Hundreds of thousands of years ago—when people still lived in small hunter-gatherer bands, when it's not even clear they were totally anatomically modern (though they probably were)—something happened in the human genome.
Somewhere in Africa, a man carried a Y chromosome that would turn out to be the only surviving Y chromosome in humans today. This man lived around plenty of other people, perhaps with their own Y chromosomes, but chance whittled away his peers' contributions until only his was left.
In a totally independent event, a woman carried mitochondria—tiny structures contained inside cells—that would become the only mitochondria people have today. Like the Y-man, she lived around other people, but over thousands of years, luck struck down all others' mitochondria save her own.
Now, in a pair of new papers published today, two separate research groups say they've determined the dates during which the last common Y-chromosome ancestor lived. One of the groups also came up with dates for when the last common mitochondrial ancestor lived. The dates vary from previous estimates—and from each other—which is sure to set off healthy debates about when these seminal genetic events occurred.
As geneticists improve their understanding of these last common ancestors, the times they find may help scientists better understand when other important events in human evolution occurred, such as the spread of people from Africa. Where the archaeological record is sparse or conflicted, genetics can help, says Brenna Henn, who researches genetics and human evolution at Stony Brook University in New York. Henn was part of one of the two teams publishing today.
One of the teams, led by Paolo Francalacci of the University of Sassari in Italy, determined that everybody's last common male ancestor lived 180,000 to 200,000 years ago. Another team, led by Carlos Bustamante of Stanford University, concluded that the modern human Y chromosome first appeared on Earth 120,000 to 156,000 years ago. Bustamante also found that modern mitochondria appeared in people beginning 99,000 to 148,000 years ago. (Henn worked with Bustamante's team.)
Both Francalacci and Bustamante graciously say that their estimates for the Y chromosome are not that far apart from each other. Researchers not involved in their work more readily acknowledge the two's discrepancy. "It's not a big difference," University of Arizona anthropologist Michael Hammer tells Popular Science. "But it is different." Hammer has long worked on dating Y chromosomes and mitochondria.
Previous estimates of the date of the last common Y ancestor varied from about 50,000 years ago to 340,000 years ago, a broad range. Previous estimates of when the last common mitochondrial ancestor live were more precise, ranging from 150,000 to 240,000 years ago.
One big advantage that Bustamante and Francalacci had was that they worked with much more of the Y chromosome than anybody had before them. Time and technology have made DNA sequencing more affordable, with lots of consequences. One of them is having much more DNA available for studies like this.
"It's great to see large-scale sequencing being applied to the Y chromosome," says Chris Tyler-Smith, who studies genetics and human evolution with the U.K.'s Wellcome Trust. "I think this is the future of Y chromosome study."
Archaeologists look at unearthed ancient artifacts, while anthropologists often work with fossils to help them reconstruct prehistory. Geneticists interested in human evolution, however, have only modern DNA to look at. Francalacci, Bustamante and others like them make their last common ancestor estimates by gathering DNA samples from men and women walking around today.
The keys are two parts of the genome, the Y chromosome—which only men have, and only men pass on—and the mitochondrial DNA—which everybody has, but only women pass on. (So if you're a man, all your mitochondrial DNA come from your mother. Your sister's mitochondrial DNA also come from your mom.)
These two parts of the human DNA are special because they're the only parts that children inherit from their parents with perfect accuracy. Every other part of the DNA gets remixed and reshuffled in every new baby, which is how you can have your mom's hair and your dad's eyes, while your sister got Mom's eyes, Dad's hair and Dad's flat ears.
The Y chromosome's and the mitochondria's straightforward inheritance patterns make them comparatively easy to trace through time, so geneticists often focus on them. Because the two bits had to come from a man and a woman, respectively, the people who gave all modern humans these parts of their genome are often called something like the "Y-chromosome Adam" and the "mitochondrial Eve," which is a fun way to think about them. However, it's vanishingly unlikely the two ever met each other and mated, and they didn't live in an unpeopled Eden.
Now, it's been a long time since this Adam and Eve walked the Earth, so the inheritance they left us has changed over time. Theoretically, fathers pass on their Y chromosomes with perfect accuracy to their sons, and mothers pass on their mitochondrial DNA with perfect accuracy to all their children. In reality, mistakes happen. Over time, random mutations work their way in.
Geneticists theorize that such mutations occur at a regular rate, with X number of mutations spontaneously appearing in the genome over Y number of years. So when geneticists make their estimates of last common ancestors, they take DNA samples from a large number of people, see how different those people's DNA are from each other, and then use some outside information to help them calculate how long it should have taken for those differences to arise. "It's basically distance equals rate times time," says David Poznik, the Stanford University scientist who did much of the dating work in his the paper with Bustamante.
Different geneticists calculate this rate of change differently. There's no standard way to do it. That's why people have come up with different times for the last common Y-chromosome and mitochondrial ancestors.
Francalacci and Bustamante used a relatively new way of calculating the rate of DNA change. They used dates determined by archaeology as mile markers. Francalacci and his lab, for example, used the spread of people over the Italian island of Sardinia 7,700 years ago as their mile marker. They sampled DNA from 1,204 Sardinian men, calculated how different those men's Y chromosomes were from each other, and then calculated the mutation rate required for Sardinian diversity to have arisen over 7,700 years. Bustamante and his colleagues did something similar with the peopling of the Americas 15,000 years ago.
Others calculate the human mutation rate in other ways, including dating from the time humans and chimpanzees branched away from each other and simply checking the mutation rate between modern parents and their children. Every researcher, of course, argues the way he or she has chosen is best; we won't get into that. "The diversity of views and results is healthy," Tyler-Smith says. "It's a really exciting time in the field."
Suffice it to say this isn't the last word on when the Y-chromosome Adam and the mitochondrial Eve lived. Given the range in recent estimates, it's not even necessarily true that the two folks were anatomically modern, which is kind of cool to think about. But as long as modern humans carry in them these relatively unchanged pieces of DNA, the keys are there for us to find out.
I have three degrees in science and have attended a meeting in DC where hundreds of scientists believe in the biblical account of creation. I'll take the Bible over all the evolutionary theory from scientists who don't wish to be accountable to a Creator.
An astounding amount of scientific evidence disproves evolutionary theory. Take a minute to scan the index at pathlights.com/ce_encyclopedia/creation-encyclopediaTOC.html
one word for you two...retards,,,,all pun intended
one word for you two...retards...all pun intended
I find it amusing when people make comments like yours. It always sounds like they are trying to convince everyone somehow that their opinion is a fact just because they have some degrees.
Anyways I am always curious about what evidence creationists use to support their beliefs so I checked out the website you referenced. I have to say I am dissappointed if that is the best you have. That website is so unprofessional and constantly resorts to belittling any beliefs contrary to creation. That alone is enough for them to lose pretty much all credibility in my book. That said I did find some of the stuff about the big bang interesting and will have to think more about it. However when I got to the natural selection section it became quite clear that the authors had no real understanding of the theory. They do not even come close in their explanation of how it is supposed to work so it makes any of their arguments against it irrelevant. Just saying I would never reference a site like this to support my beliefs or to try to educate others.
If it matters to you I have a master's degree in molecular biology.
This article has really brought out the religious wackos from hiding I see
At least Wonder has half a brain. I'd be a lot more likely to believe Wonders explanation than even consider Richard's. All of Richard's knowledge was probably spoon fed to him from the priest that molested him his whole life. The bible is nothing but stories ... may as well get your information from cartoons.
The Annunaki don't want none unless you got (frontal) lobes hun.
If it's credibility you're looking for you may want to avoid using stereotypes and offensive assumptions.
It's interesting that you compare the Bible to cartoons.
Here's a question for you - if you found a series of cartoons that had a common theme and story running through them all, and then you found out that they were composed by over 40 different cartoonists over a period of 2,000 years (which means they were also carried, copied, and handed down over that time period), wouldn't those cartoons be something worth looking into? If you don't even consider what the cartoons are about, if you found them you would have to say, 'whoa, these meant a whole lot to a whole lot of people'. Once you find out what the cartoons are about, it becomes even more important.
One other question I'd like to ask you - Do you think everyone sitting in a church learning from an old book is 'spoon-fed' and naive, but everyone sitting in a classroom is englightened and intelligent?
There are communities of scientists supporting very different theories, and to dismiss either one as religion or accept either one as fact is naive.
It is sad, Richard, that someone with your quantity of learning has such a huge blind spot that you simply cannot see. I'm not going to try to make a case, since you have already clearly stated that you have your opinion and science be damned. I can only hope that someday the weight of scientific evidence will at last force you to confront your prejudices and see the truth you are currently ignoring.