human life and evolution

7/31/2019 Human Life and Evolution

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The basic definition of evolution is a change in the gene pool of a population of organisms

over time. All of evolution is based on genetic change. While scientists still have a lot to

learn about the workings of genetic code science has built up a large volume of knowledge

about how the genetic material of living organisms works. While there are a lot of details

still to be learned we have a pretty good understanding of what DNA does in general and,equally important to evolution, how DNA changes.

The foundation of evolution is not just working DNA but changing DNA. The primary

mechanism of significant change in DNA ismutation. That DNA is subject to mutation is a

fact. This has been directly observed. In addition, many of the mechanisms of mutation are

understood including mutations that can lead to drastic changes in an organism. So, there

are understood mechanisms by which change can be affected.

All living organisms have in common that they posses genetic material that is subject to

these mechanisms of change. What's more, we understand that the characteristics an

organism possesses are determined by its genetic code. Its genes are largely what makes

an organism what it is. These facts, that 1) DNA determines the nature of an organism and

that 2) there are mechanisms through which DNA can be modified, are the basis of

evolution. It is through these facts that evolution happens.

Now, given that DNA makes the organism what it is and DNA is subject to change it seems

reasonable that, through successive changes that are passed to successive offspring that

large-scale changes in genetic code can take place over time. The only way this would not

make sense is if some mechanism were identified which would prevent such accumulation of

changes from happening. No such mechanism is known.

So, we have a mechanism for encoding the characteristics of a life form, a mechanism for

this code to be changed, no known mechanism to definitively limit the amount of changes

that can take place, and lots of time for changes to take place. The very basis of evolution,

genetics, supports the idea that common descent is at least possible.

I cannot do justice to the subject of evolutionary genetics in this article and I have had to

make very broad, sweeping statements to keep to a reasonable scope. To really understand

these ideas you need to do some reading on genetics. The important aspect to keep in mind

is that genetic change is possible and there is no known mechanism that would prevent

successive changes from accumulating over time resulting in large-scale changes.

Where Did We Come From? Where Did We Go?Zuni legend tells us that humankind evolved from amphibious forms in the belly of Mother Earth, after shemated with Father Sky. Peoples all over the world have developed origin stories to explain why we'rehere, who we are, and where we're going. Now, genetic researchers are beginning to write a new accountof our origins, through the study of DNA. This program tells us how DNA may have come into existenceand how genetic studies have contributed to evolution theories so far. And it explores the controversiesraised by genetic research.
http://atheism.about.com/gi/dynamic/offsite.htm?site=http://www.talkorigins.org/faqs/mutations.htmlhttp://atheism.about.com/gi/dynamic/offsite.htm?site=http://www.talkorigins.org/faqs/mutations.htmlhttp://atheism.about.com/gi/dynamic/offsite.htm?site=http://www.talkorigins.org/faqs/mutations.htmlhttp://atheism.about.com/gi/dynamic/offsite.htm?site=http://www.talkorigins.org/faqs/mutations.html


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Our DNA - our collection of genes - is the essential mechanism of evolution. Human DNA is 98 percentthe same as the DNA of chimpanzees; but it's also 70 percent the same as the DNA of yeast. So whatmakes humans uniquely different from chimpanzees or yeast? One thing might be the way in which wecreated language and culture, and how we developed these things in different ways all over the earth. Inother words, genetic studies can tell us how human migration occurred - when we appeared, what wewere like, and where we went.By gathering genetic information from isolated populations, the Human Genome Diversity Project (HGDP)aims to decipher those mysteries. Scientists hope that this data, in combination with traditionalarchaeological and linguistic research, can tell us a great deal more about our past and our relationships.But there is strong opposition from people who see the HGDP as little more than highly unethicalopportunism: "colonialism at the molecular level."Hear both sides of the debate, and find out from the researchers themselves how they think the storybegins. We'll have to stay tuned for the ending. >>

The origins of the present-day populations can be traced by their genes, although the story is incomplete. A. Homo sapiens sapiensis thought to have evolved in Africa some 200,000 years ago. By100,000 years ago, the populations were already diversified in Africa. A small group crossed intothe Middle East at Suez and spread throughout Asia and Europe, reaching Australia some 40,000years ago and America some 20,000 years ago (highly disputed date). B. Mitochondrial DNA is particularly interesting, since it is maternally inherited and therefore doesnot recombine during meiosis. There are many versions of mtDNA today, all of which descendedfrom a single female who lived some 200,000 years ago. There were many other femaleancestors, but their mtDNA eventually was lost. Many think that female lived in Africa (thoughsome argue for Asia).C. The Y chromosome also does not recombine except for the pseudoautosomal region. Diversityin the Y chromosome is generated only by mutations, which accumulate over time. It is

theoretically possible to identify a "founding" Y chromosome, just as in the case of mitochondria.The date given for such a founding father is of the same order of magnitude as mitochondria,some 200,000 years ago. Both dates are subject to large error because of the assumptions ofrate of accumulation of mutations.D. The virtual absence of polymorphic markers on the Y chromosomes of Finns indicates a verysmall population bottleneck in the past. Analysis of mitochondrial variation in this group suggeststhat the bottleneck occurred 4000 years ago, at about the time agriculture is known to havereached Finland.E. Cultural events may also influence the gene pool of populations. For example, populations thatare better able to exploit resources may have greater biological fitness and therefore contributedisproportionately to the gene pool. This is illustrated by the development of agriculture, whichcan support more people than the hunter-gatherer cultures. Present-day allele frequencies inEurope reflect the spread of agriculture from the Middle East.F. Allele frequencies in present-day populations reflect their genetic origins and the relationshipsof the populations to each other.


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1. The African-American population is an African-European hybrid, with about 70% of thegenes having come from Africa and 30% from Europe. However, some populations (e.g.Charleston, SC, and the Sea Islands of Georgia) have over 90% African genes.2. Polynesians came from mainland Asia in fairly recent times. This is in contrast to thetheory that they came from mainland South America and are descendants of American

Indians.

3. The American Indians came from Asia and appear to be most closely related toMongolians rather than to the groups that currently occupy northeast Asia. The Hispanicpopulations of Texas have a high frequency of alleles that came from American Indianancestry and hence Asia.4. By analyzing simultaneously the variations at many loci, it is possible to constructphylogenetic trees that relate the many populations of the world.

Themes>Science>Life Sciences>Physical Anthropology>Human Genetic

Evolution> Early Models of Evolution

The Babylonian and Egyptian creation stories both include the idea of a primordial

sea from which the Earth and life arose. These stories often included the idea of

humans being born from a goddess. The primeval Chaos was a god who created

people and nature and the other gods.

In most Mediterranean civilizations, the widely-accepted theory of the universe hadthe Earth as a flat disk floating on the world ocean which surrounded it. Below waswater (forever?) and above was sky, the abode of the gods. The land portionincluded all that was known at the time, basically an area around the MediterraneanSea. Down (somewhere under the world ocean?) was the underworld. What people

were able to observe in their daily lives was an universal frame of reference.Obviously, if the Earth was round, any people, water, etc. on the bottom would falloff.The Greek philosophers were perhaps the first to separate the question of originsfrom their gods and goddesses. The Greeks believed that the gods and goddesses,too, were created out of the primordial substance(s). Greek thought went one stepfarther. They thought of air or water as the first cause of all life (both their gods andhumans). These were not an air-god or water-god, and the gods (who were alsocreated) did not create nature nor humans. The gods and humans both came
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from Gaia, mother Earth, who was not one of the gods on Mt. Olympus, but somesort of a predecessor to everything.Among the Greek philosopers were:

Thales (650 - 580 BC) regarded water as the cause, beginning, and end of

all things. His ideas were probably the beginning of the controversy amongthe Greek philosophers regarding the importance of water vs. air vs. fire asthe primordial substance.

Anaximander (611 - 546 BC) is credited with the first written work on naturalscience, a classical poem entitled On Nature. In this poem, he presentedwhat may be the first written theory ofevolution. He wrote that animalsarose from slime which had been evaporated by the sun. He thought that thefirst animals lived in the sea and had prickly, scaly coverings. As these fish-like creatures evolved, they moved onto land, shed their scaly coverings,and became humans.

Heraclitus (around the same time) felt that the universe is continuallychanging, thus it is senseless to ask for its origins in the manner of a myth.He taught that there is no beginning or end, only existence.

Xenophanes (b. 570 BC) was one of the first people to observe fossils inrock layers. Interestingly, he recognized that the rock in which the fossilswere found had at one time been submerged mud. He explained theexistance of fossils by saying that that the world evolved from a mixture ofearth and water, and that the Earth will gradually be re-dissolved. Hebelieved that the Earth has gone through this cycle several times leading upto the visible fossils.

Empedocles (~490 - ~440 BC) tried to solve the water-earth-fire debate bysaying that there were not one nor two, but four original elements: Earth, Air,Fire, and Water. He thought that everything else came about through theircombination and/or separation by the two opposite principles of Love andStrife.


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Among the many things for which Plato (427 - 343 BC) is remembered is hisidea that there were two worlds. He said the world which we see is just anillusion, evil, an imperfect copy of the real world, transitory, and will decay.

The real world which we cannot see because its invisible, is good, perfect,eternal, and static or unchanging. In the real world, there is obviously novariation or change, nor need for any, because all the organisms there areperfect. The variation we see among organisms here is because they areimperfect copies of the real types in the real world. This pagan idea wasborrowed and incorporated into Christian beliefs, and in sharp contrast to theJewish belief that we are caretakers of the Earth, has been used to justifyour wanton trashing of the planet (Who cares, since its evil and temporary,anyway).

Aristotle (384 - 322 BC), one of Platos most famous pupils, said thatspecies are fixed in a hierarchy from simplest to most complex, like rungs ona ladder (the Scala naturae) with no vacancies, no mobility, and nochange/evolution possible since all the spots were full. Later, these thoughts

were incorporated into Christian views, along with the Hebrew idea that life iscreated. This view has dominated Western thought for about 2000 years.

The Hebrew people lived in between the Babylonians (Mesopotamians) and theEgyptains, and based much of their thoughts and knowledge on the influence of theirneighbors to either side. In many respects, their creation story is similar to those oftheir neighbors, especially the Babylonians, but their God pre-existed before wasseparate from the primeval chaos, and he created both nature and people. In more recent times, Georges Buffon (mid-1700s) was a Frenchman whostudiedfossils, and was among the first to suggest the Earth is older than 6000years.

James Hutton (1726 - 1797) published a paper in 1795 (which was laterrefined/modified by Charles Lyell) in which he said that land forms can beaccounted for by current mechanisms; for example, a gorge was cut by the riverrunning through it, and was not always there. From this, he drew two conclusions:

a. slow, subtle, continuous change over a long time has a profound effect, and b. ifgeological change comes from this slow process, then the Earth is very


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old, much older than Archbishop Usher said.

Needless to say, this sparked much controversy because it was a challenge to the

prevalent theory on the age of the Earth, where we came from (a challenge to the

Christian Churchs interpretation of the book of Genesis), etc. This was a major

challenge to the authority of the Christian Church and the beginnings of our modern-

day split between religion and science (objective vs.

subjective thought).

Rev. Thomas Malthus (publ 1798), a Britishsociologist, looked at conditions in the poorneighborhoods of London. He said that in humans, theproblems of disease, suffering, starvation etc. were aconsequence of the potential for the human populationto grow faster than technology could keep up with.Things like the supplies of food, medical care, etc. werelimited in comparison to the size of the population, thusthere was competition for available resources and

only the strong and healthy would survive. He was,thus, the first to talk about survival of the fittest.William Strata Smith (1769 - 1839), an Englishsurveyor, was the first to scientifically study thedistribution of fossils. He studied the order ofrock strataor layers and noted that the same strata indifferent areas of England contained the same fossils.He found he could actually use the fossils in the various strata as indicators of whichrock layer he was examining.

Jean Baptiste Lamarck (publ

1802 or 1809) developed atheory of evolution in which the

main points were:

a. evolution or changewithin a species is driven by aninnate, inner striving towardgreater perfection,

b. use or disuse of variousorgans made them larger orsmaller, accordingly, and

c. these acquired traits

could be inherited or passed on to offspring (inheritance of acquired traits).

A number of subsequent attempts were made to prove or disprove this theory

without the benefit of our modern knowledge of genetics. One experiment involved

amputation of mouse tails for successive generations, showing that even after twenty

generations, there was no effect: baby mice were still born with tails. The Jewish

practice of circumcision was also cited as opposing evidence, since obviously it had

caused no long-lasting change in the population and still needed to be done to each

new boy baby. Lamarcks theory seemed to make sense in the light of the then -


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accepted theory of pangenes coming from the body parts to make up the

homunculus. The classic example he used was giraffes. He felt that giraffes necks

got longer because they stretched to reach higher leaves, and this was passed on to

their babies. Another example, to make the fallacy of his theory more apparent,

would be two people who developed large arm muscles because they were

blacksmiths, tennis players, or weight-lifters having a baby who was born with larger

than normal arm muscles.

Louis Pasteur (publ 1860) disproved spontaneous generation for smaller organisms(bacteria). Up until this time, people thought that bacteria and other microscopicorganisms could just come into existance from changes in the external environment.Pasteurs experiment with flasks with straight vs. curved (swan-neck) flasks showedthat for bacteria to grow in a sterile medium, their ancestors must first fall into themedium from somewhere else (there are many bacteria afloat in the air around us).Charles Darwin published the Origin of Speciesin 1859. His theories and wherethey have led will be discussed in a subsequent class period. Alexander Ivanovich Oparin (publ 1936), a Russian scientist, in The Origins of Life,described hypothetical conditions which he felt would have been necessary for life tofirst come into existence on early Earth. He thought the atmosphere was madelargely of methane, ammonia, etc. and that there was much more volcanic activityand lightening than now. This theory was later tested by an experiment doneby Stanley Miller as a grad student under Harold Urey in 1953. This experiment willbe covered in greater depth in a subsequent discussion.


Evolution> Origins of Life

The theory put forth to explain the origins of the Universe, our solar system, and our

planet is called the Big Bang Theory. The Big Bang Theory IS NOT EVOLUTION!

(The theory of evolution deals with living organisms, once they have come into

existance.) The Big Bang theory says that all matter in the Universe was, at one

time, concentrated in a giant mass (a black hole?) that blew apart about 10 - 20 bya

(billion years ago) and is still expanding. About 5 bya, some of the matter condensed

until forces were so strong that thermonuclear reactions began, and this was theorigin of our sun. A disk-shaped cloud of matter orbiting the sun subsequently

condensed into the planets. Thus, about 4.6 bya, the planets coalesced, and it is

thought that Earth began as cold world. Later, due to whatever factors, the planet

heated up enough to melt and sort into layers by density (core, mantle, crust). It is

thought that the very first atmosphere may have been hydrogen gas, but since that

is so light weight and very chemically reactive, most of it would have floated off into

space or reacted with other substances, thus would have been rapidly dissipated.


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Alexander Ivanovich Oparin (publ. 1936), a Russian scientist, in The Origins ofLife, described hypothetical conditions which he felt would have been necessary forlife to first come into existence on early Earth. This, thus, is referred to as the OparinHypothesis. He theorized that the first atmosphere was made largely of water vapor(H2O), carbon dioxide (CO2), carbon monoxide (CO), nitrogen (N2), methane (CH4,and ammonia (NH3. As the surface of Earth cooled again, torrential rains of thismixture formed the first seas, the primordial soup. Some think this may be whatconditions are like, even now, on Venus. Lightening, ultraviolet (UV) radiation,volcanic action all were more intense than they are now.

Several possible steps/stages were suggested to get from there to living organisms.The first step is thought to have been the abiotic synthesis (syn = with,


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together;thesis = an arranging) of organic monomers, in other words, puttinginorganic chemicals like methane, carbon dioxide, and ammonia together to formsimple organic chemicals like amino acids, simple sugars, fatty acids, and nucleicacids. This portion of the hypothesis was later tested by an experiment done byStanley Miller as a grad student under Harold Urey in 1953. He used a sterile,enclosed system consisting of a flask over a heat source, a spark chamber, andvarious other tubing (see illustration). He added sterile H

2O, H

2, CH

4, and NH

3to the

sealed system. Heat was applied under the flask to simulate volcanic action, and thiswas enough to turn a significant portion of the water into steam. A spark chamberperiodically discharged electricity into the gasses to simulate lightening. In the returntube, the mixture was cooled to condense the water back into liquid, along with anyorganic compounds that might have formed from the mixture. Water and all thegasses Miller included are all clear, thus his experiment started out withtransparent water and transparent gasses. However, after only one week, Miller hada brown, murky soup. Subsequent chemical analysis showed the presence of anumber of amino acids and other organic compounds. Other researchers have sincetried similar experiments with slight variations in the initial mix of chemicals added,and by now, all 20 amino acids, and a number of sugars, lipids, and nucleotideshave been obtained in this manner. From this experiment, scientists generalize thatif this can happen in a lab, it could have happened in a similar way on early Earth.

Note that ALL that was made here was simple organic chemicals!

The next step in going from non-living to living is thought to have been the abioticsynthesis of organic polymers, possibly using hot sand or finely divided clay as acatalyst (cata = down, downward; lysis = loosen, break apart), a substance whichhelps a chemical reaction to go without being consumed in that reaction, whichcaused dehydration synthesis to occur, thereby joining the smaller molecules intolargermacromolecules such as proteins, carbohydrates, RNA or lipids.Thirdly, it is thought that non-living aggregates of these polymers formed. Thesemay have exhibited someproperties characteristic of living organisms, but were

NOT ALIVE, and did not have all the properties of living organisms. In a researchlaboratory, scientists have seen mixtures of proteins, lipids, and carbohydrates formglobules. If the proteins involved happen to be enzymes, these globules can evencarry on metabolic activity, although they have no means to replicate themselves.Simultaneous to this, the genetic code would have to have arisen. Several widely-accepted theories as to how this may have happened include the possiblyinvolvement of damp, zinc-containing clay as a catalyst to help the nucleotidespolymerize first into RNA, and later into DNA.It is thought, then, that about 4.1 to 3.5 bya, the first prokaryotes, organisms withouta true nucleus (like bacteria) came into existance. It is difficult to pinpoint a date forthis because bacteria dont have skeletons to leave behind. The first fossils(remains of colonies/secretions) of prokaryotes seem to be this age. These wouldhave been very simple cells without many of the organelles present in modern cells,especially modern eukaryotes.Note that while someof these steps have been demonstrated in a lab, Nobaoy HasEver Made a Living Cell in a lab. While people have demonstrated bits and piecesof this process, the whole process has never been done in a lab. Rather, this is atheory of how things might have happened.Once the first cells, the first living organisms, the first prokaryotes came intoexistance, then the Theory of Evolution takes over to provide an explanation for how


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(not why) these primitive cells diversified into the five kingdoms of life which werecognize today.Themes>Science>Life Sciences>Physical Anthropology>Human Genetic

Evolution> Nasa Scientists Find Clues That Life Began in Deep Space

Duplicating the harsh conditions of cold interstellar space in their laboratory, NASA

scientists have created primitive cells that mimic the membranous structures found

in all living things. These chemical compounds may have played a part in the origin

of life.

This breakthrough by scientists at NASA Ames Research Center in Californias

Silicon Valley is important because some scientists believe that the delivery - by

comets, meteorites and interplanetary dust - of similar organic compounds born in

interstellar space might have "kick-started" life on Earth.

"Scientists believe the molecules needed to make a cells membrane, and thus for

the origin of life, are all over space. This discovery implies that life could be

everywhere in the universe," said Dr. Louis Allamandola, the team's leader.

Using simple, everyday chemicals, researchers from Ames' Astrochemistry

Laboratory and the Department of Chemistry and Biochemistry at the University of

California, Santa Cruz, have created, for the first time, "proto"-cells. These are the

primitive cells that mimic the membranous structures found in all life forms. "This

process happens all the time in the dense molecular clouds of space," Allamandola

said.

This discovery has important implications for NASA's astrobiology mission. "Theformation of these biologically interesting compounds by irradiating simple

interstellar ices shows that some of the organics falling to Earth in meteorites and

interplanetary dust might have been born in the coldest regions of interstellar space,"

Allamandola said. "The delivery of these compounds could well have been critical to

the origin of life on Earth."

Their results will be published Jan. 30 in the special astrobiology issue of the

"Proceedings of the National Academy of Sciences, USA."

Scientists do not yet know whether life began as naked RNA or as genetic material

encapsulated in membranes. But at some point, membranes became important. "All

life as we know it on Earth uses membrane structures to separate and protect thechemistry involved in the life process from the outside," said Dr. Jason Dworkin of

the SETI Institute, the paper's lead author and a team member. "All known biology

uses membranes to capture and generate cellular energy."

"Membranes are like a house," Dworkin added. "Maybe these molecules were just

the raw lumber lying around that allowed origin-of-life chemicals to move in and set

up housekeeping or construct their own houses."


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In the lab, the scientists recreated the conditions found in space -- which is a cold

vacuum -- zapping a series of simple ices with the ultraviolet radiation found

everywhere. They created solid materials which, when immersed in water,

spontaneously created soap bubble-like membranous structures that contained both

an "inside" and an "outside" layer.

In contrast to current thinking, this new work shows that the early chemical steps

believed to be important for the origin of life do not require an already-formed planet.

Instead, they seem to take place in deep space long before planet formation occurs.

This implies that the vastness of space is filled with chemical compounds which, if

they land in a hospitable environment like our Earth, can readily jump-start life.

Interstellar ices are made of familiar everyday chemicals such as water, methanol

(wood alcohol), ammonia and carbon monoxide that are frozen together.

The astrobiology research team also included Dr. Scott Sandford of Ames and David

Deamer of the Chemistry and Biochemistry Department of UC Santa Cruz.


Evolution> How did the first cells evolve?

Haldane(1937) and later Oparin (1938) proposed that UV, lightning, heat caused

hydrocarbons to be formed in the early atmosphere of the earth. In 1953, Stanley

Miller and Harold Urey mixed together water, hydrogen, methane, and ammonia

gases in an apparatus which produced electrical sparks to simulate lightning. After a

week they found that many organic compounds were present, including some aminoacids. This experiment was shown by Carl Sagan, a Professor at Cornell, on the

Cosmos TV series. (Urey received the Nobel Prize for chemistry in 1934 for

separating isotopes, when Miller, who later worked in his lab, was only 4 years old.)

According to Miller, Urey, and Sagan, hydrogen gradually escaped from the earlyatmosphere because it is so light and thus the gravitational pull on it is low.Ammonia and methane are unstable in absence of a reducing atmosphere so theydecreased in concentration and nitrogen gas rose in concentration. Prokaryotic cells likely appeared about 3.5 billion years ago. These cells had nonucleus, simple, circular DNA (we suppose), no internal organelles. According to theview of Miller, Urey, and Sagan, they were heterotrophic (other-feeders) and usedfermentation (glycolysis + a couple of other steps) to extract energy from themolecules formed as the result of the heat and light in the early atmosphere.Fermentation produced carbon dioxide and so the concentration of this gas rose inthe atmosphere.Photosynthesis probably began about 3.3 billion years ago with autotrophic (self-feeders) prokaryotes. While the earliest autotrophic prokaryotes used hydrogensulfide gas and produced sulfur, later cells used water and produced oxygen gas,


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the concentration of which rose in the atmosphere.Another interesting idea is that life began around thermal vents caused by volcanic

activity on the ocean floor. In this scenario, the energy needed by the first

prokaryotic cells would have come from chemical processes, probably involving

hydrogen sulfide gas, which is abundant near such thermal vents, notfrom

molecules produced by the reductive, pressure-cooker atmosphere.

According to this idea, these first organisms would have been chemoautotrophs, notheterotrophs, and more modern heterotrophs and autotrophs both would have beenderived from them. After the first chemoautotrophs developed, the time table wouldbe similar to that discussed above and with the appearance of heterotrophs and thedevelopment of photosynthesis (photoautotrophy) about 3.3 billion years ago.Finally, eukaryotes appeared. Some people, such as Lynn Margulis at BostonUniversity, believe that eukaryotes developed as the result of ingestion ofprokaryotes by other prokaryotes (endosymbiont hypothesis). The ingestedsymbiotic prokaryotes became internal organelles such as mitochondria (if they wereheterotrophs) or chloroplasts (if they were autotrophs). The use of oxygen permittedheterotrophic metabolism to break down glucose beyond the point permitted byfermentation. As a result much more energy could be extracted from each moleculeof glucose metabolized.The endosymbiont hypothesis found some powerful support in the results of a recentarticle in the scientific journal Nature. This article showed striking similaritiesbetween the genome ofRickettsia prowazekii, which causes a form of typhus, andthat of the mitochondrial DNA from some eukaryotes.

human life and evolution

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