Sink a spade into the ground near any area of long-term human habitation and you're likely to experience something not unlike time travel. Where day-to-day observations and recorded history fail us, discarded remnants shed light on ages past.
Such is the very meat of archaeology. Buried tombs, forgotten habitations and even garbage heaps cast a shadow through time. Dig deep enough, however, and the knickknacks and tools will begin to vanish. The further back into prehistoric time we delve, the more it becomes evident that the ascension of man is a tale told in bones.
Humans have left an evolutionary trail of fossils ever since our earliest ancestors split off from the rest of the hominid family. Before that, fossils clue us into the various hominids that roamed the Earth before us. Yet paleoanthropologists study these bones not only to discover all the links in the great chain of evolution, but also to learn about the biological and technical origins of evolution.
Following are 10 of the most important hominid fossil finds in order of discovery. All 10 take us to the very cradle of humanity: the African continent.
The dots on this map indicate locations of early hominid fossil finds.
Image Credit: HowStuffWorks
10: Paranthropus Boisei
Famed British archaeologist and anthropologist Mary Leakey discovered the first specimen of Paranthropus boisei in 1959 at Olduvai Gorge in Tanzania. The specimen was nicknamed "nutcracker man" as, indeed, the skull bears a resemblance to the wooden holiday icon with its thick cheekbones, enormous lower jaw and impressive array of molars. The skull also featured a pronounced cranial crest, which gives P. boisei a bit of a Kewpie doll look as well.
Sure, his skull reminds us of antique dolls and nut-shattering figurines, but what makes this specimen notable in the world of paleoanthropology? Well, nutcracker man played a key role in disproving the single species hypothesis in 1969. The popular 1950s theory argued that there was only one hominid species in southern Africa between 3 and 1 million years ago, as only one species can fill a single environmental niche at any given time.
Single species proponents initially made the case that P. boisei was merely the male specimen and Australopithecus afarensis (our next hominid) was the female. By uncovering a female P. boisei, the single species hypothesis was disproven sufficiently.
9: Australopithecus Afarensis
Although the word "love" might be a bit strong, we can safely say that nearly everyone knows "Lucy." At least that was the nickname attributed to the 3.2-million-year-old specimen that Donald Johanson and Tom Gray discovered in Hadar, Ethiopia, in 1974. They named it after the Beatles song "Lucy in the Sky with Diamonds," which aired on the radio during post-find celebrations back at camp. Might we have been just one record flip away from knowing A. afarensis as "Lovely Rita?"
Lucy made major waves in the years to follow. While she exemplified many features associated with chimpanzees (such as short legs, long arms and a small brain), the bones of her knees and pelvis suggested predominantly bipedal movement. The find gave paleoanthropologists a definite marker on the evolutionary road from ape to human and supported the importance of bipedalism in our evolution. In a time when climate change may have wreaked havoc on forest environments, coming down from the trees to live upright was an essential survival tactic.
This life-sized reconstruction gives us an idea of what Lucy once may have looked like.
Image Credit: AP Photo/Michael Stravato
8: Australopithecus Anamensis
Change necessitates change. This truth underlies the entire history of life on Earth, and the long, arduous evolution of man is no exception. Paleoanthropologists believe that African climate changes affected habitat, reducing massive woodlands to savannas. To deal with the changes, apes had to alter how they scoured for food, which affected their very physiology. Bipedalism emerged as the number of climbing trees diminished. As society became less competitive and males took on more parenting responsibilities, sharp, chimplike canines gave way to blunter, hardier teeth.
In 1965, a Harvard University expedition discovered the first specimen of Australopithecus anamensis in Kanapoi, Kenya. At the time, however, they didn't know exactly what they had. It wasn't until the mid-1990s that other specimens turned up to shed light on the place of A. anamensis in the pantheon of human evolution: an ancestor of Lucy's dating back nearly 4 million years. While primitive, the specimen featured blunt, hard-enameled teeth that spoke of an already altered diet of tougher scavenged fare.
Where'd you get those chompers? Well, it's a long story -- millions of years long, in fact.
Image Credit: David De Lossy/Photodisc/Getty Images
7: Ardipithecus Ramidus
The split between human and chimpanzee lineages is a pivotal one in human evolution. One species would go on to rule the planet while the other would be made to dress in funny outfits. The big question is not only when did such a split occur, but what factors and mechanisms allowed it to happen?
In 1994, anthropologist Tim White discovered the remains of an early hominid in the Middle Awash region of Ethiopia. The specimen eventually would be classified as Ardipithecus ramidus, dating back an estimated 4.4 million years. Specimens of A. ramidus display both apelike and chimplike features, but subsequent finds in 2005 confirmed that the species walked upright [source: BBC]. Analysis of the species continues to this day, but the find provides another point of comparison in human evolution.
What do these guys all have in common? A last common ancestor, that's what.
Image Credit: Hulton Archive/Hulton Archive/Getty Images
6: Kenyanthropus Platyops
Behold, the "flat-faced man of Kenya," the hominid specimen between 3.2 and 3.5 million years old that Meave Leakey's team discovered in Lake Turkana, Kenya, in 1999. At this point in the list, your eyes may already be glazing over at the prospect of another ancient, bipedal hominid ancestor of man -- but consider the date on this one. This is roughly the same time that Lucy the Australopithecus afarensis roamed the Earth.
If Kenyanthropus platypus lived at the same time as Lucy, that means that two bipedal human ancestors lived at the same time in the same basic area. Paleoanthropologists consider this proof of adaptive radiation, the notion that, where one species makes an adaptive leap, other similar species will also emerge to take advantage of an accommodating ecosystem. It's one of the basic tenets of Charles Darwin's theory of evolution, so seeing proof of it in action substantiates the idea of human evolution.
5: Australopithecus Garhi
Australopithecus garhi was discovered in the Middle Awash region of Ethiopia and announced in 1999. Likely a direct ancestor of modern humans, the 2.5-million-year-old species appears to have practiced a very human craft: butchery. The fossils of A. garhi were discovered in sediment along with fossilized antelope bones that appear to have been worked over with stone tools and cracked open with hammers.
This is key because the nutrients found in a meat- and marrow-rich diet may have improved survivability and may have been a key evolutionary catalyst. The genes involved in adapting to a more carnivorous diet also affect long-bone growth, hairiness and hearing -- the last of which is connected closely to the development of speech.
The map of our evolutionary past is still incomplete, as is our understanding of the mechanisms behind evolution. With new discoveries popping up every year, we can only guess at what light future finds will shed on the ascent of man.
Humanity's love of meat is closely linked to human evolution.
Image Credit: Ryan McVay/Photodisc/Getty Images
4: Orrorin Tugenensis
In the world of paleoanthropology, even a handful of bone fragments can greatly improve our understanding of human evolution. Case in point: Orrorin tugenensis (that's Tugen for "original man"). In 2000, Brigitte Senut and Martin Pickford discovered five pieces of the early hominid in Kapsomin, Kenya. Dating back an estimated 6 million years, the specimen just might be the earliest hominid on record.
The O. tugenensis find made the greatest impact in relation to our understanding of the chimpanzee/hominid split. Previously, paleoanthropologists had estimated the two evolutionary paths split from each other roughly 5 million years ago. This specimen pushed that date back another million years. Plus, Senut and Pickford argued that its dental anatomy and advanced bipedal locomotion established it in the line of descent from ape to man.
Is O. tugenensis really the "original man?" Maybe not, the species lived very close to the time during which the line to modern humans branched from that of great apes. It's just one more sign in the evolutionary road to humanity.
3: Sahelanthropus Tchadensis
In 2001, fossil hunter Ahounta Djimdoumalbaye found something amazing in the desert wastes of northern Chad. Nicknamed "Toumai," which means "hope of life" in the African language of Goran, the specimen made a huge impact in the world of paleoanthropology. Experts analyzed the specimen and determined the skull to be between 6 and 7 million years old. In other words, when Lucy still walked the Earth, Toumai's remains were already museum pieces.
Sahelanthropus tchadensis (Toumai's official name) was a very important find in that it illuminated a previously empty portion of the evolutionary time line. We knew that humanlike hominid apes began to pop on the African scene around 5 million years ago and that less evolved apes thrived 5 million years before that. The skull of S. tchadensis combined elements of both: an apelike cranium and a human face. As more specimens of this and other species from the period emerge, our understanding of Toumai's significance will improve.
2: Ardipithecus Kadabba
It may sound like a magical incantation, but Ardipithecus kadabba is yet another important early hominid. The species dates back 6 million years to just after the hominid/chimp split. When A. kadabbafossils were discovered first in 2001 in the Middle Awash region of Ethiopia, they were thought to be a subspecies of A. ramidus, but further investigation revealed the differences. More remains were announced in 2004.
By comparing the teeth of A. kadabba with those of a chimpanzee, paleoanthropologists were able to detect minute differences between the two similar species. Essentially, A. kadabba represents an intermediate evolutionary state, a close chimp relative in the early stages of its evolutionary journey toward Homo sapiens.
1: Pan Troglodytes
Although the scientific name Pan troglodytes may sound pretty, what we're talking about here is the common chimpanzee. As we discussed, the split between chimps and humans is a key event for paleoanthropologists -- the Holy Grail. Chimps are also our closest human relative, yet despite our increasing collection of early hominid fossils, we didn't have any chimp fossils for the longest time.
That changed in late 2004, when a U.S. team struck fossilized chimpanzee gold also in the Tugen Hills area of Kenya: 545,000-year-old P. troglodytes teeth. The discovery demonstrated that the region contained habitats suitable for both early humans and chimps. This find would support the notion that one of the key factors in the split was East African climate change -- from forests to savanna -- necessitating bipedalism as a survival feature.
Keep reading for more links you might like on the early days of man.
Take a good, hard look at our closest living relative.
Image Credit: Daryl Balfour/Digital Vision/Getty Images
"Amazing hominid haul in Ethiopia." BBC News. Jan. 19, 2005. (May 8, 2009)http://news.bbc.co.uk/2/hi/science/nature/4187991.stm
"The Ape that Took Over the World." BBC News. Oct. 4, 2001. (May 8, 2009)http://www.bbc.co.uk/science/horizon/2001/apetookover.shtml
"Australopithecus afarensis." Human Evolution at the Smithsonian Institute. (May 7, 2009)http://anthropology.si.edu/HumanOrigins/ha/afar.html
"Australopithecus boisei." Human Evolution at the Smithsonian Institute. (May 7, 2009)http://anthropology.si.edu/HumanOrigins/ha/bos.html
"DNA analysis for chimpanzees and humans reveals striking differences in genes for smell, metabolism and hearing." Cornell News. Dec. 18, 2003. (April 24, 2009)http://www.news.cornell.edu/releases/Dec03/chimp.life.hrs.html
"First chimpanzee fossils found." BBC News. Aug. 31, 2005. (May 8, 2009)http://news.bbc.co.uk/2/hi/science/nature/4201666.stm
"Hominid Species Time Line." Washington State University. (May 8, 2009)http://www.wsu.edu/gened/learn-modules/top_longfor/timeline/05_o_tugenensis.html
Jacobs, James Q. " Australopithecus garhi, A New Human Ancestor?" July 4, 2000. (May 8, 2009)http://www.jqjacobs.net/anthro/paleo/garhi.html
Kreger, David C. "Ardipithecus ramidus." Archeology.info. 2008. (May 7, 2009)http://www.archaeologyinfo.com/ardipithecusramidus.htm
Kreger, David C. "Australopithecus afarensis." Archeology.info. 2008. (May 7, 2009)http://www.archaeologyinfo.com/australopithecusafarensis.htm
Kreger, David C. "Australopithecus anamensis." Archeology.info. 2008. (May 7, 2009)http://www.archaeologyinfo.com/australopithecusanamensis.htm
Kreger, David C. "Australopithecus boisei." Archeology.info. 2008. (May 7, 2009)http://www.archaeologyinfo.com/australopithecusboisei.htm
Kreger, David C. "Australopithecus garhi." Archeology.info. 2008. (May 7, 2009)http://www.archaeologyinfo.com/australopithecusgarhi.htm
"Mother of man - 3.2 million years ago" BBC News. (May 7, 2009)http://www.bbc.co.uk/sn/prehistoric_life/human/human_evolution/mother_of_man1.shtml
"Origins of Humankind." PBS. 2001. (May 8, 2009)http://www.pbs.org/wgbh/evolution/humans/humankind/a.html
Sanders, Robert. "New Ethiopian fossils are form 6-million-year-old hominid living just after split from chimpanzees." UC Berkeley News. March 4, 2004. (May 8, 2009)http://www.berkeley.edu/news/media/releases/2004/03/04_Akadab.shtml
U.C. Berkeley Middle Awash Project. (May 7, 2009)http://middleawash.berkeley.edu/middle_awash.php
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