Blue Eyes
People with blue eyes have a single, common ancestor from the Black Sea area 6-10,ooo years ago, according to new research.
A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago. Before then, there were no blue eyes.
"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.
The mutation affected the so-called OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin.
"A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes," Eiberg said.
The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.
If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.
"It's exactly what I sort of expected to see from what we know about selection around this area," said John Hawks of the University of Wisconsin-Madison, referring to the study results regarding the OCA2 gene. Hawks was not involved in the current study.
Baby blues
Eiberg and his team examined DNA from mitochondria, the cells' energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. This genetic material comes from females, so it can trace maternal lineages.
They specifically looked at sequences of DNA on the OCA2 gene and the genetic mutation associated with turning down melanin production.
Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. The DNA sequence didn't have enough time to get mixed up.
"What they were able to show is that the people who have blue eyes in Denmark, as far as Jordan, these people all have this same haplotype, they all have exactly the same gene changes that are all linked to this one mutation that makes eyes blue," Hawks said in a telephone interview.
Melanin switch
The mutation is what regulates the OCA2 switch for melanin production. And depending on the amount of melanin in the iris, a person can end up with eye color ranging from brown to green. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls melanin production. But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes.
"Out of 800 persons we have only found one person which didn't fit — but his eye color was blue with a single brown spot," Eiberg told LiveScience, referring to the finding that blue-eyed individuals all had the same sequence of DNA linked with melanin production.
"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," Eiberg said. "They have all inherited the same switch at exactly the same spot in their DNA." Eiberg and his colleagues detailed their study in the Jan. 3 online edition of the journal Human Genetics.
That genetic switch somehow spread throughout Europe and now other parts of the world.
"The question really is, 'Why did we go from having nobody on Earth with blue eyes 10,000 years ago to having 20 or 40 percent of Europeans having blue eyes now?" Hawks said. "This gene does something good for people. It makes them have more kids."
People with blue eyes have a single, common ancestor, according to new research.
A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago. Before then, there were no blue eyes.
"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.
Eiberg says the mutation shuts off the production of the pigment responsible for brown eye color, resulting in a pure blue iris. Because the mutation is so specific, it can only be explained one way: "There must be a common ancestor for people with blue eye color," Eiberg told SPIEGEL ONLINE.
Eiberg started his search for the elusive mutation close to home. Using the Copenhagen Family Bank, a massive genetic database with detailed information on over 6,000 Danes, Eiberg found a family with three generations of blue-eyes. Looking at DNA from their blood, Eiberg homed in on a single, tiny blip in the genetic code. "All of the family had the same mutation," he said.
Originally, Eiberg says, everyone in the world had brown eyes. But the mutation acts as a switch that shuts off the OCA2 gene, which controls the eye's production of melanin. Melanin is the pigment that gives color to eyes and hair.
The mutation limits the OCA2 gene, restricting production of melanin in the eye. The result: The eye's brown color is diluted, giving people with the mutation pure blue eyes. (Shutting melanin production down entirely would result in albinism, affecting hair and skin color as well.)
People without the off-switch, on the other hand, have eye color ranging from deep brown to blue flecked with brown. (Green-eyed people can thank an entirely different part of the genome for their pretty peepers.)
The mutation is extremely specific: All people with blue eyes have the exact same genetic variation, and anyone with brown or green eyes do not. As a result, Eiberg said, it must have been passed down from a single person. "It's not a guess," Eiberg says. "It has to be."
To make sure the Danish family wasn't a fluke, Eiberg tested hundreds more samples, including people from Turkey with dark hair, light skin and blue eyes and Jordanians with dark hair, dark skin and blue eyes. They all had the same mutation as the Danes. "I have analyzed 800 samples," Eiberg says. "Out of the 800, 799 eyes are the same."
Eiberg has long been fascinated by the genetics of eye color. In 1996, he discovered the OCA2 gene, which helps control eye color. The blue-eye mutation works directly to turn off the OCA2 gene's production of melanin in the eye.
Eye color is a good example of how research is complicating our understanding of heredity. "Eye color is a textbook example of how genes work in a simple way, and now it turns out it's a bit more complicated than that," said Zoltan Bochdanovits, a statistical geneticist at the Vrije University in Amsterdam. "They do present quite convincing evidence it's a single mutation causing this."
Where and when the mutation occurred is more speculative, but based on the number of people with pure blue eyes in the world today, Eiberg argues that the original Ol' Blue Eyes lived between 6,000 and 10,000 years ago. Existing research on prehistoric population movements suggest that the original blue-eyed babe may have lived around the Black Sea, near modern-day Ukraine or Turkey, and that their descendants migrated to Northern Europe during the Stone Age. Like freckles, hair color or baldness, there's no real physical advantage to being blue-eyed. Says Eiberg: “It simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”
That doesn't mean eye color isn't important. After all, that long-distant ancestor managed to get quite a few copies of his or her mutation passed along. "I can very much imagine mate choice depends on eye color in humans," said Vrije University's Bochdanovits. "Personally, I tend to believe if you're blond and blue-eyed you have an advantage, at least in some populations."
A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago. Before then, there were no blue eyes.
"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.
The mutation affected the so-called OCA2 gene, which is involved in the production of melanin, the pigment that gives color to our hair, eyes and skin.
"A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes," Eiberg said.
The genetic switch is located in the gene adjacent to OCA2 and rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.
If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.
"It's exactly what I sort of expected to see from what we know about selection around this area," said John Hawks of the University of Wisconsin-Madison, referring to the study results regarding the OCA2 gene. Hawks was not involved in the current study.
Baby blues
Eiberg and his team examined DNA from mitochondria, the cells' energy-making structures, of blue-eyed individuals in countries including Jordan, Denmark and Turkey. This genetic material comes from females, so it can trace maternal lineages.
They specifically looked at sequences of DNA on the OCA2 gene and the genetic mutation associated with turning down melanin production.
Over the course of several generations, segments of ancestral DNA get shuffled so that individuals have varying sequences. Some of these segments, however, that haven't been reshuffled are called haplotypes. If a group of individuals shares long haplotypes, that means the sequence arose relatively recently in our human ancestors. The DNA sequence didn't have enough time to get mixed up.
"What they were able to show is that the people who have blue eyes in Denmark, as far as Jordan, these people all have this same haplotype, they all have exactly the same gene changes that are all linked to this one mutation that makes eyes blue," Hawks said in a telephone interview.
Melanin switch
The mutation is what regulates the OCA2 switch for melanin production. And depending on the amount of melanin in the iris, a person can end up with eye color ranging from brown to green. Brown-eyed individuals have considerable individual variation in the area of their DNA that controls melanin production. But they found that blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes.
"Out of 800 persons we have only found one person which didn't fit — but his eye color was blue with a single brown spot," Eiberg told LiveScience, referring to the finding that blue-eyed individuals all had the same sequence of DNA linked with melanin production.
"From this we can conclude that all blue-eyed individuals are linked to the same ancestor," Eiberg said. "They have all inherited the same switch at exactly the same spot in their DNA." Eiberg and his colleagues detailed their study in the Jan. 3 online edition of the journal Human Genetics.
That genetic switch somehow spread throughout Europe and now other parts of the world.
"The question really is, 'Why did we go from having nobody on Earth with blue eyes 10,000 years ago to having 20 or 40 percent of Europeans having blue eyes now?" Hawks said. "This gene does something good for people. It makes them have more kids."
People with blue eyes have a single, common ancestor, according to new research.
A team of scientists has tracked down a genetic mutation that leads to blue eyes. The mutation occurred between 6,000 and 10,000 years ago. Before then, there were no blue eyes.
"Originally, we all had brown eyes," said Hans Eiberg from the Department of Cellular and Molecular Medicine at the University of Copenhagen.
Eiberg says the mutation shuts off the production of the pigment responsible for brown eye color, resulting in a pure blue iris. Because the mutation is so specific, it can only be explained one way: "There must be a common ancestor for people with blue eye color," Eiberg told SPIEGEL ONLINE.
Eiberg started his search for the elusive mutation close to home. Using the Copenhagen Family Bank, a massive genetic database with detailed information on over 6,000 Danes, Eiberg found a family with three generations of blue-eyes. Looking at DNA from their blood, Eiberg homed in on a single, tiny blip in the genetic code. "All of the family had the same mutation," he said.
Originally, Eiberg says, everyone in the world had brown eyes. But the mutation acts as a switch that shuts off the OCA2 gene, which controls the eye's production of melanin. Melanin is the pigment that gives color to eyes and hair.
The mutation limits the OCA2 gene, restricting production of melanin in the eye. The result: The eye's brown color is diluted, giving people with the mutation pure blue eyes. (Shutting melanin production down entirely would result in albinism, affecting hair and skin color as well.)
People without the off-switch, on the other hand, have eye color ranging from deep brown to blue flecked with brown. (Green-eyed people can thank an entirely different part of the genome for their pretty peepers.)
The mutation is extremely specific: All people with blue eyes have the exact same genetic variation, and anyone with brown or green eyes do not. As a result, Eiberg said, it must have been passed down from a single person. "It's not a guess," Eiberg says. "It has to be."
To make sure the Danish family wasn't a fluke, Eiberg tested hundreds more samples, including people from Turkey with dark hair, light skin and blue eyes and Jordanians with dark hair, dark skin and blue eyes. They all had the same mutation as the Danes. "I have analyzed 800 samples," Eiberg says. "Out of the 800, 799 eyes are the same."
Eiberg has long been fascinated by the genetics of eye color. In 1996, he discovered the OCA2 gene, which helps control eye color. The blue-eye mutation works directly to turn off the OCA2 gene's production of melanin in the eye.
Eye color is a good example of how research is complicating our understanding of heredity. "Eye color is a textbook example of how genes work in a simple way, and now it turns out it's a bit more complicated than that," said Zoltan Bochdanovits, a statistical geneticist at the Vrije University in Amsterdam. "They do present quite convincing evidence it's a single mutation causing this."
Where and when the mutation occurred is more speculative, but based on the number of people with pure blue eyes in the world today, Eiberg argues that the original Ol' Blue Eyes lived between 6,000 and 10,000 years ago. Existing research on prehistoric population movements suggest that the original blue-eyed babe may have lived around the Black Sea, near modern-day Ukraine or Turkey, and that their descendants migrated to Northern Europe during the Stone Age. Like freckles, hair color or baldness, there's no real physical advantage to being blue-eyed. Says Eiberg: “It simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”
That doesn't mean eye color isn't important. After all, that long-distant ancestor managed to get quite a few copies of his or her mutation passed along. "I can very much imagine mate choice depends on eye color in humans," said Vrije University's Bochdanovits. "Personally, I tend to believe if you're blond and blue-eyed you have an advantage, at least in some populations."
Blue-Eyed Humans Have A Single, Common Ancestor Jan. 31, 2008 — New research shows that people with blue eyes have a single, common ancestor. A team at the University of Copenhagen have tracked down a genetic mutation which took place 6-10,000 years ago and is the cause of the eye colour of all blue-eyed humans alive on the planet today.
What is the genetic mutation
“Originally, we all had brown eyes”, said Professor Eiberg from the Department of Cellular and Molecular Medicine. “But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a “switch”, which literally “turned off” the ability to produce brown eyes”. The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives colour to our hair, eyes and skin. The “switch”, which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris – effectively “diluting” brown eyes to blue. The switch’s effect on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin colour – a condition known as albinism.
Limited genetic variation
Variation in the colour of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” says Professor Eiberg. “They have all inherited the same switch at exactly the same spot in their DNA.” Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production.
Professor Eiberg and his team examined mitochondrial DNA and compared the eye colour of blue-eyed individuals in countries as diverse as Jordan, Denmark and Turkey. His findings are the latest in a decade of genetic research, which began in 1996, when Professor Eiberg first implicated the OCA2 gene as being responsible for eye colour.
Nature shuffles our genes
The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair color, baldness, freckles and beauty spots, which neither increases nor reduces a human’s chance of survival. As Professor Eiberg says, “it simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”
What is the genetic mutation
“Originally, we all had brown eyes”, said Professor Eiberg from the Department of Cellular and Molecular Medicine. “But a genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a “switch”, which literally “turned off” the ability to produce brown eyes”. The OCA2 gene codes for the so-called P protein, which is involved in the production of melanin, the pigment that gives colour to our hair, eyes and skin. The “switch”, which is located in the gene adjacent to OCA2 does not, however, turn off the gene entirely, but rather limits its action to reducing the production of melanin in the iris – effectively “diluting” brown eyes to blue. The switch’s effect on OCA2 is very specific therefore. If the OCA2 gene had been completely destroyed or turned off, human beings would be without melanin in their hair, eyes or skin colour – a condition known as albinism.
Limited genetic variation
Variation in the colour of the eyes from brown to green can all be explained by the amount of melanin in the iris, but blue-eyed individuals only have a small degree of variation in the amount of melanin in their eyes. “From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” says Professor Eiberg. “They have all inherited the same switch at exactly the same spot in their DNA.” Brown-eyed individuals, by contrast, have considerable individual variation in the area of their DNA that controls melanin production.
Professor Eiberg and his team examined mitochondrial DNA and compared the eye colour of blue-eyed individuals in countries as diverse as Jordan, Denmark and Turkey. His findings are the latest in a decade of genetic research, which began in 1996, when Professor Eiberg first implicated the OCA2 gene as being responsible for eye colour.
Nature shuffles our genes
The mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair color, baldness, freckles and beauty spots, which neither increases nor reduces a human’s chance of survival. As Professor Eiberg says, “it simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”
Updated 2/5/2008
By Elizabeth Weise, USA TODAY
If you have blue eyes, you may be related to every other blue-eyed person in the world. Researchers in Denmark have found that every person with blue eyes descends from just one "founder," an ancestor whose genes mutated 6,000 to 10,000 years ago. Before then, everyone had brown eyes.
Lead scientist Hans Eiberg, a geneticist at Copenhagen University, began in 1973 to study a Danish father with 17 children who carried the gene for both blue and brown eyes. Over time, researchers were able to trace the blue-eyed trait to one specific area near a gene called OCA2. The paper appears in the journal Human Genetics.
Eiberg's team then tested 155 blue-eyed people from Scandinavia, Turkey, Jordan and India, looking to see whether they, too, had similar DNA sequences on that gene. To their amazement, they found that each individual had identical DNA sequences in that region of that gene, an indication that the original mutation happened recently enough that it hasn't had time to change.
Everyone has two genes for eye color, one from their father and one from their mother. Brown eyes are dominant, so even if someone has one blue and one brown-eye gene, he'll still have brown eyes.
That means that the recessive genes for blue eyes can be invisible for generations, with blue-eyed children popping up only when both parents carry at least one blue-eye gene, Eiberg says.
Blue eyes are actually what happens when the human default — brown eyes — is turned off. Brown eyes are caused by the pigment melanin, which also gives color to hair and skin, building up in the eyes. It's why many light-skinned babies are born with blue eyes but gradually develop brown eyes as their body produces melanin in their irises. The blue-eye mutation turned off the gene that produces melanin in the eyes.
When the original mutation occurred, the person who carried it would still have had brown eyes, says Eiberg. But in the generations that followed, a man and a woman who each had one blue-eye gene mated, producing the world's first blue-eyed baby.
Imagine what a surprise that was, Eiberg notes. "If the child was the only one to have blue eye color and everyone else has brown, it could have been very interesting."
That one mutation now exists in an estimated 300 million people, Eiberg says. Why it has become so common in some populations is unknown. It has been suggested that blue eyes and the lighter coloring that often accompanies them might have given an advantage to people in colder climates because they could absorb more vitamin D from the sun. Others have suggested it's simply a roll of the historical dice, with the original group that had the blue-eye genes coming through a genetic bottleneck.
"Maybe the population almost went extinct. If just a few individuals survived at some point and they were blue-eyed," then it could have happened much more recently, says Klaus Kjaer, a geneticist at the University of Copenhagen who also worked on the paper.
Blue eyes, though somewhat rare in the USA, are common in countries near the mutation epicenter, which previous researchers have pinpointed as probably somewhere in the Balkans or near the Black Sea.
In Estonia, 99% of people have blue eyes, Eiberg says. In Denmark 30 years ago, only 8% of the population had brown eyes, though through immigration, today that number is about 11%. In Germany, about 75% have blue eyes.
By Elizabeth Weise, USA TODAY
If you have blue eyes, you may be related to every other blue-eyed person in the world. Researchers in Denmark have found that every person with blue eyes descends from just one "founder," an ancestor whose genes mutated 6,000 to 10,000 years ago. Before then, everyone had brown eyes.
Lead scientist Hans Eiberg, a geneticist at Copenhagen University, began in 1973 to study a Danish father with 17 children who carried the gene for both blue and brown eyes. Over time, researchers were able to trace the blue-eyed trait to one specific area near a gene called OCA2. The paper appears in the journal Human Genetics.
Eiberg's team then tested 155 blue-eyed people from Scandinavia, Turkey, Jordan and India, looking to see whether they, too, had similar DNA sequences on that gene. To their amazement, they found that each individual had identical DNA sequences in that region of that gene, an indication that the original mutation happened recently enough that it hasn't had time to change.
Everyone has two genes for eye color, one from their father and one from their mother. Brown eyes are dominant, so even if someone has one blue and one brown-eye gene, he'll still have brown eyes.
That means that the recessive genes for blue eyes can be invisible for generations, with blue-eyed children popping up only when both parents carry at least one blue-eye gene, Eiberg says.
Blue eyes are actually what happens when the human default — brown eyes — is turned off. Brown eyes are caused by the pigment melanin, which also gives color to hair and skin, building up in the eyes. It's why many light-skinned babies are born with blue eyes but gradually develop brown eyes as their body produces melanin in their irises. The blue-eye mutation turned off the gene that produces melanin in the eyes.
When the original mutation occurred, the person who carried it would still have had brown eyes, says Eiberg. But in the generations that followed, a man and a woman who each had one blue-eye gene mated, producing the world's first blue-eyed baby.
Imagine what a surprise that was, Eiberg notes. "If the child was the only one to have blue eye color and everyone else has brown, it could have been very interesting."
That one mutation now exists in an estimated 300 million people, Eiberg says. Why it has become so common in some populations is unknown. It has been suggested that blue eyes and the lighter coloring that often accompanies them might have given an advantage to people in colder climates because they could absorb more vitamin D from the sun. Others have suggested it's simply a roll of the historical dice, with the original group that had the blue-eye genes coming through a genetic bottleneck.
"Maybe the population almost went extinct. If just a few individuals survived at some point and they were blue-eyed," then it could have happened much more recently, says Klaus Kjaer, a geneticist at the University of Copenhagen who also worked on the paper.
Blue eyes, though somewhat rare in the USA, are common in countries near the mutation epicenter, which previous researchers have pinpointed as probably somewhere in the Balkans or near the Black Sea.
In Estonia, 99% of people have blue eyes, Eiberg says. In Denmark 30 years ago, only 8% of the population had brown eyes, though through immigration, today that number is about 11%. In Germany, about 75% have blue eyes.
New Genes Involved in Human Eye Color Identified May 7, 2010 — Three new genetic loci have been identified with involvement in subtle and quantitative variation of human eye color.
The study, led by Manfred Kayser of the Erasmus University Medical Center Rotterdam, The Netherlands, is published May 6 in the open-access journal PLoS Genetics.
Previous studies on the genetics of human eye color used broadly-categorized trait information such as 'blue', 'green', and 'brown'; however, variation in eye color exists in a continuous grading from the lightest blue to the darkest brown.
In this genome-wide association study, the eye color of about 6000 Dutch Europeans from the Rotterdam Study was digitally quantified using high-resolution full-eye photographs. This quantitative approach, which is cost-effective, portable, and time efficient, revealed that human eye color varies along more dimensions than are represented by the color categories used previously.
The researchers identified three new loci significantly associated with quantitative eye color. One of these, the LYST gene, was previously considered a pigmentation gene in mice and cattle, whereas the other two had no previous association with pigmentation.
These three genes, together with previously identified ones, explained over 50% of eye color variance, representing the highest accuracy achieved so far in genomic prediction of complex and quantitative human traits.
"These findings are also of relevance for future forensic applications," said Kayser, "where appearance prediction from biological material found at crime scenes may provide investigative leads to trace unknown persons."
The study, led by Manfred Kayser of the Erasmus University Medical Center Rotterdam, The Netherlands, is published May 6 in the open-access journal PLoS Genetics.
Previous studies on the genetics of human eye color used broadly-categorized trait information such as 'blue', 'green', and 'brown'; however, variation in eye color exists in a continuous grading from the lightest blue to the darkest brown.
In this genome-wide association study, the eye color of about 6000 Dutch Europeans from the Rotterdam Study was digitally quantified using high-resolution full-eye photographs. This quantitative approach, which is cost-effective, portable, and time efficient, revealed that human eye color varies along more dimensions than are represented by the color categories used previously.
The researchers identified three new loci significantly associated with quantitative eye color. One of these, the LYST gene, was previously considered a pigmentation gene in mice and cattle, whereas the other two had no previous association with pigmentation.
These three genes, together with previously identified ones, explained over 50% of eye color variance, representing the highest accuracy achieved so far in genomic prediction of complex and quantitative human traits.
"These findings are also of relevance for future forensic applications," said Kayser, "where appearance prediction from biological material found at crime scenes may provide investigative leads to trace unknown persons."