The Human Story

THE HUMAN STORY

KEY WORDS AND TERMS USED IN THIS TOPIC

As you study this topic you should write the definitions for the following syllabus terms.

THE HUMAN STORY

SUMMARY OF THIS TOPIC

Humans are mammals, and are classified at the order level as primates, at the family level as hominids, at the genus level as Homo and at the species level as sapiens. Characteristics shared by primates include opposable first digits, eyes positioned towards the front of the head, nails instead of claws and large brains. Primates have been further divided into tree shrews, prosimians and anthropoids based upon brain size, thumb opposability and vision. Recent technological advances, however, have led scientists to conclude that tree shrews are not actually primates, and have led to the creation of two major sub-orders – the Strepsirhines and the Haplorhines. Under this new classification, humans are generally now grouped into a sub-family with gorillas and chimpanzees, whereas orangutans are grouped into another sub-family. Much of this new knowledge has been achieved through techniques such as karyotype analsysis, DNA hybridisation and the study of mitochondrial DNA.

Fossil evidence has also helped in the classification of humans and other primates. Absolute dating techniques using radioactive isotopes, and relative dating techniques involving the comparison of fossils found in different rock strata, are examples of methods used to establish relationships between these organisms.

Scientists who have contributed to our understanding of human evolution include the Leakey family, Donald Johansen, Robert Broom and Raymond Dart. Although their theories differ in some areas, most of them have concluded that members of the genus Homo and the

Australopithecine species arose from a common ancestor; probably either A. africanus or A.afarensis.

The ‘Out of Africa’ theory proposes that modern humans spread from Africa less than 10,000 years ago, and are descended from an African Homo erectus. These modern humans replaced archaic species that had previously moved out of Africa some 1.5 million years ago. Another theory, the theory of Regional Continuity, states that this recent migration out of Africa did not occur; instead, Homo erectus moved out of Africa 1.5 million years ago and evolved into modern humans in different countries.

Humans have adapted to their environment by expressing genes that are suitable to their particular surroundings. This results in a range of human forms and is referred to as polymorphism. The gradual change in human characteristics from one region to another is known as clinal gradation.

Human culture has developed from the group hunting of Australopithecines up to 4 million years ago to the complex social structures, industry and agriculture of today. Differences in the behaviour of humans and other primates reinforces the concept that humans are better equipped to develop culturally advanced societies, to the extent that human populations are no longer controlled by the environment. Studies such as the Human Genome Project have the potential to increase populations further by providing the knowledge and techniques to detect and cure genetic diseases and to develop more effective drugs.

THE HUMAN STORY

MAJOR OBJECTIVES OF THIS TOPIC

As indicated in the HSC Biology syllabus, the major outcomes of this topic include the ability to:

·  describe what is meant by the term, ‘species’

·  explain why humans are classified as :

-  Kingdom: Animal

-  Phlyum: Chordate

-  Class: Mammal

-  Order: Primate

-  Family: Hominid

-  Genus: Homo

-  Species: sapiens

·  distinguish between the arbitrary classification of humans as members of the family hominidae and the sub-family homininae

·  outline the major features of primates, and describe the differences and similarities between prosimians, new and old world monkeys, apes and humans

·  describe technological advances which have affected the classification of primates

·  outline how fossils form and distinguish between relative and absolute methods of dating fossils

·  outline reasons why fossil evidence alone is not enough to fully interpret the past

·  describe how the following methods can be used to compare different primates:

-  karyotype analysis

-  DNA hybridisation

-  comparison of haemoglobins

-  DNA sequencing

-  tracing mitochondrial DNA

·  model DNA hybridisation and explain its use in establishing relationships between organisms

·  carry out an activity to model karyotype analysis

·  outline two different views of human evolution to include the following species:

-  Australopithecus ramidus

-  Australopithecus afarensis

-  Australopithecus robustus

-  Australopithecus boisei

-  Australopithecus africanus

-  Homo habilis

-  Homo ergaster

-  Homo erectus

-  Homo heidelbergensis

-  Homo neanderthalensis

-  Homo sapiens

·  compare the above species in terms of their :

-  body structure

-  cranial capacity

-  fossil ages and regional locations

-  inferred culture

·  discuss the contributions of the following scientists to our knowledge of human evolution:

-  The Leakey family

-  Donald Johansen

-  Robert Broom

-  Philip Tobias

-  Raymond Dart

-  Jane Goodall

·  compare and contrast the ‘Out of Africa’ theory of human evolution and the theory of Regional Continuity

·  outline the ways in which human diversity has come about

·  define the terms ‘polymorphism’ and ‘clinal gradation’, giving examples of each

·  outline the cultural changes that have occurred in humans since they became organised hunters

·  compare human culture with that of other primates in terms of:

-  care of young

-  length of juvenile stage

-  development and size of social groups

-  use of tools

-  communication systems

·  describe how increased population mobility, modern medicine and other technology and genetic engineering may affect future human evolution

·  outline the purposes of the Human Genome Project and discuss their implications in terms of human evolution

1) Humans have characteristics that can be used to classify them with other organisms

Classification of humans and the concept of species

The taxonomic levels used to classify organisms, from least specific to most specific are: kingdom, phylum, class, order, family, genus and species. A species is generally defined as a group of organisms which share a common gene pool, and can interbreed successfully to produce fertile offspring. Each species is therefore reproductively isolated from other species. Problems can be encountered when determining whether organisms belong to the same species in the prokaryotes and in some eukaryotes, as these organisms do not reproduce sexually. Other problems with this definition of species occur in the production of genetic hybrids such as triticale, which is the result of a cross between wheat and rye plants. Many

such hybrids are fertile themselves, and yet are not

identical to either parent plant. Polyploid plants, which have more than one set of chromosomes, also pose a problem, because they are very similar to their diploid ancestors yet cannot breed with them.

THINK!!! Which of the following would have the most characteristics in common?

a) Two orders of the same class

b) Two phyla in the same kingdom

c) Two species in the same genus

d) Two species in different orders

·  As a requirement of this topic, you need to identify the features of humans that place them in each of their designated taxonomic levels

Table 7-1 , below , classifies human beings from least specific taxonomic level to the most specific.

Table 7-1 The classification of humans

Primate characteristics

Humans belong to the mammalian order known as primates. Characteristics of primates include the possession of opposable first digits on the hands and feet (see fig. 7-1), eyes which are directed towards the front of the skull, relatively large brains in comparison to body size, flat nails instead of claws and usually only two mammary glands. In addition, primates tend to produce few live young at a time, and their gestation period is comparatively long in relation to other mammals. Many of these features were initially adaptations to an arboreal (tree) existence, as they provided the physical necessities for the movement from branch to branch by these animals. Early primates developed the habit of squatting, thus freeing the hands for other, exploratory actions. Development of the forebrain occurred simultaneously with this behaviour. In the higher primates, increased care of the young and group behaviour also occur.

Primates are usually placed into three groups; the most primitive of these being the tree shrews (some recent studies have in fact excluded tree shrews from this order). The prosimians, or ‘pre-monkeys’, possess more specialised primate features than the tree shrews- examples include greater opposability of the first digits, larger brains and binocular vision. The most developed primate group is the anthropoids, which includes monkeys, apes and man. Features of this group include even greater opposability of the thumb, a flatter face, a collarbone that gives the arm strength for swinging movements, an even larger brain case and stereoscopic, colour vision.

Fig. 7-1 The foot of an orangutan, showing the opposable fifth digit which is an adaptation to its arboreal existence

Fig. 7-2 shows the main sub-orders of the primates. Note that this classification has recently been modified (see later in this chapter), due to technological advances such as DNA hybridization techniques. One result of this is that tree shrews are no longer regarded as primates in many circles. Besides physical differences such as brain sizes, degree of binocular vision and degree of thumb opposability, another difference between the primitive primates and the more developed ones can be seen in gestation periods and the length of life phases in each. The Lemur, for instance, has a gestational period of only 18 weeks, compared to 34 weeks in chimpanzees and 40 weeks in man.

Fig. 7-2 The main sub-orders of the primates. See later in this chapter for recent modifications to this classification.

THINK!!! The skulls below belong to a tree shrew, a tarsier (a prosimian), and Dryopithecus, thought to be a common ancestor of apes and man. Can you identify each? Explain your answers.

Table 7-2, below, describes the main primate groups.

Table 7-2 The main primate groups

·  As a requirement of this topic, you need to be able to discuss how technological advances have affected primate classification.

As mentioned above, traditional classifications of the primate order divided these animals into three main sub-orders; the tree shrews, prosimians

( lemurs, lorises, tarsiers) and the anthropoids

( monkeys, apes and man).Further anatomical research, fossil evidence and modern techniques such as DNA hybridisation , however, have resulted in many scientists now proposing a revised classification of these sub-orders. Firstly, tree shrews are no longer regarded as anatomically close enough to the other primates, and many researchers have placed them into their own order, Scandentia. Secondly, studies of the auditory apparatus, dental arrangement and cranial blood supply of the tarsier have led many taxonomists to place this animal in the same sub-order as the original anthropoids. This new sub-order is now often referred to as the Haplorhines, and those primates remaining in the former prosimian sub-order are now referred to as the Strepsirhines. Interestingly, another reason for re-grouping the tarsier is that, along with monkeys, apes and man, it has a dry nose whereas the Strepsirhines all have wet noses.

Within the Haplorhines/ anthropoids, humans were originally placed separately in the family Hominidae and orangutans, gorillas and chimpanzees were placed in the family Pongidae. Recent evidence, both fossil and genetic, however, has resulted in some taxonomists placing all these primates into the family Hominidae, with the orangutans placed in a sub-family, the Ponginae, and humans, chimpanzees and gorillas in the sub-family Homininae. The gibbons, previously placed with the apes in the Pongidae, are now often classified in their own family, the Hylobatidae, because they are the only apes solely confined to an arboreal existence. Other classification systems place orangutans in the family Pongidae and gorillas, chimpanzees and humans in the Hominidae. Reasons for placing gorillas, chimpanzees and humans so closely together include DNA hybridisation results, which have revealed that there is only a 1.2% difference between human and chimp DNA and a 1.4% difference between human and gorilla DNA. Some taxonomists believe that gorillas and chimps should be placed in this way with humans because they share more than 97% of DNA with the human genome and have the capacity for limited language and simple cultures beyond family groupings.