Genetics and Evolution (From the Notes of Justin Nicolas)

AN 100 General Anthropology
Notes for August 3, 2004 (August 10,17)
Prepared by Mr. Justin V. Nicolas

Summary of Genetics and Evolution (from Anthropology, Carol R. Ember et al)

If we think of the history of the universe in terms of 12 months, the history of human like primates would take up only about one and a half hours. The universe is some 15 billon years old; modern-looking humans have existed for about 100,000 years.
Ideas about evolution took a long time to take hold because they contradicted the biblical view of events; species were viewed as fixed in their form by the Creator. But in the eighteenth and early nineteenth centuries increasing evidence suggested that evolution was a viable theory. In geology, the concept of uniformitarianism suggested that the earth is constantly subject to shaping and reshaping by natural forces working over vast stretches of time. A number of thinkers during this period began to discuss evolution and how it might occur.
Charles Darwin and Alfred Wallace proposed the mechanism of natural selection to account for the evolution of species. Basic principles of the theory of natural selection are that (1) every species is composed of a great variety of individuals, some of which are better adapted to their environment than others; (2) offspring inherit traits from their parents at least to some degree and in some way; and (3) since better adapted individuals generally produce more offspring over the generations than the poorer adapted, the frequency of adaptive traits increase in subsequent generations. In theis way, natural selection results in increasing proportions of individuals with advantageous traits.
Mendel’s and subsequent research in genetics and our understanding of structure and function of DNA and mRNA help us to understand the biological mechanisms by which traits may be passed from one generation to the next.
Natural selection depends on variation within a population. The four sources of biological variation are genetic recombination, mutation, genetic drift and gene flow.
Speciation, the development of a new species, may occur if one subgroup becomes separated from other subgroups. In adapting to different environments, these populations may undergo enough genetic changes to prevent interbreeding, even if they reestablish contact. Once species differentiation occurs, it is believed that the evolutionary process cannot be reversed.
Natural selection can also operate on the behavioral characteristics of populations. The approach called sociobiology and behavioral ecology involve the application of evolutionary principles to the behavior of animals. Much controversy surrounds the degree to which the theory of natural selection can be applied to human behavior, particularly cultural behavior. There is more agreement that biological and cultural evolution in humans may influence each other.


(Discuss: Mendel’s experiment on yellow and green peas. Parent generation YY x yy = First generation Yy x Yy = Second Generation YY Yy Yy yy= 3 yellow and 1 Green)

(Discuss DNA: DNA molecule consists of two spiral sugar-phosphate strands. The strands are linked by the nitrogenous bases adenine (A), guanine (G), thymine (T), and cytosine (C). When the DNA molecule reproduces, the bases separate and the spiral strands unwind. Each original strand serves as a mold along which a new complementary chain is formed.)

DNA stores the information to make cells, but it does not directly affect formation of cells. One type of ribonucleic acid (RNA), messenger RNA (mRNA), is copied from a portion of DNA and moves outside the cell nucleus to direct formation of proteins.

Sources of Variability

Genetic Recombination - A unique offspring is thus produced by a shuffling of the parent’s genes. Once cause of this shuffling is the random segregation, or sorting of chromosomes in meiosis. Another cause of shuffling of parenta genes is crossing-over, the exchange of sections of chromosomes between one chromosome and another. (This is the reason why no sibling look exactly alike or no 50% mother, 50% father.)

Mutation – is a change in the DNA sequence. Such as change produces an altered gene. The majority of mutations are thought to occur because of occasional mismating of the chemical bases that make up DNA. Just as a typist will make errors in copying a manuscript, so will DNA, in duplicating itself, occasionally change its code.

Genetic Drift – refers to various random processes that affect gene frequencies in small, relatively isolated populations. Genetic drift is also known as the Wright effect, after the geneticist Sewall Wright, who first directed attention to this process. Over time in a small population, genetic drift may result in a neutral or nearly neutral gene becoming more or less frequent just by chance.

Founder principle- occurs when a small group recently derived from a larger population migrates t a relatively isolated loction. (Example first Native Americans may have been predominantly Type O blood.)

Gene flow – is the process whereby genes from one population to another through mating and reproduction. Unlike the other processes of natural selection and genetic drift, which generally increase the difference between populations in different environments, gene flow tends to work the opposite direction—it decreases differences between populations. Two populations at opposite ends of a region may have different frequencies of a particular gene, but the populations located between them have an intermediate gene frequency because of gene flow between them. The variation in gene frequency from one end of the region to another is called a cline.

The Origin of the Species

Species – is a population that consists of organisms able to interbreed and produce fertile and viable offspring. In general, individuals from one species cannot successfully mate with members of a different species because of genetic and behavioral differences.

Speciation - - or the development of a new species, may occur of one subgroup of a species finds itself in a radically different environment.




The Living Primates

Some Common Primate Traits

1) Rotating forearm
2) Relatively larger brain, reduction in sense of smell (olfactory bulbs), and expansion of primary visual area (as compared to a cat)
3) Forward facing eyes (as those of the Tarsier)
4) Grasping hands and feet

Primates are social animals; diurnal primates (those active during the day) find group life crucial for survival.

A Simplified Classification of the Living Primates

LIVING PRIMATES
Prosimians (Pre-monkeys)
Anthropoids
New World Monkeys (Platyrrhines)
Flat-bridged noses; nostrils facing outwards
Old World Primates
(Catarrhines)
narrow noses with nostrils facing downwards
(Ceboids)
Old World monkeys (Cerecopithcoids) same number of teeth as apes and humans
Apes and Humans (Hominoids)
Lemurs Indris
Aye-ayes
Lorises Bushbabies
Tarsiers
Cebids
Marmosets
Tamarins
Colobines
Cercopithecines
sexuam dimorphism; fruit eaters; callouses on their bottoms

Lesser Apres (Hylobates

Gibbons and Siamangs
Great Apes (Pongids)

Orangutans; gorillas and chimpanzees
Human (Homonids)


Distinctive Human traits

consistently walk erect on two feet- bipedalism
greater length and flexibility of the human thumb allow us to handle objects with greater dexterity
capable of both power grip and precision grip
remarkable hand-eye coordination
sophisticated brain; large and complex cerebral cortex, the center of speech and higher mental activities (1,300 cubic centimeters) gorilla 525 cu. Cm.; frontal areas of human brain are also larger than other primates; humans have special areas of the brain dedicated to speech and language; the way large amount of blood is carried to the brain is also unique.
Human teeth reflect completely omnivorous diet; not very specialized (the need for tools); human canines do not usually project beyond the tops of the other teeth
Sexuality of females- may engage in intercourse at anytime throughout the year

Behavior abilites

Toolmaking
Language
Gender-role specialization

Discuss Continental Drift

The First Homonids

The drying trend in climate that began about 16 million to 11 million years ago diminished the extent of African rain forests and gave rise to areas of savannas (grasslands) and scattered deciduous wood lands. The new, more open country probably favored characteristics adapted to ground living in some primates. In the evolutionary line leading to humans, the adaptations included bipedalism.
One of the crucial changes in the early homonid evolution was the development of bipedalism. There are several theories for this development: It may have increased the emerging homonid’s ability to see predators and potential prey while moving through tall grasses of the savanna; by freeing the hands for carrying, it may have facilitated transferring food from one place to another; tool use, which requires free hands, may have favored two-legged, walking; and bipedalism may have made long-distance traveling more efficient.
Ardipithecus ramidus, a species dating to 4.4 million years ago, may have walked bipedally and may be the earliest homonid. Undisputed homonids dating between 4 million and 3 million years ago have been found in East Africa. These definitely bipedal hominids are now generally classified into the genus Australopithecus.
At least six species of australopithecine have been identified, and these are generally divided into two types: gracile and robust. The gracile australopithecines have relatively smaller teeth and jaws, and include A. anamensis, A. afarensis, and A. africanus. The robust australopithcines have relatively larger teeth and jaws, and are more muscular than the gracile autralopithecines. They include A. aethiopicus, A. robustus, and A. boisei.

The Origins of Culture and the Emergence of Homo

The earliest identifiable stone tools found so far come from various sites in East Africa and date from about 2.5 million years ago. Flake tools predominate, but choppers are also common. Choppers are core that have been partially flaked and have a side that might have been used for chopping. These early stone tools are referred to as Oldowan.
Archeologists have experimented with what can be done with Oldowan tools. The flakes appear to be very versatile; they cn be used for slitting the hides of animals, can be used to hack off branches or cut and chop tough joints. Hominids shortly after 2 million years ago were cutting up animal carcasses for meat, mostly obtained through scavenging rather than hunting.
There are archeological sites dating as early as 2 million years ago that contain concentrations of a stone tools and animal bones. Some scholars thing\k these might have been early homonid home bases, others do not. If these sites were not home bases, what were they? Some archeologists are beginning to think that these early sites with many animal bones and tools may just have been places where homonids processed food but did not live.
The presence of stone tools and perhaps home bases suggests that early homonids had culture. Culture is a dynamic, adaptive process of learned, shared, and integrated behaviors.
Important physical changes in the early homonids that led to the evolution of our genus. Homo, include the expansion of the brain, the modification of the female pelvis to allow bigger-brained babies to be born, and the reduction of the face, teeth, and jaws. The physical changes are seen in the species Homo habilis and Homo rudolfensis, both of which date to around 2.3 million years ago. Early Homo appears to have used tools and scavenged or possibly hunted meat, so culture, or the evolution of cultural behavior, seems to have played a role in these physical changes as well.
Homo erectus emerged about 1.8 milion to 1.6 million years ago. It had a larger brain cpacity than Homo habilis and an essentially modern postcranial skeleton. What differentiates Homo erectus most from modern humans is the shape of the skull, which is long, low, and has prominent brow ridges.
Homo erectus was the first homonid species to be widely distributed in the Old World. Some of the locations where Homo erectus lived in eastern Europe and Asia were quite cold, and Homo erectus was able to adapt to these new and often colder environments through culture.
Lower Paleolithic tools and other cultural artifacts from about 1.6 million to about 200,00 years ago were probably produced by H. erectus. Acheulian is the name given to the most well-known tool tradition of this period. Acheulian tools include both small flake tools and large tools, but hand axes and other large bifacial tools are characteristic.
Although it is presumed that H. erectus had learned to use fire to survive in areas with cold winters, there is no definite evidence of the control of fire by H. erectus. There is evidence in some sites of big-game eating, but whether H. erectus hunted those animals is debated. There is little evidence of ritual behavior among H. erectus.











































The Emergence of Homo Sapiens

Summary

Most anthropologists agree that Homo erectus began to evolve into Homo sapiens after about 500,00 years ago. But there is disagreement about how and where the transition occurred. The mixed traits of transitional fossils include large cranial capacities (well within the range of modern humans), together with low foreheads and large bow bridges, which are characteristics of H. erectus specimens. The earliest definite H. sapiens, who did not look like modern humans appeared about 100,00 years ago.


Homo sapiens have been found in many parts of the Old World—in Africa and Asia as well as in Europe. Some of these Homo sapiens have lived earlier than the Neanderthals of Europe. There is still debate over whether the Neanderthals in western Europe became extinct or survived and were ancestral to the modern-looking people who lived in western Europe after about 40,000 years ago. (DNA shows no difference.)


The period of cultural history associated with the Neanderthals is traditionally called the Middle Paleolithic in Europe and the Near East and dates from about 300,000 to about 40,000 years ago. For Africa, the term Middle Stone Age is used. The assemblages of flake tools such from this period are generally referred to as Mousterian in Europe and the Near East as as post-Acheulian in Africa. Compared with an Acheulian assemblage, a Mousterian tool assemblage has a smaller proportion of large hand axes and cleavers and a larger proportion of small flake tools such as scrapers. Mousterian sites show signs of intentional burial.


Fossil remains of fully modern-looking humans Homo sapiens sapiens, have been found in Africa, the Near East, Asia and Australia, as well as Europe. The oldest of these fossils have been found in South Africa and may be 50,000 to 100,000 years old.


Two theories about the origins of modern humans continue to be debated among anthropologists. One, the single-origin theory, suggests that modern humans emerged in just one part of the World—the Near East, and more recently, Africa have been the postulated place of origin—and spread to other parts of the World, superseding Neanderthals. The second theory, the multiregional theory, suggests that humans emerged in various parts of the Old World, becoming varieties of humans we see today.

Homo Heidelbergensis

- Named after a jaw found in 1907 in the village of Mauer near Heidelberg, Germany.
- Transitional fossils suggest a separate species


Neandertals: Homo Sapiens neandertalensis or Homo Neandertalensis

1856, three years after Darwin’s publication of The Origin of the Species, a skullcap and other fossilized bones were discovered in a cave in the Neander Valley (tal is the German word for “valley”), near Dusseldorf, Germany.