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Archive for June, 2013

Our Human Origins—Part I

Evolution is the Real Story

 

Introduction

I am initiating a three-part series on Our Human Origins. Part I describes the background and history of how Charles Darwin came to his scientific conclusion that man descended from the Great Apes. I also describe the life of Charles Darwin in some detail. In addition, I describe the basics of the animal kingdom classification scheme of Linnaeus, and how humans fit in. In Part II I will report on the various major discoveries in paleontology since Darwin and the scientists who discovered them. In Part III I discuss the current relevance of our human origins and how each one of us can find out his own journey since humans began leaving Africa between 160,000-200,000 years ago.

I will share with my cyberspace audience how I was able to do that. In addition, I will pass on to readers how they can go find out what their journey was coming out of Africa. You will learn about the National Geographic Genome-2 Project and what you can do to become involved in their DNA program. As a by-product you will learn your own human origin. This will remove all doubt about the origin of man as you experience your own personal journey. But, to really see the big picture of evolution, I highly recommend cyberspace readers take the time to learn what is in Appendix A on the Geological Timeline. Although there isn’t perfect agreement among scientists as to the exact timeline for any Eon, Era, Period or Epoch it is to date the most solid timeframe for understanding earth formation, continental movements, and the evolution of all species, including human evolution. There is no more exciting place to be than in the sciences that show us who we are and where we come from.

Background

In my opinion Charles Darwin was the greatest scientist of the 19th Century when he provided what was then an earth-shaking revelation that man descended from the great apes. The Christian world went apoplexy with this revelation. And even various segments of the secular world wanted proof beyond a reasonable doubt. In Darwin’s day, there was no high level knowledge of DNA, the fine points of biochemistry, or extensive specific knowledge of the genetic transmission of human characteristics through one’s genes. For that matter even the fine points of evolutionary theory itself had not yet been revealed through scientific research. Also, the work of paleontologists was just getting started, meaning that the digging up of fossils that support Darwin’s theory would be many decades in the making.

A healthy skepticism is always a good approach for any scientist to take where his work is concerned. But now, after 150+ years and thousands of studies in many diverse scientific fields, evolution is not discussed any longer as a theory—but as fact. Why? Because there is an overwhelming convergence of the scientific evidence that species do evolve and primarily by the mechanisms Charles Darwin originally proposed. All of us need to remember that “truth” is what we agree it is, nothing more and nothing less. Scientific consensus building sees the concept of truth in the same way. And, the consensus is—evolution is very real. It has the scientific community supporting it, based on accumulated evidence and a 150+ year convergence of that evidence.

Our human ego would like us to believe that our one particular species is uniquely special but, unfortunately, we are neither unique nor really that different or special compared to other species. I’ll never fly on my own power, move faster than a shark through the water, or outrun a cheetah. And, the Bald Eagle  has better eyesight than any human on the planet. Case closed on superiority of our species. But, we do have a complex larger brain than all other species, and it’s about time we start using it rather than dwell on super-natural hypotheses that explain nothing and are devoid of any real scientific data or evidence.

Society’s scientific question these days is no longer whether evolution occurred, but rather centers upon unraveling the complexity of how it occurred. And indeed, there is still much complexity in this area of scientific research. I want, in this three part series, to bring the reader up-to-date on our human origins. Below is a preliminary glance at our origins and I pose a significant social question for you to think about.

All people alive on earth today originated from Mitochondrial Eve. That sort of makes us all brothers and sisters under the sun and all related by our family tree going back to Mitochondrial Eve. As the late Rodney King so famously said in 1991, “Why can’t we all just get along?”  The astute observer will however say, we don’t fight because of genetics or our human origins, we fight because of culture and cultural differences. This is very true, but I do have one question. Rodney King’s question reaches out to all of us to answer his question, even hypothetically. Hypothetically speaking, values of different groups have to change, less we destroy ourselves eventually through nuclear war. Can our human survivor instinct mitigate cultural differences through cooperation and understanding? Perhaps the current explosion of worldwide communication technology, and a burgeoning of the global economy, will one day pave a path to cooperation and understanding, or perhaps not. What do you think? In the meantime let’s get back to our collective human origins.

 

The Evidentiary Trail of Evolution

We have fossils…We win!

Lewis Black, on creationism (Comedian, 1948–present)

 

Charles Darwin was not the first person to suggest a theory of evolution. What made it work for Darwin was that he was an effective synthesizer of existing information. It remained for him to assemble all the data and to construct an unassailable theory.[1]What also set Darwin apart from many others was that he collected a vast amount of data on his own to buttress the theory of evolution. He knew this was important because of an essentially skeptical reception many scientists encounter.[2]

Two people contributed a great deal to the concept of evolution prior to Charles Darwin. One was Charles Darwin’s grandfather Erasmus Darwin (1731-1802). Charles Darwin’s grandfather was a physician, philosopher, poet, and celebrated personality.[3] In his writings between 1784 and 1802 Erasmus Darwin posed two important questions: first, whether all living creatures are ultimately descended from a single common ancestor; and second, how species would be transformed.

In order to answer the first question he assembled evidence from several fields [embryology, comparative anatomy, systematics, geography, and fossil data] for a single source of all life, an evolving web of life that included mankind.[4] “This after all was in keeping with the eighteenth-century classification of all animals and plants into families, genera and species by the Swedish botanist Carolus Linnaeus (1707-1778), who classed Homo sapiens as a close relative of old World monkeys and the apes–although scientists and theologians alike had exerted great efforts to extricate mankind from this unseemly association.”[5]

The second question was more difficult to answer. However, Erasmus Darwin’s treatment of the problem contained the seeds of almost all of the important principles of evolutionary theory.[6] According to Richard L. Leakey and Roger Lewin, “He saw that competition and selection were possible agents of change; that over-population was an important factor in sharpening competition; that plants should not be left out of evolutionary theory; that competition of males for females has important structural implications in their evaluation; and that fertility and susceptibility to disease were areas of selection.”[7]

Another historical person to impact evolutionary theory before Charles Darwin was Jean Baptiste Lamarck (1744-1829) who took up Erasmus Darwin’s mention of inheritance of acquired characteristics and expanded it to a fully-fledged theory of evolution.[8] Erasmus Darwin did not definitively state that the principal agent of evolution is passive adaptation through natural selection, but he seemed to say that animals may evolve through active adaptation to their environment, including the inheritance of acquired characteristics.[9]

One of the books Charles Darwin took on his voyage on the Beagle was Charles Lyell’s   Principles of Geology. He is known as the father of modern geology. Lyell had revised James Hutton’s Theory of the Earth which established the thesis that came to be known as uniformitarianism. The thesis came out of a debate concerning the origin of fossils. The major issues were that of attributing a correct age to the earth and the age of the strata from which fossils were retrieved. This is because fossils don’t determine their own age, but the geological strata in which fossils are found does.[10] Such prior work before Darwin established that evidence was mounting to the inescapable conclusion that Homo sapiens inhabited a planet of great antiquity.[11]

All of these early research findings on geology, the age of the earth, and early notions on evolution all came together with Charles Darwin’s data collection. Subsequent publication of his book on evolution directed everyone’s attention to answering the two most critical questions of that era: Who are we, and where do we come from? These questions continue to be asked today.

Who Are We? Where do we come from?

These are the most critical questions of this or any other era. Mankind has been on this earth only a short time when one considers that the age of the earth is estimated to be 4.6 billion years old. Homo sapiens have been on this earth perhaps only 1½ million to 2 million years. That is a drop in the bucket of geological time. At the top it is important to know that humans share their genetic material with every other creature on earth going back to the very beginning when life first began.

However, the degree of closeness to other species depends upon how much genetic material we share. Consequently, for mankind, we share the greatest amount of genetic material with the great apes. The subfamily Homininae is divided into gorillas (Gorillini) and (Hominini) which are chimpanzees and humans. Homininae is a subfamily of Hominidae, including Homo sapiens and some extinct relatives, as well as the gorillas and the chimpanzees.[12]

They comprise all those hominids, such as Australopithecus, which arose after the split from the other great apes. Humans and gorillas and chimpanzees are all closely related. “As of 1980, the family Hominidae contained only humans, with the great apes in the family Pongidae. Discoveries led to a revision of classification, with the great apes (now Pongidae) and humans (Homininae) united in Hominidae.”[13] The term “Great Apes” refers to gorillas, chimpanzees, gibbons, and orangutans.

But discoveries indicated that gorillas and chimpanzee are more closely related to humans than they are to orangutans, hence their current placement in Homininae. Evolution is not necessarily progress. It is fortuitous and highly random. “Humans arose, rather, as a fortuitous and contingent outcome of thousands of linked events, any one of which could have occurred differently and sent history on an alternate pathway that would not have led to consciousness.”[14]

Stephen J. Gould cited four examples of this. They included: (1) If our inconspicuous and fragile lineage had not been among the few survivors of the initial radiation of multicellular animal life in the Cambrian explosion 530 million years ago, then no vertebrates would have inhabited the earth at all,[15] (2) If a small and unpromising group of lobe-finned fishes had not evolved fin bones with a strong central axis capable of bearing weight on land, then vertebrates might never have become terrestrial,[16](3) If a large extraterrestrial body had not struck the earth 65 million years ago, then dinosaurs would still be dominant and mammals insignificant (the situation that had prevailed for 100 million years previously),[17] and (4) If a small lineage of primates had not evolved upright posture on the drying African savannas just two to four million years ago, then our ancestry might have ended in a line of apes. That, like the chimpanzees and gorillas today, would have become ecologically marginal and probably doomed to extinction despite their remarkable behavioral complexity.[18]  Said again, our survival to where we are today was accidental, random, and based on a non-purposeful journey that was indeed perilous.

In terms of geological time, the amount of time Homo sapiens have been on earth is very short. What most people believe about evolution is that one cell living organisms followed a linear path to human complexity. But that viewpoint is incorrect. Evolution is best thought of as a tree with many radiating branches. Just as new species evolve, so do new branches emerge on a tree. Mankind evolved on a very recent branch.

Earlier Branches of Evolution

When the dinosaurs died out 65 million years ago it paved the way for mammals. Mammals are vertebrates. They have a backbone which encloses a sheath of nerves that leads in turn to a brain in a box or skull. They also have four limbs and special pentadactyl ends to those limbs (5 fingers and toes).[19] Mankind’s descent came up this branch of the tree.

The Eocene is the second epoch of the Cenozoic. The Eocene started approximately 56 million years ago, and lasted approximately 20 million years. During this epoch the first primates evolved.[20] By the end of this epoch most of the modern order of mammals had evolved. The Eocene is regarded as the warmest epoch of the Tertiary. Increasingly these warm conditions at the start of the Eocene caused the extinction of some prominent species of the prior epoch. But, overall, land mammals flourished and new species diversified and adapted. In particular, mammals with a keen sense of smell thrived in the dense forests and warm conditions.[21]

Primates from this epoch evolved many interesting features including grasping hands and feet that had nails rather than claws. “One of the most influential developments is the primate reliance on sight rather than smell that evolved around fifty-five million years ago. These primates were abundant on several continents, but were eventually absent from South America and Antarctica. Both of the modern suborders of primates originated in the Eocene, or possibly in the late Paleocene.

One suborder includes Lemers and Lorises (Stropsirhines). The descendents of these species still thrive in the tropical forests of Africa, Madagascar, and Asia. The other suborder (Haplorhines) includes the higher primates, such as the monkeys, apes and humans, which are often referred to as ‘anthropoid primates.’”[22]

Humans, apes, and monkeys are the living descendants of the first anthropoids, which evolved in the Eocene.[23] “Anthropoids diversified greatly during the late Eocene and the Oligocene. The boundary between the two epochs is marked by a 10-million-year-long fluctuation in climate and environment.”[24] “One of the environmental results was the shrinking of the subtropical and tropical forests. These forests, which had fostered the adaptive radiation of species, started their retreat to the modern tropical zones.”[25]

“As a result of these changes, grasses evolved, which greatly influenced the evolutionary history of land mammals. At the end of the Eocene the primates of the Northern Hemisphere nearly disappeared; many primate species took refuge in Africa and Arabia. It was in this refuge area where the ancestors of Old World monkeys and apes evolved in the Oligocene.”[26]

“Comparisons of DNA show that our closest living relatives are the ape species of Africa, and most studies by geneticists show that chimpanzees and humans are more closely related to each other than either is to gorillas. However, it must be emphasized that humans did not evolve from living chimpanzees. Rather, our species and chimpanzees are both the descendants of a common ancestor that was distinct from the Africa apes.

This common ancestor was thought to have existed in the Pliocene between 5 and 8 million years ago, based on the estimated rates of genetic change. Both of our species have since undergone 5 to 8 million years of evolution after the split of the two lineages. Using the fossil record, scientists have attempted to reconstruct the evolution from the common ancestor through the series of early human species to today’s modern human species.”[27]

Paleontology comes of Age

In terms of scientific classification, where are we as a species? Based on the Linnaeus system the Genus Homo:[28]

Kingdom:  Animalia

Phylum:     Chordata

Class:         Mammalia

Order:        Primates

Family:      Hominidae

Subfamily: Homininae

Genus:        Homo

Homo is the genus that includes modern humans and their close relatives. The genus is estimated to be between 1.5 and 2.5 million years old. All species except Homo sapiens are extinct. Homo neanderthalensis, died out 30,000 years ago, while recent evidence suggests that Homo floresiensis lived as recently as 12,000 years ago. The word Homo is Latin for “man,” in the original sense of “human being.”

The first major discovery began with the finding of Neanderthal man in 1856. The idea that humans are similar to certain great apes had been obvious to people for some time; however, not until the idea of biological evolution of species in general, it was not legitimized until after Charles Darwin published On the Origin of Species in 1859. Although Darwin’s first book did not address the specific question of human evolution his next book, Descent of Man, did.[29]

Since the time of Carolus Linnaeus, the great apes were considered the closest relatives of human beings, based on morphological similarity. In the 19th Century it was speculated that our closest living relatives were the chimpanzees and gorillas, and based on the natural range of these creatures, it was surmised humans share a common ancestor with African apes and that fossils of these ancestors would ultimately be found in Africa.

Many of the ideas of Darwin were considered controversial. Even some of his supporters like Alfred Russell Wallace and Charles Lyell didn’t want to accept the idea that human beings could have evolved their apparently boundless mental capacities and moral sensibilities through natural selection.

Human Evolution is the Story

Evolutionary science is as much about the people who make discoveries as about the famous discoveries themselves. Nowhere is this true than when describing the history of discovery since the 19th Century. Those readers interested in details of the timeframe for evolution since the beginning of the earth please review the detail in Appendix A. I’d like to conclude Part I of this blog with the life of Charles Darwin.

 

The Life of Charles Darwin

 

One of the greatest scientists of the 19th Century was Charles Darwin. In fact a few years back the Science Channel produced a program that selected by scholars, researchers, and scientists the top 100 greatest scientific discoveries of all time. Through the help of Discover Magazine they decided to survey the public’s beliefs regarding ranking all 100 discoveries. They showcased in a program the results of the survey for the top 10 greatest scientific discoveries from among the 100. Although Albert Einstein held two positions among the top ten discoveries, it was the work of the first evolutionary biologist, Charles Darwin, which the public ranked #1 as the greatest scientific discovery of all time.

The influence of Darwin’s Theory of Evolution forever altered the sciences, religion and human culture as well. Many scientists today collect and analyze data. But in his era Charles Darwin was a “data collector extraordinaire.”  He authored as a naturalist many scientific books, but his work on the theory of evolution and natural selection was best described in Origin of Species (1859) and the Descent of Man (1871). Darwin did not rush to judgment on his research findings. He took more than 20 years following the conclusion of his travels on the H.M.S. Beagle before he published his works on evolution.

Like many scientists before him Darwin believed that all life on earth evolved over millions of years from a few common ancestors. Upon his return from the 5-year voyage on the Beagle he conducted thorough research of his notes and specimens. Based on his research findings he concluded that:

(1) Evolution did occur

(2) Evolutionary change was gradual, requiring millions of years

(3) The primary mechanism for evolution was a process called natural selection

(4) The millions of species alive today arose from a single original life form through a branching process called specialization.

 

Who really was Charles Darwin? Who was the man who caused a firestorm of controversy and turned religion into a train wreck, up-side-down and on its side? Charles Darwin was a mild mannered man who once studied for the ministry and never wanted to bring down the controversy upon him. But even after 150+ years since his publication, his work is still attacked and maligned. In the hiatus between Darwin’s time and now, scientific research from paleontology, genetics, geology, zoology, botany, biology, chemistry, ecology, astrophysics, anthropology, and various subfields within these sciences have all found either correlative, corroborating evidence and, at times,  overwhelmingly direct scientific proof for Darwin’s Theory of Evolution and natural selection.

Because of the data obtained, and the huge scientific findings in support of it, the late scientist Carl Sagan concluded in his special series Cosmos that evolution isn’t just a theory–it is fact. The scientific consensus building has been profound. The pieces to the puzzle of evolution (and there have been thousands upon thousands of them over the last 150+ years) has produced a picture that clearly shows the processes of evolution at work among all species, living and dead.

Charles Robert Darwin was born on February 12, 1809 in Shrewbury, England.[30] He was born into the family of Robert Waring Darwin as their second son of five children. His mother was the former Susannah Wedgwood. She died when he was only eight years old, and he was raised by his older sister. The young Charles nonetheless was very fortunate economically. His father was a doctor and his mother was the daughter of Josiah Wedgwood, who was a wealthy founder of pottery works. His grandfather was a scientist who wrote Zoonomia, or The Laws of Organic Life. Because of his background he was not expected to work for a living but use his education and talents in the professions.[31]

Early on it was clear choosing a career would prove difficult. Charles Darwin tried medicine, like his father. He studied at Edinburgh but hated it. He watched surgery, but in those days (1820s) anesthesia didn’t exist. Charles Darwin’s observation of such surgery horrified and repulsed him. It was clear to Charles and his family that medicine was not going to be his career. In 1828 he went to Cambridge (Christ’s Church) to train for the ministry.[32]

At Cambridge Charles became friends with a professor, John Stevens Henslow where he developed a great interest in zoology and geography. It was here that he began to love collecting plants, insects, and geological specimens. Charles Darwin knew that the backbone and cornerstone of science was first-and-most observation coupled with data collection.

It was professor Henslow who arranged for Charles Darwin to be invited to go on a surveying expedition on the HMS Beagle.[33] The ship’s captain needed a naturalist to serve onboard. The Beagle had been outfitted by the admiralty for an extended voyage to the South Seas. Their intention was to survey coastal South America. The ship was also equipped for ‘scientific purposes.’ Captain FitzRoy was only twenty-six and the admiralty thought he needed a young companion who could relieve the isolation of command, and share the captain’s table as messmate. Although Charles Darwin was not yet a ‘finished naturalist’ Henslow thought he was a good choice to make the voyage.

In South America Darwin found fossils of extinct animals that were similar to modern species. He studied plants and animals everywhere he went, always collecting specimens. On the Galapagos Islands in the Pacific Ocean he found many variations among plants and animals of the same general type as those in South America. It was described in the last chapter that one outcome from macroevolution was speciation.

Darwin was amazed by the diversity of finches on the Galapagos Islands. Each species of finch had a unique beak tailored to its specific diet. He theorized that the dozen or so variations arose from a single ancestor whose descendants spread out and adapted to different conditions, eventually evolving into separate species. He found different types of species of finches falling into three different groups: (1) Seed eaters who were members of a ground-feeding group who had strong bills that were adapted to crushing seeds, (2) Insect eaters whose larger beak species caught big bugs while smaller beak birds focused on little insects, and (3) the Bud eaters who used their stubby beak to grasp buds, blossoms and fruits (vegetarian finch).[34]

The voyage was originally set for 2 years but was extended. The entire voyage of the HMS Beagle took five years and lasted from 1831 to 1836. Besides South America and southern islands, Australia was added to the voyage. On the Beagle he served as a geologist, botanist, zoologist, and general man of science.[35]

Darwin’s research had a tremendous impact on religious thought, and still does to the present day. Many people strongly oppose the idea of evolution (although unable to refute it on scientific grounds) do so because it conflicts with their religious convictions. Darwin, a reserved, thorough, and hard-working scholar and scientist avoided talking about the theological aspects of evolutionary theory.

Post Script

Physiological evolution begins to now have a new partner–cultural evolution, including the appearance of ancient polytheistic and pagan cults and (animism and shamanism) type religions. Some of these developments took place during the last 190,000 years of the previous epoch, the Pleistocene. But the Holocene witnessed the culmination of the new one god concept on the block–monotheism, first Yahwey, and then Second Isiah’s pronouncement of a universal God. These extensions of the primitive cults and religions into monotheism didn’t occur or surface until approximately 2000 B.C.E. Atheism, the newest kid on the block of culture, didn’t occur until The Age of Enlightenment. And, all cultural evolution, like human physical evolution, continues to expand and evolve.

Appendix A

Geological Timeline

Geological time is divided into eons, followed by eras. This is followed by periods within eras, then finally epochs within periods. The first eon is known as the Hadean Eon at 4.5 to 3.9 billion years ago. The Archean Eon lasted from 3.9 billion to 2.5 billion years ago. The Proterozoic eon lasted from 2.5 billion to 540 million years ago. Collectively, these three eons represent Precambrian Time.[36]

Definitions of Terms[37]:

EON – Two or more geological eras form an eon, which is the largest division of geologic time, lasting many hundreds of millions of years.

ERA – Two or more geologic periods comprise an era, which is hundreds of millions of years in duration.

PERIOD – The period is the basic unit of geological time in which a single rock system is formed, lasting tens of millions of years.

EPOCH – An epoch is a division of a geologic period; it is the smallest division of geologic time, lasting several million years.

AGE – An age is a unit of geological time which is distinguished by some feature (like an Ice Age). An age is shorter than epoch, usually lasting a few million years to about a hundred million years.

What do scientists know about each of the geological time frames (eons, eras, periods, and epochs that can help one understand how life began on earth? During the Hadean Eon (4.5-3.9 billion years ago) the Earth formed a solid planet. There is no evidence of life on earth at that time.[38]   During the Archean Eon (3.2-2.5 billion years ago) the Earth’s permanent crust began to form. Vast amounts of metallic minerals were deposited. The oceans and atmosphere resulted from volcanic out-gassing. The earliest life forms evolved in the seas. They are called prokaryotes. These are single-celled organisms with no nucleus–cyanobacteria (blue-green algae). The earliest bacteria obtained energy through chemosynthesis (ingestion of organic molecules).[39]

During the Proterozoic Eon (2.5 billion years ago–540 million years ago) plate tectonics began to slow to the same rate as today. Large mountain chains began to form as continents collided. Quartz-rich sandstones, shales, and limestones were deposited over the continents. Oxygen levels increased as life on earth developed the ability to obtain energy through photosynthesis.[40]

Soon Eukaryotes, which are single-celled organisms with a nucleus, began to evolve. During this eon more advanced forms of algae and a wide variety of protozoa evolved. Eukaryotes reproduced sexually, which makes genetic diversity possible. This led to their ability to adapt and to survive environmental changes. Multi-celled, soft bodied marine organisms (metazoans) evolved.[41] Sexual reproduction evolves and leads to an explosion in the rate of evolution. While most life occurs in oceans and lakes, some cyanobacteria may already have lived in moist soil by this time.

At 600 mya sponges (Pozifere), jellyfish (Cnidaria), flat worms Platyhelminthes and other multicelluar animals appear in the oceans. Cnidaria and Ctenophora are among the earliest creatures to have neurons, in the form of a single net–no brain or nervous system.

From 545 million years ago to the present geologic time is divided into three eras: Paleozoic, Mesozoic, and Cenozoic. These are known as the Age of Invertebrates, Age of Reptiles, and Age of Mammals, respectively.[42]

 

OVERVIEW OF PALEOZOIC ERA

 

Paleozoic Era (Ancient Life)-Age of Invertebrates

Cambrian Period                                                                            545-505 mya

Ordovician Period                                                                          505-438

Silurian Period                                                                               438-410

Devonian Period                                                                            410-355

Carboniferous (Mississippian/Pennsylvanian) Period          355-290

Permian Period                                                                              290-250

OVERVIEW OF MESOZOIC ERA

 

Mesozoic Era (Middle Life)-The Age of Reptiles

Triassic Period                                                                                 250-205

Jurassic Period                                                                                 205-135

Cretaceous Period                                                                            135-65

OVERVIEW OF CENOZOIC ERA

 

Cenozoic Era (Recent Life)-The Age of Mammals

Tertiary Period

Paleocene Epoch                                     65-55

Eocene Epoch                                          55-38

Oligocene Epoch                                     38-26

Miocene Epoch                                        26-6

Pliocene Epoch                                         6-1.8

Quarternary Period

Pleistocene Epoch                                 1.8-.01

(Lower Paleolithic)                               0.1-.25

(Middle Paleolithic)                             .25-.06

(Upper Paleolithic)                              .06-.01

Holocene Epoch                                   .01-0

PALEOZOIC ERA

 

The Paleozoic Era includes six periods. These include the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.[43]

Cambrian Period

 

During the Cambrian sedimentary rocks such as sandstone, shales, limestone, conglomerate formed in shallow seas over the continents. During the period (545-505 million years ago) collisions of the earth’s plates gave rise to a super continent Gondwana.  This is composed of South America, Africa, Antarctica, and Western Australia as well as peninsular India and parts of Arabia.[44]

The global climate is generally mild. Marine metazoans with mineralized skeletons such as sponges, bryozoans, corals, brachiopods, mollusks, anthropods, and echinoderms flourish. Plant life is limited to marine algae; however, one group of anthropods, the trilobites, is particularly dominant in the seas.[45]

Ordovician Period

 

During the Ordovician Period (505-438 million years ago) North America, Europe and Africa merge. Shallow seas cover most of North America at the beginning of the period, then recede, leaving a thick layer of limestone.  Later in the period, the seas recover North America, depositing quartz, sandstones, and more limestone.[46]   As far as life is concerned invertebrates are still the dominant form of life on earth. Corals, crinoids, and small clams evolve, as well as the first early vertebrates–primitive fish with bony armor plates. Late in the Ordovician Period, mass extinction of marine life occurs, opening niches for beneath (bottom-dwelling) and planktonic (floating, swimming) organisms.[47]

Devonian Period

The Devonian period is often referred to as “The Age of Fish.”  Various forms of fish dominated the seas including sharks, lungfish and armored fish. Europe and North America merge, forming the northern part of the ancestral Appalachian mountain range.

Europe and North America strattle the equator, while Africa and South America are positioned over the South Pole.[48]  The climate during the Devonian is generally warm and moist. Ammonites evolved from Nautiloids and became one of the invertebrate forms. As ozone forms in the atmosphere, the first air-breathing anthropods–spiders and mites–venture onto the land. Amphibians evolve and plant life, including lowland forests of giant Psilphyta plants, develop and spread over the planet.[49]

Carboniferous Period

 

During the Carboniferous Period (355-290 million years ago) two major land masses form: Laurasia (North America, Greenland, northern Europe, and Scandinavia) to the north of the equator, and Gondwana (South America, Africa, peninsular India, Australia, and Antarctica) to the south. Collisions between Laurasia and Gondwana occur and form major mountain ranges. Coal-forming sediments are laid down in vast swamps.[50]   Global climatic changes occur changing from warm and wet to cooler and drier. The result is a long interval of glaciation. Ammonites were common in open marine waters. (Cordates), and ferns were common. Insects, such as cockroaches flourish. More fish and reptiles evolve. Land environments are dominated by plants–from small shrubbery growths to tall trees.[51]

Permian Period  

 

During the Permian Period (290-250 million years ago) Pangaea is formed. It is a single super continent that forms as a result of Earth’s landmasses colliding and merging. Pangaea extends beyond all climatic zones and nearly from one pole to the other.  Pangaea is surrounded by an immense world ocean. During the Permian, extensive glaciations persist in what are now India, Australia and Antarctica.[52]

Hot, dry conditions prevail on the super continent of Pangaea, and desserts become widespread.  At the beginning of the Permian invertebrate marine life is rich. Toward the end of this period, mass extinctions occur among large groups of corals, bryozoans, and other invertebrates. The last of the trilobites become extinct. Life on the terrestrial environment changes as insects evolve into their modern form as dragonflies and beetles appear.[53]   Amphibians decline in number, but reptiles undergo an evolutionary development of carnivorous and herbivorous land and aquatic forms. In terms of plant life ferns and conifers persist in the cooler air. [54]

MESOZOIC ERA

 

The Mesozoic is known as the Age of Reptiles. It consists of three periods known as the Triassic, Jurassic, and Cretaceous.[55]

Triassic Period

 

The Triassic Period occurred between (250-205 million years ago). Pangaea covers nearly a quarter of the earth’s surface. The Triassic, unlike earlier periods, is marked by few geological events. Toward the end of the Triassic Period, continent rifting begins to break apart the super continent.[56]   The general climate of the Triassic is warm, becoming semiarid to arid. As most children and adults are fascinated by what happens during the Triassic i.e., early dinosaurs evolve. Many are fast, bipedal, and relatively small.[57]

Jurassic Period

 

The Jurassic Period lasted from 205-135 million years ago. During this period the Atlantic Ocean begins to form as North America separates from Africa and South America. Tectonic plate subduction along western North America causes the Earth’s crust to fold, and mountains form in the western part of the continent.[58]

During this period reptiles adapt to life in the sea, the air, and on land. On land dinosaurs are the dominant reptile. Mammals were small, shrew-like animals. Archaeopteryx, the first bird, appears. Early amphibians extinct by the late Triassic are succeeded by the first frogs, toads, and salamanders. Plant forms are dominated by the cycads and cycadeoides. Conifers and gingkoes become widespread.[59]

Cretaceous Period

 

The Cretaceous Period was from 135 to 65 million years ago. The continents, while not in their current position on earth, are shaped much as they are today. South America and Africa separate, and the North Atlantic Ocean widens. A circu-equatorial sea–Tethys-forms between the Northern and Southern Hemisphere continents. The westward movement of North America forms the ancestral Rocky Mountains and the ancestral Sierra Nevada. Sea levels rise, submerging about 30% of the Earth’s present land surfaces. The global climate is generally warm. The poles are free of ice.[60]

Dinosaurs and other large reptiles peak as the dominant vertebrate life form on earth. Dinosaurs extend their range throughout every continent. Horned dinosaurs are common, as armored ankylosaurs and spiky nodosaurs. In the shallow seas, invertebrates live in great diversity. Ammonites are a dominant group. Gastropods, corals, sea urchins flourish.[61] The early flowering plants (angiosperms, modern trees) and many modern types of insects evolve.

Near the end of the Cretaceous Period, several mass extinctions occur of five major reptilian groups.  These include the dinosaurs, pterosaurs, ichthyosaurs, pleisosaurs, and mosasaurs. Extinctions also occurred among ammonites, corals, and other invertebrates.[62]

CENTOZOIC ERA

(Recent Life)

 

The Cenozoic Era is also known as The Age of Mammals.  There are two periods: Tertiary and the Quaternary. During the Tertiary there were five Epochs: Paleocene, Eocene, Oligocene, Miocene, and Pliocene. [63]

 

Paleocene Epoch

 

During the Paleocene Epoch (65-55 million years ago) the vast inland seas of the Cretaceous Period dry up, exposing large land areas of North America and Eurasia. Australia begins to separate from Antarctica, and Greenland splits from North America. A remnant Tethys Sea persists in the equatorial region. Mammals diversify and spread into all major environments. Placental mammals eventually dominate the land, and many differentiated forms evolve, including early ungulates (hoofed animals), primates, rodents and carnivores.[64]

Eocene Epoch

 

During the Eocene Epoch (55-38 million years ago) plate tectonics and volcanic activity form the Rockies in western North America. Erosion fills basins, laying bauxite deposits in western North America. Continental collisions between India and Asia culminate in the Alpine-Himalayan mountain system.[65] Antarctica and Australia separate and drift apart. The climate is subtropical and moist throughout North America and Europe. Early forms of horse, rhinoceros, camel, and other modern groups such as bats evolve in Europe and North America. Creodonts and ruminant ungulates, a strange carnivorous group, evolve.  Cetaceans–baleen whales, toothed whales, dolphins evolve from terrestrial meat eating ungulates. Sirenians (dugongs and manatees) first evolve in the shallow Tethys Sea.[66]

Oligocene Epoch

 

During the Oligocene Epoch (38-26 million years ago) tectonic plate movement is still very dynamic. Africa and Europe squeeze together, closing the Tethys Sea and leaving as a remnant the Mediterranean Sea. Volcanism and fragmentation of western North America is associated with the emplacement of major ore deposits. The climate was generally temperate. Glaciation begins in Antarctica.

Modern mammals become the dominant vertebrate life forms including horses, pigs, true carnivores, rhinoceroses, elephants, and camels. Oreodonts diversify in North America. Early primates appear in North America and early apes appear in Egypt. Many archaic mammals become extinct. The world’s oceans teem with more vertebrate life. Grasslands expand, and forest regions diminish.[67]

Miocene Epoch

 

During the Miocene Epoch (26-6 million years ago) modern ocean currents are essentially established. A drop in sea level isolates and dries up the Mediterranean Sea, leaving evaporite deposits on its floor. The climate is generally cooler than the Oligocene Epoch.[68]  A cold transantarctic ocean current isolates the waters around Antarctica, and the continent becomes permanently frozen. The many forms of mammals are essentially modern, and almost half of placental mammal families are present, as well as the early seals and walruses. Many modern birds such as herons, rails, ducks, eagles, hawks, crows, sparrows, are present in Europe and Asia.[69]

 

Higher primates undergo substantial evolution and advanced primates, including apes, are present in Southern Europe and Asia. Carcharocles Magalodon, the largest predatory shark ever to have lived, inhabits the seas. The coasts are submerged and kelp forests appear. On land, spreading grasslands replace forests over large areas on several continents.[70]

Pliocene Epoch

During the Pliocene Epoch (6 to 1.8 million years ago) the Isthmus of Panama changes ocean circulation patterns, and leads to the formation of an Arctic ice cap. Plate tectonic interactions result in the uplift of the Sierra Nevada, and formation of the Cascade Range, and onset of strike-slip faulting of the San Andreas Fault. Subduction of the Pacific Plate elevates the Sierra Nevada and the volcanic Cascade Range.[71]

In Europe, the Alps continue to rise. The global climates become cooler and drier. During this epoch camels and horses are abundant throughout North America. Proud Sloths also appear. In general, Pliocene mammals are larger than those of earlier epochs. Primates continue to evolve, and the Australopithecines–antecedents to Homo sapiens–develop late in the Pliocene in Africa. In North America, rhinoceroses become extinct.[72]

QUARTERNARY PERIOD: Pleistocene and Holocene Epochs

 

Pleistocene Epoch

 

The Pleistocene Epoch occurred between 1.8 million and 10,000 years ago. This epoch is best known as the “Great Ice Age.” Ice sheets and other glaciers encroach and retreat during four or five separate glacial periods. At its peak, as much as 30% of the Earth’s surface is covered by glaciers, and parts of the northern oceans are frozen. The movement of the glaciers alters the landscape. Lakes, such as the Great Lakes in North America are formed by ice retreats.[73] The oldest species of Homo–Homo habilis–evolves.

The flora and fauna of the regions not covered by ice were essentially the same as those of the earlier Pliocene Epoch. Mammal evolution includes the development of large forms: wooly mammoth, wooly rhinoceros, musk ox, moose, reindeer, elephant, mastadon, bison, and ground sloth. In the Americas, large mammals, such as horses, camels, mammoths, mastadons, saber-toothed cats, and ground sloths, are entirely extinct by the end of this epoch.[74]

Holocene Epoch

 

During the Holocene Epoch (10,000 years ago to the present) it is an interval between glacial incursions that were typical of the Pleistocene Epoch, and therefore, not a separate epoch in itself. However, it is a period marked by the presence and influence of Homo sapiens. During this time, the glaciers retreat, the climate warms, and deserts form in some areas. Human civilization develops. Activities of mankind begin to affect world climates. The extinction of other species continues.[75]


[1] Richard Leakey and Roger Lewin, Origins , (E.P. Dutton: New York, 1977), 28

[2] Ibid.

[3] Ibid, 25

[4] Ibid.

[5] Ibid.

[6] Ibid.

[7] Ibid.

[8] Ibid, 26, 28

[9] Ibid, 25

[10] Ibid.

[11] Ibid, 24

[12] “Homininae,” Wikipedia, the free encyclopedia [online];accessed 26 Jun. 2005;available from  http://en.wikipedia.org/wiki/Hominine.

[13] Ibid.

[14] Stephen Jay Gould, “The Evolution of Life on Earth,” [online]; accessed 14 Jan. 2006; available from http://www.geocities.com/CapeCanaveral/Lab/2948/gould.html.

[15] Ibid.

[16] Ibid.

[17] Ibid.

[18] Ibid.

[19] “The Evolution of Mammals,” [online]; accessed 1 Jul. 2005; available from http://www.earthlife.net/mammals/evolution.html.

[20] “Geologic Time: The Eocene,” [online]; accessed 1 Apr. 2005; available from http://www.mnh.si.edu/anthro/humanorigins/faq/gt/cenozoic/eocene.htm.

[21] Ibid.

[22] Ibid.

[23] Ibid.

[24] Ibid.

[25] Ibid.

[26] Ibid.

[27] “Human Ancestors Hall: Our Primate Origins,” [online]; accessed 1 Apr. 2005; available from http://www.mnh.si.edu/anthro/humanorigins/ha/primate.html.

[28] “Homo (genus)” Wikipedia, the free encyclopedia, [online]; available from http://en.wikipedia.org/wiki/Homo_(genus).

[29] “Human Evolution,” Wikipedia, the free encyclopedia, [online]; accessed 19 Jan. 2006; available from http://en.wikipedia.org/wiki/Human_evolution.

[30] “Biography of Charles Darwin,” [online]; accessed 8 Nov. 2004; available from  http://www.lib.virginia.edu/science/parshall/darwin.html.

[31] “Charles (Robert) Darwin (1809-1882),” [online]; accessed 12 Feb. 2005; available from  http://www.kirjasto.sci.fi/darwin.htm.

[32] “The Scientists: Charles Darwin,” [online];accessed 12 Feb. 2005;available from http://www.plupete.com/Literature/Biographies/Science/Darwin.htm.

[33] Ibid.

[34] Jerry Adler, “Charles Darwin–—Evolution of a Scientist,” Newsweek, 28 Nov. 2005, 54-55

[35] Ibid.

[36] “San Diego Natural History Museum–—Geologic Time Line,” [online]; accessed 2 Aug. 2005; available from  http://www.sdnhm.org/fieldguide/fossils/timeline.html.

[37] “Geologic Time Periods,” [online]; accessed 2 Aug. 2005;available from http://www.enchantedlearning.com/subjects/dinosaurs/glossary/Geologictimeperiods.shtml.

[38] Ibid.

[39] Ibid.

[40] Ibid.

[41] Ibid.

[42] Ibid.

[43] Ibid.

[44] Ibid.

[45] Ibid.

[46] Ibid.

[47] Ibid.

[48] Ibid.

[49] Ibid.

[50] Ibid.

[51] Ibid.

[52] Ibid.

[53] Ibid.

[54] Ibid.

[55] Ibid.

[56] Ibid.

[57] Ibid.

[58] Ibid.

[59] Ibid.

[60] Ibid.

[61] Ibid.

[62] Ibid.

[63] Ibid.

[64] Ibid.

[65] Ibid.

[66] Ibid.

[67] Ibid.

[68] Ibid.

[69] Ibid.

[70] Ibid.

[71] Ibid.

[72] Ibid.

[73] Ibid.

[74] Ibid.

[75] Ibid.

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