Lect 2

بسم الله الرحمن الرحيم

(قل سيروا في الأرض فانظروا كيف بدأ الخلق) العنكبوت 20
Al-Iraqia university Prof. Dr. Samia –Alshahwani
College of medicine Y1 L2 12. 2015
Human Biology

1.2 Human classification

Objectives:
1. Mention the human place in overall organism's classification.
2. Explain humans & biosphere relation & culture role in shaping it.

Earth is divided into atmosphere (air), lithosphere (terrestrial), hydrosphere (water), and biosphere (life). Human & all organisms are part of the biosphere. Evolution theory postulates that all organisms , both living and extinct (extinction means species death), have descended from a common ancestor or an ancestral gene pool. This last universal common ancestor of all organisms is believed to have appeared about 3.5 billion years ago.
The classification of living beings mirrors their evolutionary relationship.
Taxonomy is the organism’s classification in an ordered system that indicates natural relationship; the system has evolved over time. As scientists learn more about organism’s classification systems changes.
Linnaean taxonomy is the dominant classification system; It includes ranks and binomial nomenclature. Organism name is governed by international agreements such as the International Code of Botanical Nomenclature (ICBN), the International Code of Zoological Nomenclature (ICZN), and International Code of Nomenclature of Bacteria (ICNB).

The three domain system, developed by Carl Woese, is a system for classifying organisms, is currently used


Human being belongs to:
Domain; Eukaryote
Kingdom; Animalia
Phylum; Chordates
Sub- phylum; Vertebrates
Class; Mammals
Order; Primates
Genus: Homo
Species: Sapiens
Biologists classify living things as belonging to one of three domains. The domains and evolutionary relationships of these domains are presented in Figure 1.5
1-Domain Bacteria.
2-Domain Archaea.
prokaryotes, one-celled organisms , lack nucleus.
3 -Eukarya.




Organisms in the third domain, Eukarya, are classified as being members of one of four kingdoms (Fig. 1.6)—plants, fungi, animals, and protists. Most organisms in kingdom Animalia are invertebrates, such as the earthworm, insects, and mollusks.

Eukarya, classified to four kingdoms: (Fig. 1.6)

Animals
Fungi
Plants.
Protists
Most organisms in kingdom Animalia are invertebrates, such as the earthworm, insects, and mollusks. Vertebrates are animals that have a nerve cord protected by a vertebral column which gives them their name Fish, reptiles, amphibians, and birds are all vertebrates. Vertebrates with hair or fur and mammary glands are classified as mammals. Humans, raccoons, seals, and meekest are examples of mammals.
Human beings are most closely related to apes
Human differ from other mammals including apes by:
(1) Developed brains.
(2) Upright stance.
(3) Language.
(4) Ability to use tools.
Humans did not evolve from apes; apes and humans share a common, apelike ancestor.

Fig 1.6.a. Life characteristic

Biodiversity
Biodiversity is the totality of genes, species, and ecosystems of a region, it describe most circumstances and presents a unified view of the traditional three levels at which biological variety has been identified.
Biodiversity is the degree of variation of life forms within a given species, ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems; It is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas Polar Regions support less specie. Rapid environmental changes typically cause mass extinctions
Since life began on Earth, five major mass extinctions and several minor events have led to large and sudden biodiversity
The period since the emergence of humans has displayed an ongoing biodiversity reduction and an accompanying loss of genetic diversity. Reduction is caused by human impacts, particularly habitat destruction, biodiversity impacts human health in a number of ways.

Phylogenetic life tree

A phylogenetic tree (Fig.1.6b ) or evolutionary tree is a branching diagram or "tree" showing the inferred evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical and/or genetic characteristics. The taxa joined together in the tree are implied to have descended from a common ancestor.
In a rooted phylogenetic tree, each node with descendants represents the inferred most recent common ancestor of the descendants, and the edge lengths in some trees may be interpreted as time estimates.

Each node is called a taxonomic unit. Internal nodes are generally called hypothetical taxonomic units (HTUs) as they cannot be directly observed. Trees are useful in fields of biology such as bioinformatics, systematics and comparative phylogenetics.






Fig. 1.6b A speculatively rooted tree for rRNA genes showing major branches Bacteria, Archea and Eucaryota

A phylogenetic tree of all living things, based on rRNA gene data, shows the separation of the three domains bacteria, archaea, and eukaryotes. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, presumably owing to rapid rRNA evolution. The exact relationships of the three domains is still being debated.

Humans Have a Cultural Heritage

Human beings have a cultural heritage in addition to a biological heritage. Culture encompasses human activities and products passed on from one generation to the next. Humans have a language. Knowledge acquired by adult instruction and imitation. Members of the previous generation pass on their beliefs, values, and skills to the next generation. Many of the skills involve tool use; Human skills have also produced a rich heritage in the arts and sciences. However, a society highly dependent on science and technology has its drawbacks as well.
Humans Are Members of the Biosphere
All organisms on Earth are part of the biosphere, although humans can raise animals and crops for food, they depend on the environment for many services. Without microorganisms that decompose, the waste we create would soon cover the Earth’s surface. Some species of bacteria can clean up pollutants like heavy metals and pesticides. Freshwater ecosystems, such as rivers and lakes, provide fish to eat, drinking water, and water to irrigate crops. The water-holding capacity of forests prevents flooding, and the ability of forests and other ecosystems to retain soil prevents soil erosion. Many of our crops and prescription drugs were originally derived from plants that grew naturally in an ecosystem.
Humans Threaten the Biosphere
The human tends to modify ecosystems for his own purpose (fig. 1.7) clear forests & grasslands to grow crops. Houses are built on what was once farmland. The overuse of water supplies by large human populations can result in desertification, or expansion of desert regions. Human activities have altered almost all ecosystems and reduced biodiversity (the number of different species present). The present biodiversity has been estimated to be as high as 15 million species. So far, less than 2 million have been identified & named, many species are extinct/day due to human activities. Biologists are alarmed about the present rate of extinction. They believe it may eventually rival the rates of the five mass /extinctions that occurred earlier in our planet’s history. One of the major bioethical issues of our time is biosphere & biodiversity preservation.






Humans must adopt biosphere and biodiversity conservation ethics. A conservation ethics that preserve biosphere, and biodiversity, to insure the continued existence of human species, on this beautiful planet, human should care for the creation and practice sincere gratitude for the creator.
Thanks Samia 2015