this is a ppt on human evolution.

1. IN SEARCH OF OUR PAST
THE STORY OF HUMAN EVOLUTION

2. THE THEORY OF EVOLUTION
Evolution as a theory suggests that the great variety of
plant and animal life on earth developed gradually
through natural processes.
Although such an idea had been suggested as early as the
sixteenth century, the great English biologist Charles
Darwin (1809-1882) gave the theory prominence.
The most important of Darwin’s works is On the Origin
of Species by means of Natural Selection, first published
in 1859.
Darwin’s examination of geological formations,
collection of fossils, and study of plants and animals
from 1931 to 1936 led him to doubt that divine creation
had brought all species of living things into existence at
one moment. His doubts challenged the traditional
theory of creationism held for centuries in the western
world.

3. NATURAL SELECTION
Darwin’s theory was based on the idea that species changed or adapted over
time in response to their environment.
He based his theory on his observations that members of a single species vary
greatly in shape, size, colour, and strength. Most of these variations, he
believed, could be inherited.
He also noticed that the population of a species tended to remain the same
size, even though parents usually produced more than two offspring.
He concluded, therefore, that there had to be competition for survival. In the
struggle for survival, his theory stated, organisms with characteristics less
suited to their environments likely died without producing young. Those
organisms with more useful characteristics survived and reproduced, passing
on these variations to their offspring.As other descendants developed other
favourable variations, they passed on these characteristics as well.
As a result, Darwin argued, organisms with more helpful characteristics
survived the struggle for existence. Others died out. He called this process
Natural Selection.

4. MORE ON NATURAL SELECTION
Darwin believed that Natural selection had other effects as well.
•Many newly developed organisms remained in their old habitats and
crowded older forms out of existence.
•Other new organisms made their way into new surroundings, prospered, and
kept adapting. Therefore, there was a steady succession of new species best
suited to an environment at a particular time.
A modern extension of Darwin’s theory, known as neo-Darwinism, suggests
that evolution proceeded rapidly at some points in history, but very slowly at
others, resulting in long period of little change.
It must be understood that Charles Darwin never professed that his writings
provided proof of evolution or of the origin of species. They only proposed
the theory and suggested that evolution might help to explain a number of
mysterious facts about plants and animals.
Two later scientific developments have given the theory credibility.

5. First, the science of genetics
has helped to explain the
variations in each species and
how these variations are
passed on.
Second, evidence
gathered from fossil
remains in recent years
supports Darwin’s ideas.
Gaps in the theory still remain, however, and we do not have a
complete record of human evolution.

6. THE PHYSICAL EVOLUTION OF HUMANS
Evolution traces human development through several stages or species from
the first humanlike beings to modern humans. Although we still do not know
exactly when the evolution of humans and apes diverged or who our common
ancestor is, we do know that hominids (humanlike creatures) began to appear
over four million years ago.
Hominids are distinguished from apes most notably by their bipedalism (their
ability to walk on two feet) and by their larger brain size. All hominids are
members of the human family tree.

8. What is a Hominid?
• Modern humans & our direct
and indirect ancestors after our
lineage split from the
chimpanzee
• Until recently, earliest
hominids were dated between
3.5 and 2.4 mya & placed in
the genus Australopithecus
• In last few years, time range of
Australopithecus pushed back
to 4.2 mya, distribution
expanded to include regions
outside E. and S. Africa
• New finds from 4.5-7 mya are
thought to be hominids that
predate Australopithecines,
although their status is
debated

9. o Earliest fossil hominid sites are in
Africa
o They now span the latest Miocene
to the early Pleistocene from
about 6-7 mya to about 1.6 mya
o The major groups of sites are:
1. Ethiopia = Middle Awash valley &
Hadar (Australopithecus
afarensis)
2. Kenya = Lake Turkana
3. Tanzania = Olduvai Gorge
4. South Africa = various sites in
limestone caverns centered
around Sterkfontein

10.  Carrying behavior
 Reduction of overall heat stress - facilitates heat
loss through convection by exposing body to air
currents, only humans have sweat glands that
produce moisture to cool body
 Most energy efficient way to travel long distances
 Allows for better vision in open environments &
defensive action against predators by freeing hands
to throw objects

11.  Primates are difficult to characterize as an
order
› they lack the strong specializations found in most
other mammalian orders
 We can, however, point to several trends in
their evolution that help define primates and
are related to their arboreal, or tree-dwelling,
ancestry

12.  These include changes in the skeleton
› and mode of locomotion
› an increase in brain size
› a shift toward smaller, fewer and less specialized
teeth,
› and the evolution of stereoscopic vision
› and a grasping hand with opposable thumb
 Not all these trends took place in every
primate group nor did they evolve at the
same rate in each group

13.  The primate order is divided into two
suborders:
 Prosimians, or lower primates
› include the lemurs, lorises, tarsiers, and tree
shrews,
 Anthropoids, or higher primates,
› include monkeys, apes, and humans

15. ARDIPITHECUS RAMIDUS
Our understanding of human evolution is constantly changing. New and
different species are found and the human evolutionary tree grows more
branches.
One example of continuous change came in 1994 at Aramis, Ethiopia, where
people unearthed fossils of a previously unknown species dating from 4.4
million years ago. This humanlike creature walked the earth nearly half a
million years earlier than the oldest human ancestor identified to that point.
This exciting discovery led to the identification of a new genus called
Ardipithecus Ramidus. Ramidus has may chimplike as well as human
features, but its position on the human family tree is still not certain. It is a
mystery that still has to be solved.

16. THE AUSTRALOPITHECINES
Australopithecus Anamensis
In 1995, Maeve Leaky of the National Museums of Kenya discovered some
of the oldest representatives of a widely studied human genus, the
australopithecines. She and her team located pieces of a bipedal hominid, 4.1
million years old, which she named Australopithecus Anamensis. It is an
early species with very pronounced apelike teeth. Some scientists suggest
that this species may have given rise to Australopithecus Afarensis.

17. Australopithecus Afarensis
In 1974, at Hadar, Ethiopia, Donald
Johanson and his team unearthed a
set of fossilized bones of a female
hominid approximately 3.18 million
years old. They nicknamed their
discovery “Lucy”. These fossilized
bones led to the identification, in
1978, of Australopithecus Afarensis,
a species that may have survived
almost unchanged for 900,000
years. In Lucy’s species, Johanson
believed that he had found the
earliest common ancestor of all later
hominids. This changed with the
Aramis find in 1994, and the Leaky
find in 1995.

18. Australopithecus Africanus
Another branch of the Australopithecus
family is the Australopithecus Africanus,
which lived in the southern part of Africa
approximately 2.5 to 3 million years of age.
There are two Africanus “off” lines,
Australopithecus robustus and boisei.
Taung child

20.  Debate still surrounds the transition from H.
erectus to our own species, Homo sapiens
› Paleoanthropologists are split into two camps
 On the one side are those who support
› the "out of Africa" view
 According to this camp, early modern humans
evolved from a single woman in Africa, whose
offspring then migrated from Africa, perhaps as
recently as 100,000 years ago and populated
Europe and Asia, driving the earlier hominid
populations to extinction

22.  On the other side are those supporting the
"multiregional" view
 According to this hypothesis, early modern humans did
not have an isolated origin in Africa, but rather
established separate populations throughout Eurasia
(H. erectus > H. neanderthalenis > H. sapiens
 Occasional contact and interbreeding between these
populations enabled our species to maintain its overall
cohesiveness, while still preserving the regional
differences in people we see today

23.  Beginning in the 1980's, Rebecca Cann, at the
University of California, argued that the
geographic region in which modern people
have lived the longest should have the
greatest amount of genetic diversity today.
 Through comparisons of mitochondrial DNA
sequences from living people throughout the
world, she concluded that Africa has the
greatest genetic diversity and, therefore, must
be the homeland of all modern humans.

24.  Assuming a specific, constant rate of mutation, she
further concluded that the common ancestor of
modern people was a woman living about 200,000
years ago in Africa.
 This supposed predecessor was dubbed
"mitochondrial Eve“
 More recent genetic research at the University of
Chicago and Yale University lends support to the
replacement model.
 It has shown that variations in the DNA of the Y
chromosome and chromosome 12 also have the
greatest diversity among Africans today.

25.  Critics of the genetic argument for the
replacement model also point out that the rate
of mutation used for the "molecular clock" is
not necessarily constant, which makes the
200,000 year date for "mitochondrial Eve"
unreliable.
 The rate of inheritable mutations for a species
or a population can vary due to a number of
factors including generation time, the efficiency
of DNA repair within cells, ambient
temperature, and varying amounts of natural
environmental mutagens.

26.  Further criticism of the genetic argument for
the replacement model has come from
geneticists at Oxford University.
 They found that the human beta-globin gene
is widely distributed in Asia but not in
Africa. Since this gene is thought to have
originated more than 200,000 years ago, it
undercuts the claim that an African
population of modern Homo sapiens
replaced East Asian archaic humans less
than 60,000 years ago.

27.  Similarly, it is claimed that some Chinese
facial characteristics can be seen in an Asian
archaic human fossil from Jinniushan dating
to 200,000 years ago.
 Like Homo erectus, East Asians today
commonly have shovel-shaped incisors
while Africans and Europeans rarely do.
 This supports the contention of direct genetic
links between Asian Homo erectus and
modern Asians.

28. THE STONE AGE
The descendants of the australopithecines lived in the period called the
Stone Age. We call the period this because most of the artifacts found
from this time are mad of stone. Humans who lived in the Stone Age are
generally classified into a group or genus called Homo (“man”).
Most experts divide the Stone Age into three stages:
Paleolithic or Old Stone Age (2 million BCE-10 000 BCE)
Mesolithic or Middle Stone Age (10 000 BCE-8000 BCE)
Neolithic or New Stone Age (8000 BCE-5000 BCE)
Stone Tools

29. Homo Sapiens
The species name, Homo Sapiens, means
“man who thinks”-an appropriate title for
the species that formulated the spoken
language and developed more
sophisticated tools. The most ancient find
was discovered in Hungary in 1965, dating
from about 450 000 to 400 000 years ago.
Other remains of Homo Sapiens have been
found in England, Germany, and France.
These bones date from approximately 250
000 years ago, the period between the third
and fourth ice ages.
There are two types of Homo Sapiens; the
Neanderthals, or Homo Neanderthalis, and
Modern Human, or Homo Sapiens
Sapiens.

31. IN SEARCH OF HOMO SAPIENS
Homo Habilis
Historians believe Homo Habilis, or “handy man”, flourished in Africa about
2.5 millions year ago. Homo Habilis were the first hominids to develop and
use stone tools-proof of their ingenuity and creative ability. The brain size
and presence of humanlike teeth from fossil finds suggest that Homo Habilis
might have been our human ancestor.
Many scientists believe that Habilis bridges the evolutionary gap between
Australopithecus and Homo. Yet, the sequence of human ascent is still
uncertain. Signs of co-existence have arisen.

32. Homo Erectus
Homo Erectus first appeared about 2
million years ago. Their species
name refers to the fact that they could
walk completely upright, like modern
humans. Only a few dozen skulls of
this species have been found, notably
in Africa, Java, and China.
The first specimens were found in
Java in 1891 and 1892. Called Java
Man, they are about 700 000 years
old.
Homo Erectus was the first species to
use fire and the first to migrate into
Europe and Asia from Africa.

33. Homo Heidelbergensis
Homo Heidelbergensis lived approximately 500 000 years ago. It is often
referred to as Archaic Homo Sapiens because it combines features of Homo
Erectus with more modern features.
The first specimen was found in a Quarry in Germany in 1907. But other
specimens have been found in a variety of places around the world including,
Zambia, Southern Africa, Tanzania, and parts of Northern Europe as far North
as England.
Many researchers consider Homo Heidelbergensis a possible ancestor for both
modern humans (Homo Sapiens) and Neanderthals (Homo Neanderthalensis),
while others are still not comfortable with this label.

34. Neanderthals
Located in Europe, Neanderthals first appeared
about 230 000 years ago and disappeared
approximately 30 000 years ago.
Quarry workers in Dusseldorf first discovered the
remains of these people in the Neander Valley of
German in 1856. More finds have since been
located primarily in Belgium, France, and other
parts of Europe.
They traveled as far as China and the Middle
East. Their total population at any one time
probably numbered fewer than 100 000.
It is still unclear who the Neanderthals were,
scientists wonder whether they were our direct
ancestor or whether they were a separate species.
It is commonly held, however, that the
Neanderthals were driven to extinction by
modern humans.

35. THE MODERN HUMAN
About 40 000 years ago, modern humans moved into Europe armed with the
skills to make clothing, better shelters, and more efficient hearths.
Nineteenth-century scientists named these newcomers Cro-Magnon people
after the French rock-shelter where three anatomically modern skeletons
were discovered in 1868.
Cro-Magnons were Homo Sapiens who evolved in Africa and slowly pushed
their way into Europe. They developed the ability to endure colder
climates, even climates as cold as those found in Iceland or Greenland.
Cro-Magnon people were about as tall as modern northwestern Europeans.
They also had many of the same facial and cranial features as modern
northwestern Europeans.
Eventually, their successors moved into Asia. About 30 000 years ago, they
crossed the Bering Strait after the retreat of the ice and entered the
Americas. Others reached Australia.
With this migration, our modern human ancestors spread throughout the
world.

37. o Microevolution: change in gene
frequency - YES
o Macro evolution : formation of
species – NO
o Are we genetically different from
our Homo sapiens ancestors who
lived 10-20,000 years ago? The
answer is almost certainly yes. In
fact, it is very likely that the rate of
evolution for our species has
continuously accelerated since the
end of the last ice age, roughly
10,000 years ago.

38.  This is mostly due to the fact that our human
population has explosively grown and moved
into new kinds of environments, including cities,
where we have been subject to new natural
selection pressures.
 For instance, our larger and denser populations
have made it far easier for contagious
diseases, such as tuberculosis, small pox, the
plague, and influenza to rapidly spread through
communities and wreak havoc. This has
exerted strong selection for individuals who
were fortunate to have immune systems that
allowed them to survive.

39.  There also has been a marked change in diet
for most people since the end of the last ice
age. It is now less varied and predominantly
vegetarian around the globe with a heavy
dependence on foods made from cereal
grains. It is likely that the human species has
been able to adapt to these and other new
environmental pressures because it has
acquired a steadily greater genetic diversity.

40.  A larger population naturally has more
mutations adding variation to its gene pool
simply because there are more people. This
happens even if the mutation rate per person
remains the same. However, the mutation
rate may have actually increased because
we have been exposed to new kinds of man-
made environmental pollution that can cause
additional mutations.

41.  It is not clear what all of the consequences of
the environmental and behavioral changes
for humans have been. However, it does
appear that the average human body size
has become somewhat shorter over the last
10,000 years, and we have acquired
widespread immunity to the more severe
effects of some diseases such as measles
and influenza.

42.  It remains to be seen
› how we will use this technology in the future
› and whether we will continue as a species,
› evolve into another species,
› or become extinct as many groups have before
us