Tuesday, November 29, 2011

10 things that define Human evolution…

"We seem to live in a hazardous time, drifting along here through space. Nobody knows just when we begun, or how far we've gone in the race."

-- Benjamin Franklin King, Jr

The 19th century American humorist King may have been unsure of his origins, but that era contributed to knowledge of the human race. Highlights included:

  • Early 1800s. French naturalist Jean Baptiste Lamarck, after studying fossils, argued that organisms changed their behavior in reaction to transformations in their environment, leading to changes in physical structure (such as the "stretching" of a giraffe's neck to reach tree leaves).
  • Mid 1800s. Alfred Russel Wallace and Charles Darwin were British researchers who concurrently, but separately, developed similar ideas about evolution: Although the population of any species has much in common, there are individual differences that might be advantageous to survival. If those individuals reproduce, the differences become traits of future generations.
  • Late 1800s. Ernst Haekel was a German scientist who believed the initial growth of an embryo matches the earliest, single-cell life forms. He called this "ontogeny recapitulates phylogeny." Unfortunately, Haekel modified some of his data to conform to his proposal.

Through peer review, discovery and revision, scientists have defined and refined evolution (inherited changes that occur over many generations of a population). They have traced the evolution of flora, fauna and hominids (humans and their ancestors). The following are 10 important discoveries in human evolution.

10: The First Fossil, 1856

The study of human evolution quickly became complicated. The first fossil identified as prehistoric human wasn't the first one discovered. In 1856, a fossil found in the Neander Valley, near Dusseldorf, Germany, was recognized as a hominid. The fossil's species was named, not coincidentally, Homo neanderthalensis (Neanderthals). Similar fossils had previously been uncovered (1829, Belgium; 1848, Gibraltar), but their significance was missed.

And such fossils are significant. They revealed that Neanderthals lived only 200,000 to 28,000 years ago, demonstrating that Neanderthals shared a common timeline with modern humans. That's not all they shared with humans: Compared with earlier prehistoric species, Neanderthals had relatively large brains. There is also fossil evidence that they employed tools, hunted, built shelters and clothed themselves.

And don't stereotype Neanderthals as "cavemen." Decorative artifacts have been found, indicating an interest beyond mere survival. Furthermore, the Neanderthals buried their dead, and, intermittently, ornamented the graves.

 

9. Homo erectus, 1891

Although the oldest hominine fossils have been found in Africa, the next important discovery was located outside that continent. In 1891, a fossil found in Indonesia proved to be the oldest non-African specimen. The species, Homo erectus, lived 1.89 million to 70,000 years ago. Related fossils have since been found in Africa and other parts of Asia.

There is evidence that, contrasted with older species, our Homo erectus ancestors had developed some human-like traits. They had relatively long legs and short arms; this may have been the end of our ancestors' regular tree-climbing. Noses were very large, but there was a subtle change in nostrils: they pointed down. The size difference between males and females was reduced. Homo erectus may have performed human-like behaviors as well. Fire was used and shared for food preparation, warmth, and protection.

 

8. Taung Child, 1924

until 1924It almost seems like some fossils play hide and seek. Although evidence indicates that the oldest hominids lived in Africa, it was not until 1924 that one of their fossils was uncovered there. Discovered in South Africa, the "Taung child" lived 2.8 million years ago. Claw and beak marks found on the fossil -- a skull -- resemble those of a modern eagle and indicate death due to an eagle attack. The Taung child belonged to the species Australopithecus africanus, and, at the time of unearthing, it provided the earliest evidence of upright walking.

 

How can scientists establish locomotion without a spine, pelvis or legs? Examination of the fossil revealed that the hole at the base of the skull, allowing the connection of the spine and the brain, was situated so the skull could sit upright on the neck.

7. The Handy Man, 1960

Hominids may not have used miter saws or power drills, but some did utilize simpler tools. In 1960, a previously unknown type of fossil was found in Tanzania, and stone tools were also discovered during the dig. The species' name, Homo habilis, means, literally, "handy man." The size of the skull suggested a larger brain, and that, coupled with the proximity of tools, indicated to scientists that this species had been the first ancient human capable of crafting and using tools.

Homo habilis lived 2.3 to 1.6 million years ago, but, since 1960, somewhat older stone tools have been uncovered. Although this species did, in all likelihood, employ tools, it was not the first species to do so.

 

6. Lucy, 1974

Arguably one of the most famous fossil finds, "Lucy" was discovered in 1974 in the Afar Depression in Ethiopia. The scientists bestowed the very human name upon her because, during the dig, a Beatles tape was regularly played; it included the song, "Lucy in the Sky with Diamonds." 

Lucy's species, named Australopithecus afarensis, lived 3.85 to 2.95 million years ago. More than 300 of these fossils have been found, making Australopithecus afarensis one of the best sources of ancient human data.

This fossil was particularly noteworthy because, in 1974, Lucy presented the earliest indication of  two-legged walking, though she would have been proficient in tree climbing, as well. Other apelike traits included facial structure and smaller brain size.

 

5. Opposable Thumbs, 2000

Ah, thumbs! So useful for grasping tools, grabbing food and pinching siblings. In 2000, the fossil of an ancient ancestor discovered in Kenya proved to be a whopping six million years old. Not only was Orrorin tugenensis the oldest hominid found to date, but there was evidence that, at least sometimes, it walked upright. Even more astounding, perhaps, was the discovery of opposable thumbs on such an ancient fossil. Up to this point, the presence of opposable thumbs had been linked to tool use; now that connection was no longer solid.

Or was it? Fossils from younger species indicate that thumbs reverted back to less agile, ape-like digits until eventually becoming opposable again.

 

4. Ardi, 2009

In 2009, a fossil uncovered in the Afar Depression of Ethiopia provided some insight (and controversy) into how our ancient ancestors lived. A geographic if not temporal neighbor of Lucy, Ardipithecus ramidus("Ardi") was 4.4 million years old. The name means "ground" and "root," connoting an ape that spent time on the ground but was also at the base of the human family tree.

Why was Ardi at the base of the tree? There were ape-like physical traits: long, curving fingers and opposable thumbs on the feet, which would have facilitated tree climbing. On the other hand, the shape of pelvis and foot bones present the possibility of upright walking. This is controversial: Plant fossils discovered in conjunction with Ardi indicate she lived in a forest. It had been assumed that upright walking evolved as the environment changed into plains, but the wood-dwelling Ardi may contradict that.

 

3. Stone Tools, 2010

Step aside, "handy man" (Homo habilis); you're not the tool guy. A 2010 study revealed the oldest stone tools used to date. Until this point, it was thought that Homo habilis, who lived 2.3 to 1.6 million years ago, was the first hominid to employ stone tools. However, fossils of animal bones 3.4 million years old, discovered in Ethiopia, bore compression and cutting marks. The fossils, a cow-like rib and an antelope thigh, provided evidence of butchering: stripping meat and removing marrow.

It now appears that Lucy and her family,Australopithecus afarensis, used tools to prepare food. There is no evidence yet of this species developing tools for hunting or other activities.

 

2. Neanderthal Genome Project, 2010

Opposable thumbs, upright walking, use of fire -- just how different genetically are humans from our prehistoric ancestors? An international team of researchers evaluated human and Neanderthal DNA to begin answering this question. They analyzed the DNA of three female Neanderthal bones from Croatia and compared those findings to the DNA of five modern humans from Southern Africa, Western Africa, Papua New Guinea, China and Western Europe. 

The process was complicated, in part, because the Neanderthal bones had been contaminated over the years, first by microbes and then by human handlers. After eliminating the genetic "trash,"researchers discovered that 1 to 4 percent of the genomes from modern European and Asian samples could be traced to Neanderthals. The African and Neanderthal samples showed no connection. These results contradicted earlier beliefs about the separation of hominine species, instead suggesting that some early humans and Neanderthals interbred.

 

1. The Latest Find, 2010

A cave in South Africa yielded several fossils, and controversy, in 2010. The remains of an adult female and a boy two million years old were uncovered at the site, along with bones from an infant and an additional adult female. Named Australopithecus sediba, the fossils indicated the species was taller and stronger than Lucy's family, with long legs suggesting greater bipedal (two-legged) locomotion than earlier species. 

The controversy among the scientific community stems from the categorization of the new fossils. Although they were originally placed into the genus Australopithecus, some researchers believe that the fossils appear closer to our species, Homo sapiens, and therefore should be in the genus Homo. Although the fossils have the relatively smaller brain size, small body and long arms of Australopithecus members, the new discoveries' long legs, small teeth and pelvic bones resemble those of Homo erectus.

These 10 discoveries are some highlights in the study of human evolution.

Hitherto uncovered fossils, new technologies and additional analyses will undoubtedly narrow the knowledge gaps and further clarify the history of Homo sapiens.

Source: Curiosity @ Discovery, Smithsonian Museum of National history, National Geographic.

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