Spread of modern humans around the world (10)

Question 1

There are two main hypotheses how modern humans (H. sapiens) spread around the world. What are these?

Answer 1

1. “Out of Africa” hypothesis
2. Multiregional hypothesis

Question 2

What does the Out of Africa hypothesis propose?

Answer 2

The ‘Out of Africa’ (0OA) hypothesis proposes that modern Homo sapiens originated in North Africa between 200 000 and 150 000 years ago and over-time dispersed into Europe and Asia.

Question 3

• It is proposed that an earlier Homo (African H. erectus / H. ergaster) species left Africa and evolved into H. ____ (Asia) and H. ______ (Europe) around 1 million years ago.
• About 60 000 years ago a major wave of modern H. sapiens left _____ Africa. They spread rapidly replacing existing human populations in Asia (H. erectus) and Europe (H. neanderthalensis). This was probably because of their superior technology and communication skills. There is recent genetic evidence that there was minor ______ with H. neanderthalensis.

Answer 3

erectus

neanderthalensis

northern

interbreeding

Question 4

The hypothesis of a single origin of modern humans in ____ that left and populated the world is the one accepted by most scientists today.

Answer 4

Africa

Question 5

What does the multiregional hypothesis state?

Answer 5

The multiregional hypothesis states that after the earlier Homo species (Homo erectus) migrated out of Africa giving rise to many different populations that became reproductively isolated. These then evolved independently into different forms of H erectus, e.g. H neanderthalensis. Eventually, all of these evolved into H. sapiens, i.e. modern humans. Only a few scientists support this hypothesis today.

Question 6

The evidence for this hypothesis comes from a combination of sources: (3)

Answer 6

1. Fossils
2. Genetics links, mtDNA
3. Archaeology

Question 7

Multiregional hypothesis in terms of fossils:

Answer 7

It is in Africa that the oldest modern Homo sapiens fossils have been found, e.g. the Omo H. sapiens fossil remains, which date to 195 000 years ago. Fossils of all other modern H. sapiens found outside of Africa date to more recent times. This suggests strongly that modern H. sapiens originated in Africa. This is supported by genetic evidence.

Question 8

Multiregional hypothesis in terms of genetic links:

Answer 8

Until recently the only way of learning about early Homo sapiens was through fossil remains and stone tools. Now geneticists use DNA, nuclear and mitochondrial, to propose where H. sapiens probably evolved and work out when this might have happened. Geneticists preferably use mitochondrial DNA (mtDNA) to study human origins and migrations.

Question 9

Why do geneticists preferably use mitochondrial DNA (mtDNA) to study human origins and migrations?

Answer 9

This is because it:

• is a shorter molecule than nuclear DNA.
• mutates more quickly than nuclear DNA.
• passes unchanged from mother to offspring.

These properties make it easier to detect any changes or variations that occur in the mtDNA molecule. It is the variations that are important for these studies. Each variation (a mutation) is called a marker. As mtDNA mutates at a known rate the age of a lineage can be worked out. Therefore races with the greatest number of markers are the oldest populations, and the least, the youngest population.

Question 10

How does genetics show where modem Homo sapiens originated?

Answer 10

Geneticists compared markers from mtDNA that had accumulated in humans from around the world. They found that the indigenous African people have the greatest number of different markers, nearly double that of any other group anywhere in the world. The large number of variations could only have evolved over a long period of time. Therefore the African populations must be the oldest. Thus, H. sapiens must have originated in Africa. This can be seen in the cladogram in the next column.

Question 11

How does genetics show when modem Homo sapiens originated?

Answer 11

The differences in markers between two population groups tell scientists how long ago they separated. As mentioned earlier if there are few differences (markers), they separated recently. Many differences indicate that they separated a long tỉme ago. By comparing mtDNA genetic markers geneticists have concluded that the last female common ancestor, with a genetic marker found in all living humans, must have lived roughly 150 000 years ago in Africa (Ethiopia or Sudan) ‘Mitochondrial Eve’. While 150 000 years ago is not exactly the same as the dating of the earliest modern H. sapiens fossil (195 000) it is remarkably similar. So the evidence from both genetics and fossils tell us the same thing, modern Homo sapiens had their origin in Africa between 195 000 and 200 000 years ago.

Question 12

It is also possible to use mtDNA to trace ______ dates and patterns. . All markers seen in non-Africans show the date of the earliest successful ‘Out of Africa’ migration as being about 60 000 years ago. According to the genetic markers, the route was into the Middle East and then across the world to ____ (50 000 years ago), _____ (40 000 years ago), _____ (40 000 years ago) and the _____ (20 000 years ago). These dates can be very variable, depending on the source used. However, the route and relative dates are correct. The further one goes from Africa where there are fewer differences in genetic markers between groups. This means these are ‘newer’ populations.

Answer 12

migratory

Middle East

Eurasia

Australia

Europe

Americas

Question 13

How are human populations linked genetically?

Answer 13

By examining mtDNA sequences in different populations, the closeness of relationships between populations (or within populations). Certain similarities in the genetic anthropologists determine whether or not different groups of people came from the same geographical area. This is significant because it allows anthropologists to trace patterns of migration and settlement, which gives helpful insight as to how contemporary populations have formed and progressed over time. geneticists can determine the makeup of humans let genetic.

Question 14

• Each of us living today has ____ that contains the story of our ancient ancestors’ journeys.
• Mitochondrial DNA extracted from bones of 38 000-year-old ______ individuals is quite different from that of modern humans, strongly suggesting that modern humans replaced Neanderthals in Europe without interbreeding.

Answer 14

mtDNA

Neanderthal

Question 15

Where do the San fit in?

Answer 15

The San (!Kung or Bushmen) people of Southern Africa, who have lived as hunter-gatherers for thousands of years, are likely to be the oldest extant population of humans on earth, members of the San people who live in ! Kung eastern Namibia and western Botswana extant.

Question 16

Scientists have found that the San people have the oldest mtDNA ____, shown by their having the most genetic markers on their mtDNA.

Answer 16

lineage

Question 17

The San are therefore the oldest _____ population of humans on the continent - and on earth. According to their genes, they branched off from the original modern H. sapiens line very early in human history, about 160 000 years ago. Therefore they are directly descended from the original population of early human ancestors who gave rise to all other groups of eventually, to the people who left the continent to populate other parts of the world. It can be said that the San are remnants of human’s ancient _____ and have a unique place in the history of the world. Sadly, this uniqueness has been largely overlooked. It is to the great discredit of other groups who moved into the San’s homeland region, i.e. Southern Africa that the San have lost so much; they have been killed, mistreated, moved out of their territory and discriminated against.

Answer 17

continuous

ancestors

Question 18

3. Archaeological evidence

One possible hypothesis about how modern ____ ____ originated is that a population of H. heildelbergensis (archaic H. sapiens) became isolated along the southern approximately: off from the interior by high mountains and the Karoo and Kalahari deserts. In this area there were fewer of the animals they normally hunted. They, therefore, had to rely largely on a seafood diet. Evidence of this is extensive shell middens at numerous places along the southern coast. It is known that seafood contains high protein levels and Omega-3 oils, which are essential for brain growth and development. This could have contributed to the development of a more advanced human brain like that found in modern H. sapiens. coast of South Africa 200 000 years ago. This group was cut The enlarged brain could be the reason H. sapiens developed to become a fully sensate being that could think and communicate symbolically, was adaptable, self-aware and creative and formed ____ and _____ groups.

Answer 18

Homo sapiens

complex social

cultural

Question 19

In our modern world, evolutionary principles have become very relevant and are used for example in: (5)

Answer 19

• Resolving legal issues, by ‘DNA fingerprinting’
• Tracing evolutionary origins of diseases and developing treatments.
• Selective breeding of plants and animals.
• Understanding resistance of insect pests to insecticides.
• Modern warfare, by the use of biological pathogens and mutation-inducing chemicals.

Question 20

Evolution is always happening, but for many species, including humans, it occurs extremely slowly over thousands of years, which makes it difficult, if not impossible, to observe. However, evolutionary change can be: (5)

Answer 20

• demonstrated in a laboratory using rapidly reproducing life forms such as single-celled organisms and certain invertebrates. See the examples below.
• seen as a result of the breeding of new varieties of plants and animals by artificial selection.
• noticed in a situation where resistance: to TB drugs developed in the TB bacterium to an insecticide developed in insects.
• seen in the alarming adaptation of HIV to drugs.
• shown by the development of new species of plants by polyploidy and hybridisation.

Question 21

Populations of pathogenic organisms, e.g. bacteria and insects can evolve quickly as: (2)

Answer 21

• they have natural variation.
• mutations occur often because the individuals breed very rapidly.

In the process of evolving, they can gain resistance to many chemicals that should kill them. The antibiotics or insecticides, therefore, cease to be useful.

Question 22

Bacterial resistance to the antibiotic can now develop as follows: (2)

Answer 22

• Due to natural variation (which exists in all populations) and (common populations), some bacteria have a ‘new’ gene that offers resistance to the antibiotic. These will survive the initial doses of the antibiotic. chance mutations rapidly producing
• As bacteria reproduce rapidly the bacteria with the resistant gene could soon form a new antibiotic-resistant population. In the course of 12 hours, one bacterium can multiply to become a billion.