The species that you and all other living human beings on this planet belong to is Homo sapiens. During a time of dramatic climate change , years ago, Homo sapiens evolved in Africa. Like other early humans that were living at this time, they gathered and hunted food, and evolved behaviors that helped them respond to the challenges of survival in unstable environments.
Anatomically, modern humans can generally be characterized by the lighter build of their skeletons compared to earlier humans. Modern humans have very large brains, which vary in size from population to population and between males and females, but the average size is approximately cubic centimeters. Housing this big brain involved the reorganization of the skull into what is thought of as "modern" -- a thin-walled, high vaulted skull with a flat and near vertical forehead.
Modern human faces also show much less if any of the heavy brow ridges and prognathism of other early humans. Our jaws are also less heavily developed, with smaller teeth. Unlike every other human species, Homo sapiens does not have a true type specimen.
In other words, there is not a particular Homo sapiens individual that researchers recognize as being the specimen that gave Homo sapiens its name. Even though Linnaeus first described our species in , it was not customary at that time to designate type specimens.
When Cope, himself a great paleontologist, died in , he willed his remains to science, and they are held by the University of Pennsylvania. Prehistoric Homo sapiens not only made and used stone tools, they also specialized them and made a variety of smaller, more complex, refined and specialized tools including composite stone tools, fishhooks and harpoons, bows and arrows, spear throwers and sewing needles.
For millions of years all humans, early and modern alike, had to find their own food. They spent a large part of each day gathering plants and hunting or scavenging animals. By , years ago modern humans were collecting and cooking shellfish and by 90, years ago modern humans had begun making special fishing tools.
Then, within just the past 12, years, our species, Homo sapiens , made the transition to producing food and changing our surroundings. Humans found they could control the growth and breeding of certain plants and animals. As humans invested more time in producing food, they settled down.
Villages became towns, and towns became cities. With more food available, the human population began to increase dramatically. Our species had been so successful that it has inadvertently created a turning point in the history of life on Earth.
Why did we need hundreds of millennia to invent bows, sewing needles, boats? And what changed? Probably several things. First, we journeyed out of Africa , occupying more of the planet. There were then simply more humans to invent, increasing the odds of a prehistoric Steve Jobs or Leonardo da Vinci. We also faced new environments in the Middle East, the Arctic, India, Indonesia, with unique climates, foods and dangers, including other human species.
Survival demanded innovation. Many of these new lands were far more habitable than the Kalahari or the Congo. Climates were milder, but Homo sapiens also left behind African diseases and parasites. That let tribes grow larger, and larger tribes meant more heads to innovate and remember ideas, more manpower, and better ability to specialise. Population drove innovation.
This triggered feedback cycles. As new technologies appeared and spread — better weapons, clothing, shelters — human numbers could increase further, accelerating cultural evolution again. Numbers drove culture, culture increased numbers, accelerating cultural evolution, on and on, ultimately pushing human populations to outstrip their ecosystems, devastating the megafauna and forcing the evolution of farming.
Finally, agriculture caused an explosive population increase, culminating in civilisations of millions of people. Now, cultural evolution kicked into hyperdrive. Artefacts reflect culture, and cultural complexity is an emergent property. Like networking millions of processors to make a supercomputer, we increased cultural complexity by increasing the number of people and the links between them.
So our societies and world evolved rapidly in the past , years, while our brains evolved slowly. We expanded our numbers to almost 8 billion , spread across the globe, reshaped the planet. We did it not by adapting our brains but by changing our cultures. The video below presents evidence of pockets of archaic humans surviving in West Africa until at least 13, years ago. Expansion Out of the Old World.
Homo sapiens began migrating into the lower latitudes of East Asia by at least 70, years ago. Along the way, some of them interbred with archaic humans, including both Neandertals and Denisovans. Genetic markers from these archaic human populations are found in the gene pool of some Southern Chinese, New Guinean, and other Micronesian Island populations today.
Homo sapiens from Southeast Asia travelled to Australia by 46, years ago and possibly as early as 60, years ago. Because Australia was not connected to Southeast Asia by land, it is probable that the se first Australian Aborigines arrived by simple boats or rafts.
Modern humans reached the Japanese Islands by 30, years ago or somewhat earlier. Around 35,, years ago, Homo sapiens big game hunters moved into Northeastern Siberia. Some of them migrated into North America via the Bering Plain , or Beringia , by 20,, years ago.
Some Homo sapiens may have reached the Americas a bit earlier than this, but the evidence is still considered questionable by most paleoanthropologists. Th e Bering Plain intercontinental land connection appeared between Siberia and Alaska as a result of sea levels dropping up to feet m. Until that time, all human evolution had occurred in the Old World. A consequence of human migrations into new regions of the world has been the extinction of many animal species indigenous to those areas.
Most of these extinctions apparently occurred within a few hundred years. It is likely that the rapidly changing climate at the end of the last ice age was a contributing factor.
However, the addition of human hunters with spears to the existing top predators mostly saber-toothed cats, lions, and dire-wolves very likely disrupted the equilibrium between large herbivores and their predators. As a consequence there was a major ecosystem disruption resulting in the rapid decline of both non-human carnivores and their prey.
Humans were very likely the trigger that set off this "trophic cascade". Unlike most other major predators, people survived by switching their food quest to smaller animals and plants.
F ollowing the arrival of aboriginal people in Australia and Polynesians in New Zealand there were similar dramatic animal extinctions. In both of these cases humans apparently were directly responsible for wiping out easily hunted species. Large vulnerable marsupials were the main victims in Australia. In New Zealand, it was mostly large flightless birds that were driven to extinction by human hunters following their arrival in the 10thth centuries A. It is sobering to realize that the rate of animal and plant extinction has once again accelerated dramatically.
During the last century and a half, the explosion in our global human population and our rapid technological development has allowed us to move into and over-exploit most areas of our planet including the oceans. That exploitation has usually involved cutting down forests, changing the courses of rivers, pushing wild animals and plants out of farm and urban areas, polluting wetlands with pesticides and other man-made chemicals, and industrial-scale hunting of large land animals, whales, and fish.
During the early 19th century, there were at least 40,, bison roaming the Great Plains of North America. By the end of that century, there were only a few hundred remaining.
They had been hunted to near extinction with guns. The same fate came to the African elephant and rhinoceros during the 20th century. Likewise, commercial fishermen have depleted one species of fish after another during the last half century.
Governments have had to step in to try to stem the tide of these human population effects on other species. However, they have been only marginally successful.
The World Conservation Union conservatively estimates that 7, animal species and 8, plant and lichen species are now at risk of extinction primarily due to human caused habitat degradation. This list does not include the many millions of species that are still unknown to science. It is likely that most of them will become extinct before they can be described and studied.
People Today. Are we genetically different from our Homo sapiens ancestors who lived , years ago? The answer is almost certainly yes. In fact, it is very likely that the rate of evolution for our species has continuously accelerated since the end of the last ice age, roughly 10, years ago. This is mostly due to the fact that our human population has explosively grown and moved into new kinds of environments, including cities, where we have been subject to new natural selection pressures.
For instance, our larger and denser populations have made it far easier for contagious diseases, such as tuberculosis, small pox, the plague, and influenza to rapidly spread through communities and wreak havoc. This has exerted strong selection for individuals who were fortunate to have immune systems that allowed them to survive.
There also has been a marked change in diet for most people since the end of the last ice age. It is now less varied and predominantly vegetarian around the globe with a heavy dependence on foods made from cereal grains.
It is likely that the human species has been able to adapt to these and other new environmental pressures because it has acquired a steadily greater genetic diversity.
A larger population naturally has more mutations adding variation to its gene pool simply because there are more people. This happens even if the mutation rate per person remains the same. However, the mutation rate may have actually increased because we have been exposed to new kinds of man-made environmental pollution that can cause additional mutations.
It is not clear what all of the consequences of the environmental and behavioral changes for humans have been. However, it does appear that the average human body size has become somewhat shorter over the last 10, years, and we have acquired widespread immunity to the more severe effects of some diseases such as measles and influenza.
Finally, c an we say what direction human evolution will take in the future? This is a fascinating question to consider but impossible to answer because of innumerable unknown factors. Though, it is certain that we will continue to evolve until we reach the point of extinction. A 17, year old adult skeleton from Siberia also had genetic markers indicating European origin. This indicates that ice age Homo sapiens from Europe migrated much farther beyond that continent than commonly believed.
It also implies that the New World native populations owe their ancestry not only to East Asians but to Europeans as well. All rights reserved. Neandertal modern Homo sapiens. Becoming Human: Part 3 -- biological and cultural evolution of Homo heidelbergensis, Neandertals, and modern humans.
This link takes you to another web page. To return here, you must click the "back" button on your browser program.
0コメント