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Human Evolution: Theories

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Revi tal

on 21 September 2014

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Transcript of Human Evolution: Theories

Human Evolution: Past, Present, and Future Theories
Evolution; The Triumph of an Idea, by Carl Zimmer
Sunday post, Section B, Sunday, September 22, 2013
Evolution; it’s not over yet, by Tom Chivers
What are the two theories about the origin of early humans?
Multiregional vs. Out of Africa, by John Hawks
Origins of Modern Humans: Multiregional or Out of Africa?, by Donald Johanson
Is human evolution finally over?, by Robin McKie
The Future of Evolution: What Will We Become?, by Charles Q. Choi
FUTURE HUMANS: Four Ways We May, or May Not, Evolve, by James Owen
Projecting human evolution: 5 traits we might possess in the future, by Bryan Nelson
Humans in 100,000 years: What will we look like?, by Michael Roppolo
Origin of Humans:
Multiregional, or
Out of Africa?
Few facts to consider:
Humans first left Africa and created populations in other parts of the world by 1.8 million years ago.

Humans today are different anatomically and behaviorally from archaic people (most humans before 40,000 years ago) anywhere in the world.

Human populations today are genetically very similar to each other.

African populations today are the most genetically diverse, compared to populations around the world.

Recent humans in Europe and Asia share a few features with the ancient archaic people who lived in those places before 40,000 years ago.
The apes evolved into man in few regions, after
Homo erectus
went to each of those regions.
Asiatic, African and european people would have genetic continuity since each evolved independently of the others into
Homo sapiens
According to this theory:
Some level of gene flow between the geographically separated populations prevented speciation
All living humans evolved from the species
Homo erectus
that left Africa about two million-years-ago
Natural selection in regional populations (since their original dispersal) is responsible for the regional variants (races) existing today
The arise of
Homo sapiens
was not limited to one area, it occurred throughout the entire geographic range where humans lived
"Out of Africa"
Homo erectus
migrated out of Africa the different populations evolved independently, and in some cases into separate species
Homo sapiens
arose in one place, probably Africa (including the Middle East)
Homo sapiens
eventually migrated out of Africa and replaced all other human populations, without interbreeding
Modern human variation is a relatively recent phenomenon
About 1 million years ago
Homo ergaster
, left Africa. Living in all the different geographical areas created diversity in their morphology due to the processes of genetic drift and natural selection.
• In Asia these hominids evolved into
Homo erectus
, while in Europe and western Asia they evolved into the Neanderthals.
The Neanderthals lived isolated in Europe during a long, relatively cool period.

By 130,000 years ago, Neanderthals were so anatomically distinct that they are classified as a separate species —
Homo neanderthalensis.
At roughly the same time, in Africa,
Homo sapiens
, who had anatomicaly similar body structure were evolving.

The anatomical and paleogeographic evidence suggests that Neanderthals and early modern humans had been isolated from one another and were evolving separately into two distinct species.
Anatomical Evidence
Homo sapiens
• a large, long, low cranial vault with a well-developed double-arched browridge
• a massive facial skeleton with a very projecting mid-face, backward sloping cheeks, and large nasal aperture, with large nasal sinuses
• an oddly shaped occipital region of the skull with a bulge or bun
• molars with enlarged pulp chambers, and large, often very heavily worn incisors
• a mandible lacking a chin and possessing a large gap behind the last molar
• a massive thorax, and relatively short forearms and lower legs
• although short in stature they possessed robustly built skeletons with thick walled limb bones
• long clavicles and very wide scapulas

• a cranial vault with a vertical forehead, rounded occipital and reduced brow ridge
• a reduced facial skeleton lacking a projecting mid-face
• a lower jaw sporting a chin
• a more modern, less robustly built skeleton

Archaeological evidence
Even though Neanderthals and early
Homo sapiens
were developing different anatomical features, archaeologically they were very similar. Hominids of the Middle Stone Age of Africa
(H. sapiens
) and the European Neanderthals had few similarities:
• little variation in stone tool types, with a majority of flake tools
• over long periods of time and wide geographical distances there was general similarity in tool kits
• a virtual lack of tools fashioned out of bone, antler or ivory
• burials lacked grave goods and signs of ritual or ceremony
• evidence for fishing is absent
• population densities were low
• evidence for art or decoration is also lacking

Around 40-50,000 years ago with the appearance of behaviorally modern humans, the archaeological picture changed.
The appearance of fully modern behavior occurred in Africa before it did anywhere else, but it spread very quickly.
In the Upper Paleolithic lifestyle (based on hunting and gathering) of Eurasia, the archaeological signature is different than that of the Middle Paleolithic/Middle Stone Age. It was characterized by significant changes:
• a great diversity in stone tool types
• artifacts were fashioned out of bone, antler and ivory, in addition to stone
• stone artifacts were made mostly on blades
• burials were accompanied by ritual or ceremony and contained a rich diversity of grave goods
• fishing occurred regularly population densities
• abundant and elaborate art as well as items of personal adornment were widespread

This transformation in their (
H. sapiens
) appearance and behavior did not occur in Neanderthals

Shortly after fully modern humans entered Europe the Neanderthals began to go extinct. Neanderthals were no match for the technologically advanced fully modern humans who invaded Europe and evidence for interbreeding of these two types of hominids is ambiguous.
Genetic Evidence
Investigation of the genetics in modern human populations supports the Out of Africa Model.
• Studies of modern DNA and mitochondrial DNA (mtDNA, occurs in the mitochondria), reveal that humans are significantly homogeneous, with little genetic variation
• There is significantly more genetic variation between two individual chimpanzees from the same population than there is between two humans from a single population. Moreover, Genetic variation between individual chimpanzees and populations of chimpanzees is much greater than the differences between human individuals from the same population, and between European, Asian and African human populations.
• Africans have higher genetic variation than other populations, supporting the idea that they were the first modern humans (Out of Africa)
• A research has shown that the highest level of genetic variation in mtDNA occurs in African populations. This supports Out of Africa theory;
Homo sapiens
arose first in Africa, makes sense they had more time to develop genetic diversity.
• Scientists succeeded in take out DNA from several Neanderthal skeletons. After analysis of the mtDNA, and some nuclear
DNA, they found out that Neanderthal DNA is very different from our own. Scientists suggest that
Homo sapiens
and the Neanderthals have been separated for more than 400,000 years.

Many genetic studies support the view that Neanderthals did not interbreed with
Homo sapiens
who migrated into Europe. It is likely that modern humans do not carry Neanderthal genes in their DNA.
Anatomical Evidence
Gקמקenetic Evidence
• Neanderthals and modern humans coexisted in some parts of the world for thousands of years.
• The age of Neanderthals found at caves in Israel show that Neanderthals’ and
Homo sapiens
’ existence overlapped in this region. Therefore, if
Homo sapiens
were in this region before the disappearance of the Neanderthals, there is no reason to assume that Neanderthals evolved into modern humans.
•Scientists assume Neanderthals and fully modern humans overlapped for as much as 10,000 years in Europe, if Neanderthals and Homo sapiens lived at the same time, Homo sapiens necessarily evolved from the Neanderthals, it also strengthens the belief Homo sapiens replaced the Neanderthals
• A potential 24,500-year-old Neanderthal/sapiens hybrid was found in Portugal. This 4-year-old has a short, squat body like a Neanderthal, but possesses an anatomically modern skull. There are problems with interpreting it as a Neanderthal/sapiens hybrid. First of all, it should have a mixture of traits throughout its body and not possess the body of a Neanderthal and skull of a modern human. Secondly, acceptance of this specimen as a hybrid would suggest that Neanderthal traits had been retained for some 6,000 to 10,000 years after Neanderthals went extinct, which is highly unlikely
The Past
Where we stand today, most evidence indicate that modern humans are a recent evolutionary phenomenon, and the most suitable explanation to our origin is "Out of Africa" Theory, which discusses a single origin for
Homo sapiens
The Present
The Future
Is the journey over?;
Have we stopped evolving?
According to British broadcaster and naturalist Sir David Attenborough, it might be.
According to him; if natural selection is the main mechanism of evolution, then we’ve stopped natural selection; unlike any other species, we use technology to keep our-selves alive until breeding age “We stopped natural selection as soon as we started being able to rear 95-99 percent of our babies that are born...”. He suggests that human evolution has ended, that we reached the final ‘stop’ on the journey; if we can take even the most vulnerable babies, who could have died within hours of birth 100 years ago, and keep them alive - in other words, repair them so that they can live into adulthood and breed - have we not ended the cruel process of natural selection?

Some scientists believe humans are becoming less brainy and more neurotic; others see signs of growing intelligence and decreasing robustness, while some, see evidence of us having reached a standstill. All base their arguments on the same principles of natural selection.
Other scientists insist that we are still influenced by evolutionary forces, like Professor Chris Stringer, from Natural History Museum, in London. According to him if we looked at Stone Age people in Europe, we would assume that people will get bigger and stronger as time goes, though, the Stone Age people were replaced by light, tall, highly intelligent people who arrived from Africa. In other words, ‘We cannot predict evolutionary events like this. Who knows where we are headed?'
The biologist Christopher Wills, of the University of California, San Diego, believes evolutionary pressures are still taking their toll on humanity, despite the protection afforded by Western life. In his opinion, ideas are now driving our evolution. 'There is a premium on sharpness of mind and the ability to accumulate money. Such people tend to have more children and have a better chance of survival,' he says. In other words, intellect is the defining characteristic of our species and it is still driving our evolution.
Several studies which suggest that human evolution has actually speeded up; in the past few thousand years some humans have evolved the ability to digest milk, unlike any other adult mammals.
Dr. Adam Rutherford, a geneticist, says that the fact that certain evolutionary pressures have been reduced does not mean that all of them have gone. The right answer to the question ‘are humans evolving?’ is: we don't know, because the time spans are too short to make a judgment, human generations are too slow.
If you look at changes in the frequency of genes in a population, which is the true measure of evolution, then there’s probably no evidence to suggest we’re not evolving.
There have been many suggestions, ‘of varying stupidity’, including the suggestion that we’ll evolve fatter thumbs to help us text. (“That’s called Lamarckism, and it’s just wrong. The Jewish people have been cutting foreskins off their boys for 5,000 years and not one has been born without it yet”, says Rutherford.)
The real question is how we’re evolving
What is the answer?
It seems that human evolution isn't over. Whether it will change the way we look, or the way we think is a harder question since it too long for results to appear.
“The only real way we can determine whether we are physically evolving”, Rutherford says, “is to come back 10,000 years and see if we’re different”
Some major questions that scientists keep asking include the following ones;
In what ways are humans evolving? What traits might we possess if we projected human evolution into the future?
Since many scientists believe human evolution is over, there is an obvious assumption among them, that there is no evolution in the future of mankind, we will stay the same.
Although, different scientists have a different perspective about the question whether evolution is over or not; those scientists have many theories about the future of our species.

What Is Next? Will We Get 'Even' Better?
There are many theories about future humans, some suggesting humans will have large heads to hold their enlarged brains, some say that the human species would split in two, that humans will lose their pinky, some theories even suggest humans will get less intelligent, to which paleontologist Peter Ward at the University of Washington at Seattle, author of "Future Evolution”, says that intelligence in coded on too many genes to lose that trait.
Humans of the future may have less hair:
Even though humans have hair, they are usually referred to as hairless apes.
Although the evolutionary fate of body hair can be particularly difficult to project because it can also act as a signifier for sexual selection, it is likely that humans of the future will have less body hair than they do today.
Humans of the future may lack wisdom teeth:
Many modern humans have jaws, not big enough to contain the wisdom teeth without them interrupting other teeth, so that they need to have them removed. The common belief is that they are a vestige, which originally evolved in ancestral humans who fed on hard plants.
35% of people are born without wisdom teeth, others with just one, two, or three. ‘When a trait is no longer necessary, evolution tends to favor the elimination of that trait to save on the unnecessary energy it takes to develop it.’ Which means, in the future may not have wisdom teeth.

Race differences may disappear:
Today, our world is very global; transportation is easy and accessible, which means there are only few populations remaining isolated. When genetic material gets mixed between populations, it causes gene flow, one of the driving forces of evolution.
Gene flow causes the genetic difference between populations to disappear, since gene flow occurs more and more, racial differences are likely to ‘blend together’, in other words, vanish. The people of the future, according to this, might all look alike.

Humans of the future may be physically weaker and more susceptible to pathogens:
Since humans no longer require physical strength; we have machines to complete tasks that our muscles were needed for, physical strength is a trait scientists predict may get eliminated. Studies have shown that we are weaker than our ancestors; therefore future humans may be even weaker and more petite than we are today.

Future humans may have weakened immune systems and be more sensitive to pathogen, for similar reasons; modern medicine, medical technology, and the discovery of antibiotics have increased humans’ health and life expectancy, but they also caused our immune system to be less necessary than they used to be. Therefore, humans in the future might become even more dependent on medicine.

Humans of the future may be more resistant to diabetes and heart disease:
Some of the most common causes of death in the developed world are heart disease and diabetes, mostly because modern diets include many fats.
The assumption is that in the future humans will be better adapted to these diets, therefore, more resistant to heart diseases and diabetes.

Dietary adaptations are not uncommon for instance; lactose intolerance has greatly decreased among human populations.

There was a study published in the journal ‘Proceedings of the National Academy of Sciences’ suggesting that the “...women of the future could become shorter and stouter”, A team led by Yale University evolutionary biologist, Stephen Stearns found that, shorter, slightly plumper women tend to have more children. And these traits are passed on to their offspring.
Another theory known as “transhumanism” suggests the humankind will become ‘immortal’ by having human minds transferred to computers.
’In addition to living forever, “uploaded” beings would be able to “travel the speed of light as an information pattern”, download themselves into robots, think faster when running on advanced operating systems, and cut their food budget down to zero.’
This is a new type of evolution, says Nick Bostrom, director of the Future of Humanity Institute at the University of Oxford. It means evolutionary selection could occur in a population of artificial intelligence, it might happen much faster, since artificial intellects could reproduce a lot faster.

By using viruses and other techniques, we can in theory modify our genomes. Over time, scientists may uncover the genes responsible of intelligence, health, longevity and other traits.

In the future we might be able to engineer our genes and create ‘super humans’. Some scientists speculate that genetic engineering is how new species of humans might emerge.

Geoffrey Miller, an evolutionary psychologist at the University of New Mexico, believes human evolution is speeding up; by the option we have today to choose who to mate with, we are shaping mental traits, traits that are needed for economical success and raising our offspring.

Furthermore, he thinks that artificial selection, will likely accentuate those changes in the future. He explains that in the future, parents will be able to choose which sperm and egg get fertilized to produce a baby based on which genetic information has desirable physical and mental traits, he explains."If the rich and powerful keep the artificial-selection technology to themselves, then you could get that kind of split between a kind of upper-class, dominant population and a lower-class, genetically oppressed population", although he believes both the poor and rich will be able to have the best kids they can genetically have. Though he believes natural selection will continue being a major part.

Modern Day
20,000 years from now
60,000 years from now
100,000 years from now
Modern-day humans may someday evolve to have larger eyes, more pigmented skin and a thicker eyelids, thanks to genetic engineering technology. Here's how they'll change.
In 20,000 years, in a world where genetic engineering is commonplace and humans have established colonies in space, human knowledge of the universe will increase and as such, the size of the brain will increase, Dr. Alan Kwan theorizes. As a result, the human head will have to become larger to accommodate the larger brain size.
In 60,000 years, Dr. Alan Kwan states that after millennia of traveling through space, zygotic genome engineering will be used to create humans with larger eyes, more pigmented skin and a thicker eyelids. This will be done in order to see better in the dimmer environment of space, to shield humans from the UV rays and alleviate the effects of low to no gravity like today’s astronauts on the International Space Station
100,000 years from now, Dr. Alan Kwan believes that future humans will have much larger eyes and “eye-shine” due to the tapetum lucidum, a layer of tissue behind the retina of the eye. This would be done to help protect our eyes from cosmic rays.
Visual artist, Nickolay Lamm of Pittsburgh, Pa., was interested in illustrating how humans would look like in 100,000 years, he asked science for the answers.

“Because I'm not expert in evolution, I got in touch with Dr. Alan Kwan who gave me his educated guess at what we may look like,” Lamm says.

Working with Dr. Kwan, who has a PhD in computational genomics from Washington University, they established “one possible timeline”.

From many of those predictions, we can see that humans may continue evolving regardless of modern technology in general and in particular modern medicine.
But we might evolve into an even more technology dependent specie, and we might not necessarily be ‘better’ the way we perceive ‘better’ today.
Information, Images & More..
Humans first existed in Africa. While hominids were in Africa and went to Europe and Asia, only the ones still in Africa became
Homo sapiens
. Those African
Homo sapiens
migarted into Eurasia and replaced the existing popullations (which descended from
Homo erectus
According to this theory:
Full transcript