Footprints laid down near Lake Turkana in Kenya 1.5 million years ago were made by human ancestors with essentially modern foot anatomy and gait, a new study has found.

These are the second oldest hominin footprints known, after the 3.7-million-year-old Laetoli prints found by anthropologist Mary Leakey in 1978. More importantly, they are the oldest made by human ancestors – most likely early Homo erectus – who shared our stature, foot anatomy and springy, efficient stride.

“Between 1.8 and 1.5 million years ago, H. erectus evolved into an ancestor very different to anything that came before,” says , a geologist at Bournemouth University, UK, and part of the team that studied the footprints. Those differences included shorter arms, longer legs, and – the footprints show – a modern foot and gait.

That’s important, he says, because the increasing mobility of H. erectus opened up a wider range of potential habitats. This can be seen in their long-distance transport of tools and occupation of drier and higher-altitude landscapes. In turn, the combination of increased mobility and tool use may have contributed to more efficient scavenging and increased meat consumption.

Compelling evidence

Bennett and his colleagues unearthed two layers of footprints at Koobi Fora, a rich archaeological site near Ileret in Kenya. The lower layer includes two trails of two steps each plus an isolated footprint. The upper layer contains three trails, one showing seven steps.

The footprints are sandwiched between layered deposits of volcanic ash that are firmly dated throughout the Turkana basin. The prints were made between 1.53 and 1.51 million years ago.

“We see characteristic human prints, with a clear heel, an imprint on the outside of the foot, and then a really deep impression underneath the ball of the foot,” says team member , a palaeoanthropologist at George Washington University in Washington DC. “Whereas the Laetoli prints have debatable evidence of these modern characteristics, the prints from Kenya show compelling evidence of them.”

Neat feet feat

Bennett digitised the footprints using a laser scanner. The scans preserved the prints and allowed the researchers to analyse their geometry in three dimensions and compare them quantitatively with other footprints. This emerging methodology is known as geometric morphometrics.

On a variety of key features including length, a pronounced arch, and the alignment of the big toe with the other toes, the Turkana prints are much more modern than those from Laetoli. Crucially, they reveal a modern stride, in which weight shifts from the heel to the ball of the foot and then to the big toe, which provides a platform to push off from.

For team member , a palaeoanthropologist at Rutgers University in New Jersey, the footprints vividly confirm what researchers have been piecing together about how H. erectus traversed and exploited a changing landscape. “They had the anatomy to range over longer distances across the landscape and move into more diverse habitats,” he says.

Adaptive shift

Rather than mobility in itself, he suggests, adaptation to a wider range of environments may have been what let H. erectus become the first hominin to leave Africa. “They just happened to adapt to environments that eventually connected them with Europe and Asia,” he says.

Palaeoanthropologist at Stony Brook University, New York State, who was not a member of the research team, is equally intrigued by them.

“Fossil foot bones are poorly known for this time period, so the footprints are a precious window into precisely how these ancestors walked,” he says. “The emergence of our own genus Homo is linked to the adaptive shift revealed by these fossilised footprints.”

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Growing a mixed “lawn” of two kinds of nanowires can make a new kind of light-sensing array that could be made in metre-scale sheets. The researchers behind the prototype say such cheap, high-quality image sensors would allow uses not conceivable using today’s more expensive technology.

Current sensors, such as those found in digital cameras, are made like any other silicon chip – they are carved out from a block of material. The new nanowire sensors are instead built from the bottom up, using chemically-grown nano-sized components.

A research team led by , at the University of California, Berkeley, developed the process. They start by growing an unruly “lawn” of nanowires on a surface.

Brush up

The crop is then printed onto another surface, a step that simultaneously tidies them up.

“At the first stage, the nanowires are more-or-less standing up, like a bad hair day. But during the printing process, they effectively get combed,” says Javey.

The nanowires, which are a few tenths of a millimetre long and a few tens of nanometres wide, can be printed onto anything from silicon to plastic or paper. Whatever the surface, it must be prepared with a pattern that guides the nanowires to predetermined locations.

To make the functioning sensor, two different “crops” of nanotubes are printed onto the same surface. Cadmium selenide nanowires produce electric charge when hit by light, while those made from silicon-coated germanium act as transistors to amplify that charge.

Proof of concept

The team built a prototype sensor with 260 pixels, each made from up to 5 sensor nanowires for each transistor nanowire. In tests, 80% of the sensor circuits worked as desired (see image, right). “It’s the largest integrated device to date based on nanowires,” Javey says.

Javey says the arrays are reliable, flexible and easy to scale up. He envisions growing self-powered, wireless versions on rolls of tape several metres in diameter.

“Imagine having a tape – just like your sticky tape – that you can grab and put on anywhere you want,” he says. “This tape will have all the needed components to do the active sensing, translate the data, and transmit it wirelessly.”

Producing image sensors in large, cheap areas could encourage new uses for imaging to emerge, says Javey. His team is working on the extra parts needed: nano-scale batteries for power and equally small wireless components.

“Outstanding application”

Javey and colleagues are among the very first to successfully demonstrate that different kinds of nanowires can be brought together to make integrated sensor circuitry, says , a specialist in organic electronics at the University of Illinois at Urbana-Champaign. “I really like what they have done here,” he told ��è����Ƶ.

, who leads a nanotechnology group at Georgia Institute of Technology, Atlanta, Georgia, added: “It demonstrates an outstanding application of nanowires in integrated electronics.”

Journal reference: ,

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Eventually, the researchers say, they may be able to add them into the genetic code of living organisms.

The diversity of life on earth evolved using genetic code made from arrangements of four genetic “bases”, sometimes described as letters. They are divided into two pairs, which bond together from opposite strands of a DNA molecule to form the rungs of its characteristic double-helix shape.

The unnatural but functional new base pair is the fruit of nearly a decade of research by chemical biologist , at the Scripps Research Institute, La Jolla, California, US.

Romesberg and colleagues painstakingly created a library of nearly 200 potential new genetic bases that are slight variations on the natural ones. Unfortunately, none of them were similar enough in structure and chemistry to the real thing to be copied accurately by the polymerase enzymes that replicate DNA inside cells.

Random generation

Frustrated by the slow pace designing and synthesising potential new bases one at a time, Romesberg borrowed some tricks from drug development companies. The resulting large scale experiments generated many potential bases at random, which were then screened to see if they would be treated normally by a polymerase enzyme.

With the help of graduate student Aaron Leconte, the group synthesized and screened 3600 candidates. Two different screening approaches turned up the same pair of molecules, called dSICS and dMMO2.

The molecular pair that worked surprised Romesberg. “We got it and said, ‘Wow!’ It would have been very difficult to have designed that pair rationally.”

But the team still faced a challenge. The dSICS base paired with itself more readily than with its intended partner, so the group made minor chemical tweaks until the new compounds behaved properly.

Novel DNA

“We probably made 15 modifications,” says Romesberg, “and 14 made it worse.” Sticking a carbon atom attached to three hydrogen atoms onto the side of dSICS, changing it to d5SICS, finally solved the problem. “We now have an unnatural base pair that’s efficiently replicated and doesn’t need an unnatural polymerase,” says Romesberg. “It’s staring to behave like a real base pair.”

The team is now eager to find out just what makes it work. “We still don’t have a detailed understanding of how replication happens,” says Romesberg. “Now that we have an unnatural base pair, we are continuing experiments to understand it better.”

In the near future, Romesberg expects the new base pairs will be used to synthesize DNA with novel and unnatural properties. These might include highly specific primers for DNA amplification; tags for materials, such as explosives, that could be detected without risk of contamination from natural DNA; and building novel DNA-based nanomaterials.

Increased ‘evolvability’

More generally, Romesberg notes that DNA and RNA are now being used for hundreds of purposes: for example, to build complex shapes, build complex nanostructures, silence disease genes, or even perform calculations. A new, unnatural, base pair could multiply and diversify these applications.

The most challenging goal, says Romesberg, will be to incorporate unnatural base pairs into the genetic code of organisms. “We want to import these into a cell, study RNA trafficking, and in the longest term, expand the genetic code and ‘evolvability’ of an organism.”

Stanford University chemist , has studied the fundamental chemistry of base-pair bonding. He foresees challenges, but great potential in the unnatural bases.

“It requires a long effort by multiple laboratories, but I think ultimately it will lead to some important tools,” he says. “The ability to encode amino acids with unnatural base pairs will be quite powerful when it comes.”

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