1. Evolution is define as the process by which
new types of organisms develop from other
existing organisms, for example amphibians
evolved from fish.

2.  Main sources of evolution are the following
 Fossil records
 Structural similarities
 Development of embryo
 Biochemical similarities

3.  Plants and animals that lived million years
ago are no longer exist today. These plants
and animals are extinct, fossils of this plant
and animals are recorded, fossils are
preserved remaining's of living organisms
found in rocks.
 Fossils can also tell us about ancient climate
and environment, for example if
paleontogist-scientists who study fossils-find
fossil of animals such as fish and amphibians
that live in or near water, they know that
that area was covered with water

4.  Fossils are formed in sedimentary rocks,
these rocks form as a result layers of sands
and clay pilling up on the seabed or the
bottoms of inland lakes and seas, sediments
builds over the dead plants and animals.
 All fossils forms when dead plants and
animals become covered with a substance
that exclude oxygen. The particles of
minerals in the bones or shell move into the
surrounding rock, and the particles of silica
in the rocks move into the bones, causing the
bones to change into crystalline substance.

5.  Sometimes if the layers of sediments are
deposited over the dead organism very
quickly, you can sea the outline of the
organism that was formed before its tissue
decompose away. Most plant fossils form in
this way, an example of fossil is shown on the
picture below.

6.  According to calculations of scientists the
earth is about 4 500 million years old. From
fossil evidence it seems that the first life on
earth is 3 800 million years ago and the first
living things were very small and simple.

7.  Figure1.2 geological timescale showing evolution of
species

8.  Fossilrecords also show us how living
organisms have changed and developed over
time. When scientists study the fossil record
they look for similarities and differences in
the type, origin and functions of body
structures. This is one way in which they get
clues as to relationships that exist between
extinct fossil species and living species.
 Some body structures are analogous
structures, which means same function in
different species but developed
independently.

9.  Lamarck’s theory of evolution
• According to Lamarck, evolution occurs when the
characteristics an organism acquire during its
lifetime are passed on its offspring. In this way
organisms were able to change from generation
to generation. Lamarck believe that if certain
organs were used more often they would become
more developed and if organs were not used
more often they would eventually disappear.
Lamarck’s best known example is giraffe’s neck.
He argued that giraffes have long neck because,
for many generations, they stretched their necks
to reach leaves on high branches of tree, its
neck would get longer.

10. Lamarck then suggest that if giraffes repedeately
stretched its neck to reach leaves high up on a tree,
its neck would get longer and giraffes will pass on
this acquired characteristics to its offspring
therefore giraffes will develop long necks.
 Figure 1.3
 Lamarck theory of evolution about giraffes

11.  Darwin’s theory of evolution
 According to Charles Darwin organisms are
competing for resources, any variation in an
organism faivour survival in a particular
environment, this will increase a chances of
reproducing and leaving fertile offspring,
organisms with less favourable variation are less
likely to and leave offspring. This means more
favourable variations are transferred to future
generation and as time goes, variation within
individual species increase, it result to a new
species. The theory of natural selection is
referred to as survival of the fittest.

12.  Biological evolution is the evolution which
result in a change in frequency of some
alleles in a population over time, allele is
two or more different forms of a gene. New
allele can be formed by means of mutation.
 The proportion of a particular allele in a
population is called the allelic frequency,
and it is a measure of genetic diversity.

13.  Evolutionis divided into two types which is
microevolution and macroevolution. The
difference between the two is that
microevolution involve evolutionary change
within individual members of the same
species, while macroevolution involve change
on a large scale, such as within families or
organisms.

14.  Small changes in populations of organisms lead
to the development of new species. For example
two wild flower populations that grow on two
separate side of the mountain. Population will
be different, it can be on pollination.
 The formation of new species is called
speciation, there are two types of speciation
which is allopatric speciation-occurs when a new
species forms when the populations are
physically or geographical separated from one
another. Sympatric speciation occurs when a new
species forms when populations are not
physically or geographically separated from one
another.