her mission must wait until nightfall. the conditions are perfect -- it's quiet and pitch black. but she has chosen this beach for another reason. it's the very beach where she was born. in one of nature's great feats of navigation, she has traveled hundreds of miles to cuba for a single hour of work. she creates a cavity deep enough to protect her fragile cargo from the elements. finally, she is ready. for about 20 minutes she is in a near-ecstatic state... releasing up to 200 eggs into the sand. when she's finished, she buries her precious payload... and drags herself back out to sea. she leaves her hatchlings with a one-in-a-thousand chance of survival. and she has no idea what her beach has become. cuba may be off-limits for americans, but for the rest of the world, the secret is out. in 1991, when the collapse of the soviet union nearly bankrupted the country, the regime opened its pristine beaches to europeans, canadians, south americans. for decades, a financial embargo by the united states has spared many turtle nesting beaches from a full-scale tourist onslaught. but it's just a matter of time before the embargo is lifted... and then how will cuba's sea turtles fare? bretos: sea turtles are very very susceptible to development. it's probably the number one threat. they're so dependent on beaches, clean beaches, beaches free of pollution, free of lighting... and once the pressure to develop these very pristine beaches picks up, that's going to come at the expense of some very, very healthy sea turtle nesting habitat. narrator: even on cayo largo the beaches are beginning to show the effects of tourism, and pollution is just one of the dangers the turtles face. in cuba, sea turtle eggs are a delicacy. enterprising cubans hunt for nests and dig up the eggs to sell on the black market. fortunately for the turtles of cayo largo, gonzalo nodarse and felix moncada have something else in mind. [ man speaking spanish ] interpreter: sea turtles are a charismatic species. you get the feeling that the more we know about them, the less we understand them. like, how they are born on one beach, and later they come back to the same beach to reproduce. how do they do it? narrator: felix and gonzalo are cuba's top sea turtle biologists, and they're monitoring cayo largo's beaches during nesting season. the steady advance of pollution and development is pushing turtles to build their nests in increasingly dangerous areas. [ speaking spanish ] interpreter: you can see that the waves come all the way up to here. this is a nest that is potentially threatened. if the sea reaches the nest, the saltwater will penetrate the embryos and they'll die. narrator: gonzalo and felix attempt to rescue the eggs from their hazardous site, and call in their local colleague, leonardo valido who runs a small hatchery on the island. the eggs are transported in the same orientation they're found in the nest. the smell of the sand from their nesting beach will permeate the soft eggs, imprinting on the turtles. in the future, the females that survive to adulthood will follow the scent to this exact spot. at the hatchery, leonardo raises a few turtles from each season until they're over a year old and big enough to tag for migration studies. he may never leave cuba himself, but he has devoted his life to these little global travelers that he sends off to see the world each summer. [ valido speaking spanish ] interpreter: i've been here in cayo largo for about 19 years, in one way or another doing this kind of work. i love it. i love everything that has to do with nature, especially the turtles -- they're like my symbol. [ counting in spanish ] narrator: the temperature of the eggs will determine the sex of the hatchlings, so the team is careful to mimic the exact dimensions of a natural nest. as the threats to turtles have grown so has the scale of leonardo's operation. now, in a single season, he'll hatch as many as 15,000 baby turtles. he has made it his personal responsibility to ensure that one of the sea's most essential creatures doesn't disappear. interpreter: this work requires a lot of energy. because it's not something that's going to make you financially comfortable, you must be a person that first, before everything, does it with heart. if you are waiting for other benefits... there will be no positive result in the end. narrator: in 45 days the buried hatchlings will emerge from the sand. for now, leonardo must remain in cuba, but his newborn turtles will begin their journey into a vast, mysterious world. [ bell ringing ] man: cuba holds some of the greatest mysteries of the caribbean. its so uniquely situated right at the confluence of the gulf, the caribbean and the atlantic ocean. and because of the political situation over time, and the economic situation in cuba, a lot less research has been done here and a lot less is known about this ecosystem. narrator: in a land off-limits to americans for over half a century, david guggenheim is a rarity -- one of the few scientists from the united states to gain access to this secretive island. through a partnership with the university of havana, david has worked in cuba for nearly ten years. on a course due northwest of the island, he is heading into a virtual demilitarized zone where cuba shares its waters with its capitalist neighbors. to the north are the busy ports of the united states. 90 miles to the west a steady stream of cruise ships pours into cancun. but here, where soviet gunboats once policed the marine border cuba's waters are strikingly free of traffic... on the surface. below the waves, powerful currents form a marine superhighway, where convoys of whale sharks patrol the coastline. [ dolphins squeal and click ] schools of dolphin and grouper follow the steady stream of nutrients gathering to spawn and feed. for years, david's focus has been on the foundation of this marine world -- clusters of tiny creatures that are under attack across the globe -- coral reefs. in parts of the caribbean, more than two-thirds of the corals have died. guggenheim: coral reefs are considered to be "the rainforests of the sea." and roughly 25% of the world's corals have died in the last 25 to 50 years. and the estimates for the future are that half of the world's corals will be gone within another 20 to 25 years. narrator: these undersea cities are besieged by a barrage of forces -- pollution, rising ocean temperatures, overfishing, and algae. but for ten years, david has been documenting an extraordinary phenomenon -- cuba's corals are fighting back. guggenheim: corals are animals. some of them look like plants. and here we have corals which have been wiped out, but we also have these young corals coming right back again. and that is very very significant to see. narrator: today, david is heading to an unexplored reef. for months he has been waiting for permits to visit the site, and finally his request has been granted. guggenheim: working here is incredibly difficult and often frustrating. this expedition requires signatures from 15 different ministries, including the army because the north coast is considered very sensitive. narrator: this site, so close to the cuban coast, has never been studied by scientists. just 90 miles south of the diseased reefs of florida, will these corals be as unhealthy as their northern neighbors? guggenheim: so much of this coast is completely unexplored. that's the point of our research. a lot it is just dropping yourself in the water and documenting what you're seeing. so, honestly, i don't know what we're going to see. narrator: great gardens of healthy brain corals spread out across the sea floor. vibrant sea fans and tube sponges show few signs of the coral die-off plaguing the rest of the planet. guggenheim: it really is a profoundly emotional experience. you get in the water and it is like turning back time 50 years to what coral reefs looked like before human beings started messing with the way these ecosystems work. narrator: david believes cuba's defiantly resilient corals are tied directly to the history of the island, perhaps as far back as the collapse of the soviet union when fertilizers were no longer available. guggenheim: essentially, cuba was forced to implement organic farming practices. and without all of those nutrients flowing into the water it's very possible that that had the effect of lessening the impacts on coral reefs -- less fertilizer, less algae growth. narrator: then david spots an old friend, a species he hasn't seen in years... a spectacular stand of acropora palmata... elkhorn coral. these breathtaking colonies of creatures are the most important reef-builders in the caribbean. but they're also one of the most sensitive. nearly 95% of the world's elkhorn has been destroyed by pollution and disease. here in cuba's waters, these could be some of the last of their kind on the planet. guggenheim: why are cuba's corals so healthy? we don't know the answer. but there's a mystery we can unlock here that could provide lessons for us to conserve corals in many other places including our backyard 90 miles north of here. narrator: cuba is the giant of the caribbean. with nearly half of the region's landmass the sprawling island was forged using nearly every trick in nature's book... [ thunderclap ] wet, tropical forests meet pine-cloaked mountains... and sultry wetlands give way to dry desert coasts. but despite the island's impressive grandeur, much of cuba's natural splendor plays out on a decidedly smaller stage... cuba is home to the world's smallest bat one of the smallest owls and the smallest bird of all a hummingbird that weighs less than a penny. the bee hummingbird is a miracle of evolution, a descendant of the dinosaurs barely two inches tall. from their treetop lookouts, they perform acrobatic aerial displays, scouting for the best blossoms to satisfy their outsized appetites. in a single day, they'll eat half their bodyweight in nectar and insects. the bird's size does have its disadvantages... when competing for food, its bigger neighbor, the cuban emerald, insists on first pick. one of the tiniest of cuba's creatures lives not in the trees but on the forest floor -- a frog barely half the size of its own name... eleutherodactylus iberia the smallest frog in the northern hemisphere. life among the leaf litter is full of constant danger and this bite-size frog knows he can be a tempting treat for hungry neighbors... but not today. making their way down from their treetop shelters, some of the forest's gaudiest creatures are also on the hunt. these are cuba's famous painted snails the polymita. with eyes perched on long stalks the polymita seek out water and lichen on the leaves of ferns and other plants. today, something else has caught this snail's eye... an attractive mate. like most snails polymita are hermaphrodites -- both male and female which means anyone is a possible partner. the affair begins with a mysterious dance as the couple slowly circles one another. but when they're ready to make their move it's anything but gentle. the snails extend a piercing weapon known as a love dart. they puncture one another in the so-called "sensitive zone," until they successfully exchange sperm. eventually, both snails will go on to lay fertilized eggs. for now, these two are content to linger in the moment. they should enjoy it while they can -- mating partners are becoming harder and harder to find. the polymita's elegant armor is no defense for their latest threat. poachers hunt them to sell as shell necklaces and trinkets and the snails are now endangered. when the u.s. embargo lifts, a sudden influx of curiosity-seeking tourists could deal the final blow. bretos: the tourism impact has really been minimal in cuba, but that's going to change because when you do have more tourists to cuba there's going to be a much bigger demand for these sorts of artisanal products. it's all determined by the market now. when you go from two million tourists a year to four to six to eight, everything will change. narrator: in cuba, the pace of life has changed little in decades. a small population on a large island lives in a deep association with the land. in the island's far west the red-soiled valleys of viñales are fertile ground for the country's most famous export. the farmers of viñales live as they have for centuries making the most of what the land affords them. others are tied to the land in even more remarkable ways. one woman has discovered that this sleepy valley offers more than just fertile soil. it provides her with answers to some of the most complex questions in science today -- answers hidden in the cousins of cuba's painted snails. interpreter: cuba is known as the paradise of snails. many live here in this area and nowhere else. they have fascinated me since i was a student. and i like them because of their lifestyle -- so free, so relaxed, so interesting. narrator: in one of the most remote regions in cuba biologist emma palacios lemagne is cracking the mysteries of evolution. cuba doesn't provide emma with much money for her research and can't supply her with expensive equipment. but what cuba does give her is one of the most extraordinary laboratories on earth. instead of test tubes, emma uses mammoth limestone karsts called mogotes. centuries of erosion have carved them into towering island worlds a virtual galapagos, where, like darwin's finches emma's snails evolve in extreme isolation. the snails on these separated hills never venture more than 60 feet from home, making this the ideal place for emma to discover how their shapes, colors and behaviors are dictated by the land. interpreter: each slope on these mogotes has its own species, and different variations of snails which all belong to the same species. on each slope, they are different from the next, because of the conditions in the habitat, humidity feeding conditions or wind resistance. you can see the diversity of forms in such a small area. narrator: the strange landscape has led to some stranger adaptations... like one of emma's least favorite subjects, the homely bistec de mogote -- the pancake slug. this bizarre creature has traded its shell for a different defense... it's perfectly camouflaged to disappear into its limestone hideout. but hiding may not be enough. emma's snails are losing habitat to expanding tobacco farms and many are hunted for much-needed protein. she runs a small breeding center to ensure her precious subjects don't disappear for good. interpreter: today, with how the world is and with all the problems that there are what interests me most is conservation. and this little thing we do with this little species of snails contributes. narrator: in a land where money is scarce and travel nearly impossible conservationists have turned inward and found all the riches of the natural world on one remarkable island. bretos: a cuban biologist doesn't make more than $25 a month. that's just amazing to think about. there's so much passion for what they do down there. and that definitely has a positive impact on the environment. narrator: the streets of havana are lined with reminders of the island's colonial history. but just a hundred miles to the south civilization gives way to cuba's primeval past. over a million acres of unspoiled caribbean wetlands -- cienaga de zapata -- zapata swamp. [ thunderclap, rain splashing ] zapata is considered the most important wetland in the hemisphere, and despite the embargo, the swamp already draws thousands of visitors from north america every year. cuba is a way station for nearly 300 species of migratory birds that breed in the united states. encompassing the infamous bay of pigs, every fall, zapata is now home to a different kind of invasion. clouds of warblers, ibis cranes and herons leave their summer homes along the eastern united states on a direct flight to cuba. millions of birds in flocks so enormous they blanket the sky on radar images. some fly over 1,500 miles, from as far north as new england and canada. many spend their winter here in the caribbean's largest protected wetlands. some will simply pause before hopping across the caribbean all the way to south america. sprawling mangroves, forests and lagoons provide ideal habitat for the visitors and also for birds found nowhere else on earth -- the cuban parrot the multicolored cuban tody, and the island's national bird the cuban trogon. but below the surface of zapata's vast swamps lives one of cuba's oldest most iconic creatures... one that once lurked throughout the caribbean but is now found only here in its last refuge -- the cuban crocodile. the cuban croc shares the swamp with its larger cousin the american crocodile. but what it lacks in size it makes up for with a notoriously aggressive temperament. among the fastest crocodiles in the world the cuban croc has evolved feet with less webbing, to enable powerful bursts of speed. known as the "pearly crocodile" because of its yellow and black coloring the croc has powerful jaws for crushing its prey -- turtles, crabs and fish. it's best known for jumping out of the water to snatch small mammals from overhanging trees. cuban crocs once ranged all the way to the cayman islands and the bahamas... but overhunting and competition for habitat have now confined them to cuba. as few as 3,000 animals now hang on to survival in zapata swamp. roberto "toby" ramos is cuba's leading authority on the cuban croc. for over 30 years, toby has navigated the waterways of zapata on a quest to understand these ancient reptiles. the cuban crocodiles prefer the freshwater marshes deep inside the swamp. toby's team has to wait for the summer rainy season, when the water is high enough to access their nesting grounds. with only the most basic tools they're just beginning to uncover the mysteries of the world's rarest crocodile. interpreter: the cuban crocodile is almost completely unknown. all we've done is try to give answers to basic questions of ecology -- where are they how many are there their reproductive success and their habitat. i don't think the most important thing is to know the number of animals, but rather what is the stability of the population. is this population increasing, is it stable or is it decreasing? narrator: the team heads deep into the muddy mangroves to conduct field surveys on the swamp's feistiest inhabitants. [ men speaking spanish ] interpreter: the cuban crocodile is considered one of the most aggressive crocodiles. it can be dangerous at any moment. god gave him many teeth, and he gave them to him for a reason. you have to be careful and have an understanding and experience with animals. but either way they will kill whomever. narrator: toby and his team are conducting a study detailing the physical differences between the rhombifer, or cuban crocodile and the american acutus species. interpreter: we measure the amount of ventral lines, and the dorsal lines which are these. we also count the teeth because the acutus has more mandibular teeth. narrator: cuban crocs can live for up to 75 years and grow up to 11 feet long. toby believes this specimen is a juvenile male. while the team takes their measurements the croc's patience appears to be wearing thin. but one final procedure reveals a surprise... interpreter: this is a large crocodile, so we can check it manually. if it were a male, the penis would come out. narrator: the croc is a female. she is then subjected to one final indignity. she's marked to avoid recapturing her during the rest of the study. it's a low-tech but effective operation, with the team's imagination unconfined by economics. [ ramos speaking spanish ] interpreter: conservation in cuba is very difficult because research in any field needs money. but still, even though we have very little, we've accomplished the same things other naturalists have in other parts of the world. we do our research to our full capacity with whatever we have. narrator: while the population of cuban crocs appears stable for now new pressures still threaten their numbers. american and cuban crocodiles are encroaching on each other's territories mating and producing a hybrid species. poachers target the crocs for hides and meat and more and more tourists come to zapata each year. now, with the possibility of the u.s. embargo lifting, can the swamp and its inhabitants survive a sudden invasion of american tourists? so far, cuba has been spared from the high-volume tourism and industry the united states could bring. but is the embargo the sole reason for the island's pristine state? guggenheim: i think the reasons that explain why we have an environmentally flourishing island here are both, in terms of policies legitimate policies and enforcement by the cuban government, and also partially an accident of history of the way this island developed, which was so different. it is a bit of an accident in that they have been blessed with this very large country relative to their population. it's roughly the size of florida. instead of having 18 or 19 million people, it has 11. and that has been beneficial to a lot of the natural areas in cuba. narrator: in spite of the embargo, tourism in cuba is big business -- and getting bigger every day. in some parts of the country the environment is already paying the price. guggenheim: as americans we often think of cuba as completely devoid of any outside presence. we forget that we're the only ones who have embargoed cuba. and we do see some of that florida-style development from the '60s that you know we would prefer never to see again anywhere in the world. man: the vice minister for tourism said looking at what might happen in cuba if it really opened up to western tourism fully his guess was that it might take many hundreds of additional golf courses -- maybe a thousand maybe two thousand. and it's hard for me to even imagine where in cuba i would like to see a thousand additional golf courses. narrator: along the northern keys, mangroves and sand dunes are bulldozed to carve out a growing number of beach resorts. in 1989, the regime built a causeway linking cayo coco, the biggest tourist key, to the main island. the ecological repercussions became a wake-up call across cuba. bretos: by building this highway through an estuary and coastal area they basically cut off the seawater that was coming in and nourishing the rest of the coastal area. this was a huge environmental issue in cuba. people were amazed at how this could have happened. and it did really change the minds of cubans. narrator: after the cayo coco debacle, the regime reversed course by announcing conservation as official state policy and environmental laws were enshrined in the constitution. today, about 22% of cuba's land and a quarter of its marine habitat are protected by law. if the embargo is lifted and a flood of american tourists come, cuba has the right laws and policies to ensure that it protects its environment and sustains its resources while growing at an unprecedented rate. it's got the right stuff. it certainly has the right laws. but laws are only as good as their implementation. narrator: tourism isn't the only industry setting its sights on the island. mining companies and oil prospectors are also jostling to cash in on cuba. if we look at other examples of history around the world, the soviet union and other countries, when the forces of capitalism start to kick in they can accelerate so rapidly and the power of the dollar being what it is, it's something very definitely to worry about. narrator: back on cayo largo after 45 days in the sand, leonardo's clutch of eggs hatches. tourists from nearby hotels can pay a small fee to release the baby turtles, and the money helps keep leonardo's hatchery going. it's ecotourism on a small scale and an example of a positive path cuba could take in the future. [ moncada speaking spanish ] interpreter: i think we can continue with conservation in this country, even though tourism is growing. and tourism can be good, because there are activities the tourists can participate in, and financially it benefits conservation for the whole country. interpreter: i will continue this as long as i can, to maintain it so my kids and other generations in the future can see this beauty, and to teach them how to love all the animals that are a part of life. interpreter: development and conservation, i think, can exist together perfectly. it's not easy -- it will be very difficult. but if we don't do it, the world will be destroyed. [ applause ] narrator: years from now when these turtles make the pilgrimage home to lay their eggs, to what kind of island will they return? will hotels and swimming pools line their nesting beaches? scientists all agree that what happens next will have repercussions far beyond cuba's borders. bretos: what's at stake is more than what's in cuba, or what's all around cuba. the fish that we eat in florida, many of those are born off the coast of cuba. the birds that people watch in arkansas probably winter in cuba. if cuba can't adapt when things open up, and if cuba can't hold on and do things the right way, and protect their protected areas or their beaches or their rivers and swamps then everyone suffers. where the rest of us made a lot of mistakes because we didn't know any better they've paid attention. it's almost as if cuba picked the perfect time not to follow the leader in terms of development. they did something radically different, and now they have the benefit of half a century of knowledge and they have a chance to really be the model of how to do it right. narrator: cuba is now poised for a leap into the future, with an opportunity the rest of us have lost. it could be that cuba's most lasting revolution will be not red, but green. neanderthals rediscovered. who were these primitive cavemen from our prehistoric past? man: neanderthals have the mother of all image problems. they're brooding they're stupid-looking they have no personality... new evidence paints a startling picture. this is the smoking gun. man: i think they had language. man: they were engineering their rocks. "decoding neanderthals," on nova. next on most pbs stations. the slow-moving koala is renowned for its sedentary lifestyle. but scientists are discovering that their social life is colored with rivalry and cheating. and it's their bellowing calls which are the true fabric of their social life. [ koalas calling ] by unlocking the koala communication code we are lifting the veil on this australian icon. don't miss a single moment -- now you can watch "nature" online! go to pbs.org to screen complete episodes from this season and seasons past. visit "nature" online for production updates from the field. well, here we are on the alaska coast... go behind the scenes with our filmmakers. we also used a borescope lens and that allowed us to put the lens right into a flower. and get connected with "nature's" online community -- all at pbs.org. "nature" is made possible in part by... leave it untouched by your presence capture its image and preserve it forever. canon -- living and working together to appreciate today and care for tomorrow. additional funding for "nature" is provided by... the lillian goldman charitable trust. the john d. and catherine t. macarthur foundation. the corporation for public broadcasting. and by contributions to your pbs station from viewers like you. this "nature" program is available on dvd for $24.99 plus shipping. to order, call 1-800-336-1917. to learn about what you've seen on this "nature" program visit pbs.org. available now on shoppbs downton still stands. i'm looking forward to all sorts of things. what?! no one must know! i'm warning you... to order, visit shoppbs. also available on itunes. narrator: they were the brutes of ice age europe. although a branch of our human family tree they were seen as a dead end deep in our prehistoric past. they were called neanderthals. neanderthals have the mother of all image problems. narrator: they eked out a marginal existence hunting by brute force with only simple stone tools. they were considered primitive with no language, art or the higher-level thinking of advanced species like us. they lacked the same intelligence as modern humans. narrator: they began to disappear 40,000 years ago as modern humans, our species, came on the scene. but this primitive picture is being replaced by a different image of neanderthals. it's bringing them much closer to us, as genetic evidence revises our human family tree and reveals their mysterious presence right within our genes. we started to look at the problem from different angles. they answer would come back, "it's neanderthal." that was quite shaking to me and i thought, "this must be a statistical fluke." narrator: now archaeologists are finding new evidence to help resolve bitter debates. this is the smoking gun. we have the case to settle the controversy. narrator: in toolmaking, they're seeing signs of language. there is some sort of advanced talking going on. narrator: a new neanderthal mind emerges. we're not talking about idiots. narrator: and if scientists are finally finding the real legacy of the neanderthals buried deep in our history and our genes what does it say about all of us? "decoding neanderthals," right now on nova. major funding for nova is provided by the following: supporting nova and promoting public understanding of science. and the corporation for public broadcasting, and by pbs viewers like you. narrator: 40,000 years ago, europe is in the grip of an ice age. in harsh, unforgiving terrain live members of an ancient human species. the neanderthals. it is a brutal time to be alive. only the toughest survive. they were very muscular, short wide, very stocky, very powerfully built. thomas wynn: they were hunter-gatherers. they had scarce game to find. most neanderthals were probably dead by 30 years old. so it was a brief, brutal life. narrator: hunting was extremely dangerous. stringer: they were confrontational hunters, so they had to get close in to their prey with stabbing spears. this required not only a lot of bravery but a lot of sheer physical strength. frederick l. coolidge: these neanderthals could bench-press 300 to 500 pounds. they had big thrusting spears that they thrust into the side of 2,000- and 3,000-pound animals. narrator: the neanderthals survived the harsh conditions in europe for at least 300,000 years. then, around 40,000 years ago, a different human species arrives on the scene... our species, homo sapiens. they migrated from africa, spreading across neanderthal territory, outnumbering them ten to one. suddenly you've got two species competing for the same resources hunting the same animals collecting the same plant resources wanting to live in the best territories and the best caves. narrator: after another 10,000 years the neanderthals disappear. ed green: the story of the neanderthals is a murder mystery. they were there and now they're gone and they go away at about the same time as we are showing up on the scene. narrator: so why did they vanish while we survived? for years, many scientists believed we wiped them out a simple case of our brain outclassing their brawn. this theory emerged when archaeologists unearthed the very first neanderthal skulls over 150 years ago. to scientists at the time, skulls like these looked primitive compared to ours. chris stringer is one of the world's preeminent neanderthal experts. stringer: we can tell a neanderthal skull 100% of the time. we've got a very broad skull this double-arched brow ridge, and perhaps their most distinctive feature the middle of the face is pulled forwards the cheekbones are swept back. narrator: one influential discovery featured a skeleton crippled by acute arthritis, incorrectly reconstructed with a hunched posture and a shuffling walk. this early find helped shape popular perceptions of neanderthals for decades, launching a wave of images of the neanderthal as a brutish caveman. neanderthals have the mother of all image problems. they're brooding they're stupid-looking... they have no personality. stringer: they were reconstructed as being much more apelike stooped, grasping big toes very hairy, head hung forward, shambling in their gait. narrator: critically, scientists believed the neanderthals lacked the one thing that defines us... our brainpower. they lacked the same intelligence as modern humans. narrator: with only limited stone tools and no art or personal ornaments, neanderthals seemed less advanced than modern humans. but was that really the whole story? now, new discoveries in genetics and archaeology are challenging this traditional view of the neanderthals. (stones tapping) metin eren has spent six years studying neanderthal technology. these levallois flakes named after the place in france where they were first found, were the neanderthals' tool of choice. at first glance, they look rudimentary, the product more of luck than judgment. but when eren tried to reproduce one, he got a surprise. i find the levallois technology much more difficult to make than any of the modern homo sapien technologies. it took me about 18 months to master levallois technology and this was after i'd been flint-knapping for a number of years. the fact that there seems to be a goal involved. they're not simply just striking flakes to get a sharp cutting edge. narrator: eren began to realize this was no hit-or-miss process. he wanted to discover just how they did it. so he turned to morphometrics, a technique which analyzes the exact shapes and angles of objects. it revealed neanderthals must have used a precise set of strikes to turn a raw flint block into a carefully shaped object known as the core. the final crucial step involved striking the core with a single precision blow. only if aimed just right would this create the perfect flake and a remarkably versatile tool. eren: i shape this in such a way that the core has a gentle convexity such that the large flake that comes off has a sharp edge all around its perimeter and that enhances the utility of this particular piece in a number of ways. because it's uniformly thick you can resharpen it more times than you can other types of stone flakes. we also found that the levallois flake is statistically more symmetrical. that means when you use it you basically reduce torque, so it actually has ergonomic properties. i can actually get a lot more force with each cut and each slice. i'll just put a little more pressure and the levallois flake goes right through it and we got one big piece of gammon. that took about a minute and a half. no problem. this is an amazing tool. they were engineering their rocks to get particular products that have specific properties. they were able to discover a technique that is incredibly difficult to do. it is just a testament to how intelligent they must have been to actually invent it in the first place. narrator: metin eren's work reveals the complexity of neanderthal toolmaking. but there's even more surprising evidence of sophisticated neanderthal technologies. dutch archaeologist wil roebroeks is studying new finds, one of them dating back a quarter of a million years. this is a flint spearhead, at its base, a large sticky black mass most likely used as a glue. evidence from many sites had already shown how neanderthals attached stone flakes to wooden shafts, first binding them with sinew or leather, then securing the binding with a gluelike substance. this turned the flake and its shaft into a robust weapon. roebroeks: what you see there is a nice flint flake at least for an archaeologist, a nice, sharp, razor-sharp flint flake, which is covered at the base in this pitch material. it is a material that they used probably in many aspects of everyday life. narrator: at first, it was thought this neanderthal glue was nothing more than sap from a pine tree, easy for them to find and use. but detailed analysis revealed something different. it was a type of manmade pitch from birch trees. chemical studies have shown that that material was produced from heating birch bark. neanderthals were producing these pitches. so it is not something like the stuff that you can retrieve from a pine when you hit a tree, the natural stuff that comes out. narrator: this is the world's oldest known synthetic material. it makes neanderthals, and not us the inventors of perhaps the first industrial process. but how could an allegedly primitive species have done this? to find out more, wil roebroeks decides to mount an experiment with a colleague friedrich palmer. they will try to replicate the neanderthal technique of pitch extraction, a complex process called "dry distillation." crucially, they'll use only materials available to neanderthals 250,000 years ago: an upturned animal skull to catch the pitch... a small stone on which the pitch would condense... some rolls of birch bark the source of the pitch... and a layer of ash to exclude oxygen and prevent the bark from burning. roebroeks and palmer need to heat the bark to 400 degrees centigrade. any less and it won't produce pitch. any more and it will simply burn. after eight hours, any pitch should have condensed on the stone within the skull. yeah. oh, look at that. yeah, that's a bit dry. narrator: today, roebroeks and palmer manage to extract only a tiny smear of pitch. that's not much. narrator: they are on the right track, but it isn't nearly enough to glue a spearhead to a shaft as the neanderthals did. it seems this experiment is on too small a scale to produce enough pitch. neanderthals must have figured out how to scale up the technique in a way we haven't yet reproduced. however they managed it, the neanderthals had evidently mastered a complex thermal process. the neanderthals' extraction of pitch and their distinctive toolmaking suggest their technology was more advanced than previously thought. what's more, artifacts like these have been found across a wide area of europe. and this raises a question. how did neanderthals communicate these complex ideas? could it be they shared that one ability we usually think of as unique to us? language. one could infer that there was some communication maybe between generations or between peers in a group. but language, of course, is very difficult to excavate. narrator: now, fresh evidence is emerging from a completely different branch of science, applied to neanderthal research for the first time. svante paabo is one of a new breed of detectives examining our deepest past. he's not an archaeologist. he does his digging in the lab. paabo is interested in humans and what sets us apart from our closest relatives. as a geneticist, his work involves comparing our genetic material with that of the rest of our family tree. it's really about finding out what makes us special in the world... ...what made things such as modern humans spreading across the entire globe, developing all the technology, all the culture that's typical in modern humans. david scott: there's a fundamental truth to our nature. man must explore. narrator: paabo and his colleagues want to look at specific genes, where you'd expect humans and our closest relatives to differ-- like a gene fundamental for language named foxp2. foxp2 is a very interesting gene in that it's one of a few genes that's directly related to this uniquely human characteristic speech and language. four violets, a fiver! four violets a fiver! (chanting) (phone rings) nine hundred, nine hundred. narrator: foxp2 is found in many species although the human version is distinctive. by comparing it with a potential neanderthal version, paabo was hoping to shed light on what makes human language special. but before he could even begin paabo needed to have the genetic blueprint for both neanderthals and humans-- their genomes. a genome is the distinctive genetic recipe for a species made up of a specific set of chromosomes. these are responsible for the characteristics that make every species different. within the chromosomes genes determine whether we have two legs or four grow feathers or fur and every part of this unique recipe is encoded within just one molecule... dna. when svante paabo started his work the human genome had already been decoded. no one had attempted to map the neanderthal genome. paabo faced a seemingly impossible task in attempting to map the dna in the nucleus of a 30,000-year-old cell. ed green is a geneticist on paabo's team. as soon as it was obvious that this was possible in theory, we started to think about how do we do this in practice, if we can get nuclear data if we can get some amount. and we did some back-of-the-envelope calculations and it looked like yes, this is feasible. paabo: so we spent a lot of time looking at many archaeological sites and many different bones... ...and eventually identified this site in croatia. narrator: the vindija cave in northern croatia contained genetic gold dust-- the 30,000-year-old leg bone fragments of three female neanderthals. the exceptionally well-preserved bones offered paabo's team the best chance of extracting neanderthal dna. in sterile conditions, the team took samples of bone, carefully dissolving them in solution before spinning them at high speed in a centrifuge to retrieve the strands of dna. but then the real difficulties began. the bone samples carried billions of unwanted passengers. paabo: most bones we look at might contain a few molecules of neanderthal dna but the vast, vast majority come from bacteria and fungi that colonized the bone when it was in the ground in the cave for tens of thousands of years. narrator: before the team could go any further, they'd have to destroy the rogue dna. so they invented a cleanup technique using enzymes that target and eliminate bacterial dna from the sample. the resulting clean sample contained five times the concentration of neanderthal dna compared to the original which made the analysis easier. still, reconstructing the genome remained a formidable challenge. the dna molecule's intertwining strands are held together by four key chemicals, represented by letters. these bond together as pairs-- always c to g and a to t. these letters are like building blocks repeating units which spell out the genome's unique recipe. their order is critical. just one letter out of place within three billion pairs and the genome would be inaccurate. but the dna was in tiny fragments, like a colossal jigsaw puzzle. the team would have to place each piece in precisely the right order. svante and others were very skeptical. it was in the realm of the impossible that a genome would ever be sequenced. during the course of this project there were actually many times when we despaired about being able to make it. narrator: it would take them four years. but finally, the last piece of the puzzle fell into place. human evolution is something that everyone cares about and it's such an incredible thing, technically to be able to do. add to that that it's our closest extinct ancestor and all that it can tell us about human evolution and human biology. it's the most exciting thing i've ever worked on. narrator: this is the result of all their work-- the neanderthal genome. here is one tiny part of the actual sequence of over three billion letters corresponding to each dna building block the genetic blueprint of a species of human that became extinct 30,000 years ago. now, at last, paabo's team could begin comparing neanderthal to modern human genes. one of the first areas they looked at was foxp2 the gene associated with language. would an identical gene be shared between human and neanderthal? would the gene be there at all? to my surprise, i must say it turned out that it's shared. narrator: neanderthals had exactly the same version of the foxp2 gene as humans-- the same chemical letters in exactly the same order. paabo: i'm very sure that the neanderthals had communication. if it was a language exactly as we would understand language, that's another question. stringer: i think they had language. that doesn't mean it was the same as our language as complex as our language. i think, again, that modern humans probably had another level of complexity. but i think they had language. yes, i absolutely think they couldn't have survived the way they did without it. narrator: paabo's work adds weight to the growing argument that neanderthals and modern humans shared more abilities than previously thought. but it begged a billion-dollar question. did we have enough in common that we could have interbred? if neanderthals and modern humans had interbred successfully traces of their dna would be found in ours. most scientists, paabo included, thought this highly unlikely. when different species mate, their offspring are usually infertile. paabo: i was biased against interbreeding. there is no evidence for it so i don't think it really happened. narrator: but with the neanderthal genome now sequenced, paabo and his team could examine this question. the first step was to map the individual genomes of five people from different ethnic groups. then they compared this modern dna with neanderthal. they focused only on small specific regions, called "variable areas," where the order of the dna letters often differs from one individual to the next. here, if interbreeding had taken place, letter sequences typical of neanderthal dna would show up in the human dna strand. but with no interbreeding, there would be no trace of neanderthal dna in the variable areas. paabo expected to see the same negative result in the genomes of all five modern humans, regardless of ethnic group. well, if neanderthals are equally distantly related to everybody then neanderthal should match the french guy and the west african guy equally often. narrator: but that is not what they found. when we compared one african to a european individual the neanderthal matched the european individual more often than the african one. narrator: the result indicated that neanderthals were genetically closer to europeans and asians than they were to africans. it meant that somewhere along the line european and asian humans had picked up neanderthal dna.

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