The Evolutionary Origins of Human Population Variation

1
The Evolutionary Origins of Human Population
Variation

• As we have seen, there is a geographically based
  pattern to human biological variation.
• Later on, we will explore more of the varying
  biological features that have been studied.
• Today, our task is to trace the evolutionary
  origins of modern human population variation
• How did it arise?
• What are the evolutionary and other processes
  that have brought it about?

2
Evidence for Human Evolution

• Comparative Anatomy
• The examination of the gross anatomical
  features of humans and apes reveals their close
  similarity and evolutionary relatedness.
• Comparative Genetics
• Comparisons of the genetic materials of the
  African apes and humans documents that these
  creatures are more closely related to each other
  than to any other living animal.
• Fossil Evidence

3
Fossil Evidence

• The direct evidence of our extinct ancestors.
• Other evidence documents relationships only
  fossil evidence provides data on the biology and
  adaptation of our actual ancestors.
• Because of the nature of the fossilization
  process, this evidence is often difficult to
  fully understand and interpret.

4
A mud site
5
Ape man
6
Whats in a name?

• Although there is much debate about what terms to
  use when referring to our extinct ancestors, for
  our purposes, we will call them hominids, and
  speak of human evolution as the evolution of the
  hominids (Using this term places ourselves and
  our extinct bipedal ancestors in a separate
  family Hominidae) .
• Thus, we can say that hominid evolution seems to
  have begun in Africa, and it is only much later
  in our evolutionary history that we find signs of
  our ancestors outside the African continent.
• We are, more specifically, members in the genus
  Homo, of which there are a number of now extinct
  species, and we are the only living member Homo
  sapiens.

7
Human Origins
humans chimpanzees gorillas
Hominid evolution
5 - 8 myr
10 myr.
common ancestry of humans and African apes
An evolutionary diagram of human and African ape
relationships, based on various genetic studies
8
(No Transcript)
9
The Human Fossil Record

• With recently found fossil discoveries from
  western Kenya and Chad, the human evolutionary
  line may now begin as early as about 6 million
  years ago.
• The earliest evidence is of animals that
  possessed some biological traits like those of
  the modern humans, some that resembled the apes,
  and many unique traits (these are not humans in
  fur suits, or bipedal apes, but a wholly extinct
  set of species with their own biology).
• Later-in-time members of our line look more and
  more like living people.
• A number of genera and species have been
  proposed.
• For us, this afternoon, we will be interested in
  the last 200,000 years of human evolution and the
  emergence of modern people.

10
Human Evolution Beginnings

• Our earliest ancestors, mainly of the group known
  as the australopithecines, are characterized by a
  combination of ape-like and human traits. They
  were bipeds, with small, non-projecting canines,
  but they had small, ape-sized brains in a skull
  that was very ape-like. Uniquely, they had
  massive back chewing teeth and huge jaw muscles.
  There were a number of species of this group. We
  know virtually nothing about their adaptation,
  diet, social organization or general behavior.
• By about 2 million years ago, members of our own
  genus, Homo, appear on the scene, probably
  evolving from one of the later australopithecines.
  They had bigger brains and smaller back teeth,
  but were still quite different from living
  humans. The first stone tools appear in the
  fossil record about two million years ago, as
  well as indications from scratch marks on animal
  bones that meat eating was occurring, but from
  hunting or scavenging is not known.

11
(No Transcript)
12
(No Transcript)
13
Human EvolutionFirst Out of Africa

• Early members of the modern human genus Homo are
  found in Africa between 2 - 1.8 million years
  ago. There is evidence of these early humans on
  the island of Java sometime after 1.8 million
  years ago Thus, about this time, there is a
  spread out of Africa, and into Eurasia. No one
  knows why this expansion of range occurred.
• From this point in human evolution on, the Old
  World is more or less populated by human
  ancestors. Keep in mind that the glacials, or
  ice ages, periodically descended in the northern
  hemisphere, making large areas uninhabitable.
• After our ancestors spread out of Africa, there
  begins a time of human evolution which will
  culminate with the appearance of modern humans in
  various parts of the world. How they evolved and
  the precise evolutionary pathways, are much in
  dispute.

14
(No Transcript)
15
1st fire
16
The First Europeans

• Some archaeologists claim that the very earliest
  sites in Europe are in southern Spain and central
  France and are dated to more than one million
  years ago.
• The earliest well documented site in Europe,
  however, is in central Spain, near Burgos, where
  human fossils are dated to about 780,000 years.
  There is no agreement as to the species of these
  fossils.
• This is considerably later than Homo expansion
  into Asia, and was probably dictated by glacial
  activity and the limited routes into Europe.
• Other sites in Europe, in Germany, France, Italy
  and Greece are all probably 500,000 years or
  later.

17
Europe first
18
(No Transcript)
19
Theories of Modern Human Origins

• Two major theories attempt to explain the latter
  phases of human evolution and the development of
  modern human population variation (human races)
• They view human origins very differently, with
  the differences based primarily on how isolated
  hominid populations were after spreading out
  from Africa around 1.8myr.
• Both theories have long histories, and in one
  guise or another, have been around since the
  recognition of the essential non-modern human
  qualities of the neandertals in the middle of the
  19th century

20
Competing Models of Human Origins

• The two competing models are known as
• 1. The Multi Regional Evolutionary Model.
• 2. The Single Origins Model (usually called Out
  of Africa).

21
theories
22
Multi Regional Evolution I

• With expansion of early Homo into Eurasia,
  hominid populations moved into new environments
  and began to evolve biological features for life
  in those places.
• In this model, hominid populations were
  continuously distributed over the continents, and
  were in more or less constant contact with other
  populations, thus sharing genes.
• This gene flow insured that the hominids remained
  one evolving species.
• By about 700,-400,00 years ago, archaic members
  of H. sapiens had appeared.

23
Multi Regional Evolution II

• These archaic H. sapiens populations in the
  different areas eventually evolve into living
  human regional populations (races).
• Thus, human races have a long antiquity in their
  local environments, having evolved from earlier
  archaic sapiens, and before that, from the local
  early Homo populations.
• Multi regional evolution stresses the ebb and
  flow of gene flow as a crucial factor in human
  evolution and in modern human origins.

24
Single Origins Theory I

• Begins in the same fashion as multi regional
  evolution with the spread of early Homo out of
  Africa into Eurasia. Hominid populations move
  into new environments and begin to evolve
  biological features for life in those places.
• In this theory, hominids lived in small, isolated
  populations and, lacking genetic contact, evolved
  into a number of new species.
• In Europe, this new species will eventually
  evolve into the neandertals, who become extinct
  toward the end of human evolution.

25
Single Origins Theory II

• While in Europe these now isolated hominids
  evolve into a new species, the Neandertals, In
  Africa and Asia, other species of Homo were also
  evolving. Like the Neandertals in Europe, they
  also possess low sloping brain cases, and large
  projecting faces lacking a chin. They had large
  brains, often within the range of living humans.

26
Single Origins Theory III

• Between about 200,-100,000 years ago, modern
  humans, Homo sapiens, evolved from an earlier
  Homo ancestor.
• This evolutionary origin apparently took place in
  one locale, most probably somewhere in sub-
  Saharan Africa.
• Soon after this origin, these modern humans begin
  to expand out of Africa, marking a second
  expansion out of Africa.
• These modern humans move into all parts of the
  Old World, replacing earlier species of Homo,
  like the Neandertals, in those areas.

27
Single Origins Theory IV

• Thus, in this theory, modern humans, Homo
  sapiens, evolve relatively recently in one locale
  and spread out from there.
• Modern human races all have a relatively recent
  origin in Africa.
• Earlier humans in other parts of the Old World
  were separate species from modern humans. They
  were not part of the ancestry of modern humans
  but an extinct side branch, replaced by these
  newcomers who moved out of Africa.

28
Modern Human Origins

• Thus, two different theories
• 1) Multi Regional Evolution
• 2) Single Origins Out of Africa
• Because they are amongst the most numerous of
  fossils, much of the emphasis of both theories
  centers on the Neandertals.

29
Neandertal Discoveries

• Earliest of the fossil hominids to be found and
  identified.
• First recognized in 1856 from a quarry find in
  the Neander Valley of Germany.
• Because it was the first discovery of a fossil
  hominid, and because this find came just 3 years
  before the publication of The Origin of Species,
  it quickly became part of the controversy
  surrounding Darwinian evolution.

30
Ape man
31
The Neandertals

• Fossil hominids who occupied Europe and the
  Middle East from about 150,000-30,000 years ago,
  when they disappear from the scene.
• Some view them as a subspecies of Homo sapiens,
  while others place them in their own species H.
  neanderthalensis.
• Morphologically, they possessed large brain
  cases, with low and long skulls and large
  projecting faces lacking a chin.
• They were capable of very complex behavior,
  including the deliberate burial of their dead.

32
The Neandertals

• Said one English anatomist of the first find in
  the Neander Valley
• It may have been one of those wild men,
  half-crazed, half idiotic, cruel and strong, who
  are always more or less to be found living on the
  outskirts of barbarous tribes, and who now and
  then appear in civilized communities to be
  consigned perhaps to the penitentiary or the
  gallows, when their murderous propensities
  manifest themselves.

33
Pity neandertal
34
Full Neandertal
35
Scene I
36
Neandertal Discoveries II

• After the initial discovery, many other fossils
  similar to the original Neander Valley find were
  excavated in many parts of Western and Eastern
  Europe, in the Middle East and as far East as
  Iraqi Kurdistan and Uzbekistan .
• Early on, they became stereotypes of the brutish,
  primitive, bestial ancestors of humans....and the
  term Congresspeople often hurl at each other
  when they wish to convey their opponents lack of
  humanity (did the Neandertals, one wonders, call
  their adversaries Congresspeople?).

37
Europe II
38
(No Transcript)
39
La Chappelle Skull
The Skull of a Neandertal from France
Large brain case with a brain often larger than
those of living humans
No chin
40
Modern Human Origins

• So, what are the relationships between the
  Neandertals (and their contemporaries in other
  parts of the Old World) and living humans?
• Multi Regional evolution and Single Origins
  theories rely on different sorts of evidence.
• 1) Multi regional evolution relies primarily on
  fossil evidence from Asia.
• 2) Single Origins emphasizes fossil evidence
  from Africa and comparative genetic evidence from
  living human populations.

41
Skulls I
42
Single Origins Theory Fossil Evidence

• This theory would be acceptable if fossils were
  found that were modern human in form, but dated
  earlier in time than Neandertals. Clearly, it
  would be difficult to support multi-regional
  evolution if modern humans were around either
  before or at the same time as their presumed
  ancestors, the Neandertals.

43
Single Origins Theory The Fossil Evidence

• Three sites in Africa appear to have modern human
  fossil remains, and each seems dated to the time
  of the Neandertals, or earlier.
• Unfortunately, each of these sites has problems
  associated with either the dates or the
  interpretation of the anatomy.
• The Three sites are located in
• 1) southern Ethiopia
• 2) on the border between South Africa and
  Swaziland
• 3) on the very southern most coast of South
  Africa

44
Problems Fossil Evidence for Single Origins
Theory

• Unfortunately, as these three sites in Africa all
  have a variety of difficulties associated with
  their total acceptance as evidence for the early
  appearance of modern humans in Africa, the
  evidence has to be carefully evaluated.
• There are other sites, however, not in Africa,
  but in Israel, in the Middle East, which would
  appear to offer much better evidence for the very
  early appearance of modern humans.
• We will examine this fossil evidence later on.

45
Single Origins Theory Genetic Evidence

• At the moment, this is the strongest evidence for
  a recent origin of modern humans in Africa.
• It is based on the analysis of DNA, but not
  primarily the DNA found on the chromosomes in the
  neucleus. Other genetic material is found in
  structures called mitochondria (known as mtDNA).
• Mitochondria (singular mitochondrion) are cell
  structures responsible for carrying out the
  conversion of the sugar glucose into a form
  usable to the cell for energy.

46
mtDNA Results

• Comparisons based on segments of the mtDNA from a
  number of human populations
• 1) Documents a greater amount of mtDNA
  variation in Africans in comparison to human
  populations in other parts of the world.
• 2) Discovered unique variations in Africa.
• Conclusions drawn from this data
• 1) Modern humans originated in Africa.
• 2) There was a subsequent spread to other parts
  of the Old World, replacing earlier hominid
  populations.

47
Debates about mtDNA Results

• Many scientists believe that these results are
  simplistic and do not reflect the realities of
  human origins.
• Some suggest that because Africa was an optimal
  environment for earlier hominids, population size
  was always larger there than elsewhere thus
  there was a greater number of mutations, and more
  variability.
• Others argue that if there was significant
  evolutionary selection on the mtDNA genes, then
  it would be very difficult to predict the nature
  of this evolution.

48
Multi Regional Evolution Fossil Evidence

• The evidence for multi regional evolution is
  primarily centered on a number of fossils from
  Asia.
• In China, for example, there is fossil evidence
  that the distinctive facial features of living
  Asian peoples had already appeared early in Asian
  human evolution, before any possibility of modern
  human migration out of Africa.

49
Dalioblique
50
Northchineseneol
51
Problems with both Theories

• Fossil and archaeological evidence from the
  Middle East would appear to be damaging to both
  theories.
• 1) Human fossil evidence argues against multi
  regional evolution.
• 2) Archaeological evidence argues against a
  Single Origins theory.

52
Early Modern Humans from Israel

• At two sites in Israel, early modern human
  skeletons have been excavated.
• Unlike the African sites, at both of these
  Israeli sites, there are complete skeletons that
  are directly associated with dates of between
  90-115,000 years.
• In contrast, at other Israeli sites,
  Neandertal-like fossils have been found. These
  are dated both earlier and later than the early
  modern human fossils

53
Ancestors II
54
Mid-East Neander
A neandertal from Iraq an
early modern human from Israel (probable date
60,000 years) (date 92,000 years)
55
Implications for Human Evolution

• This fossil evidence would seem to argue strongly
  against the multi regional evolution theory.
• If Neandertals are known both before, as well as
  after, well dated occurrences of modern humans in
  the Middle East, it would appear unreasonable to
  suggest that there was regional evolutionary
  continuity between Neandertals and early modern
  humans.

56
A Basic Problem Fossil Hominids and Archaeology
in the Middle East

• All of the fossil hominids in the Middle East,
  including the Neandertals, and the early modern
  humans from Israel, are all found with the very
  same sort of stone tools.
• Moreover, the archaeological sites contain the
  same sorts of hunted animal bones and the
  arrangement and organization of the sites is the
  same.
• Both the early modern humans and the Neandertals
  buried their dead, and in the same fashion,
  without any grave offerings.

57
How Can the differences between Neandertals and
Modern Humans be explained?

• If Neandertals and modern humans are different
  species, with a long evolutionary separation, how
  can the common use of the same stone tools be
  explained? The process of speciation requires
  reproductive isolation, which would have
  prevented separated populations from sharing
  knowledge of tools.

58
Modern Humans

• By 30,000 years ago, modern humans, associated
  with more sophisticated stone and bone tools, are
  found in parts of Central and Eastern Europe.
• At the same time, there are well dated
  Neandertals at sites in Spain and France.
• What were the relationships between the
  Neandertals and modern humans
• were they a separate species?
• did neandertals contribute to the
  ancestry of living humans?
• How did modern humans evolve?
  Quickly in one place or slowly over the Old
  World?
• Stay Tuned!

59
And of Course The Essential Question When does
Humanness first appear?

• What are the unique features of a modern human?
• When did these unique traits develop, and under
  what circumstances?
• Did they appear suddenly, at once, or gradually
  over a long time?
• Were the Neandertals, and their contemporaries,
  also human? Did they share these traits with us?
• Were the origins of these features the reason
  modern humans were able to spread over the whole
  world?

60
Lascaux Bison
61
Sculpture
62
pechmerle