BENJAMIN FRANKLIN (1706-1790)

1752 – The New World

Portrait of BENJAMIN FRANKLIN ©

BENJAMIN FRANKLIN

‘If you would not be forgotten when you are dead and rotten, either write things worth reading, or do things worth writing about’

Curious about how just about everything works, from governments to lightning rods, Franklin’s legacy, in addition to the many inventions such as lightning conductors, bifocal lenses and street lamps, was one of learning. He established one of the first public libraries as well as one of the first universities in America, Pennsylvania. He established the Democratic Party. Franklin was one of the five signatories of the Declaration of Independence from Great Britain in 1776 and was a later participant in the drafting of the American Constitution.

‘Benjamin Franklin’s choice for the signs of electric charges leads to electric current being positive, even though the charge carriers themselves are negative — thereby cursing electrical engineers with confusing minus signs ever since.
The sign of the charge carriers could not be determined with the technology of Franklin’s time, so this isn’t his fault. It’s just bad luck’

Franklin was a pioneer in understanding the properties and potential of electricity. He undertook studies involving electric charge and introduced the terms ‘positive’ and ‘negative’ in explaining the way substances could be attracted to or repelled by each other according to the nature of their charge. He believed these charges ultimately cancelled each other out so that if something lost electrical charge, another substance would instantly gain the same amount.

 

His work on electricity climaxed with his kite flying experiment of 1752. In order to prove lightning to be a form of electricity, Franklin launched a kite into a thunderstorm on a long piece of conducting string. Tying the string to a capacitor, which became charged when struck by lightning, vindicated his theories.

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

NEXT buttonELECTRICITY

BENJAMIN THOMPSON (1753-1814) known as Count Rumford

1798 – England

‘Mechanical work can be converted into heat. Heat is the energy of motion of particles’

Heat is a form of energy associated with the random motion of atoms or molecules. Temperature is a measure of the hotness of an object.

In the eighteenth century, scientists imagined heat as a flow of a fluid substance called CALORIC. Each object contained a certain amount of caloric. If caloric flowed out, the object’s temperature decreased; if more caloric flowed into the object, its temperature increased.

Like PHLOGISTON, caloric was a weightless fluid, a quality that could be transmitted from one substance to another, so that the first warmed the second up. What is being transmitted is heat energy.

Working for the Elector of Bavaria, Rumford investigated the heat generated during the reaming out of the metal core when the bore of a cannon is formed. According to the caloric theory, the heat was released from the shards of metal during boring; Rumford noticed that if the tools were blunt and removed little or no metal, more heat was generated, rather than less.

Rumford postulated that the heat source had to be the work done in drilling the hole. Heat was not an indestructible caloric fluid, as LAVOISIER had argued, but something that could come and go. Mechanical energy could produce heat and heat could lead to mechanical energy.

One analogy he drew was to a bell; heat was like sound, with cold being similar to low notes and hot, to high ones. Temperature was therefore just the frequency of the bell. A hot object would emit ‘calorific rays’, whilst a cold one would emit ‘frigorific rays’ – an idea raised in Plutarch’s De Primo Frigido. Cold was an entity in itself, not simply the absence of heat.

Rumford thought there was no separate caloric fluid and that the heat content of an object was associated with motion or internal vibrations – motion which in the case of the cannon was bolstered by the friction of the tools. He had recognized the relationship between heat energy and the physicists’ concept of ‘work’ – the transfer of energy from a system into the surroundings, caused by the work done, results in a difference in temperature.
This transfer of energy measured as a temperature difference is called ‘heat’.

Half a century was to pass before in 1849, JAMES JOULE established the ‘mechanical equivalent of heat’ and JAMES CLERK MAXWELL launched the kinetic theory. According to Maxwell, the heat content of a body is equivalent to the sum of the individual energies of motion (kinetic energies) of its constituent atoms and molecules.

US born Rumford founded the Royal Institution in London and invented the calorimeter, a device measuring heat.

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

NEXT buttonHEAT

THOMAS ALVA EDISON (1847-1931)

1875 – USA

‘We don’t know one millionth of one percent of anything’

photo portrait of THOMAS ALVA EDISON ©

THOMAS ALVA EDISON

‘Genius is one percent inspiration and ninety-nine percent perspiration’
Scorning high-minded theoretical and mathematical methods was the basis of Edison’s trial and error approach to scientific enquiry and the root of his genius.

1877 – Patents the carbon button transmitter, still in use in telephones today.
1877 – Invents the phonograph.
1879 – Invents the first commercial incandescent light after more than 6000 attempts at finding the right filament and finally settling on carbonized bamboo fibre.

Edison held 1093 patents either jointly or singularly and was responsible for inventing the Kinetograph and the Kinetoscope (available from 1894) the Dictaphone, the mimeograph, the electronic vote-recording machine and the stock ticker.

His laboratory was established at Menlo Park in 1876, establishing dedicated research and development centres full of inventors, engineers and scientists. In 1882 he set up a commercial heat, light and power company in Lower Manhattan, which became the company General Electric.

Experimenting with light bulbs, in 1883 one of his technicians found that in a vacuüm, electrons flow from a heated element – such as an incandescent lamp filament – to a cooler metal plate.
The electrons can flow only from the hot element to the cool plate, but never the other way. When English physicist JOHN AMBROSE FLEMING heard of this ‘Edison effect’ he used the phenomenon to convert an alternating electric current into a direct current, calling his device a valve. Although the valve has been replaced by diodes, the principle is still used.

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

ALEXANDER GRAHAM BELL (1847-1922)

1875 – USA

‘The inventor of the telephone, Bell devoted much of his life to working with the deaf’

After emigrating to Canada from Scotland in 1870, Bell met Thomas Watson, who would help Bell’s theoretical ideas become physical reality. Bell believed that if the right apparatus could be devised, sound waves from the mouth could be converted into electric current, which could then be sent down a wire relatively simply and converted into sound at the other end using a suitable device. Bell’s telephone was patented in 1876.

Bell used the money brought in from his invention to found his company AT & T and the Bell Laboratories.
Just as THOMAS EDISON improved the viability of Bell’s telephone, so Bell enhanced Edison’s phonograph.

Bell spent some time educating Helen Keller and was instrumental in founding the journal ‘Science‘.

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

ALBERT MICHELSON (1852-1931) EDWARD MORLEY (1838-1923)

1887 – USA

‘The aim of the experiment was to measure the effect of the Earth’s motion on the speed of light’

This celebrated experiment found no evidence of there being an effect.

picture of the Nobel medal - link to nobelprize.org

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

NEXT buttonRELATIVITY

nobelprize_org_colorbox_logo - link to http://www.nobelprize.org/nobel_prizes/physics/laureates/2001/illpres/introduction.html

GEORGE FITZGERALD (1851-1901) HENDRICK LORENTZ (1853-1928)

1890 – Ireland
1904 – Holland

‘A moving object appears to contract’

The contraction is negligible unless the object’s speed is close to the speed of light.

In 1890 Fitzgerald suggested that an object moving through space would shrink slightly in its direction of travel by an amount dependent on its speed.

In 1904 Lorentz independently studied this problem from an atomic point of view and derived a set of equations to explain it. A year later, Einstein derived Lorentz’s equations independently from his special theory of relativity.

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

NEXT buttonRELATIVITY

NIKOLA TESLA (1856-1943)

1888 – USA

‘The transmission of high voltage alternating current (AC) over long distances is more efficient than the transmission of direct current (DC)’

DC transmission is no longer used anywhere in the world.

Early photograph of NikolaTesla ©

NIKOLA TESLA

In the 1880s THOMAS EDISON (1847-1931) developed DC generation and set up his Edison light company to build power plants. DC loses much of its energy when transmitted through wires at long distances and DC power plants had to be close to cities.

In 1888 Tesla came up with an idea involving a rotating magnetic field in an induction motor, which would generate an ‘alternating current’. He invented the AC induction motor and suggested that the transmission of AC power is more efficient.

On 16th November 1896 the AC power plant at Niagara Falls built by George Westinghouse (1864-1914) became the first power plant to transmit electric power between two cities (from Niagara Falls to Buffalo).

Tesla’s development of AC power led to the invention of induction motors, dynamos, transformers, condensers, bladeless turbines, mechanical rev. counters, automobile speedometers, gas discharge lamps (forerunners of fluorescent lights), radio broadcasting and hundreds of other things. His patents number over 700.

The tesla (T), the SI unit of magnetic flux density, for measuring magnetism, is named in his honour.

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

LINUS PAULING (1901- 94)

1931 USA

‘A framework for understanding the electronic and geometric structure of molecules and crystals’

An important aspect of this framework is the concept of hybridisation: in order to create stronger bonds, atoms change the shape of their orbitals (the space around a nucleus in which an electron is most likely to be found) into petal shapes, which allow more effective overlapping of orbitals.

A chemical bond is a strong force of attraction linking atoms in a molecule or crystal. BOHR had already shown that electrons inhabit fixed orbits around the nucleus of the atom. Atoms strive to have a full outer shell (allowed orbit), which gives a stable structure. They may share, give away or receive extra electrons to achieve stability. The way atoms will form bonds with others, and the ease with which they will do it, is determined by the configuration of electrons.

Earlier in the century, Gilbert Lewis (1875-1946) had offered many of the basic explanations for the structural bonding between elements, including the sharing of a pair of electrons between atoms and the tendency of elements to combine with others to fill their electron shells according to rigidly defined orbits (with two electrons in the closest orbit to the nucleus, eight in the second orbit, eight in the third and so on).

Pauling was the first to enunciate an understanding of a physical interpretation of the bonds between molecules from a chemical perspective, and of the nature of crystals.

In a covalent bond, one or more electrons are shared between two atoms. The two atoms are bound together by the shared electrons. This was proposed by Lewis and Irving Langmuir in 1916. Two hydrogen atoms form the hydrogen molecule, H2, by each sharing their single electron.

In an ionic bond, one atom gives away one or more electrons to another atom. So in common salt, sodium chloride, sodium gives away its spare electron to chlorine. As the electron is not shared, the sodium and chlorine atoms are not bound together in a molecule. However, by losing an electron, sodium acquires a positive charge and chlorine, by gaining an electron, acquires a negative charge. The resulting sodium and chlorine ions are held in a crystalline structure.
Until Pauling’s explanation it was thought that they were held in place only by electrical charges, the negative and positive ions being drawn to each other.

Pauling’s work provided a value for the energy involved in the small, weak hydrogen bond.
When a hydrogen atom forms a bond with an atom which strongly attracts its single electron, little negative charge is left on the opposite side of the hydrogen atom. As there are no other electrons orbiting the hydrogen nucleus, the other side of the atom has a noticeable positive charge – from the proton in the nucleus. This attracts nearby atoms with a negative charge. The attraction – the hydrogen bond – is about a tenth of the strength of a covalent bond.
In water, attraction between the hydrogen atoms in one water molecule and the oxygen atoms in other water molecules makes water molecules ‘sticky’. It gives ice a regular crystalline structure it would not have otherwise. It makes water liquid at room temperature, when other compounds with similarly small molecules are gases at room temperature.Water_animation

He devised the electronegativity scale, which ranks elements in order of their electronegativity – a measure of the attraction an atom has for the electrons involved in bonding ( 0.7 for caesium and francium to 4.0 for fluorine ). The electronegativity scale lets us say how covalent or ionic a bond is.

One aspect of the revolution he brought to chemistry was to insist on considering structures in terms of their three-dimensional space. Pauling showed that the shape of a protein is a long chain twisted into a helix or spiral, now known as an alpha-helix. The structure is held in shape by hydrogen bonds.
He also explained the beta-sheet, a pleated sheet arrangement given strength by a line of hydrogen bonds.

1922 – while investigating why atoms in metals arrange themselves into regular patterns, Pauling used X-ray diffraction at CalTech to determine the structure of molybdenum.

When X-rays are directed at a crystal, some are knocked off course by striking atoms, while others pass straight through as if there are no atoms in their path. The result is a diffraction pattern – a pattern of dark and light lines that reveal the positions of the atoms in the crystal.
Pauling used X-ray and electron diffraction, magnetic effects and measurements of the heat of chemical reactions to calculate the distances and angles between atoms forming bonds. In 1928 he published his findings as a set of rules for working out probable crystalline structures from the X-ray diffraction patterns.

Pauling’s application of quantum theory to structural chemistry helped to establish the subject. He took from quantum mechanics the idea of an electron having both wave-like and particle-like properties and applied it to hydrogen bonds. Instead of there being just an electrical attraction between water molecules, Pauling suggested that wave properties of the particles involved in hydrogen bonding and those involved in covalent bonding overlap. This gives the hydrogen bonds some properties of covalent bonds.

1939 – ‘The Nature of the Chemical Bond and the Structure of Molecules’
Pauling suggests that in order to create stronger bonds, atoms change the shapes of their waves into petal shapes; this was the ‘hydridisation of orbitals’.

Pauling developed six key rules to explain and predict chemical structure. Three of them are mathematical rules relating to the way electrons behave within bonds, and three relate to the orientation of the orbitals in which the electrons move and the relative position of the atomic nuclei.

      

      

Describing hybridisation, he showed that the labels ‘ionic’ and ‘covalent’ are little more than a convenience to group bonds that really lie on a continuous spectrum from wholly ionic to wholly co-valent.

1951 – published his findings one year after WILLIAM LAWRENCE BRAGG’s team at the Cavendish Laboratory.

CARBON BONDING
As carbon has four filled and four unfilled electron shells it can form bonds in many different ways, making possible the myriad organic compounds found in plants and animals. The concept of hybridisation proved useful in explaining the way carbon bonds often fall between recognised states, which opened the door to the realm of organic chemistry.

X-ray diffraction alone is not very useful for determining the structure of complex organic molecules, but it can show the general shape of the molecule. Pauling’s work showed that physical chemistry at the molecular level could be used to solve problems in biology and medicine.

A problem that needed resolving was the distance between particular atoms when they joined together. Carbon has four bonds, for instance, while oxygen can form two. It would seem that in a molecule of carbon dioxide, which is made of one carbon and two oxygen atoms, two of carbon’s bonds will be devoted to each oxygen.

Well-established calculations gave the distance between the carbon and oxygen atoms as 1.22 × 10-10m. Analysis gave the size of the bond as 1.16 Angstroms. The bond is stronger, and hence shorter. Pauling’s quantum .3-2. explanation was that the bonds within carbon dioxide are constantly resonating between two alternatives. In one position, carbon makes three bonds with one of the oxygen molecules and has only one bond with the other, and then the situation is reversed.

(image source)

picture of the Nobel medal - link to nobelprize.org

Link to WIKIPEDIA

Link to WIKIPEDIA

NEXT buttonTIMELINE

NEXT buttonX-RAY DIFFRACTION

<< top of page

EDWIN McMILLAN (1907- 90) GLENN SEABORG (1912- 99)

1940 – USA

‘Elements heavier than uranium in the periodic table (transuranium elements) are made artificially. Uranium (U, atomic number 92) is the heaviest element known to exist naturally in detectable amounts on the Earth’

In 1933 ENRICO FERMI showed that the nucleus of most elements would absorb a neutron.
In 1940 McMillan, a nuclear physicist, produced and identified the first artificial element, neptunium (Np, 93). In 1943 Seaborg, a chemist, succeeded in creating plutonium (Pu, 94).

So far more than 20 synthetic elements have been created. All are unstable, decaying with half-lives ranging from a year to a few milliseconds.
At least thirteen transuranium elements have been named after scientists:-
curium (Cm, 96: Marie and Pierre Curie [1944]), einsteinium (Es, 99: Albert Einstein [1952]), fermium (Fm, 100: Enrico Fermi [1952]), mendelevium (Md, 101: Dmitri Mendeleev [1955]), nobelium (No, 102: Swedish chemist Alfred Nobel (1833-96), known for his bequest for the foundation of the Nobel Prizes [1956]), lawrencium (Lr, 103: Ernest O. Lawrence, a physicist best known for development of the cyclotron [1961]), rutherfordium (Rf, 104: Ernest Rutherford [1968]), seaborgium (Sg, 106: Glenn Seaborg [1974]), bohrium (Bh, 107: Niels Bohr [1981]), meitnerium (Mt, 109: Lise Meitner [1982]); roentgenium (Rg, 111: named after Wilhelm Conrad Röntgen was first created in 1994 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany [1994]), copernicium (Cn, 112: named after astronomer Nicolaus Copernicus [1996]), flerovium (Fl, 114: named after Soviet physicist Georgy Flyorov [2012]).

picture of the Nobel medal - link to nobelprize.org

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

WILLIAM SHOCKLEY (1910- 89)

1947 – USA

‘The First Transistor’

Shockley was a member of the team at Bell Laboratories investigating the properties of electricity conducting crystals, focusing in particular on germanium.
This research led to the development of the junction transistor, virtually invalidating the vacuüm tube overnight.

The First Transistor The transistor was developed in 1947 as a replacement for bulky vacuum tubes and mechanical relays. The invention revolutionized the world of electronics and became the basic building block upon which all modern computer technology rests. In 1956, Bell Labs scientists William Shockley, John Bardeen and Walter Brattain shared the Nobel Prize in Physics for the transistor. Shockley also founded Shockley Semiconductor in Mountain View, California -- one of the first high-tech companies in what would later become known as Silicon Valley. Photo: Bell Labs (581 x 580)

The First Transistor
Photo: Bell Labs

The transistor was developed in 1947 as a replacement for bulky vacuum tubes and mechanical relays. The invention revolutionized the world of electronics and became the basic building block upon which all modern computer technology rests.
In 1956, Bell Labs scientists William Shockley, John Bardeen and Walter Brattain shared the Nobel Prize in Physics for the transistor.

Shockley also founded Shockley Semiconductor in Mountain View, California — one of the first high-tech companies in what would later become known as Silicon Valley.

picture of the Nobel medal - link to nobelprize.org

Wikipedia-logo © (link to wikipedia)

NEXT buttonTIMELINE

NEXT buttonCOMPUTERS

Related articles

MELVIN CALVIN (1911- 97)

1958 – USA

‘The cycle of chemical reactions by which plants turn carbon dioxide and water into sugar during photosynthesis’

In the Calvin cycle, which takes place in most plants, the initial product of the dark reactions (in which carbon is converted to sugar) is a compound with three carbon atoms per molecule. These are known as 3C plants.

A small group of plants – including maize, sorghum and sugar cane – are formed by a different cycle, known as the Hatch and Slack pathway. In this cycle the initial product of the dark reactions is a compound with four carbon atoms per molecule. These are 4C plants and can assimilate carbon dioxide at about twice or more the rate of 3C plants, and hence grow faster.
Calvin used radioactive 14C to study the photosynthesis cycle.

picture of the Nobel medal - link to nobelprize.org

Link to WIKIPEDIA

NEXT buttonTIMELINE

RICHARD FEYNMAN (1918- 88)

1963 – USA

‘Quantum electrodynamics’

Quantum electrodynamics was the successor to quantum mechanics. One of the problems with the quantum theory of electromagnetic fields was that for the theory to work electrons needed to have an infinite energy of interaction and an infinite number of degrees of freedom. Feynman’s way of calculating quantum electrodynamics set quantum theory on a firm footing.

After being invited to join the commission investigating the January 28, 1986 Challenger shuttle disaster by NASA, Feynman demonstrated his determination to remain an independent observer by publishing his own appendix to the report. Feynman added to the commission’s criticism of its system of management by finding that NASA’s own method of using statistics that showed the shuttle was safe was for two reasons. “ …an attempt to assure the government of NASA perfection and success in order to ensure the supply of funds. The other may be that they sincerely believed it to be true, demonstrating an almost incredible lack of communication between themselves and their working engineers…. For a successful technology, reality must take precedence over public relations, for nature cannot be fooled ”.

Wikipedia-logo © (link to wikipedia)

picture of the Nobel medal - link to nobelprize.org

picture of the Nobel medal - link to nobelprize.org

NEXT - QUANTUM COMPUTINGQUANTUM COMPUTING

NEXT buttonTIMELINE

NEXT buttonSTANDARD MODEL

Link to richard feynman Douglas Robb Memorial Lectures on video

EDWARD LORENZ (1917-2008)

1963 – USA

‘The behaviour of a dynamic system depends on its small initial conditions’

Photograph of EDWARD LORENZ ©

EDWARD LORENZ

While working at the Massachusetts Institute of Technology, Lorenz developed a simple computer model to forecast changes in weather at a number of places. In one of his equations he used a rounded number (for example 0.156 127 became 0.156). His model now predicted quite different conditions. He suggested that even a small initial unpredictable condition such as a flapping butterfly could produce a larger global change in weather.

The butterfly effect is one aspect of chaos theory that describes disorderly systems. The behaviour of a chaotic system is difficult to predict because there are so many variable or unknown factors in the system.

Wikipedia-logo © (link to wikipedia)
NEXT - MURRAY GELL-MANNTIMELINE

Chaos in a driven double well system

MURRAY GELL-MANN (b.1929)

1964 – USA

‘Neutrons and protons are made up of particles called quarks. Like electrons, they cannot be subdivided further’

Photograph of MURRAY GELL-MANN ©

MURRAY GELL-MANN

The standard model of particle physics divides all elementary particles into three groups:

six types of leptons
electron, electron neutrino, muon, muon neutrino, tau and tau neutrino
six types of quarks
up, down, charm, strange, top and bottom    and
four types of bosons

   
Ordinary matter is made up of:

protons
each an up-up-down quark triplet
neutrons
each an up-down-down quark triplet    and
electrons

 

Gell-Mann predicted the existence of three quarks; up, down and strange. Other scientists predicted another three. Quarks cannot exist singly.

picture of the Nobel medal - link to nobelprize.org

Link to WIKIPEDIA

NEXT button - GORDON MOORETIMELINE

NEXT button - ABDUS SALAMSTANDARD MODEL

GORDON MOORE (b.1929)

1965 – USA

‘The number of transistors on a computer doubles every 18 months or so’

library photo of GORDON MOORE

GORDON MOORE

In 1965, one of the founders of chipmaker Intel observed the exponential growth in the number of transistors per silicon chip and made his prediction which is now generally referred to as Moore’s law.

3D reconstruction chip surface (500x)

In 1971 the first Intel chip, 4004, had 2300 transistors. In 1982 the number of transistors increased to 120,000 in the 286, in 1993 to 3.1 million in the Pentium and in 2000 to 42 million in the Pentium 4.
Heat production is now the limiting factor in the production of silicon chips with millions of transistors.

Link to WIKIPEDIA

NEXT buttonTIMELINE

NEXT button - COMPUTERSCOMPUTERS

ROBERT CURL (USA b.1933) HAROLD KROTO (UK b.1939) RICHARD SMALLEY (USA 1943-2005)

1985 – USA

‘A form of the element carbon exists in which the atoms are arranged in tiny, hollow spheres shaped like soccer-balls’

Carbon may form long chains, but a structure of 60 atoms arrayed in a sphere of interlocking 20 hexagons and 12 pentagons also would form a stable structure.

Photograph of HAROLD KROTO - one of the team who first described 'Bucky balls' &copy:

HAROLD KROTO

Photograph of ROBERT CURL ©

ROBERT CURL

Photograph of RICHARD SMALLEY - one of the team who first described 'Bucky balls'

RICHARD SMALLEY

Such structures are termed ‘buckyballs’ – after architect Buckminster Fuller’s geodesic domes made from glass and metal, which demonstrate a similar structure on a macroscopic scale.

picture of the Nobel medal - link to nobelprize.org

Link to WIKIPEDIA

NEXT - ALLAN WILSONTIMELINE

ALLAN WILSON (1934- 91)

1987 – USA

‘All humans have evolved from a single woman – dubbed Eve – or, more likely from a small group of women, who lived about 200,000 years ago in Africa’

This hypothesis has been proposed after examining the mitochondrial DNA from 147 individuals from Africa, Europe, Australia and Papua New Guinea.

Lucy

The mtDNA is passed to the next generation only in the mother’s egg cell – with no contribution from the father because the sperms’ mitochondria do not survive fertilisation. The mtDNA of an individual is thus inherited from the female line.
133 different mtDNA types were used to draw an evolutionary tree that relates these types to each other and to a derived ancestral mtDNA tree. Their mtDNA tree had a common primary root of descent.

Not all scientists support the hypothesis. They argue that humans originated about one million years ago in different regions of the world.

Link to WIKIPEDIA

next-1TIMELINE

NEXT button - GENETICSGENETICS

australopithecus_africanus_-_cast_of_taung_child - link to 'evoanth' website
‘evoanth’ on WORDPRESS