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origin of an idea about origins, fundamentals and formation of new species
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Evolution:Scientific theory of evolution emerges from different
lines of evidence:
Fossil records
Modification by descent
Evidence from biogeography
Genetics
As well as other forms.
1. Origin of an idea about origins:
What is evolution?
Gradual change or development of something.
Can be used in various sense in social or economic structures and general use.
What is biological evolution?
change in gene pool of a population during course of time by such processes as
mutation, natural selection, and genetic drift.
Descent with modification.
Covers micro-evolution (within species) and macro-evolution (decent of diff. species
from common ancestor over many generations).
Why is it so important that we know about biological evolution?
Biological evolution:
- Has become unifying concept that acts as a foundation for understanding all Biology
- Supports and explains many aspects of our everyday lives.
- Challenges people to really think for themselves.
How did life originate?
Current scientific opinion is that there was a single origin of life – this idea is
supported by the fact that all life shares the same genetic code and similar basic
enzymes, but science is still a long ay off from explaining how life originated.
What is certain is that life on earth appeared very early – about 3.7 mya.
How did species diversity originate?
A. Before 1700
- Species were unrelated and remained unchanged
- Earth was young, perhaps only 6000 years old and static (unchanging).
,B. 1700 to early 1800
- Erasmus Darwin, and Jean-Baptiste Lamarck began to challenge these concepts.
- Through the study of the fossil collections and being aware of the huge diversity of
living organisms they became convinced that:
• species had changed gradually over time.
• the earth was millions of years old rather than only a few thousand years
old.
Erasmus Darwin:
Famous book, Zoonomia, he put forward that species must have changed (or
evolved) over time but he offered no mechanism for what he termed
‘transformation’ (evolution).
Jean-Baptiste Lamarck:
Proposed that species were not fixed.
Reached conclusion as a result of making various observations such as:
1. Living species are different to fossil types, so life forms must have changed
over time
2. Domestication and selective breeding resulted in animals and plants
changing
3. Crossbreeding of plant species often led to new characters appearing.
How did Lamarck suggest that species changed?
* Suggested organisms changed during lifetime so that they could survive in new
environments and that these acquired changes were then passed on to
offspring.
* Hypothesis on how change took place was as follows:
+ Use and disuse of body parts
As the environment changed, an organism responded actively by
changing so it could adapt to new environment. Some parts would
increase in size while others would decrease.
+ Inheritance of acquired characteristics
These physical changes were then passed on to offspring. In this way,
populations changed, and new species were formed.
Also known as Lamarckism
Some examples of Lamarckism:
Lamarck considered that long neck and legs of modern giraffes were result of
generations of short-necked and short-legged ancestors stretching necks to
feed on leaves at progressively higher levels.
Thought that acquired characteristics, longer legs and
longer neck were passed on to offspring of each
generation until eventually new species of giraffe with
very long neck and long legs appeared.
, Was Lamarck’s mechanism for evolution correct?
No, because the characteristics acquired during life cannot be passed on to
offspring as they only affect the phenotype and not the genotype of the gametes,
which is necessary for any change to be transmitted to next generation.
C. Early 1800 to early 1900
Charles Darwin:
The data he collected made him aware of the:
o Immense diversity among organisms, both living and extinct.
o Variation of individuals of the same species.
Darwin realised that:
o Earth is extremely old which allowed time for species to evolve. Changes in
fossils from diff. sedimentary rock layers.
o There has been great geological change over time with diff. areas and land
masses becoming isolated.
o Isolation leads to species changing.
Two vitally important hypotheses:
o Modification with descent (or evolutionary change)
o Natural selection – a mechanism causing evolution.
How did Darwin explain descent with modification?
o All related organisms descended from a common ancestor
o Ancestral species spread into a variety of new habitats – because they
adapted to new local condition. (became modified)
o Diversification was by branching – ancestral species gave rise to 2/+ new
related species, each in a new habitat.
o Some species died out (became extinct).
Alfred Russel Wallace:
Noticed that organisms in former were more like those on Asian mainland, while those
in latter were more like those Australia.
Suggested that ancestors of modern species would have become isolated from each
other by water and in course of time evolved differently, even though they lived in
similar climates.
Evidence for the theory of evolution:
1) Fossil Record
2) Biogeography
3) DNA (genetics) and molecular biology
4) Homologies and comparative anatomy
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