Do you remember our study of diveristy in living organisms in grade 9? In that chapter we explored the bewildering diversity of organisms that exist on earth.
There are animals and plant species which exist in extremely harsh climates. For example, cactuses (shown below) can survive in desert conditions where they have little water available.
This is because cactus have special features which allow them to survive in conditions most normal plants would not be able to.
A cactus plant has long roots which go deep into the soil for absorbing water.
They have leaves in the form of spines which minimises water loss in the form of transpiration.
And their stem is covered with a thick waxy layer which helps them retain water!
You could say the cactus has adapted to its surroundings to survive.
Do you remember how we classified some animals as warm blooded and some as cold blooded?
Why do you think some animals are cold blooded while some are warm blooded.
While this question is a difficult one to answer, some scientists believe that cold blooded animals adapted to become warm blooded animals so that they could survive through periods of drastic climate change.
The process by which species accumulate changes in characteristics to ensure their survival, over several generations is called evolution.
Human beings as we currently exist evolved over many million years.
The earliest members of the human species can be traced to Africa!
Charles Darwin was an English naturalist scientists. He is widely credited with cominng up with the idea of natural selection.
Natural selection is the process by which individuals which have developed favorable traits for survival in their environment reproduce more prolifically.
According to Darwin, natural selection was an outcome of three principles that operated in nature.
Note that this was in the 1800's and well accepted ideas of evolution were not known at the time.
1. Darwin proposed that most characteristics of an individual are passed on or inherited from their parent.
2. More offsprings are produced than are able to survive. This simply means if an animal reproduces and gives birth to 6 offsprings, not all six will survive.
3. There are variations in the characteristics that offsprings inherit from their parents.
You have the benefit of standing on the shoulders of scientific giants and you know now that characteristics are inherited through DNA.
There can be mutations in the DNA and these mutations are the ultimate source of genetic variation.
Accumulation of genetic mutations over generations can lead to organisms which are very different from each other.
Beyond natural selection, there can also be accidents in small populations which can change the frequency of some changes.
This process is known as genetic drift.
Due to natural selection and genetic drift, populations of different groups can evolve in divergent directions.
When a group of individual evolves such that they can no longer reproduce with each other then they are known as seperate species.
Based on the similarities of characteristics then we can classify them, as we did in Grade 9.
Now that you have an idea about what evolution is, lets study a bit more about inheritance.
You've learnt that the information needed for producing an offspring is stored within the DNA of our cells.
A sequence of DNA is known as a gene. A gene codes a particular sequence of protiens (amino acids).
Variations in genes can mainfest in simple ways. Some people have brown hair, some have black. This is because they have different genes for hair color.
While inheritance from previous generations provides a common body design, small variations in genes can accumulate over time.
The scientist Gregor Mendel disocvered there are rules for inheritance of traits.