Week 14:
Chapter 17 of your textbook
 

THE HOLOCENE
PRIMATES
A PRIMATE EVOLUTIONARY TREE AND TIME SCALE:
   The prosimians ("before monkeys")
   The Anthropoids
HUMAN ORIGINS
   Australopithecines
   Comparing Apes to Hominids
   Early Hominids
   Differing Views of the Hominid Family Tree
       The Genus Homo
       The First Human: Homo habilis
       How Diverse Was Early Homo?
       Cro-Magnons Replace the Neanderthals
       Our Own Species: Homo sapiens
       The Humans
       Superfamily the Hominoidea
           Dental formula
           Humans differ from other animals in several ways

Paleogeography: Last Gacial Maximum 18,000 years ago <http://www.scotese.com/lastice.htm>
                          Modern World <http://www.scotese.com/modern.htm>
Future Geography: +50 Ma <http://www.scotese.com/future.htm>
                             +100 Ma <http://www.scotese.com/future1.htm>
                             +250 Ma <http://www.scotese.com/future2.htm>



THE HOLOCENE

>The Holocene is the name given to the last ~10,000 years of the Earth's history -- the time since the end of the last major glacial epoch, or "ice age."

>To observe a Holocene environment, simply look around you!

>Since then, there have been small-scale climate shifts -- notably the "Little Ice Age" between about 1200 and 1700 A.D. -- but in general, the Holocene has been a relatively warm period in between ice ages.

>Another name for the Holocene that is sometimes used is the Anthropogene, the "Age of Man."
This is somewhat misleading: humans of our own subspecies, Homo sapiens sapiens, had evolved and dispersed all over the world well before the start of the Holocene. Yet the Holocene has witnessed all of humanity's recorded history and the rise and fall of all its civilizations.
Humanity has greatly influenced the Holocene environment; while all organisms influence their environments to some degree, few have ever changed the globe as much, or as fast, as our species is doing.

>The vast majority of scientists agree that human activity is responsible for "global warming," an observed increase in mean global temperatures that is still going on.

>Habitat destruction, pollution, and other factors are causing an ongoing mass extinction of plant and animal species; according to some projections, 20% of all plant and animal species on Earth will be extinct within the next 25 years.

>The Holocene has also seen the great development of human knowledge and technology, which can be used -- and are being used -- to understand the changes that we see, to predict their effects, and to stop or ameliorate the damage they may do to the Earth and to us.

>Paleontologists are part of this effort to understand global change. Since many fossils provide data on climates and environments of the past, paleontologists are contributing to our understanding of how future environmental change will affect the Earth's life.


PRIMATES
>Primates have movable fingers and toes, and most have flattened nails rather than claws. The hands and, in some species, the feet are prehensile or grasping. Unlike most mammals, primates have color vision. This may have arisen when primates became more active during the day than at night, a change that occurred about 60 million years ago. The front-facing eyes found in primates result in broadly overlapping fields of vision. This allows primates to perceive depth-a useful trait for an animal that moves by swing¬ing or jumping from branch to branch in trees.

>Primates include the prosimians and anthropoids. The apes, monkeys, and hominids make up the anthropoids, and chimpanzees seem the most closely related to humans.

>Primates are mammals with two distinct features that allowed them to succeed in the arboreal, insect-eating environment:

1.-Grasping fingers and toes. Unlike the clawed feet of tree shrews and squirrels, primates have grasping hands and feet that let them grip limbs, hang from branches, seize food, and in some primates, use tools. The first digit in many primates is opposable and at least some, if not all, of the digits have nails.

2.- binocular vision. Unlike the eyes of shrews and squirrels, which sit on each side of the head so that the two fields of vision do not overlap, the eyes of primates re shifted forward to the front of he face. This produces overlap¬ping binocular vision that lets the brain judge distance precisely important to an animal moving through the trees.

>Other mammals have binocular vi¬sion, but only primates have both binocular vision and grasping hands, making them particularly well adapted to their environment.

A PRIMATE EVOLUTIONARY TREE AND TIME SCALE (SIX MAJOR EVENTS):
>Event 1: 40 million years ago, the earliest primates split into two groups: the prosimians and the anthropoids.

The prosimians ("before monkeys")
>Looked something like a cross between a squirrel and a cat and were common in North America, Europe, Asia, and Africa.
>Only a few prosimians survive today: lemurs, lorises, and tarsiers (slide).
>In addition to grasping digits and binocular vi¬sion, prosimians have large eyes with increased visual acu¬ity.
>Most prosimians are nocturnal, feeding on fruits, leaves, and flowers, and many lemurs have long tails for balancing.

More feature of prosimians primates:
Many resem¬ble very early primate forms; include lemurs, lorises, and tarsiers.

Fossils of extinct primates reveal that the majority of them lived in trees, as do most modern species.

Many of the characteristics that primates share apparently evolved as adaptations to life in trees.

The Anthropoids
>Anthropoid primates, such as the gibbon have a well-developed collarbone, rotating shoulder joints, and partially rotating elbow joints. Anthropoids also have an opposable thumb that can be positioned opposite the other fingers. This arrangement of fingers results in increased precision in the use of the hands. Additionally, nonhuman anthropoids have an opposable big toe, as seen on the chimpanzee, and this prehensile foot is an important aid to climbing.

>All anthropoids have a similar dental formula, or number and arrangement of teeth. In humans, apes, and African and Asian monkeys, each half of the upper and lower dental arches includes two incisors, one canine, two premolars, and three molars, as shown in Figure slide

>Compared with other primates, anthropoids have a large brain relative to their body size. The fossil record shows that as primates evolved, brain size increased. Humans and the great apes (gibbons, orangutans, gorillas, and chimpanzees) have a larger cranial capac¬ity relative to body size and a more complex brain structure than other primates have.

>Of the anthropoid species, the chimpanzees may be the most closely related to humans. Comparisons of chimpanzee and human DNA have shown a very high degree of similarity. This similarity sug¬gests that humans and chimpanzees may have shared an ancestor less than 6 million years ago. It is important to understand, however, that humans are not descended from chimpanzees or from any other modern ape. Rather, modern apes and humans are probably descended from a more primitive apelike ancestor.

>Anthropoids include monkeys, apes, and humans. Anthro¬poids are almost all diurnal-that is, active during the day¬ feeding mainly on fruits and leaves. Evolution favored many changes in eye design, including color vision, that were adaptations to daytime foraging.

Event 2: 30 million years ago, some anthropoids migrated to South America. Their descendants, known as the New World monkeys, are easy to identify: All are arboreal; they have flat, spreading noses; and many of them grasp objects with long, prehensile tails.

>Anthropoids that remained in Africa gave rise to two lineages: the Old World monkeys and the hominoids (apes and humans). Old World mon¬keys include ground-dwelling as well as arboreal species. None of them have prehensile tails, their nostrils are close together, their noses point downward, and some have toughened pads of skin for prolonged sitting.

>The hominoids include the apes and the hominids (humans and their direct ancestors). The living apes consist of the gibbon (genus Hylobates), orangutan (Pongo), gorilla (Gorilla), and chimpanzee (Pan). Apes have larger brains than monkeys, and they lack tails. With the ex¬ception of the gibbon, which is small, all living apes are larger than any monkey. Apes exhibit the most adaptable behavior of any mammal except human beings. Once widespread in Africa and Asia, apes are rare today, living in relatively small areas. No apes ever occurred in North or South America.

Event 3: 15 mya. Studies of ape DNA have explained a great deal about how the living apes evolved. The Asian apes evolved first. The line of apes leading to gibbons diverged from other apes about 15 million years ago, while orangutans split off about 10 million years ago (figure). Neither group is closely related to humans.

Event 4: 10 to 6 mya.  The African apes evolved more recently, between 6 and 10 million years ago. These apes are the closest living rela¬tives to humans; some taxonomists have even advocated placing humans and the African apes in the same zoological family, the Hominidae. Fossils of the earliest hominids (hu¬mans and their direct ancestors), suggest that the common ancestor of the hominids was more like a chimpanzee than a gorilla.

Event 5: 8 million years ago. Based on genetic differences, scientists estimate that gorillas diverged from the line leading to chimpanzees and humans.

Event 6: Soon after the gorilla lineage diverged, the common an¬cestor of all hominids split off from the chimpanzee line to begin the evolutionary journey leading to humans. Because this split was so recent, the genes of humans and chim¬panzees have not had time to evolve many genetic differ¬ences. For example, a human hemoglobin molecule differs from its chimpanzee counterpart in only a single amino acid. In general, humans and chimpanzees exhibit a level of genetic similarity normally found between closely related sibling species of the same genus!

>Humans depart from apes in several areas of anatomy related to bipedal locomotion. Because humans walk on two legs, their vertebral column is more curved than an ape's, and the human spinal cord exits from the bottom rather than the back of the skull. The human pelvis has be¬come broader and more bowl-shaped, with the bones curv¬ing forward to center the weight of the body over the legs. The hip, knee, and foot (in which the human big toe no longer splays sideways) have all changed proportions. Being bipedal, humans carry much of the body's weight on the lower limbs, which comprise 32 to 38% of the body's weight and are longer than the upper limbs; human upper limbs do not bear the body's weight and make up only 7 to 9% of human body weight. African apes walk on all fours, with the upper and lower limbs both bearing the body's weight; in gorillas, the longer upper limbs account for 14 to 16% of body weight, the somewhat shorter lower limbs for about 18%.


HUMAN ORIGINS
Australopithecines
Five to 10 million years ago, the world's climate began to get cooler, and the great forests of Mrica were largely re¬placed with savannas and open woodland. In response to these changes, a new kind of hominoid was evolving, one that was bipedal. These new hominoids are classified as hominids-that is, of the human line.

The major groups of hominids include three to seven species of the genus Homo (depending how you count them), seven species of the older, smaller-brained genus Australopithecus, and several even older lineages. In every case where the fossils allow a determination to be made, the hominids are bipedal, the hallmark of hominid evolution.

Comparing Apes to Hominids
The common ancestor of apes and hominids is thought to have been an arboreal climber. Much of the subsequent evolution of the hominoids reflected different approaches to locomotion. Hominids became bipedal, walking up¬right, while the apes evolved knuckle-walking, supporting their weight on the back sides of their fingers. (Monkeys, by contrast, use the palms of their hands.)

To understand the story of human evolution, we must understand both our ancestry and our relationship to our closest living kin. Humans are members of the ancient mammalian order Primates. Primates have grasping hands, acute vision, and large brains. Primate parents provide extended periods of intense care for their young, and many primate species live in complex social groups. As you will see, many of our behaviors and characteristics are similar to those of other primates, and some are uniquely human.
 

Early Hominids
In recent years, anthropologists have found a remarkable series of early hominid fossils extending as far back as 6-7 million years. Often displaying a mixture of primitive and modern traits, these fossils have thrown the study of early hominids into turmoil. "While the inclusion of these fossils among the hominids seems warranted, only a few speci¬mens of these early genera have been discovered, and they do not provide enough information to determine with any degree of certainty their relationships to australopithecines and humans. The search for additional early hominid fos¬sils continues.

Much of the information available about human evolu¬tion comes from the fossilized bones of early hominids a group that comprises humans and their immediate ancestors. Fossilized hominid remains are seldom complete skele¬tons-often only fragments of fossilized bone are found. Scientists pay close attention to subtle clues in these fossils. For example, the curvature of the spine, the position at which the spine attaches to the skull, and the shape of the pelvis, or hipbones, can indicate whether an organism walked upright. Similarly, a skull fragment can be used to estimate brain size, and wear on a fossil tooth can give some indication of an organism's diet.

Hominid from the Latin homo, meaning "human being," and the Greek -ides, meaning "a thing belonging to"

Hominids belong to the order of mammals known as primates. Two large divisions of modern primates are recognized: The Prosimians and the anthropoid primates:  include marmosets, monkeys, apes, and humans.

Differing Views of the Hominid Family Tree
Investigators take two different philosophical approaches to characterizing the diverse group of African hominid fossils. One group (the "lumpers") focuses on common elements in different fossils, and tends to lump together fossils that share key characters, attributing differences among the fossils to diversity within the group. Other investigators (the "splitters") are more inclined to assign fossils that exhibit differences to different species. For example, in the hominid evolutionary tree presented by lumpers recognize three species of Homo, while splitters recognize no fewer than seven!

The Genus Homo
The first humans evolved from australopithecine ancestors about 2 million years ago. The exact ancestor has not been clearly defined, but is commonly thought to be A. afarensis.

The First Human: Homo habilis
In the early 1960s, stone tools were found scattered among hominid bones close to the site where A. boisei had been unearthed. Although the fossils were badly crushed, painstaking reconstruction of the many pieces suggested a skull with a brain volume of about 680 cubic centimeters, larger than the australopithecine range of 400 to 550 cubic centimeters. Because of its association with tools, this early human was called Homo habilis, meaning "handy man."

How Diverse Was Early Homo?
Because so few fossils of early Homo have been found, lively debate has ensued concerning whether they should all be lumped into H. habilis or split into three species: H. rudolfensis, H. habilis, and H. ergaster (Greek ergaster, "workman"). If the three species designations are accepted, as increasing numbers of researchers are doing, it would appear that Homo underwent an adaptive radiation, with H. rudolfensis the most ancient species, followed by H. ha¬bilis and then H. ergaster. Because of its modern skeleton, H. ergaster (figure) is thought to be the most likely ancestor to later species of Homo.

Cro-Magnons Replace the Neanderthals
The Neanderthals (classified by many paleontologists as a separate species, Homo neanderthalensis) were named after the Neander Valley of Germany where their fossils were first dis¬covered in 1856. Rare at first outside of Africa, they became progressively more abundant in Europe and Asia, and by 70,000 years ago had become common. The Neanderthals made diverse tools, including scrapers, spearheads, and hand axes. They lived in huts or caves. Neanderthals took care of their injured and sick and commonly buried their dead, often placing food, weapons, and even flowers with the bodies. Such attention to the dead strongly suggests that they be¬lieved in a life after death. This is the first evidence of the symbolic thinking characteristic of modern humans.

Our Own Species: Homo sapiens
H. sapiens is the only surviving species of the genus Homo, and indeed the only surviving hominid. Some of the best fossils of Homo sapiens are 20 well-preserved skeletons with skulls found in a cave near Nazareth in Israel. Modern dat¬ing techniques estimate these humans to be between 90,000 and 100,000 years old. The skulls are modern in appear¬ance and size, with high, short braincases, vertical fore¬ heads with only slight brow ridges, and a cranial capacity of roughly 1550 cubic centimeters.

We humans are animals and the product of evolution. Our evolution has been marked by a progressive increase in brain size.

The Humans
>Bipedalism, the ability to walk primarily on two legs, is a uniquely human trait among mammals. The cup-shaped human pelvis supports the internal organs dur¬ing upright walking. The human spine has two curves, resulting in an 5 shape that allows for upright posture.

>In the human foot, the toes are much shorter than those of apes and are aligned with each other. Because humans are the only pri¬mates that have this foot structure, we can infer that the shape of the human foot is a specific adaptation for bipedalism.

>The enlargement of the brain in humans has resulted in a more vertical face than that found in apes. Among other differences, the larger human brain has extensive areas devoted to the production and understanding of speech.

>Apes have homologous areas in their brains that are important in the production of sounds used in communication, and apes can also be taught to mimic certain forms of sign language. However, apes living in the wild have not developed any complex, flexible set of signals that can compare to those that make up the languages of humans.

>Bipedalism is the principal trait that defines the hominid line. Modern nonhuman anthropoid primates are quadrupedal that is, they walk on four limbs. The apelike ancestors of the first hominids likely were quadrupedal as well. How long ago did the first bipedal primate, that is, the first hominid, evolve? This question has not yet been answered conclusively.

>Apes and humans differ from all of the other primates in that they lack external tails.  They also are more intelligent and more dependent for survival on learned behavior patterns.  This is especially true of the great apes and people.

>All of the apes and humans are members of the same superfamily, the Hominoidea.

Within the Hominoidea, there are at least two families of apes and one of humans.

1.- Hylobatidae (gibbons, and siamangs )
2.- Pongidae  (orangutans, gorillas, chimpanzees, and bonobos)
3.- Hominidae  (humans)

Gibbons, siamangs, and orangutans live in Southeast Asia, while gorillas, chimpanzees, and bonobos are exclusively African apes.

Dental formula Image Source: <http://upload.wikimedia.org/wikipedia/en/1/17/Upper_Jaw_Dentition.jpeg>
The quantity of each type of tooth (e.g., incisor, canine, premolar, and molar) in each quadrant of the mouth, counting from the front.  The human dental formula is 2.1.2.3. The milk tooth formula for humans is: 2.1.0.2. The Old World monkeys and apes also share this dental formula.

The comparatively minor anatomical differences between humans and apes
>are largely a result of our habitual bipedalism.  A number of changes in our bodies were related to the development of this form of locomotion.
>Unlike apes, our arms are relatively short and weak compared to our legs.  Our feet no longer have the ability to effectively grasp and manipulate objects since the big toe moved up into line with the others.  Human feet also have lengthened and acquired an arch, making them better body supports.  The human pelvis and spinal column also have been modified for an erect posture and bipedal locomotion.  We are now essentially fully terrestrial animals.   Nature very likely selected for longer legs in humans  because it is more efficient for walking and especially running bipedally.

>With the exception of these few outward differences, we are quite similar to the African apes anatomically and genetically, especially to the chimpanzees and bonobos.  Work on discovering the entire genome of common chimpanzees was completed in 2005.  A comparison between this and the human genome (completed in 2001) shows that 98.77% of DNA base pairs of humans and chimpanzees are the same.  However, there are an additional 2.7% differences between the two species in duplicated segments of DNA.  Where we differ appears to be largely in the genes that control speech, smelling, hearing, digesting proteins, and susceptibility to certain diseases.  These minor differences are to be expected given that we have been on essentially separate evolutionary tracks for 6-7 million years.  During that time, we have been subject to somewhat different natural selection pressures.  These differences led to bipedalism for our ancestors along with a much larger brain and, ultimately, speech.

Humans differ from other animals in several ways.
>First, humans are able to make and use tools effectively-a capability that, more than any other factor, has been responsible for our dominant position in the ani¬mal kingdom.

>Second, although not the only animal capa¬ble of conceptual thought, humans have refined and ex¬tended this ability until it has become the hallmark of our species.

>Third, we use symbolic language and can, with words, shape concepts out of experience and transmit that accumulated experience from one generation to another. Thus, we have undergone what no other animal ever has: extensive cultural evolution. Through culture, we have found ways to change and mold our environment, rather than changing evolutionarily in response to the demands of the environment. We control our biological future in a way never before possible-an exciting potential and a frightening responsibility.