1 Coelomate animals or Coelomata (also known as eucoelomates â true coelom) have a fluid filled body cavity called a coelom /ËsiËlÉm/ with a complete lining called peritoneum derived from mesoderm (one of the three primary tissue layers).he coelom allows muscles to grow independently of the body wall â this feature can be seen in the digestive tract of tardigrades (also known as water bears) which is suspended within the body in the mesentery derived from a mesoderm-lined coelom.
At a 3 percent growth rate, its doubling time â or the number of years to double in size â is 23 years. (The doubling time for a population can be roughly determined by dividing the current growth rate into the number 69. Therefore, 69/3=23 years. Of course, if a population's growth rate does not remain at this rate, the projected doubling time would need to be recalculated.)
For the last 50 years, world population multiplied more rapidly than ever before, and more rapidly than it is projected to grow in the future. In 1950, the world had 2.5 billion people; and in 2005, the world had 6.5 billion people. By 2050, this number could rise to more than 9 billion (see chart World Population Growth, 1950-2050). Anthropologists believe the human species dates back at least 3 million years.