Download Biology Week 1

Week 1
EVOLUTION
Evolution is change in the heritable traits of biological populations over successive
generations.
Evolution is technically defined as: “a gradual process in which something changes
into a different and usually more complex or better form”. As ii is most famously used,
“evolution” is the process by which an organism becomes more sophisticated over time and
in response to its environment. The theory is favoured by many scientists to explain
phenomena in nature, so much so that it is generally assumed as factual in most studies.
EVIDENCES OF EVOLUTION
SIMILARITIES OF EMBROYOLOGY
The study of one type of evidence of evolution is called embryology, the study of
embryos. An embryo is an unborn (or unhatched) animal or human young in its earliest
phases.
Embryos of many different kinds of animals: mammals, birds, reptiles, fish etc look
very similar and it is offer difficult to tell them apart. Many traits of one type of animal appear
in the embryos and human embryos both have gill slits. In fish they develop into gills, but in
humans they disappear before birth.
This shows that the animals are similar and that they develop similarity implying that
they are related have common ancestors and that they started out the same, gradually
evolving different traits but hat the basic plan or a creatures beginning remains the same.
FOSSILS: Are important for estimating when various lineages developed in geologic time.
As fossilization is an uncommon occurrence. Usually requiring hard body parts and death
near a site where sediments are being deposited, the fossil records only provides sparse
and intermittent information about the evolution of life.
Evidence of VESTIGIAL ORGAN
Vestigial organs have long been one of the classic arguments used as evidence for
evolution. The argument living organisms, including man contain organs that were once
functional in our evolutionary past but that are now useless or have reduced function.
This is considered by many to be compelling evidence for evolution.
EVIDENCE FROM GEOGRAPHICAL DISTRIBUTION
The distribution of living things on the globe provides information about the past
histories of both living things and the surface of the earth.
Living things can exhibit variation in form, structures and functions in relations to
different climate. The same type of plant and animals which have some resemblance can’t
be cultivated from the same climate. Usually organisms of one climate tend to differ slightly
from organisms of the same climate after several years of isolation.
THEORIES OF EVOLUTION
The theory of evolution by natural selection, first formulated in Darwin’s book”on the origin of
species in 1859, is the process by which organisms change over time as a rebuilt of
changes in heritable physical or behavioural traits.
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LAMARCK’S Theory of Evolution
A French zoologist caked Jean Lamarck was known to be the first to suggest that
organisms undergo evolution. His theory which was propounded in 1801 is also called the
theory of USE and DISUSE.
The contributions or postulates of Lamarck’s are:
(i).
(ii).
Great changes in environment result in corresponding changes in the species.
These changes causes the organism to form new structures or habits to adjust to the new
prevailing environment.
(iii). Organism develop specialized characters by use and disuse of organs.
(iv) Frequently used organs become well developed while the ones not used degenerate
and become useless.
(v). The well developed or dominant acquired characters are inheritable.
Lamarck used the long neck of giraffe to give example of his theory. The long in neck
of giraffe arose from the need to browse on tree tops. Since this was useful adaption,
subsequent generations of giraffe have been inheriting this acquired character.
Modern Scientists did not accept Lamarck’s theory because their findings show that
physical features of a parent acquired through use and disuse are not inheritable by
offspring. Only characteristics represented in the genes are inheritable.
DARWIN’S THEORY OF EVOLUTION
A British naturalist in 1859 also propounded another theory of evolution. Darwin’s
theory is known as natural selection.
Darwin’s contributed that:
1.
Species have the ability to produce large number of offspring into the environment with
limited resources.
2.
This process then leads to competition by these offspring.
3.
The survivors must have inheritable the useful traits.
4.
Then reproduce and pass on these good traits to their offspring.
5.
Those that could not survive the struggle die off or are eliminated.
6.
This process leads to the survival of the fittest or natural selection.
7.
There is great variability with population as this process continued through many
generations.
8.
The population gradually become better adopted tot eh environment leading to the origin of
new species.
It should be noted that the theory of Darwin is popularly upheld by many scientists.
Importance of Environment in evolution is recognized by Lamarck and Darwin. A lot of
scientists also recognize it and it is also the elimination of the much less adapted ones and
by natural selection of the better adapted organisms by chance that evolution or changes
take place.
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