Fallible DNA evidence can mean prison or freedom
would you trust DNA evidence? Most people regard it as near infallible- it produces the right result or no result, exonerating the innocent and securing convictions where other evidence fails.
But DNA is not as objective as you might think. In the first of a two-part investigation, New Scientist reveals that much of the DNA analysis now conducted in crime labs can suffer from worrying subjectivity and bias. We asked forensic analysts to interpret a sample of real DNA evidence and found that they reached opposing conclusions about whether the suspect matched it or not. Our subsequent survey of labs around the world also shows that there are significant inconsistencies in the guidelines on how to interpret a sample. The findings suggest that the difference between prison and freedom could often rest on the opinions of a single individual.
The introduction of DNA evidence to the courtroom in the mid 1980s revolutionised forensic science, resulting in thousands of convictions and exonerating 255 wrongly convicted people so far in the US alone. The reason for more than 50 per cent of these wrongful convictions was unvalidated or improper forensic testing, including incorrect hair, blood or fingerprint analysis.
"It's not unreasonable to hold up DNA as a way that the rest of forensic science should be done," says William Thompson of the University of California, Irvine, and an occasional expert witness on DNA. "It is better validated, and often more carefully done and more rigorously interpreted than many areas of forensic science."
That's not the same as saying DNA is perfect, however. In a growing number of cases, DNA samples taken from crime scenes produce partial profiles, partly because smaller samples are collected. "Labs are trying to get more samples and they're trying to [get results from] lower and lower amounts of DNA," says John Butler, head of the US National Institute of Standards and Technology's genetics group, which aims to improve standards in DNA testing.
A standard DNA profile consists of a series of peaks relating to the number of repeating stretches of DNA found in certain genetic sequences, or alleles (see diagram). The repeats occur at specific locations on the chromosomes, called loci, and there are two alleles at each locus- one inherited from each parent. The number of repeats in each allele varies widely between individuals, allowing a person to be identified this way. Labs in the US typically look at 13 loci, while UK labs tend to look at 10.
Yet in partial profiles, alleles may fail to show up, a phenomenon called "drop-out". False peaks in the profile created by imperfections in the analysis machine may also be mistaken for alleles. This is called "drop-in".
It gets more complicated when several people's DNA is mixed (see "Mix and mismatch"). Butler has reviewed more than 5000 DNA samples from 14 US labs and found that mixing is a common occurrence: 34 per cent of the samples he studied included DNA from two people, while 11 per cent were three or four-person mixtures.
Interpreting alleles in a mixed or partial sample is where the subjective opinion of an analyst could play a part. To test this, New Scientist teamed up with Itiel Dror, a neuroscientist at University College London and head of Cognitive Consultants International, and Greg Hampikian of Boise State University in Idaho.
We took a mixed sample of DNA evidence from an actual crime scene- a gang rape committed in Georgia, US- which helped to convict a man called Kerry Robinson, who is currently in prison. We presented it, and Robinson's DNA profile, to 17 experienced analysts working in the same accredited government lab in the US, without any contextual information that might bias their judgement.
In the original case, two analysts from the Georgia Bureau of Investigation concluded that Robinson "could not be excluded" from the crime scene sample, based on his DNA profile. (A second man convicted of the same crime also testified that Robinson was an assailant, in return for a lesser jail term.) Each of our 17 analysts independently examined the profiles from the DNA mixture, the victim's profile and those of two other suspects and was asked to judge whether the suspects' profiles could be "excluded", "cannot be excluded" or whether the results were "inconclusive".
If DNA analysis were totally objective, then all 17 analysts should reach the same conclusion. However, we found that just one agreed with the original judgement that Robinson "cannot be excluded". Four analysts said the evidence was inconclusive and 12 said he could be excluded.
"Fingerprinting and other forensic disciplines have now accepted that subjectivity and context may affect their judgement and decisions," says Dror. "It is now time that DNA analysts accept that under certain conditions, subjectivity and even bias may affect their work." Dror presented the results at the Green Mountain DNA conference in Burlington, Vermont, last month.
"It's not unreasonable to hold up DNA as a way that the rest of forensic science should be done," says William Thompson of the University of California, Irvine, and an occasional expert witness on DNA. "It is better validated, and often more carefully done and more rigorously interpreted than many areas of forensic science."
That's not the same as saying DNA is perfect, however. In a growing number of cases, DNA samples taken from crime scenes produce partial profiles, partly because smaller samples are collected. "Labs are trying to get more samples and they're trying to [get results from] lower and lower amounts of DNA," says John Butler, head of the US National Institute of Standards and Technology's genetics group, which aims to improve standards in DNA testing.
A standard DNA profile consists of a series of peaks relating to the number of repeating stretches of DNA found in certain genetic sequences, or alleles (see diagram). The repeats occur at specific locations on the chromosomes, called loci, and there are two alleles at each locus- one inherited from each parent. The number of repeats in each allele varies widely between individuals, allowing a person to be identified this way. Labs in the US typically look at 13 loci, while UK labs tend to look at 10.
Yet in partial profiles, alleles may fail to show up, a phenomenon called "drop-out". False peaks in the profile created by imperfections in the analysis machine may also be mistaken for alleles. This is called "drop-in".
It gets more complicated when several people's DNA is mixed (see "Mix and mismatch"). Butler has reviewed more than 5000 DNA samples from 14 US labs and found that mixing is a common occurrence: 34 per cent of the samples he studied included DNA from two people, while 11 per cent were three or four-person mixtures.
Interpreting alleles in a mixed or partial sample is where the subjective opinion of an analyst could play a part. To test this, New Scientist teamed up with Itiel Dror, a neuroscientist at University College London and head of Cognitive Consultants International, and Greg Hampikian of Boise State University in Idaho.
We took a mixed sample of DNA evidence from an actual crime scene- a gang rape committed in Georgia, US- which helped to convict a man called Kerry Robinson, who is currently in prison. We presented it, and Robinson's DNA profile, to 17 experienced analysts working in the same accredited government lab in the US, without any contextual information that might bias their judgement.
In the original case, two analysts from the Georgia Bureau of Investigation concluded that Robinson "could not be excluded" from the crime scene sample, based on his DNA profile. (A second man convicted of the same crime also testified that Robinson was an assailant, in return for a lesser jail term.) Each of our 17 analysts independently examined the profiles from the DNA mixture, the victim's profile and those of two other suspects and was asked to judge whether the suspects' profiles could be "excluded", "cannot be excluded" or whether the results were "inconclusive".
If DNA analysis were totally objective, then all 17 analysts should reach the same conclusion. However, we found that just one agreed with the original judgement that Robinson "cannot be excluded". Four analysts said the evidence was inconclusive and 12 said he could be excluded.
"Fingerprinting and other forensic disciplines have now accepted that subjectivity and context may affect their judgement and decisions," says Dror. "It is now time that DNA analysts accept that under certain conditions, subjectivity and even bias may affect their work." Dror presented the results at the Green Mountain DNA conference in Burlington, Vermont, last month.
Zoologger: The world's most fecund vertebrate
It sounds like many people's perfect lifestyle. Spend half your time lying around in sunny tropical warmth, then retire somewhere cooler and eat an enormous quantity of seafood. This is the day-to-day life of the ocean sunfish.
These whopping fish look distinctly peculiar. They have no true tail, and resemble nothing so much as gigantic severed fish heads, with striking fins rather like those of sharks.
If reputation is anything to go by, sunfish are slow-moving and lazy: the marine equivalent of sloths. But a new study that tracked molas over many months reveals that they are much more active than that – though there's still a fair amount of sunbathing going on.
Heidi Dewar of the US National Marine Fisheries Service in La Jolla, California, and colleagues went out to Japan between 2001 and 2006, and fitted sunfish with pop-up satellite archival tags. These transmit data to the researchers via satellites, and don't need to be collected.
These whopping fish look distinctly peculiar. They have no true tail, and resemble nothing so much as gigantic severed fish heads, with striking fins rather like those of sharks.
If reputation is anything to go by, sunfish are slow-moving and lazy: the marine equivalent of sloths. But a new study that tracked molas over many months reveals that they are much more active than that – though there's still a fair amount of sunbathing going on.
Heidi Dewar of the US National Marine Fisheries Service in La Jolla, California, and colleagues went out to Japan between 2001 and 2006, and fitted sunfish with pop-up satellite archival tags. These transmit data to the researchers via satellites, and don't need to be collected.
Hydrogen bombshell: Rewriting life's history
Oxygen is supposed to have driven the evolution of complex life – but the discovery of animals that thrive without it tells a different story
GO WEST, young man! More specifically, go about 200 kilometres west of Crete, then straight down to the bottom of the Mediterranean Sea 3.5 kilometres below. There you will find a lake with some extraordinary inhabitants.
Around 6 million years ago when the Mediterranean nearly dried up, vast amounts of salt were deposited on the sea floor. Some of these deposits were exposed about 30,000 years ago. As this salt dissolves, extra-salty, dense water is sinking to the depths, forming a brine lake up to 60 metres deep. Even more surprising than the existence of this lake beneath the sea, however, is what lives in it.
The water in the brine lake does not mix with the water above and so ran out of oxygen long ago. Instead, the toxic gas hydrogen sulphide oozes from the black mud. It's the last place you would expect to find animals. But that's exactly what has been discovered: the first animals, as far as we know, that can grow and reproduce without a whiff of oxygen.
These tiny mud-dwellers are far more than a curiosity. They could be the best pointer yet to the origin of complex cells: the basis of most life on Earth, from amoebae to oak trees.
GO WEST, young man! More specifically, go about 200 kilometres west of Crete, then straight down to the bottom of the Mediterranean Sea 3.5 kilometres below. There you will find a lake with some extraordinary inhabitants.
Around 6 million years ago when the Mediterranean nearly dried up, vast amounts of salt were deposited on the sea floor. Some of these deposits were exposed about 30,000 years ago. As this salt dissolves, extra-salty, dense water is sinking to the depths, forming a brine lake up to 60 metres deep. Even more surprising than the existence of this lake beneath the sea, however, is what lives in it.
The water in the brine lake does not mix with the water above and so ran out of oxygen long ago. Instead, the toxic gas hydrogen sulphide oozes from the black mud. It's the last place you would expect to find animals. But that's exactly what has been discovered: the first animals, as far as we know, that can grow and reproduce without a whiff of oxygen.
These tiny mud-dwellers are far more than a curiosity. They could be the best pointer yet to the origin of complex cells: the basis of most life on Earth, from amoebae to oak trees.
Thank your thalamus for a good night's sleep
Do you sleep like a baby? You may have your thalamus to thank, according to research that suggests this brain region helps people sleep through bumps in the night.
To discover why some people can sleep through noise while others awake at the faintest disruption, Jeffrey Ellenbogen and colleagues at Harvard Medical School used electrodes to monitor the brain activity of 12 people while they slept in a pitch-black, soundproof room. They then repeated the experiment, this time playing 14 sounds, such as a toilet flushing and street traffic, at 30-second intervals, increasing the volume until the volunteers' brainwaves showed signs of arousal.
Sleepers who tolerated louder sounds before waking showed a higher frequency of "sleep spindles" – short bursts of activity of specific wavelength – during non-REM sleep than those who woke more easily.
The spindles arise in the brain's sensory relay centre in the thalamus. The team suspects the thalamus acts as a sort of insulator, sending out spindle activity to stop areas of the brain from perceiving and responding to sounds.
Ellenbogen hopes this work will contribute to future solutions to promote these bursts and provide people with a sounder night's sleep.
To discover why some people can sleep through noise while others awake at the faintest disruption, Jeffrey Ellenbogen and colleagues at Harvard Medical School used electrodes to monitor the brain activity of 12 people while they slept in a pitch-black, soundproof room. They then repeated the experiment, this time playing 14 sounds, such as a toilet flushing and street traffic, at 30-second intervals, increasing the volume until the volunteers' brainwaves showed signs of arousal.
Sleepers who tolerated louder sounds before waking showed a higher frequency of "sleep spindles" – short bursts of activity of specific wavelength – during non-REM sleep than those who woke more easily.
The spindles arise in the brain's sensory relay centre in the thalamus. The team suspects the thalamus acts as a sort of insulator, sending out spindle activity to stop areas of the brain from perceiving and responding to sounds.
Ellenbogen hopes this work will contribute to future solutions to promote these bursts and provide people with a sounder night's sleep.
Early humans were butchers 3.4 million years ago
Our ancestors were carving meat some 800,000 years earlier than previously thought. Marks on fossilised animal bones found in Ethiopia indicate that early-human butchers were using stone tools as early as 3.4 million years ago.
Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues say the find is evidence that Australopithecus afarensis – the only known hominin species present in the region at the time – used tools.
The finds suggest that the evolution of toolmaking and meat-eating among our human ancestors is more complex than existing theories admit.
They also add to a growing body of evidence that A. afarensis may have been more human-like and less primitive than some have assumed.
Shannon McPherron of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and colleagues say the find is evidence that Australopithecus afarensis – the only known hominin species present in the region at the time – used tools.
The finds suggest that the evolution of toolmaking and meat-eating among our human ancestors is more complex than existing theories admit.
They also add to a growing body of evidence that A. afarensis may have been more human-like and less primitive than some have assumed.
Meat and tools
"What we have done is push back in time, rather dramatically, two of the more fundamental behaviours that played such an important role in our evolution – meat consumption and tool use," says McPherron. "This find forces us to rethink the idea that the origins of stone tool use, meat consumption and the origins of our genus Homo all occurred together, around 2.5 million years ago."
Instead, he says, it's likely that hominins at least experimented with stone tools to help them eat meat and marrow much earlier. "It's quite exciting from that point of view," he says.
McPherron discovered the rib of a cow-sized animal and the thigh bone of a goat-sized antelope in January last year while carrying out fieldwork for the Dikika Research Project in northern Ethiopia. The surface of both bones carried deep markings suggestive of stone tools.
Detailed analysis using environmental scanning electron microscopy ruled out trampling by other animals as a possible cause for the marks. The team concluded the markings were made by sharp-edged stone tools used to cut and scrape flesh off the bones, and a blunt tool used to crack the bones open to get at nutrient-rich bone marrow.
Instead, he says, it's likely that hominins at least experimented with stone tools to help them eat meat and marrow much earlier. "It's quite exciting from that point of view," he says.
McPherron discovered the rib of a cow-sized animal and the thigh bone of a goat-sized antelope in January last year while carrying out fieldwork for the Dikika Research Project in northern Ethiopia. The surface of both bones carried deep markings suggestive of stone tools.
Detailed analysis using environmental scanning electron microscopy ruled out trampling by other animals as a possible cause for the marks. The team concluded the markings were made by sharp-edged stone tools used to cut and scrape flesh off the bones, and a blunt tool used to crack the bones open to get at nutrient-rich bone marrow.
