Road to bipedalism, tool use long, twisty

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When did human ancestors begin to use tools? It is important to first understand a pitfall in thinking about how human traits were acquired. The problem arises from statements such as, "Walking upright on two legs (being bipedal) freed up the hands of hominids to make and use tools".

This statement about our branch of the family tree is truthful. However, it is an abbreviated way of thinking that can be misleading. It implies tool-use was a purposeful objective.

Becoming bipedal and tool-making were essential developments, but nature doesn't follow a script. These traits were no more inevitable than was the ultimate emergence of modern humans.

The developmental path of hominids was not unwavering. As the fossil record shows, it is strewn with many trials ending in extinction.

Many of our extinct kin had traits that were successful over long periods of time. Eventually, those characteristics became inadequate for survival. This occurred because of environmental changes and/or displacement by competitors.

Our ancestors did not acquire nimble, highly sensitive hands with opposable thumbs for the purpose of making tools. Rather, those agile hands were honed over millions of years by creatures living in trees.

Having become adept at manipulating objects, the descendants of those animals adapted their hands to ever more demanding tasks under changing conditions. It did not happen spontaneously or quickly.

This is typical of all life. Organisms survive, change or expand into new settings if they have adaptable traits, like nimble hands, that help them thrive in the new conditions.

Over the nearly six million years hominids developed in Africa their environment was changing. In many places wet, dense forests gave way to open savannahs. Old food sources became scarce while new opportunities presented themselves.

In response, a host of different hominid species developed. It is not as if parents were able to foresee or understand adaptations that would be needed by their offspring. They didn't chose mates with the intent of producing offspring that would be better adapted.

Rather, over the course of very many generations, those of our predecessors with slightly better skeletal and muscular configurations for handy work succeeded at important tasks. Consequently, they made good mates that left descendents with those attributes.

As hominids became adept at tool-use they sought different food sources. They scavenged and hunted cooperatively for more difficult prey. Those that developed greater social cooperation did better at providing for their families.

Each of these adaptations was accompanied by brain development. For much of the period from 4.4 to 1.2 million years ago, some of our closest relatives were a variety of hominids called australopithecines. Their brains were only 35 to 40 percent the size of modern human brains.

Deciding when tool use began revolves around what counts as a tool. A number of animals have been observed using twigs or thorns as probes to extract food from hideaways or stones to break shells.

Since hominids would simply have selected such tools for their shapes from what was available, their artifacts are difficult for paleoanthropologist to recognize.

The birth of real technology, the manufacture of purposeful tools for specific tasks, begins around 2.6 million years ago.

The earliest evidence comes from a large cache of manufactured stone tools found near Gona, Ethiopia. The tools, or materials for making them, were carried a substantial distance to this location.

Such evidence demonstrates important advancements. These creatures were capable of long range planning, an ability to evaluate the qualities of the stone, and skill to shape the stone for a specific purpose.

It is thought these tools are the work of Australopithecine garhi. A. garhi is a species discovered in 1996. Its specialized teeth and a somewhat larger brain make it a strong candidate for the immediate predecessor to the genus homo.

Modern humans, homo sapiens, are the last surviving members of the Homo genus. A number of candidates for the distinction of the first species of the homo genus have been discovered.

Homo habilis, or handy man, was unearthed in the early 1960s. Subsequently, Homo rudolfensis was discovered in 1972 and, in 2010, Homo gautengenis.

All these species used primitive stone tools referred to as Olduwan technology. They were a significant departure from earlier hominids. Importantly, meat was a substantial part of their diet.

An energy-rich, high fat diet enabled homo species to adapt to a wider range of environments. Since brain metabolism has high energy requirements, the stage was set for larger brains. Though their brain size was larger than that of australopithecines, their brains were still less than 50 percent that of modern humans.

By 2.6 million years ago the hominid lineage had come a long way. Hominids walked on two legs, had begun making and using primitive tools, had an energy rich meat diet and had a brain capable of invention and long range planning.

Steve Luckstead is a medical physicist in the radiation oncology department at St. Mary Medical Center. He can be reached at steveluckstead@charter.net.

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