Africa earlier than 50,000 years ago, said Dr. Richard Klein, an archaeologist at Stanford. Also, if something happened 65,000 years ago to allow people to leave Africa, as Dr. Macaulay's team suggests, there should surely be some record of that in the archaeological record in Africa, Dr. Klein said. Yet signs of modern human behavior do not appear in Africa until 50,000 years ago, the transition between the Middle and Later Stone Ages, he said.
"If they want to push such an idea, find me a 65,000-year-old site with evidence of human occupation outside of Africa," Dr. Klein said.
Geneticists counter that many of the coastline sites occupied by the first emigrants would now lie under water, because the sea level has risen more than 200 feet since the last Ice Age. Dr. Klein expressed reservations about that argument, noting that people would not wait for the slowly rising sea levels to overwhelm them but would build new sites farther inland.
Dr. Macaulay said genetic dates had improved in recent years, now that it is affordable to decode the whole ring of mitochondrial DNA, and not just a small segment.
But he said he agreed "that archaeological dates are much firmer than the genetic ones" and that it was possible his 65,000-year date for the African exodus was too old.
Dr. Macaulay's team has been able to estimate the size of the population in Africa from which the founders descended. The calculation indicates a maximum of 550 women. The true size may have been considerably less. This points to a single group of hunter-gatherers, perhaps a couple of hundred strong, as the ancestors of all humans outside of Africa, Dr. Macaulay said.
黑人是黑猩猩进化的，白人是……有白猴子吧？
如此还可以解释个头、体能等等差别的由来。。。
澳大利亚国家大学的几位科学家近日指出，此前有关人类起源于非洲并由此向其他各洲迁移的理论令人怀疑，甚至有可能是不正确的，因为他们在澳大利亚发现了据信是迄今为止最古老的现代人DNA的化石。
所谓的“走出非洲”的人类起源理论认为，在15万年前，现代人类开始由非洲向世界其他各洲迁移，并在同一时间由穴居人类演变为真正的现代意义上的人类。但澳大利亚的科学家在对上述DNA化石进行研究分析后却发现，现代人类开始在澳大利亚生活的时间较之根据“走出非洲”理论推断出的现代人移居澳大利亚的时间要早得多。
几位科学家指出，上述DNA化石是从一具大约有6万年历史、从新南威尔士地区发现的人体遗骸中发现的，对DNA的研究显示这具遗骸的生理特征与现代人类毫无二致。
美国的人类学家阿兰-曼恩表示，上述发现具有划时代的意义，而且令人震惊。他说：“这一发现具有非凡的意义，没有人能够预料得到。与此同时，这一发现还表明，随着人们对人类起源这一问题的进一步研究，科学家将发现有关人类起源的真正时间和背景正在变得愈发复杂。”