Out Of Africa?

[Gorilla]

Are africans our ancestors, or are asians part erectus, and caucasians part neanderthal?

http://www.actionbioscience.org/evolution/johanson.html

The Multiregional Continuity Model15 contends that after Homo erectus left Africa and dispersed into other portions of the Old World, regional populations slowly evolved into modern humans. This model contains the following components:

some level of gene flow between geographically separated populations prevented speciation, after the dispersal

all living humans derive from the species Homo erectus that left Africa nearly two million-years-ago

natural selection in regional populations, ever since their original dispersal, is responsible for the regional variants (sometimes called races) we see today
the emergence of Homo sapiens was not restricted to any one area, but was a phenomenon that occurred throughout the entire geographic range where humans lived

Out of Africa theory: homo sapiens arose in Africa and migrated to other parts of the world to replace other hominid species, including homo erectus. In contrast, the Out of Africa Model13 asserts that modern humans evolved relatively recently in Africa, migrated into Eurasia and replaced all populations which had descended from Homo erectus. Critical to this model are the following tenets:
after Homo erectus migrated out of Africa the different populations became reproductively isolated, evolving independently, and in some cases like the Neanderthals, into separate species
Homo sapiens arose in one place, probably Africa (geographically this includes the Middle East)
Homo sapiens ultimately migrated out of Africa and replaced all other human populations, without interbreeding
modern human variation is a relatively recent phenomenon
The multiregional view posits that genes from all human populations of the Old World flowed between different regions and by mixing together, contributed to what we see today as fully modern humans. The replacement hypothesis suggests that the genes in fully modern humans all came out of Africa. As these peoples migrated they replaced all other human populations with little or no interbreeding.

[jcs]

but was a phenomenon that occurred throughout the entire geographic range where humans lived
If this is true, it would be pretty interesting to know how this phenomenon came about. Do proponents of this hypothesis give any explaination?

[Der Sozialist]

All the evidence I have seen supports the Out of Africa theory much more than the Multiregional theory. I have a book somewhere—I will try to find it.

[Alvo]

Ender,

National Geographic magazine in its April issue has a five-page article on the Out of Africa theory. According to the magazine, our ancestors really left Africa thousands of years ago and dispersed throughout the planet. That's an old and well known theory, OK, but the beauty of it is that this time it's been validated by DNA studies.

[Der Sozialist]

The ‘Out-of-Africa’ (or mitochondrial ‘Eve’) hypothesis was the result of Cann, Stoneking, and Wilson’s (1987) study using sequence markers on mtDNA to trace the maternal ancestry of 147 people from widely-dispersed indigenous populations (see Wilson and Cann 1992 for a general review). The Eve hypothesis is a set of hypotheses (see below) proposing that all modern humans have a common maternal ancestor who lived in Africa around 200,000 years ago. Similar ideas have been developed earlier for nuclear-coded protein polymorphisms (Nei and Roychoudhury 1982). An opposing hypothesis, that modern human races evolved in situ from interbreeding populations of Homo erectus and its descendant populations (for example Neanderthals), is referred to as the ‘multi-regional hypothesis’ (Wilson and Cann 1992). Perhaps the most common misunderstanding of the Eve hypothesis is that there was just a single female in the population. However, calculations referred to below suggest a population of 1000 to 10,000 females. It is probabilistic processes, referred to earlier under the neutral theory, that eventually lead to all mitochondria being derived from just a single female.

[snip]

Africa has been suggested as the ancestral area of humans by two criteria: (1) the location of the root of the human mtDNA tree, with its first lineages leading to large African branches; and (2) the fact that present-day African populations include the most divergent human mtDNA sequences (Vigilant et al. 1991). The mere presence of such large blocks of purely African sequences argues strongly against multiregional hypothesis, which requires a large amount of interbreeding between all descendants populations of Homo erectus (Wilson and Cann 1992). Further, the very recent nature of all human mtDNA diversity makes even the whole of Africa look unlikely as the place where Homo sapiens first evolved, and suggests that the earliest origin of modern humans was in a part of Africa perhaps supporting a population of the order of 10,000 or even less (from expected polymorphism of different population sizes under the neutral model). As yet there is no direct genetic evidence for the exact location.

[snip]

Fig. 3.3 [sorry, I cannot reproduce that tree here] Median tree from the re-analysis of the 135 human mtDNA sequences of Vigilant et al. (1991). This is the median tree of over 400 independent runs with the maximum parsimony criterion (as found by found amongst non-Africans—which is in agreement with an African origin of H. s. sapiens, followed by expansion out of Africa by a subset of the total African diversity.

The positions in the tree of the African-American sequences are consistent with their being members of the African groups (excepting the Pygmies and the !Kung) recently displaced by the slave trade.

[snip]

The sequences used here are from Kocher and Wilson (1991), who sequenced complete Dloop sequences (1135 base pairs) for about 20 individuals. They sequenced the DNA going in both directions, and we expect that the sequencing error rate was 1 in 2000. This can be expected to inflate by about 5% our estimate (below) of the age of the root of human mtDNA.


Handbook of human symbolic evolution. Lock and Peters. Clarendon Press--Oxford 1996.

[Professor John Frink]

OOA, basically.

[Dan Dare]

OOAAA (http://cogweb.ucla.edu/ep/Templeton_02.html) seems to make more sense to me.

There's also this (http://news-info.wustl.edu/tips/page/normal/6349.html) as well.

http://img112.imageshack.us/img112/476/ooaaa0fi.jpg (http://imageshack.us)

[Petyr Baelish]

Ender,

National Geographic magazine in its April issue has a five-page article on the Out of Africa theory. According to the magazine, our ancestors really left Africa thousands of years ago and dispersed throughout the planet. That's an old and well known theory, OK, but the beauty of it is that this time it's been validated by DNA studies.

Last time I checked, National Geographic was not a peer reviewed journal of human population genetics (thankfully).

[The Retard]

We all came from China



An Evolution Revolution (http://www.exn.ca/Stories/2001/03/20/52.asp)

Every so often science is forced to question the status quo and to rethink the views that dominate our world. And sometimes, it takes only a small event to trigger such major change, such as Galileo's telescope, Darwin's trip to the Galapagos Islands, and Einstein's pondering of the nature of space and light.

The same thing might have just happened to our understanding of human prehistory with the radioactive dating of Nanjing Man.

Nanjing Man is the name given to a Homo erectus fossil found in China. He was thought to be around 400,000 years old. But, last month, a quartet of scientists from China and Australia re-dated Nanjing Man using uranium-series dating and found he was actually at least 620,000 years old.

This made the scientists question the dates given to other major archaeological finds - finds that have come to shape evolutionary theory as the world knows it.

Suddenly, Nanjing Man became the catalyst for an evolutionary coup d'etat that could end Mitochondrial Eve's reign as the most accepted theory of human evolution.

The Mitochondrial Eve theory claims Homo sapien populations migrated from Africa between 100,000 and 200,000 years ago and replaced Homo erectus populations wherever they went.

But, based on his new age, Nanjing Man could very well be chalked up as another victory for the less-popular multi-regional model of evolution.

Multi-regionalism argues that modern Asian populations were not replaced by African sapiens. Instead, they evolved directly from Asian Homo erectus and Nanjing Man's new age would provide more time for this evolutionary process to have occurred.

Nanjing Man's age and his implications for evolutionary theory have prompted the Chinese-Australian team of scientists who dated him to re-date other major archaeological finds using the uranium-series dating technique that derived Nanjing Man's age.

"Many Homo erectus sites are not well-dated," says Dr. Ken Collerson, a member of the team who dated Nanjing Man.

This is because of the limited capabilities or questionable results from other dating techniques such as electron-spin resonance, which Collerson refers to as "in the realms of alchemy."

By re-dating major archaeological finds, Collerson says he thinks the multi-regional theory of evolution will displace the Mitochondrial Eve theory as the most accepted evolutionary model.

"If I had to bet, I think the multi-regional model will probably be the one to emerge as a more realistic interpretation."

Zhao Jian-xin, a member of the team that dated Nanjing Man, agrees. An archaeologist since 1997, he started his career as a geologist who knew little about evolutionary theory.

"I think the multi-regional theory, within the next 10 years, will take the upper hand," Zhao says. "The most important thing we want to push is a chronological framework to show that (Mitochondrial Eve) is wrong,"

Zhao says the Eve model's timeline of human evolution is too compressed to be accurate. Modern hominids had to have evolved and replaced ancient hominids around the world in too short a time period for the Eve theory to be plausible.

Nanjing Man's age suggests that Asian erectus had a longer time to evolve into modern hominids than previously thought. This makes it less likely for modern hominids from Africa to have replaced Asian erectus. The two populations would not have overlapped as the Eve theory speculates.

The four scientists credited with dating Nanjing Man measured the decay of radioactive uranium (U) by counting the number of thorium (th) atoms present in the stratigraphic layers above and below where Nanjing Man's fossil was found. They used thermal ionization mass spectrometry (TIMS) to do this.

Over time and at a steady rate, uranium transforms at the atomic level into thorium. This means that as objects age, the amount of thorium they contain increases as the uranium in them decrease. Because this happens at a steady rate, thorium provides a good estimate for the age of rocks.

This provides a bracket of dates between which Nanjing Man lived with the bottom layer providing the earliest possible date and the top layer the latest date.

TIMS U-Th dating is particularly helpful in dating fossils found in limestone caves where a method like potassium argon (KAr) dating would be inadequate.

Potassium argon (KAr) dating uses crystallized volcanic ash found on or around a fossil in an open area to derive the fossil's age. KAr dating is not suited for dating cave fossils because there is often little volcanic ash to be found inside caves for this method to work.

But, TIMS U-Th dating is suited for dating cave fossils because the limestone retains radioactive elements.

TIMS U-Th dating also provides a larger, more accurate window of time for fossil dates, possibly up to one million years, unlike other techniques such as carbon dating.

Carbon dating actually dates the fossil itself, which does not retain any radioactive elements, and only provides a maximum age of up to 50,000 years.

However, TIMS U-Th dating is nothing new. Henry Schwarcz, a geologist at McMaster University in Hamilton, developed it in 1975.

"We've looked for many different clocks to trace human evolution," Schwarcz says. "The decay (of uranium) is like a ticking clock and this will give us an answer. It is the most precise and accurate."

As for the impact that his dating method will have on evolutionary theory, Schwarcz says that while everyone thinks Africa was where all the action was, this idea won't last.

"It appears China was an important area for evolution. This opens up a whole new window into the time scale of human evolution in that part of the world."

[Professor John Frink]

OOAAA (http://cogweb.ucla.edu/ep/Templeton_02.html) seems to make more sense to me.

There's also this (http://news-info.wustl.edu/tips/page/normal/6349.html) as well.

http://img112.imageshack.us/img112/476/ooaaa0fi.jpg (http://imageshack.us)
There are several objections to Templeton's theories:

While acknowledging that mtDNA supports replacement, Templeton (2002) argues that several nuclear DNA polymorphisms are much older than the expansion of modern humans out of Africa and must therefore reflect intermixture with Neanderthals and other archaic humans. Templeton’s analysis suffers, however, from two flaws: (1) a wide margin of error in the time estimates based on nuclear DNA polymorphisms, combined with a bias in favour of polymorphisms that look older than they really are; and (2) a disregard for selection pressures that would inflate the variability of these polymorphisms and thereby inflate the time estimates.

As Templeton himself concedes, nuclear DNA accumulates variability at a slower rate than does mtDNA, so any time estimates would suffer from a wider margin of error. Although this may explain why some polymorphisms yield very old dates (oldest = 1.9 million BP), it is not readily apparent why none yield very young ones (youngest = 230,000 BP). Keep in mind that if a polymorphism looks much younger than its real age it would also have much less variability. A significant proportion would have none at all or not enough to attract the interest of population geneticists. Templeton is thus using a biased sample that includes polymorphisms that have much more variability than they should for their age but excludes many that have much less.

The second flaw is that all but one of Templeton’s nine nuclear DNA loci produce proteins of one sort or another. They are thus exposed to selection pressures that may inflate genetic variability, i.e., through heterozygote advantage, frequency-dependent sexual selection, disease-resistance polymorphisms, and other balanced polymorphisms. Templeton uses the hemoglobin β-chain locus in his analysis, yet many of its alleles (e.g., β-Thalassemia) are clearly balanced polymorphisms that provide some protection against malaria. The MC1R locus is used even though its alleles code for highly visible differences in hair colour that may have been maintained through sexual selection (Rana et al. 1999). The PDHA1 locus is used, yet different portions of the PDHA1 region have evolved at different rates, a strong indication of natural selection (Disotell 1999). The MX1 locus is used even though one of its alleles causes alopecia areata in the homozygous state and is likely maintained through some form of heterozygote advantage (Tazi-Ahnini R et al. 2000).

http://human-nature.com/nibbs/02/frost.html

[Dan Dare]

Support for the middle ground between the RAO (recent-out-of-Africa) and the MRE (multi-regional evolution) models appears to growing.

Genomics refutes an exclusively African origin of humans (http://www.sciencedirect.com/science?_ob=ArticleURL&_aset=V-WA-A-W-V-MsSAYZW-UUA-U-AAAECDDVEB-AAADACYWEB-ABAEDZDYW-V-U&_rdoc=1&_fmt=summary&_udi=B6WJS-4G3SC6X-1&_coverDate=05%2F23%2F2005&_cdi=6886&_orig=search&_st=13&_sort=d&view=c&_acct=C000056308&_version=1&_urlVersion=0&_userid=2148430&md5=82972347f9c4de4acd8ccb19a531dbbc)

A hat-tip to GNXP (http://www.gnxp.com/MT2/archives/004017.html) for posting the introduction to this for-fee article.

Disclaimer: Much of the technical argument is over my head, however I have had long had reservations about the standard RAO/OOA thesis on both philosphical and common-sense grounds.