Evolution Earlier Theories

WHY EVOLUTION? Evolution as a PROCESS is a SETTLED THEORY accepted by biologists all over the world. Evolution provides a framework for understanding all aspects of biology (classification e.g. simple to complex organisms, adaptation e.g. function, environment & structure)

WHY EVOLUTION? Cont. Evolutionary biology provides tools for many studies in genetics/genomics - Relationships between groups, - Research, - Resolving legal issues such as DNA fingerprinting & Sources of AIDS infections,

Evolution is NOT the process of superior animals triumphing over inferior ones, but is rather a series of alternative strategies that have arisen in response to changing environments.

No organism is better or worse than another. No organism is better or worse than another. Arthropods (crabs, spiders, insects etc.) are more successful than vertebrates when one considers the number of species, number of individuals, and number of adaptations to different environments and habitats. Arthropods (crabs, spiders, insects etc.) are more successful than vertebrates when one considers the number of species, number of individuals, and number of adaptations to different environments and habitats. In a similar way, humans are more successful than other modern apes in having a large number of individuals adapted to living in different environments. In a similar way, humans are more successful than other modern apes in having a large number of individuals adapted to living in different environments.

EARLY THEORIES Describe the two “laws” of Lamarck History and observations of Darwin ideas/theory Application of the theories with examples Why Lamarck`s theory was rejected Differences

Jean-Baptiste Lamarck French Biologist ( ) French Biologist ( ) Professor of “Worms and Insects” in Paris Professor of “Worms and Insects” in Paris The first scientific theory of evolution The first scientific theory of evolution

Lamarck theory Use and disuse of organs Changes in the environment create new needs that cause organisms to modify their existing organs to meet the need. Repeated use of the organ would cause it to enlarge and become more efficient. Disuse of a organ would cause it to degenerate Changes in the environment create new needs that cause organisms to modify their existing organs to meet the need. Repeated use of the organ would cause it to enlarge and become more efficient. Disuse of a organ would cause it to degenerate Inheritance of acquired characteristics The modification an organism acquired during its life time could be pass on to its offspring.

Explain that Lamarck’s theory is not accepted by most life scientists today Acquired characteristics are not inherited /do not cause any change to the DNA of an organism's gametes (sperms or ova) OR OR Organisms did not evolve because they want Organisms did not evolve because they want to evolve to evolve OR Lamarck believed in determinism (internal drive of organisms to change)

Lamarck - All giraffes had short necks originally - All giraffes had short necks originally -Giraffes frequently stretched /used their necks to reach -for leaves of tall trees -for leaves of tall trees -necks become longer -necks become longer - The long necks acquired in this way could be passed on to the next generation /were inherited How did Lamarck explained the long necks of giraffes? Snake

Jean Baptiste de Lamarck Two “Laws” 1. Law of use and disuse: Use or disuse causes structures to enlarge or shrink.

DISUSE & USE

2. “Law” of inheritance of acquired traits Acquired traits can be inherited All such changes are heritable

Misuse Legs of snake disappeared because it did not use them in its gliding movement; also their bodies became thin and long to allow them to crawl through narrow spaces Legs of snake disappeared because it did not use them in its gliding movement; also their bodies became thin and long to allow them to crawl through narrow spaces

Lamarck`s “Law” rejected His idea was that there is a ladder of life with superior forms (humans of course) near the top and lower forms on lower rungs (plants near the bottom). His idea was that there is a ladder of life with superior forms (humans of course) near the top and lower forms on lower rungs (plants near the bottom). Theory is deterministic. He imagined that all organisms had an internal drive to ascend the ladder during evolution. Those that started earlier (or had a stronger drive) would be higher than those that evolved later. He did not think of evolution in a tree-like form. Theory is deterministic. He imagined that all organisms had an internal drive to ascend the ladder during evolution. Those that started earlier (or had a stronger drive) would be higher than those that evolved later. He did not think of evolution in a tree-like form.

Lamarck`s “Laws” rejected (Cont.) He imagined that when an organism tries to use an organ for some purpose REPEATEDLY that organ will grow and, moreover, its offspring would start with an already enlarged organ. For example a giraffe would stretch for high leaves throughout its life and this would result in its offspring being borne with a longer neck and legs. He imagined that when an organism tries to use an organ for some purpose REPEATEDLY that organ will grow and, moreover, its offspring would start with an already enlarged organ. For example a giraffe would stretch for high leaves throughout its life and this would result in its offspring being borne with a longer neck and legs. That there is no way that an event going on during an organisms life can causes directed changes in its HERITABLE MATERIAL. That there is no way that an event going on during an organisms life can causes directed changes in its HERITABLE MATERIAL.

Charles Darwin ( ) English Naturalist English Naturalist College dropout College dropout Traveled around the world Traveled around the world Best known for On the Origin of Species (1859) Best known for On the Origin of Species (1859) Abundant evidence for evolution Abundant evidence for evolution Proposed a mechanism: natural selection Proposed a mechanism: natural selection

Envisaged evolution as a tree A radical and novel view

Summary of Charles Darwin’s theory 1.More individuals are born than survive to reproduce. 2.Variety exists among individuals of a species. 3.‘Fitter’ individuals are more likely to reproduce = “Survival of the fittest”: Natural selection eliminates less well-adapted individuals. 4.If characteristics are inherited, species slowly evolve. = adaptation, or ‘microevolution’ eventually giving rise to new species = speciation, or ‘macroevolution’.

Summary of Charles Darwin’s theory 1.More individuals are born than survive to reproduce. 2.Variety exists among individuals of a species. 3.‘Fitter’ individuals are more likely to reproduce = “Survival of the fittest”: Natural selection eliminates less well-adapted individuals. 4.If characteristics are inherited, species slowly evolve = adaptation, or ‘microevolution’ eventually even giving rise to new species = speciation, or ‘macroevolution. Evidence Then Now

Summary of Darwin’s theory Based on Natural Selection observations: Fraction of offspring survive to maturity Natural resources are limited Population size fluctuate around carrying capacity A population has variations of similar traits Traits best fitted to environment are passed on to next generation - unsuitable traits disappear

How would Darwin account for the long necks of the giraffes As a result of genetic variation in the giraffe population As a result of genetic variation in the giraffe population some giraffes have longer necks than others some giraffes have longer necks than others Environmental change /competition for resources occurred causing those with shorter necks to die Environmental change /competition for resources occurred causing those with shorter necks to die and those with longer necks to survive and those with longer necks to survive This is natural selection /survival of the fittest This is natural selection /survival of the fittest The genes /genotype for longer necks The genes /genotype for longer necks were passed on to subsequent generations most of which now have long necks were passed on to subsequent generations most of which now have long necks

Differences: Theories of evolution Lamarck’s theory 1809 Darwin’s theory 1859

Tabulate differences Lamarck Variation because individual change Variation because individual change Individuals in population change Individuals in population change Because they want to adapt to the environment Because they want to adapt to the environment Change acquired inherited from parent to offspring Change acquired inherited from parent to offspring Darwin Offspring showed variation when produced Change because of environmental factors Natural selection – best suited Best suited characteristics are passed inherited from parent to offspring