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Bar graph shows the number of years it has taken to add each billion people to the world population. By 1800, there were about a billion people on Earth. It took 123 years, until 1930, for the number to reach two million. Thirty-three years later, in 1960, the number reached three billion, and 15 years after that, in 1975, the number reached four billion. The population reached five billion in 1987, and six billion in 1999, each twelve years apart. Currently, the world population is nearly seven billion. The population is projected to reach 8 billion in 2028, and 9 billion in 2054.
The time between the addition of each billion human beings to Earth decreases over time. (credit: modification of work by Ryan T. Cragun)

Click through this interactive view of how human populations have changed over time.

Overcoming density-dependent regulation

Humans are unique in their ability to alter their environment with the conscious purpose of increasing its carrying capacity. This ability is a major factor responsible for human population growth and a way of overcoming density-dependent growth regulation. Much of this ability is related to human intelligence, society, and communication. Humans can construct shelter to protect them from the elements and have developed agriculture and domesticated animals to increase their food supplies. In addition, humans use language to communicate this technology to new generations, allowing them to improve upon previous accomplishments.

Other factors in human population growth are migration and public health. Humans originated in Africa, but have since migrated to nearly all inhabitable land on the Earth. Public health, sanitation, and the use of antibiotics and vaccines have decreased the ability of infectious disease to limit human population growth. In the past, diseases such as the bubonic plaque of the fourteenth century killed between 30 and 60 percent of Europe’s population and reduced the overall world population by as many as 100 million people. Today, the threat of infectious disease, while not gone, is certainly less severe. According to the World Health Organization, global death from infectious disease declined from 16.4 million in 1993 to 14.7 million in 1992. To compare to some of the epidemics of the past, the percentage of the world's population killed between 1993 and 2002 decreased from 0.30 percent of the world's population to 0.24 percent. Thus, it appears that the influence of infectious disease on human population growth is becoming less significant.

Age structure, population growth, and economic development

The age structure of a population is an important factor in population dynamics. Age structure is the proportion of a population at different age ranges. Age structure allows better prediction of population growth, plus the ability to associate this growth with the level of economic development in the region. Countries with rapid growth have a pyramidal shape in their age structure diagrams, showing a preponderance of younger individuals, many of whom are of reproductive age or will be soon ( [link] ). This pattern is most often observed in underdeveloped countries where individuals do not live to old age because of less-than-optimal living conditions. Age structures of areas with slow growth, including developed countries such as the United States, still have a pyramidal structure, but with many fewer young and reproductive-aged individuals and a greater proportion of older individuals. Other developed countries, such as Italy, have zero population growth. The age structure of these populations is more conical, with an even greater percentage of middle-aged and older individuals. The actual growth rates in different countries are shown in [link] , with the highest rates tending to be in the less economically developed countries of Africa and Asia.

Questions & Answers

double stranded DNA is found in which viruses?
Deborah Reply
Virusws usually dont hsve double strnaded DNA they have a single strand RNA. U should probably check them in gpogle just to be sure
Danisha
what would happen if humans were not multicellular
Grace Reply
ettr
Grace
sorry but no
Grace
i haven't any things
mascuud
Is there any other type of a eukaryotic cell.
Grace Reply
what is bionomial nomenclature
Rachaelda Reply
state the role of mitochondria
Rachaelda
mitochondria ia power House of the cell. it provides energy and as ATP. Cells energy currency.
Haider
The scientific method of giving short names on the basis of genius and species.
Haider
it is introduce by carlous Lennieus
Haider
it is naming of living organism where by they are given two names one generic and the other specific name
Kenneth
what is element
Kofi Reply
Structure of water molecule and it's biological significance. .....help guys
Ashly
what is the formula for chemical equetion
Justo Reply
Why mitochondria is called the power house of the congo the bahamas cell
Farrukh Reply
how can I learn this subject?
mascuud Reply
what's microscope?
Mathias Reply
A device used to study a very small specimen thst cannt br seen with the naked eyes for example cells, or microorganisms.
Danisha
a medical device used to study cells bacteria viruses and parasites e.g electron microscope for studying cells.
Grace
exactly microscope
Randa
is an instrument use to view microorganisms such as viruses and bacteria
Ohene
it is an instrument used to magnify micro-scopic organism
Kenneth
microscopic
Coster
microscope
Adam
what does multi seminar mean
Grace Reply
many seminars
Grace
how many cells on the human
Amar Reply
how is genetic testing?
Nyabuoy
test
Nyuongatdet
which party of an internal leaf which represent organ and tissue
fernando
3 trilleons cells on the human
Jyoti
name the groups of bacteria, what they cause and explain the components of bacterial cell
Emmanuel
what are the three level of relationship that exist between organism?
Chinedu
trillions of cells
Grace
unicellular
Kenneth
who many cell are in the human body
Ayasso Reply
trillions of cells
Grace
what causes coloring of skin variation
Prince Reply
what is your answer
Jonathan Reply
which qn
Randa
what is chemosynthesis
Irene
who many cell are in the human body
Ayasso
there are billion cells in human body
fazeela
what are three stages of mitosis
jerry
they're alot cells in our body
jerry
what are the stages of mitosis
jerry
they are prophez methaphez anaphez. thelophez
fazeela
anyone to explain each of the following,, prophase, metaphase, anaphase and telophase
jerry
what is a filial
Mbah Reply
denoting the offspring of a cross
Grace

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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