Download Lemark, Wallace and Darwin

LAMARCK, WALLACE AND
DARWIN
Theories of Evolution
LAMARCK (1774-1829)
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environment plays a role in evolution
uses and disuse
allows species to become better adapted to their environment
 structures that the species used becoming larger and stronger
 structures not in use becoming smaller and weaker
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inheritance of acquired characteristics
each species becomes more and more complex through the
process of acquired traits from parents
 adaptations to environmental conditions during the
organism’s lifetime could be inherited by future generations
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new simple species are created by spontaneous generation
LAMARCK (1774-1829)
http://www.scienceinseconds.com/episodes/Lamarckian-Evolution
MALTHUS
published essay “Principle of Population”
 population sizes would increase exponentially if
not limited
 population sizes are dependant on limiting
factors such as food supply
 other environmental factors, such as accidents,
war and disease help control population sizes
 populations experience a struggle for existence
 Malthus’ ideas had huge impacts on the
development of Darwin and Wallace’s Theories of
Natural Selection

http://www.ask.com/youtube?q=malthus+video&v=QAkW_i0bDpQ
WALLACE (1823-1913)
can up with a theory for the mechanism of
evolution within a few days with very little
evidence
 send his theory to Darwin and the two theories
were very similar
 pushed Darwin to publish his theory as Darwin
wanted to be the first to publish

http://www.nhm.ac.uk/nature-online/science-of-natural-history/biographies/wallace/
DARWIN (1809-1882)
collected observations for 20 years on
ananotomical differences within and between
species, biogeography and fossil records
 published his theory of evolution (Theory of
Natural Selection) in 1859 in the book “On the
Origin of the Species”

http://science.discovery.com/videos/galapagos-beyond-darwin-charles-darwin.html
DARWIN (1809-1882)

Darwin’s Observations
there is variety between individuals within
populations
 some of the variation among individuals is inherited
by the offspring from their parents
 more offspring than can survive are produced every
generation
 population size usually remains stable over time

DARWIN (1809-1882)

Darwin’s Inferences
 members of the same species compete with each other for
survival
 in every generation, some individuals are more successful at
surviving and reproducing than others
 successful individuals have more favourable adaptations and
are more likely to pass their traits on to offspring
 survival and reproduction of individuals is not random
 individuals with the most favourable adaptations, those who
are better as surviving and reproducing, are naturally selected
 as the individuals with more favourable adaptation produce
more offspring than those lacking the favourable adaptation,
the favourable adaptation will become more common in the
population
DARWIN (1809-1882)

Darwin’s Theory of
Natural Selection


Natural selection
preserves favourable
variations within a
population of organisms,
while those that are
injurious will eventually
be eliminated.
Survival of the Fittest

phrase coined by Spencer
to describe Darwin’s
theory
DARWIN (1809-1882)

Darwin’s Finches - Example of Natural Selection
DARWIN (1809-1882)
DARWIN (1809-1882)
Issues with Darwin’s Theories
Resolution
There are too many gaps in the
fossil record. Where are the
transitional species between
major groups of species.

Many adaptations are bizarre or
unexplainable.

There was no clear mechanism
for the inheritance of variable
traits.
How can minor variations
between individuals explain the
appearance of complex features
(eyes) and behaviours (mating
dances).
How can the existence of
altruism be explained (where an
organism sacrifices for the
benefit of others).
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there are many transitional fossils, particularly of shelled marine
invertebrates that fossilize well
overall, fossilization is a rare event, and finding a significant
proportion of fossils is unlikely, so it will always be a spotty and
incomplete record
many adaptations are being explained with supporting evidence, but it
takes time and expertise
it will never be possible to explain every adaptation of every
organism, let alone prove that each explanation is correct
modern discoveries in genetics mesh well with his work and make his
ideas even more workable
plausible sequences have been made for the evolution of many
complex features such as eyes (which have evolved at least seven
separate times)
it can be seen why behaviours become more elaborate over time,
especially if it involves mate selection and reproduction.
most altruistic behaviour that has been studied occurs amongst
relatives
if fitness means passing on your genes, then helping your relatives is
one way to do that, the price has to be carefully evaluated