Reflections and Conclusions

This semester, we've discussed many topics dealing with evolution and though it is still just a theory, there is substantial evidence supporting it. We all worked as a team, gathering data and conducting research to make this blog as informative as possible. And while we all got something different out of it, everyone seemed to agree that biology and culture play a vital role in the process of evolution.


Chanwoo David Kim:

Overall, doing research on each question helped me easily understand the theory of evolution. Several processes working together help an organism evolve, and examples for this are darker-colored moths and domesticated wolves. I was fascinated by the facts about bipedalism and survival issues too.

There are a couple of theories explaining how humans populated the old world. I find the third theory, “the partial replacement model” more convincing. There must have been modern humans interbreeding with late archaic humans. Europeans that migrated from Africa could have interbred with Neanderthals when they shared the continent of Europe for 12,000 years. The other two theories don’t sound as convincing to me because I just think that it is impossible to have no interaction with other human species living in nearby areas.

Furthermore, I think there must be a close relationship between culture and biology. For example , humans didn’t produce a protein that allowed them to digest lactose after being weaned prior to 4000 BCE, but after Europeans began to drink the milk of domesticated animals, the genetic adaptation favoring lactose consumptions spread quickly throughout the continent. It shows that cultural shifts lead to changes in behavior, affecting biology. Hence, humans are more than biology because we are also continuously interacting with complex cultures.



Heath L. Johnson:

The information I acquired during the research on my field notes was somewhat similar to what was written in our blog, although the field notes and timeline gave me more of an idea of the continuation of hominins through mutated DNA. I felt and will propose that over millions of years, enough mutations occurred to suggest that Australopithecus Afarensis was an ancestor of modern humans. The climate also had much to do with natural selection.

I learned a great deal from my studies on hominins and evolution due to natural selection, partly from mutations and climate. It is interesting just looking at tooth development. We can determine the diet of hominins from their teeth. We know how much processing, breaking down and/or cooking, was done over history just by tooth development and wear.



Jacky Torres:

I believe the extinct bipeds were able to survive because of certain characteristics they had/inherited. For example, physical changes in pelvic/foot structure lead to a more efficient stride in bipedalism. The existence of extant bipedal primates was made possible because they were able to adapt physically and culturally to the various environments they lived in, and the various tasks they faced. An example would be the language and culture associated with larger brains and certain neurological changes. Biocultural evolution has also played a role in the existence of extant bipedal primates. The fact that bipedal primates inherited the ability to form groups and coexist plays a huge role in this.


Jessica Polk:

I found it interesting that all human DNA contains up to 4% Neanderthal DNA. (Excluded from this category are people originating from Africa.) This leads me to believe in the partial replacement model where early hominins left Africa and met up with Neanderthals in the Middle East. There, they interbred and that is why we can still find traces of Neanderthal in our current human DNA. I sometimes even wonder if perhaps a few "Big Foot" or Cro-Magnums aren't still out there, hidden away, living in seclusion.

Taking this class has given me a better perspective on the human race. We tend to think we are all that ever was or ever will be. We forget that there were many populations before us that ruled the Earth but died out after one million years, and yet we have only been "ruling" Earth ourselves for half that time. We have amazing technology now and you would think that with all of that, we'd be able to make it one million years or more, but our technology and need to consume are destroying our planet and ultimately us. If we don't all make it to one million years, I'm sure some of us will squeak by and perhaps see the evolution of the next species.

How Can We Explain Modern Humans?

THE RELATIONSHIP BETWEEN CULTURE AND BIOLOGY IN HUMANS AND WHAT SITUATIONS EXEMPLIFIED HOW THIS WORKS

In our textbook, culture is defined as “nonbiological adaptations to the environment.” In a community, people’s values, norms, symbols, language and objects are passed on from one generation to the next. The relationship between culture and biology is very complicated, but according to anthropologists and sociologists, necessary cultural differences among racial groups are caused by biological differences. For example, prior to 4000 BCE, humans didn’t produce a protein that allowed them to digest lactose after being weaned, but later when Europeans began to drink the milk of domesticated animals, a genetic adaptation favoring lactose consumptions spread quickly throughout the continent. This illustrates how cultural shifts can lead to changes in behavior, thus affecting biology. Therefore, humans are more than biological beings, we are also cultural. We are continuously interacting with complex cultures.

Culture has driven human evolution from the beginning. Humans started using tools and as time went by, the next generations developed these tools. With this cumulative cultural evolution, human brains expanded. “Cultural brain hypothesis” explains that the real driver in the expansion of human brains is the growing cumulative body of cultural information, so humans gradually have acquired the ability to gather information, store, process and retransmit. Tools and artifacts are products of cultural evolution, and fire and cooking caused the changes of human body structure. Cooking and fire making spread culturally all over the world and these skills eventually made the human stomach and teeth smaller and also changed the length of the intestines. Furthermore, after the origins of agriculture, there has been an evolution of societal complexity. Societies have gotten so big and complex. People have been interacting with others, in areas such as cooperation, religion, learning, etc. These societal changes have affected our genes and changed our biology.

100,000 years ago there was a diverse group of hominids in the Old World. However, around 30,000 years ago, things changed as humans evolved into our modern day form. There are several schools of thought as to how this happened but the complete replacement model seems to have the most evidence supporting it. This is the idea that humans evolved first in Africa and then migrated to other parts of the world.

Anatomical evidence supporting this idea suggests that over one million years ago the Homo ergaster population left Africa and entered various regions of the Old World. Due to genetic drift and natural selection, Homo ergaster’s morphology became diversified since they were living in different regions. Homo erectus appeared in Asia, while Neanderthals appeared in Europe and Western Asia. Neanderthals are unique in the way that they lived in isolation during glaciation periods, and have unique anatomical features. After living in isolation for so long and experiencing independent evolution, the Neanderthals became so anatomically distinct they became their own separate species (Homo neanderthalensis). It was at around the same time that, in Africa, modern humans (Homo sapiens) began to emerge. Although Homo sapiens were anatomically modern, they were not behaviorally modern.

Archaeological evidence supporting the complete replacement model includes the Herto fossils. The Herto fossils are Homo sapiens fossils from Ethiopia. These fossils include a mostly complete adult cranium, a fairly complete child cranium, and an incomplete adult cranium, along with a few other cranial fragments. They have been dated to about 160,000 to 154,000 years ago.

Herto Skull Fossil

These fossils are near modern; they were probably from a population that was on the verge of anatomical modernity. These fossils are great evidence for supporting an African origin of modern humans. Jurmain, et al describes these fossils as being the "most conclusive fossil evidence yet indicating an African origin of modern humans. They are also compatible with strong genetic data indicating a form of replacement model for human origin."



Archaeological evidence suggests that Homo neanderthalensis and Homo sapiens were archaeologically similar. Both Homo neanderthalensis and Homo sapiens can be described by: using flake tools; making tools out of bone, antler or ivory; and having low population densities. However, once behaviorally modern humans appeared, this was no longer the case. According to Johanson, “The stunning change in cultural adaptation was not merely a quantitative one, but one that represented a significant departure from all earlier human behavior, reflecting a major qualitative transformation.” With this change came technological innovations, social formations, and hunter-gatherer techniques.

This modern human behavior occurred in Africa first then spread to other regions of the Old World once the behaviorally modern humans began migrating. However, these changes were seen only in the Homo sapiens. It is believed that cultural/biological changes are what brought about these archaeological changes in the Homo sapiens. Johanson states, “Changes in social relations, such as development of the nuclear family, played a key role in bringing about the transformation.” Burials containing a variety of grave goods have been found along with living structures with fireplaces, elaborate artworks, and evidence of higher population densities and raw materials being traded over some distances. Could it be more than a coincidence that only shortly after the modern humans entered Europe, the Neanderthals began to decline and eventually disappeared altogether? After all, between modern humans and the Neanderthals, the Neanderthals certainly would have been the weakest link.

Recently, it was discovered that every human is 4% Neanderthal. This is true for native inhabitants of every country except for Africa. This seems a little strange and perhaps startling but it makes sense. As humans migrated from Africa to other parts of the world, they most likely met up with the Neanderthals in Europe and Western Asia and mated. So it makes sense that true Africans would have no Neanderthal DNA as the Neanderthal never lived in Africa. In fact, it seems we have inherited some very important traits from the Neanderthal. Studies "found that genes involved in making keratin—the protein found in our skin, hair, and nails—are especially rich in Neanderthal DNA."

Genetic evidence supports the complete replacement model. This evidence includes studies showing that humans have very little genetic variation. There is more genetic variation between two individual chimpanzees that come from the same population than there is between two humans that come from the same population. It has been made apparent that the highest level of genetic variation in mtDNA occurs in African populations; this supports the idea that Homo sapiens arose first in Africa and had a longer time period to accumulate genetic diversity.

Additional evidence supporting the complete replacement model includes the presence of Neanderthals at Amus and Kebara caves in Israel. These specimens were dated to about 55,000 years ago. This would mean that Homo sapiens and Neanderthals overlapped in this region for about 55,000 years. Therefore, there is no reason to assume Neanderthals evolved into modern humans. There has been evidence found suggesting Neanderthals possibly survived in the Iberian Peninsula up to about 35,000 years ago. Modern humans first appeared in this region about 35,000 years ago. It is possible that Homo sapiens and Neanderthals overlapped in this region for about 10,000 years. There is, again, no need to assume Neanderthals evolved into modern humans.

Resources:
http://news.nationalgeographic.com/news/2014/01/140129-neanderthal-genes-genetics-migration-africa-eurasian-science/
http://www.actionbioscience.org/evolution/johanson.html

How can we explain the survival and success of bipedal primates?

There are many theories about how bipedalism came to be the dominant trait that would lead humans into a successful survival, but the most important of these are physical characteristics that adapted as man began to walk upright.

The Australopithecines:

The Australopithecines, whose fossils "represent the first stage in the evolution of bipedalism", had brains about the size of chimpanzees. They were shorter than us had long arms and were most likely covered in fur. Most importantly, they were bipedal. These Australopithecines were different from their primate predecessors in two ways:

1). They walked on two legs.
2). They had smaller canine teeth.

These above mentioned teeth were important because long sharp canine teeth were used as weapons and because they no longer had them they needed other means to defend themselves.

In "The Descent of Man" Darwin stated "The free use of the arms and hands, partly the cause and partly the result of man's erect position, appears to have led in an indirect manner to other modifications of structure. The early male forefathers of man, were, as previously stated, probably furnished with great canine teeth; but a they gradually acquired the habit of using stones, clubs, or other weapons, for fighting with other enemies or rivals, they would use their jaws less and less."

We see this defense mechanism in the Chimpanzee who throws sticks and stones. However, their method of throwing is not very effective. They always throw underarm which is weak when compared to how humans throw. Chimpanzees also need their forelimbs and arms whenever they (and other quadrupeds) want to move easily and quickly.

The Australopithecines, which are related to the chimpanzee, were bipeds and probably able to move as quickly as modern men. They could use their hands and arms to throw and also to handle weapons and tools. Because of this, they would have been able to keep predators at a safer distance relying less on their sharp canine teeth that adapted for eating only. Although their is no evidence that they made artificial weapons, it is supposed that they probably used stones and clubs as weapons. This gave them a competitive advantage over other animals.

Even if the Australopithecines couldn't throw as well as humans, this ability to be able to throw was a fundamental factor in bipedal survival. It may seem like a small thing, but the action of throwing is quite complex. It involves the coordinating all the muscles of the arm, wrist, fingers, back and legs. And the actual evolution of these muscles, including the brain, were probably motivated by the necessity to develop better throwing capabilities.


Comparison of Chimpanzee & Human Hands:

2 Evolved Human Grips: Precision & Power

Primates typically have a diminutive thumb and long curved fingers while the human hand has a fully opposable thumb with shorter, straightened fingers. The evolution of the hand led to tools becoming hand-held weapons. During disputes, a club was swung to settle the disagreement.

As time went on, the best throwers/clubbers rose to dominate the male hierarchy which means that had more opportunity to breed and pass on their traits. The better fighters also obtained better lands and food, which continued to increase their reproductive success. And now, humans today can throw/fight better. NATURAL SELECTION!!!

All of this clubbing led to the need for hands to be free at all times for better success. As the Australopithecines continued in their bipedality, their legs and feet became more powerful. This increased use of walking upright eventually led to habitual bipedalism.

Though bipedalism was the wave of the future, it created problems for females that they hadn't faced before was quadrupeds. This was especially true of pregnant females who experienced more weight in their abdomen that was supported firmly between four legs. Because of this, females developed stronger stomach muscles and the shape of their pelvis changed. We see this in the Australopithecines who started walking upright. Their pelvis structure changed, giving them a new center of gravity. The shape of the pelvis was needed in order to birth these new bipedal offspring as they had developed larger brains, thus making their heads larger. (A change in pelvis structure=a bigger brain/head)

This wider birth canal reduced bipedal females' agility and speed which led them to depend more on males for protection.

Change in Pelvic Structure:

Time and necessity have favored humans walking on two legs instead of all fours. As we continue to go on living, it is interesting to think of how we will continue to change and evolve. Like the dinosaur, we may find that taking to the skies is better!

Resources:
href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1571064/">

href="http://evolution-of-man.info/combined.htm">

href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1571064/figure/fig01/">

href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1571064/figure/fig03/">

How Does the Theory of Evolution Apply to Bipedal Primates?

We no longer walk on all fours, and this change is the result of evolution. There is no real satisfactory answer as to why this happened. It could be said that primates already had adaptations for standing on two feet, running upright and climbing vertically. We see examples of this in gibbons who do all of these activities and have the same amount of vertebrae as humans. All apes have these same abilities and chimpanzees are also sometimes bipedal. Whatever the case, whether it made carrying objects easier, conserved energy, provided for more solar protection or was a better presentation of one's sexuality, we do know that the lower limbs of primates adapted, becoming stronger.

Gibbon Jumping

The limb bones, joints and feet changed to support an upright body. It is believed that Homo sapiens respiratory system changed in conjunction with being in a tropical environment and with their increased mobility, bipedalism was most favorable for their survival, for running, trekking, etc. More sweat glands are also contained on the torso of humans and the top of the head that aid in cooling the body using sweat evaporation. Humans are also not as hairy as apes and so we don't need to pause to cool down.

The human calf is also built for energy conservation and acts as a spring when we walk or run. This adaptation allowed humans to see above tall grasses. {1}It also helped them to travel further as their hips also changed becoming less wide and more bowl shaped. The human brain also grew, becoming bigger and allowing us to become a dominant species. Chimps and humans share 96% of their DNA and new research suggests that humans and chimpanzees may have split off from a common ancestor 4 million years ago. {2}

Paranthropus Aethiopicus
Parathropus was one of the earliest robust species that lived about 2.5 million years ago and has only been found in east Africa. It had a smaller brain than other species like it so it may have been a transitional form from a species that came before it. It is believed that humans are Paranthropus' contemporaries. Another species, Australopithecus anamensis appeared a little over 4.2 million years ago for which we have no hominin fossils on record. However fossils of what may have been Australopithecus' immediate ancestor were found in Ethiopia. These teeth fossils look to be the transition between apes and Australopithecus. Dating back to 4.4 million years ago, these fossils could "represent the first stage in the evolution of bipedalism." {3} "Beginning around 2.5 million years ago or a bit earlier, there was a major forking in the evolutionary path of hominins. The australopithecines diverged into at least two very different evolutionary directions. One led to the paranthropoids and a genetic dead-end by about 1.4 million years ago. The other led to the first humans. It is likely that these diverging evolutionary paths were the result of exploiting different environmental opportunities." {3}

Resources:
{1} http://www.britannica.com/EBchecked/topic/275670/human-evolution/250597/Theories-of-bipedalism

{2} http://www.animalplanet.com/mammals/chimp.htm

{3} http://anthro.palomar.edu/hominid/australo_2.htm

What is Evolutionary Theory?

"The theory of evolution refers to a change in the genetic structure of a population. The term is frequently used to refer to the appearance of a new species." -Essentials of Physical Anthropology, Jurmain, et al.

This definition is fairly broad and doesn't include the modern definition of evolution which includes several processes that produce and redistribute variation. They are as follows:

1). Increase Variation
•Mutation (a change in DNA; includes point mutation where changes occur in DNA bases, and/or in chromosome number or structure; Mutations are caused by radiation, harmful chemicals and replication errors. Though these are usually unfavorable in the present, they can be favorable in the long run, and because mutations are recessive, it can take a long time for them to become obvious or dominant within a population.)
•Recombination (exchange of genetic material between paired chromosomes during meiosis; crossing over; by itself, recombination doesn't change allele frequencies or cause evolution. It instead changes the composition of parts of chromosomes and can affect how some genes act.These changes can then be acted upon by natural selection. Natural selection is defined as genetic changes of certain traits due to biological variation.)
•Gene flow (exchange of genes between populations; occurs because people move among populations, which increases the variation and reduces the difference between two populations)

2). Decrease Variation
•Genetic Drift/Founder Effect (Results when a small population is involved; made by random factors in small populations. The Founder Effect is a type of genetic drift where allele frequencies are altered in small populations that are taken from or are remnants of large populations. This isolation could lead to this species becoming so different or "drifting" so far that they are no longer able to mate with anyone that is not inside of their small population. It also operates on the idea that humans don't reproduce alleles in the same proportions that they receive them. This results in some alleles being passed on while others aren't. This phenomenon is up to chance and causes allele frequencies to randomly fluctuate from generation to generation.)
•Non-random Mating (Humans select their mates based on some type of criteria. Major histocompatibility complex or MHC plays a major part in this. The basic idea is that these genes detect favorable odors, the most favorable odors being those that come from individuals whose DNA is the most different from your own. {1} The long-term effect here is the alteration of gene frequency. Humans either marry within a group, whether it be social class, culture, religion, gender or race. This is known as endogamy and results in genetic drift. Exogamy, which is marrying outside of a group, results in gene flow.

Examples:
During the Industrial Revolution, the pollution caused trees to turn a darker color. In response to this environmental change, light colored moths also began to change color, becoming darker-colored to blend in with the trees for protection from birds. The ones that remained light-colored died off because they were easy targets for the birds, leaving the darker-colored ones safe.

Another example of evolution is seen in domesticated animals. Darwin focused on domestication because he believed it gave rise to more variation. He believed that this was mostly because of their environment. The best example of this is the morphology of the dog from the wolf. Darwin also noted that all domesticated animals tended to evolve in the same direction.we see this primarily in animals response to humans, namely in their loss of the "species-specific wild-animal behavorial response to humans." {2} We also see variation in body size, body shape and hair type.

Resources:

{1} http://m.rspb.royalsocietypublishing.org/content/275/1652/2715.long

{2} http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763232/