8 Human Origin and Evolution

Dr. Ajeet Jaiswal

Contents of this unit

1. Introduction: Origin of Life

     2. Scientific Hypothesis for Origin of Life

 a. The Primitive Earth

 b. Conditions on the Primordial Earth

 c. Miller and Urey’s Experiment and Molecules of life

 d. From Molecules to Cell

3. Life on other Planets

4. Definition of Evolution

5. Evolution of Man

6. Evolution in Modern Populations

7. Evidences of Evolution

a. Comparative Morphological Evidences

b. Comparative Physiological Evidences

c. Comparative Embryological Evidences

d. Comparative Palaeontological Evidences

8. Variations

9. Causes of variations

10. Summary

Learning objectives:

• The purpose of the module is to make the reader understand the concept of Origin of life on earth.
• This module is also intended to acquaint the students with some of the significant issues like evolution of man and evidences of evolution.
• This module also addresses human variation and the causes of variations.

1. Introduction: Origin of Life

   How did life originate? This question has perplexed scientists and philosophers throughout human history. There was a time when it was believed that life began spontaneously from nonliving matter. It was thought that fish and frogs were produced from mud, maggots arose from decaying meat, insects were formed from plant juices and that micro-organisms arose spontaneously from air or water. It was the great French microbiologist Louis Pasteur who finally disposed such theories of ‘spontaneous generation’ and demonstrated once and for all that life originates only from pre-existing life.

2. Scientific Hypothesis for Origin of Life

   How then did life originate in the first place? Charles Darwin in a letter to his friend and distinguished botanist Sir Joseph Hooker provided a clue to this puzzle when he wrote “if (and oh, what a pit if) we could conceive in some warm little pond with all sorts of ammonia and phosphoric salts, heat electricity, etc., present that a protein compound was chemically formed, need to undergo still more complex changes at the present day such matter could be instantly devoured, or observed, which would not have been the case before living creatures were formed”. The idea that life could have originated on the primordial earth even though it might not today, because the conditions on the primordial earth were rather different from those that we see today, has since become the basis of the most widely accepted scientific theory of the origin of life. A detailed theory based on this idea was proposed in the year 1923 by the Russian biochemist A.J. Oparin and in 1928 independently one of the most outstanding biochemist of our time J.R.S. Haldane.

2.1 The Primitive Earth

   There is evidence that the earth was formed about 4600 million years ago. The earth and other planets and the sun, too are believed to have been formed by the condensation of clouds of cosmic dust and gas. At the time of its formation, the earth was so hot that everything in it was probably in gaseous form. As the earth began to cool, its matter began to condense so that solids, liquids as well as gases could co-exist. Recent studies suggest that simple one celled organism, somewhat similar to today’s cyanobacteria, were present in the earth about 3600 million years ago. This finding suggests that life originated sometime between 4600 and 3600 million years ago.

2.2 Conditions on the Primordial Earth

 About 3600 million years ago conditions were strikingly different from those found today. The earth’s atmosphere at that time was reducing and not oxidizing as it is today. You would recall that large quantities of hydrogen, nitrogen, water vapour, carbon dioxide, lipids and amino acid were present on  the primitive earth but free oxygen is unlikely to have been present in any significant amounts. The Oparin Haldane theory suggests that complex organic molecules would have been formed through a series of chemical reactions in the earth’s “primordial soup” or we might say Darwin’s warm little pound. The theory also reasoned that these chemical reactions were driven by the available form of heat, cosmic rays and lighting.

2.3 Miller and Urey’s Experiment and Molecules of life

Stanly Miller and Harold C. Urey put the Oparin-Haldane theory to test in year 1953 by recreating in the laboratory, the probable conditions on the primitive earth. They built an apparatus of glass tubes and flasks and created an atmosphere containing Hydrogen, ammonia, methane and water vapor in one chamber and allowed condensed liquids to accumulate in another chamber. Energy was supplied by heating the liquid-containing chamber as well as by electric sparks from electrodes in the gaseous chamber. Miller and Urey let their experiment run continuously for about one week and then analyzed the chemical composition of the liquid inside the apparatus.

  To their great delight they found a large number of complex organic compounds including some amino acids such as glycine alkaline and aspartic acid. This so called process of abiotic synthesis of organic molecules has since then been repeated many times and scientists have recovered most amino acids that are present, in protein molecules as well as adenine and other nucleic acid bases. The essential ‘building-blocks’ of living organism could thus have formed on the primitive earth. These results of Miller and Urey and those of numerous other scientists since provided support the hypothesis of Oparin and Haldane. It is now clear why a reducing atmosphere was essential for such abiotic synthesis. Free oxygen would destroy most intermediate products in such synthesis. Thus the presence of abundant free oxygen on the earth today is thought to prevent abiotic ‘origin of life’.

  The first photosynthetic organisms were cyanobacteria, believed to have evolved about 3300 to 3500 million years ago began to release oxygen as a byproduct of Photosynthesis and thereby converted the earth’s atmosphere into an oxidizing one. This probably put an end to the kind of abiotic synthesis that was possible in the reducing atmosphere. Moreover, as Darwin pointed out in his letter even if some molecules are formed they would be absorbed and digested by the living organisms present on today’s earth. All this leads to the most interesting conclusion that life originated from the earth’s inorganic atmosphere in the past but this no longer happens today. On today’s earth therefore as Louis Pasteur showed life originated only from pre-existing life.

  The next step in the origin of life is how these simple building blocks, were combined to form large and complex polymers such as protein and nucleic acids. In cells of the present day proteins are formed only by the action of enzymes. But enzymes themselves are proteins. The early proteins and nucleic acids must, therefore have been formed by some non-enzymatic processes.

2.4 From Molecules to Cell

   The real problem that scientists face in explaining the origin of life is how proteins and nucleic acids, that might have been formed on the primitive earth, become organized to from cells. Both Oparin and another scientist Sydney Fox, discovered that aqueous suspensions of the kinds of polymers that might have been abiotically synthesized on primitive earth when heated from spherical aggregates can be seen under the microscope and remind us of bacteria and other simple unicellular organisms. The coacervates grew by absorbing molecules from their environment. They can divide by budding like bacteria. Moreover, many familiar chemical reactions including the decomposition of glucose take place inside the coacervates. It is thus possible that the first cells arose in much the same way as coacervates at the edges of primitive lakes and oceans. The sun provided the energy for such processes.

3. Life on other Planets

If all these events occurred on the primordial earth could they not also have occurred on some other planets? While most planets may not have the necessary conditions for the origin of life. The reason for such belief that there are at least 10 stars in the universe which seem to have planets and thus even if only one in a billion planets has the appropriate conditions, we would still have 7-8 planets on which life could have originated. In fact, one solution that has occasionally been suggested for the origin of life is that it was somehow infected by primitive forms of life (such as micro-organisms) through space. For this reason search for life on other planets is being seriously pursued.

4. Definition of Evolution

Darwin saw evolution as the gradual unfolding of new varieties of life form previous forms over long periods of time. This depiction is what most of us think of as “evolution”, and it is indeed the end result of the evolutionary process. But these long-term effects can only come about by the accumulation of many small evolutionary changes occurring every generation. It is important understand how our modern understanding of the evolutionary process came about through contributions of biologists in the United States, Great Britain and the Soviet Union.

   While mutationists’ were arguing with selectionists about the single primary mechanism in evolution, several population geneticists began to realize that both small genetic changes and natural selection were necessary ingredients in evolutionary formula.

   These population geneticists were largely concerned with mathematical reconstructions of Evolution – in particular, measuring those small accumulations of genetic changes, in populations over just a few generations. Central figures in these early theoretical developments, included Ronald Fisher and B.S. Haldane in Great Britain, Sewall Wright in the United States, and Sergei Chetverikov in the Soviet Union.

  While the work of these scientists often produced brilliant insights, their conclusions were largely unknown to most evolutionary biologists, especially in North America. It remained therefore for an individual to transcend Genetics and the general constructs of theoretical evolutionary biologists. The scientist who performed this task (and to whom we owe most credit as the first true synthesizer) was Theologian Dobzhansky. In his Genetics and the Origin of Species (1937), Dobzhansky skillfully integrated the mathematics of population genetics with overall evolutionary theory. His insights then became the basis for a period of tremendous activity in evolutionary thinking that directly led to major contributions by George Gaylord Simpson (who brought palaeontology into synthesis), Ernst Meyer and others. In fact the “Modern synthesis” produced by these scientists stood basically unchallenged for an entire generation as the explanation of the evolutionary process. In recent years, however, some aspects of theory have been brought about serious question.

   The process of evolution works; we must necessarily study these short-term events. Darwin attempted this kind of study in his breeding experiments, but because the science of genetics was still in its infancy, he was not able to comprehend fully the mechanics of evolutionary change. Today, we study in various organisms (including humans) evolutionary changes occurring between generations, and are able to demonstrate how evolution works. From such a modern genetic perspective, we define evolution as a change in allele frequency from one generation to the next.

   Allele frequencies are numerical indicators of the genetic makeup of an interbreeding group of individuals known as a population. First of all, we must look at a physical trait that is inherited, in this case human blood type. The best known of the human blood type traits is ABO. There are however, many similar blood type controlled by different genes, which determine genetically transmitted properties of the red blood cells.

   An inherited trait, such as human blood type, may be of slightly different from in different individuals. As mentioned, we call the variant genes that underlie these different forms of an inherited trait allele. The best known blood type allele are A, B, and O. These different expressions of inherited traits constitute genetic variation within a population. Let us assume that your present class represents a population of an interbreeding group of individuals and that we have ascertained the blood type of each member for the ABO trait.

     To be a population, individuals in your class must choose mates more often from within the group than from outside it. Of course, the individuals in your class will not meet this requirement, but for this example sake we will make the assumption that they do. The proportions of each of the A, B and O allele are the assumption that they do. The proportions of each of the A, B and O, allele are the allele frequency for this trait. For example, suppose we find that the proportion of allele in your class (population) is as follows: A = 50, B = 40, O = 10.

      Since the frequency for combinations of these genes represent only proportions of a total, it is obvious that allele frequencies can refer only to whole group of individuals: that is population. Individuals do not have an allele frequency; they have A, B or O (or a combination of these). From conception onward, the genetic composition of an individual is fixed. If you start with blood type A, you will remain type A. Therefore, an individual cannot evolve: Only a group of individuals – a population – can evolve over time.

   What happens when populations evolve? Evolution is not an unusual or a mysterious process. In fact, it is incredibly commonplace, and may occur between every generation for every group of organisms in the world including humans. Assume that we measure the allele combination frequently in a population and find the following: A=30, B =40, O= 30.

  We can see that relative proportions have changed: A has decreased; O has increased while B has remained the same in frequency. Such a simple, apparently minor change is what we call evolution. Over a short run of just a few generation, such changes in inherited traits may be only very small, but if further continued and elaborated, the results can and do produce spectacular kinds of adaptation and whole new varieties of life.

  Whether we are talking about such short-term effects as our classroom population from one generation to the next, which is sometimes called microevolution, or the long term effect through fossil history sometimes called macroevolution the basic evolutionary mechanisms are similar. As we will discuss below, however, they are not necessarily identical.

  The question may be asked, how do allele frequencies change? Or, to put it in another way, what causes evolution. The modern theory of evolution isolates general factors that can produce alterations in allele frequencies. As we have noted, evolution is a two-stage process, genetic variation must be first produced and distributed before it can be acted upon by natural selection.

5. Evolution of Man

The origin and evolution of man, the wonder and glory of the universe, has been the most attractive and complicated problem of man himself since time immemorial. Religion had shed a false and dominant notion until the last century when Charles Darwin was able to put forward his Theory of evolution of Organic world. Until the middle of the 19th century it was supposed that life including man had been created by the super-natural power ‘God’. Various theories were put to explain such type of origin. Father Saurezi put forward his Special Creation Theory which tells that man was created on the sixth day from Anima rationalis. Female was created out of a part from the male’s rib. Lucretius (95-51 BC) was of the opinion that man was born directly out of the earth. He called man as “Babies born of the womb of earth”. Philosophers like Socrates, Aristotle, and Hippocrates, etc. studied human body and put man in the animal kingdom. Carolus Linnaeus placed man in its proper position in the animal kingdom. Charles Darwin’s theory of evolution gave a severe blow to the religious conception about origin of man and revolutionized this topic. His work on Decent of man and Selection in relation to sex (1871) has provided important proof of the human descent from other anthropoids. His book provided some geological evidences including fossils and implements.

6. Evolution in Modern Populations

The process of evolution acts on all species including Homo sapiens. In modern populations, recombination and mutation continue to produce variation, the fuel for natural selection. Can we then see these ongoing evolutionary processes at work in human population?

  Today we find only one species of hominid represented by over six billion individuals widely scattered over most of the earth. However, the distribution is by no means even, since both geographical and social factors influence where people live, how many individuals collect to form a group and who mates with whom. Moreover, there are obvious visible physical differences as well as numerous biochemically detectable variations among groups of modern human beings. How do we explain these differences?

  The branch of anthropology dealing with modern human variation is centrally concerned with answering such questions in evolutionary terms. As discussed throughout this module, anthropology is the study of human evolution not just in the past but the present as well.

  Human populations continue to be influenced by the process of evolution, continue to adapt to their bio-cultural environments, and thus give the continuing value. Investigating the dynamic processes that mold our species is the domain of study of why Homo sapiens vary from area to area (as well as from individual) but we also can more fully comprehend how Homo sapiens came to be in the first place.

  The following module tells the tale of a long succession of hominid fossils but these are simply luckily preserved bits and pieces of earlier populations who were subject to the same dynamic evolutionary process influencing humankind today. Over the span of several tens of thousands or millions of years small micro evolutionary changes can be modified into macro evolutionary ones, given the process of punctuated equilibrium, macro evolutionary changes do not necessarily translate completely from micro evolutionary events.

7. Evidences of Evolution

There are convincing evidences to support that man has not been created by God but through evolutionary mechanism from the common ancestors of anthropoids like Chimpanzee and Gorilla.

The evidences are:

7.1 Comparative Morphological Evidences

a. Close resemblances- Man closely resembles other anthropoid in the following characters: 1. Tailless body;     2. Erect posture; 3. Bipedal locomotion; 4. Dental formula; 5. Paired laryngeal sacs.

b. Vestigial organs- The body of man has more than 100 vestigial organs such as a muscles of external ear,      coccyx, hairs, canines, appendix, segmental abdominal muscles, mammary glands in male, clitoris in female, etc. such organs are also present and are functional in other mammals.

c. Atavistic characters- These are ancestral characters which occur in the newborn e.g. inward position of the human infant legs, hairy body, grasping power of the hands and sometimes presence of a short tail like growth called a ‘candal appesdage’.

7.2 Comparative Physiological Evidences

The following physiological evidences support the common ancestral relationship between man and other anthropoids:

 a. Dr George H.F. Nuttal has shown blood relationship between anthropoids and man by his precipitation theory tests as serological evidences.

b. The leucocytes of man, gorilla and chimpanzee have similar types of neutrophils and eosinophils.

c. Like man the anthropoids have blood groups. J. Troisier (1931) transfused blood of chimpanzee to the man without any adverse effect.

d. The menstrual cycle period of anthropoids are quite within a limited range; Chimpanzee 28-32 days, Gorilla 30-35 and Man 28-32 days.

e. The gestation period are: Chimpanzee 210-252, Gorilla 265-280 days and Man 270-290 days.

7.3 Comparative Embryological Evidences

These evidences provide a striking support of evolution of man along with other anthropoids as per

Haeckel’s Biogenetic Law “Ontogeny recapitulate Phylogeny”. These are:

a. The number of chromosomes is almost similar; Chimpanzee-48, Gorilla-48 and Man-46.

b. The eggs and sperms of these anthropoids are so similar that these are indistinguishable.

c. The six week embryo of man has several pairs of mammae like those of other anthropoids.

d. The embryos of man are covered with hairs.

7.4 Comparative Paleontological Evidences

   From the study of living and fossil primates it has been established that primates including monkey and man has descended from a common ancestor and separated from the main stock at a very early period, Oligocene. The earliest and one of the most primitive ape, the Parapithecus lives during Oligocene about 40 million years ago. It was a small monkey like ape from which all members of Homoinoidea have evolved. Another ape of Miocene, about 20 million years ago, the Proconsul has been considered as ancestor of modern chimpanzee and man. Proconsul was somewhat human in appearance and resembled man in similar condyles of jaws, incisors and frontal bones. It was developed in a Hominid direction; these ancestral anthropoids gave rise to apes, the Chimpanzee, Gorilla and ancestors of Man.

  The fossil records of man are very poor and limited in comparison to other mammals. The fossils discovered are no doubt intermediate between apes and man but it is very much doubtful whether they represent direct ancestor of man, although they point outlines of the descent.

  The principal fossil forms now on record are:

a. African ape man (Australopithecus africanus)

b. Java ape man (Pithecanthropus erectus)

c. Peking man (Sinanthropus pekinensis)

d. Heidelberg man (Homo heidelbergensis)

e. Neanderthal man (Homo neanderthalenensis)

f. Cro-Magnon man (Homo sapiens fossilis)

g. Modern man (Homo sapiens)

8. Variations:

Variations are the dissimilarities which help in distinguishing one member of the species from another. It is commonly observed that no two individuals are completely alike, even dissimilarities can be present in two identical twins. The heritable variations contribute to evolution. In the absence of variation no change can occur without which evolution is not possible. It is a fact that variations constitute the basic requirement for evolution.

Variations can be classified as follows:

Variation may be grouped in to four pairs of contrasting nature:

8.1 Continuous and Discontinuous

Continuous variation: These variations are always quantitative and found in a graded series. They are the minute changes which can be seen in an organism generation after generation and ultimately they lead to the occurrence of a new well formed character. These variations are the main cause of evolution according to Darwin’s theory of Natural selection. The best example of continuous variation is the: a) milk production in cow, b). height in case of human beings.

Discontinuous variation: These sudden changes which are not repetitive or serial in nature are the discontinuous variations or sports or mutations. Darwin has not considered them for the purpose of evolution but modern researcher have shown their significance for evolution. The example of discontinuous variation is the presence of abnormal number of digits in vertebrates. In man six, seven or sometimes more digits are seen in some cases.

8.2 Germinal and Acquired

Germinal variations (Blastogenic): Those variations which originate inside the body (intrinsic) in the germ cells are known as germinal variations. They are inherited and transmitted to the offspring. They are not affected by environmental factors. Germinal variations are of two types:

(a) Arising from chromosomal changes.

(b) Arising by the change in a particular gene.

The former includes the change in number or structure of chromosome resulting in Polyploidy or chromosomal aberration respectively. The second one is the gene or point mutation. The example for germinal variation is the occurrence of supernumerary digits in man. These are inherited through several generations occasionally.

Acquired variations (Somatogenic): Those variations which are produced in the somatic cells of the body as an effect of environmental factors are called the somatogenic variations. They are the acquired characters during the lifetime based on the use and disuse of organs. They are extrinsic and nonheritable, e.g.:

(a) Better developed muscles in an athlete.

(b) Slender wrist in European and American ladies.

(c) Loss of eye in cave dwellers.

8.3 Determinate and Indeterminate

Determinate variations: Those variations which occur in certain definite lines and directions are known as determinate variations. These variations are usually in adaptive directions and are also known as orthogenic variations as they also take place in a definite line in the evolution (theory of orthogenesis). Example is the overgrown antlers in Irish deers.

8.4 Meristic and Substantive: The nature of variation is of two types:

Meristic variations: are those variations which occur in any part but in number only e.g.

1. Presence of six fingers instead of five (normal number).

2. Presence of thirteen ribs instead of twelve (normal number).

Substantive variations: are those variations which effects the size, weight, shape, colour and form of the body. For example- variations in the length of fingers, shape of nose and ear, etc.

9. Causes of variations:

1. Causes of Acquired variations- these are caused during the lifetime of an individual due to environmental factors (external influenced). The environmental factors may be scarcity or abundance of food, heat, cold, use or disuse. These variations are only for individuals and does not imply for a race as a whole. They are not heritable and so they don’t have any concern with evolution.

 2. Causes of Germinal variations- these are the heritable variations and so they are in close concern with evolution. The causes of these variations are:

 a. Biparental parentage (amphimixis) is a principal cause of it. It is well known that during sexual reproduction the zygote (later on individual) receives germplasm from both male and female parents. Half of the chromosomes come from mother and half from the father. In this way, new combinations take place which are the cause of variation in the offspring.

b. All individuals have the inherent tendency to vary.

c. Variations also occur due to abnormalities in the process of meiosis.

d. External influences such as X-rays and ultra–violet rays also cause the modifications in the germplasm.

e. Secretion of endocrine glands are also upto some extent, the cause of germinal variations.

10. Summary

• • There was a time when it was believed that life began spontaneously from nonliving matter.
  • There is evidence that the earth was formed about 4600 million years ago.
  • About 3600 million years ago conditions were strikingly different from those found today.
  • The Oparin Haldane theory suggests that complex organic molecules would have been formed through a series of chemical reactions in the earth’s “primordial soup” or we might say Darwin’s ‘warm little pond’.
  • The presence of abundant free oxygen on the earth today is thought to prevent abiotic ‘origin of life’.
  • The first photosynthetic organisms were cyanobacteria.
  • Louis Pasteur showed life originates only from pre-existing life.
  • The real problem that scientists face in explaining the origin of life is how proteins and nucleic acids, that might have been formed on the primitive earth, become organized to form cells.
  • Planets may not have the necessary conditions for the origin of life.
  • Darwin saw evolution as the gradual unfolding of new varieties of life form previous forms over long periods of time.
  • Evolution is not an unusual or a mysterious process.
  • Evolution is a two-stage process, genetic variation must be first produced and distributed before it can be acted upon by natural selection.
  • The process of evolution acts on all species including Homo sapiens.
  • There are convincing evidences to support that man has not been created by God but through evolutionary mechanism from the common ancestor of anthropoids like Chimpanzee and Gorilla.
  • Variations are the dissimilarities which help in distinguishing one member of the species from another.

References

• Abi-Rached, Laurent; Jobin, Matthew J.; Kulkarni, Subhash et al. 2011.”The Shaping of Modern Human         Immune Systems by  Multiregional  Admixture  with Archaic Humans”. Science (Washington, D.C.:    American   Association    for    the    Advancement   of Science) 334 (6052): 89–94.
• Andrews, R, and Stringer C.1989, Human Evolution, An Illustrated Guide, London, British Museum.
• Andrews, P., 1986. Fossil evidence on human origins and dispersal. Cold Spring Harbor Symposia of quantitative Biology 51 : 419 – 428.
• Ayala, Francisco I. and John A. Kigar, Jr. 1980. Modern Genetics. The Banjamin/Cummings Publishing Company Inc.
• Birdsell, J.B. 1972, Human Evolution, Heinemann Educational Books, London.
• Buettner-Janusch, J.1969, Origins of Man : Physical Anthropology. Wiley Eastern Pvt. Ltd., New Delhi.
• Campbell, B, 1964.Quantitative Taxonomy And Human Evolution. In : Classification and Human Evolution, S.L. Washburn (Ed.) Methuen and Co. Ltd., London.
• Clochon, R.L. and Corruccini, R.S. (ed.), 1983. New Interpretations of Ape and Human Ancestry; New-York, Plenum.
• Craig B. Stanford 1996,The Hunting Ecology of Wild Chimpanzees: Implications for the Evolutionary Ecology of Pliocene Hominids, American Anthropologist, Vol. 98, No. 1, 96-113
• Craig Stanford , 2013, Biological Anthropology, 3rd Edition, Prentice Hall publication.
• Fleagle, J.G. 1988- Primate Adaptation and Evolution, San Diego; Academic Press.
• Ghosh, P. 2015. “First human’ discovered in Ethiopia”. BBC News (London: BBC). 2015- 04-19.
• Kimura, M., 1983. The Neutral Theory of Molecular Evolution. Cambridge University Press, Cambridge.
• Heng, H. H. Q. 2009. “The genome-centric concept: Resynthesis of evolutionary theory”. BioEssays; John Wiley & Sons. 31 (5)
• Jaiswal, A. 2007. “The Hominization process of Homo Sapience”, EAA Summer e-Book 1:43-46, European Anthropology Association, Prague, Czech Republic, 2007.
• Jaiswal, A, 2013. Human Genetics and Applied Biophysical Anthropology: A Comprehensive Treatment of Biophysical Anthropology, Heritage Publishers, New Delhi, India.
• Jurmain, R, et al, 2013, Introduction to Physical Anthropology, Belmont, CA: Cengage Learning
• Lieberman, D. E. 1995, Curr. Anthropol. 36, 159-197.
• Lieberman, Hampton, Littlefield & Hallead 1992, Race in Biology and Anthropology: A Study of College Texts and Professors,Journal of Research in Science Teaching 29,301-321.
• Mellars, P., 1990. The Emergence of modern human. Cornel! University Press. Ithaca,N.Y.
• Mellars, P. and C.B. Stringer (eds.) 1989. The Human Revolutions. Princeton University Press, Princeton, New.
• Mixon, Bobbie; Ehardt, Carolyn; Hammer, Michael 2011. “Evolution’s Past Is Modern Human’s Present” (Press release). National Science Foundation. Press Release 11-181.
• Noonan, James P. 2010. “Neanderthal genomics and the evolution of modern humans”. Genome Research (Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press) 20 (5): 547–553.
• O’Neil, Dennis. 2015, “Early Modern Homo sapiens”. Evolution of Modern Humans: A Survey of the Biological and Cultural Evolution of Archaic and Modern Homo sapiens (Tutorial). San Marcos, CA: Palomar College.
• Reich, David; Green, Richard E.; Kircher, Martin et al. 2010. “Genetic history of an archaic hominin group from Denisova Cave in Siberia”. Nature (London: Nature Publishing Group) 468 (7327): 1053–1060.
• Stringer, Chris 2003. “Human evolution: Out of Ethiopia”. Nature (London: Nature Publishing Group) 423 (6941): 692–695.
• Tyson, Peter, 2008. “Meet Your Ancestors”. NOVA science NOW. PBS; WGBH Educational Foundation.
• Andrews, R, and Stringer C.1989, Human Evolution, An Illustrated Guide, London, British Museum.
• Bernard Wood, 1994. The oldest hominid yet. Nature 371 :280 – 281.
• Bruce, E.J. and F.J. Ayala, 1978. Humans and apes are genetically very similar. Nature, Lond. 276 : 264 – 265.
• Craig Stanford , 2013, Biological Anthropology, 3rd Edition, Prentice Hall publication.
• Jaiswal, A, 2013. Glossary of Biophysical Anthropology Terms: A Comprehensive Treatment of Biophysical Anthropology, Heritage Publishers, New Delhi, India.
• Jaiswal, A, 2013. Human Origin and Variation: A Comprehensive Treatment of Biophysical Anthropology, Heritage Publishers, New Delhi, India.
• Johanson, D. 2001. “Origins of Modern Humans:  Multiregional  or Out of Africa?”. actionbioscience. Washington, D.C.: American Institute of Biological Sciences.
• Leakey, M.G., Feibel, C.S., McDougall, I. & Walker, A. 1995. New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya. Nature 376, 565-571.
• White, T.D., Suwa, G & Asfaw, B. 1994. Australopithecus ramidus, a new species of early hominid from Aramis, Ethiopia. Nature 371, 306-312
• Young, J.Z., E.M. Jope and K.P. Oakley, 1981. The Emergence of Man. The Royal Society and British Academy, London.