Tues 930 Part II of Course

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Tues 9/30 Part II of Course Evolution of Brain
and Behavior (will go over Exam I first)
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• Evolution
• process that results in heritable changes in a
  population from one generation to the next.
• Process acts on individuals
• scientific fact equivalent to fact of gravity

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• Evolution
• I. Darwin (1859)
• summarized all of the evidence in favor of idea
  that all organisms have descended with
  modification from a common ancestor
• proposed natural selection as the mechanism

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Evolution I. Darwin (1859) Natural selection -
mechanism through which a differential production
of offspring occurs by selected members of a
species
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• Natural selection depends on
• presence of many individuals with variable
  characteristics
• environment determines who has right
  characteristics to survive and leave offspring
• selection acts on the individual but determines
  characteristics of the next generation

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• Modern theory of evolution
• recognizes that characteristics are inherited as
  discrete entities called genes
• recognizes other mechanisms of evolution
  (mutation, random genetic drift)
• postulates that species can occur gradually over
  long periods of time or due to punctuated changes

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• Basis of Heredity
• Chromosomes (23 pairs) - long thin structures in
  the nucleus of each cell.
• Each chromosome is a double-stranded molecule of
  DNA. DNA consists of a sequence of nucleotide
  bases this is the genetic code.
• DNA - blueprint for life instruction set for
  creating and sustaining life (and death).
• Humans have 23 pairs of chromosomes one member
  of each pair (and the corresponding set of genes)
  comes from the father and the other from the
  mother.

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Basis of Heredity 2. Genes units of
inheritance the sections of a chromosome (the
segment of base pairs on DNA) that controls the
synthesis of one protein responsible for one
trait. For each trait, we have one gene from
Dad and one from Mom The 2 genes that control the
same trait known as alleles.
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Two genes code for one expressed trait. When both
are the same - homozygous When the 2 are
different - heterozygous When different, 1
dominant gene determines the trait. For moth
color brown is dominant over white. If one
parent contributes a brown gene and other a white
baby moth is brown. If both contribute a white
gene moth is white (a recessive trait)
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Genotype - genetic makeup all genes (half from
Dad, half from Mom) Phenotype - the traits that
are expressed. Natural selection acts on the
phenotype the individuals traits.
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Dark color Light color 2 genes
2 genes DD or Dl ll
Dark (D) is dominant Light (ll) is recessive
and is expressed only
when 2 l recessive genes are
inherited.
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Examples of Natural Selection 1. An English moth
- light (98) and dark (2) types --gt a few years
passed --gt 95 dark type present. Why? -
industrial revolution presence of soot made it
easier for birds to see the light moths - ate
them. Dark survived and passed on genes to next
generation.
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2. Humans with sickle cell genes Red blood cells
- round or sickle shaped. 2 genes for round -
healthiest normally (carry oxygen well). 2 genes
for sickle - unhealthy anemic (cannot carry
oxygen well enough). 1 round and 1 sickle -
provides resistance to malaria. Shape makes it
harder for malaria organism to enter cell)
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2. Humans with sickle cell genes Malaria present
- best survival by sickle cell heterozygotes. Sick
le gene at high frequency in Africa, India, parts
of Middle East where malaria was/is a problem.
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3. Evolution provides useful explanations for
strange traits or behaviors. Balloon courtship
display of a small fly (Kessel 1950s) Males make
a delicate silk balloon. Then swarm together
until a female arrives. Female selects male with
best balloon as her mate. ???? Why ????
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Studies of 1000s of fly species, shows 8
ancestrally related types and 8 behavior
patterns (in order by ancestry) Species 1.
Carnivorous flies - solitary courtship of
females Species 2. Males take a captured prey
(mosquito) to female as gift - she eats then
mates. Species 3. As above, but males swarm and
female selects one.
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Species 4. Males swarm with prey gift wrapped in
a little silk (keeps it from falling) Species 5.
Males swarm with heavily wrapped prey gift (even
better) Species 6. Same but before wrapping it,
fly sucks juices from prey (non-nutritive
gift) Species 7. Flies no longer eat insect
parts feed on nectar instead. But same behavior
(silk balloon) is important to mating.
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Species 8. Empty balloon offered as necessary
courtship gift This behavior continued to be
selected for, but eating habits changed. Sequence
of change shows that each step required only a
modest change from prior practice.
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In example, the sequence of change shows that
each step required only a modest change from
prior practice. Genetic changes contributed to
behavioral changes. Now established that the more
related 2 species are anatomically and
genetically, the more similar their behaviors.