Transcript evolution - Scituate Science Department

EVOLUTION
The Unifying Concept
 “Nothing in biology makes sense, except in
the light of evolution.”
• Theodosius Dobzhansky
 Evolution: The descent of modern
organisms with modification from preexisting life-forms; strictly speaking, any
change in the proportions of different
genotypes in a population from one
generation to the next
All Life Shares a Common
Ancestry
Are the these organisms...
…related?
YES!!!
 How can that be?
They are so very
different.
 But they share at least seven
characteristics…right?
 So, if all organisms have an unbroken chain
of ancestors leading back to the first of its
kind, then each of those ancestors must
have its own chain of ancestors
EXAMPLE
 Some distant ancestor of today’s elephants
is also the ancestor of the extinct
mammoths
 If we follow this line back far enough, it
links up with other ancestors of other
organisms which ultimately links up with
the HUGE tree of life, linking ALL organisms
Chuck D!!!
 We can’t discuss evolution without
mentioning Charles Darwin
 His pivotal idea that all organisms are the
result of descent with modification from
common ancestors is the foundation of
evolution and a bedrock principle of
biology
 He also delivered a theory for the cause of
evolution: natural selection
Sooooo…...
 Thanks Chuck!
Oh yeah, what about Wallace?
 Who?
 Wallace... Alfred Russell Wallace
 He devised the same theory that Darwin did
but he didn’t know enough big wigs so they
wouldn’t publish his work until after Darwin
published his…and he sat on it for a few
years
Let’s Summarize Their Theories

Observation 1.
• Natural populations have the potential to increase
rapidly because organisms can produce far more
offspring than are required to replace their parents

Observation 2.
• Nevertheless, the sizes of most natural populations
and the resources available to maintain them remain
relatively constant over time
Conclusion
 There is competition for survival and
reproduction. In each generation, many
individuals must die young, fail to
reproduce, produce few offspring, or
produce less fit offspring that fail to
survive and reproduce in their turn
Observation 3
 Individual members of a population differ
from each other in their abilities to obtain
resources, escape predators and survive
change in their environments
Conclusion 2
 The most well-adapted individuals in any
generation tend to be the ones that leave
the most offspring
Observation 4
 At least some of the variation among
individuals, in traits necessary for survival
or reproduction, is due to genetic
differences that may be passed on from
parent to offspring (don’t forget, genotype
controls phenotype)
Conclusion 3
 Over many generations, differential or
unequal, reproduction among individuals
with different genetic makeup changes the
overall genetic composition of the
population
How do we know evolution has
occurred?
 What do you think?
 Fossil record, comparative anatomy,
embryology, biochemistry, and genetics
The Fossil Record
 The fossil record shows a slow change over
time
 We see a progressive series of fossils
leading from an ancient, primitive form,
through intermediate stages culminating
in the modern form
The best example we have
 The fossil record of the horse is the best
example of this
 That of elephants, giraffes and mollusks
are good as well
 They all suggest that species evolved from
and replaced previous species
Comparative anatomy
 Appearance has long been used as an
indicator of the relatedness of organisms
 The elephant and the mammoth clearly
have similar anatomies and share a
common ancestor
Unrelated species in similar
environments…
…have evolved similar forms
 Natural selection predicts that unrelated species,
given similar environmental demands,
independently evolve superficially similar
structures. This is called convergent evolution.
 Outwardly similar structures in unrelated
organisms are termed analogous structures

Examples of convergent evolution
and analogous structures
What about related organisms?
Modern organisms are adapted to a wide variety
of habitats and lifestyles
 The forelimbs of birds and mammals, for example,
are variously used for flying, swimming, running
(over several different types of terrain), and
grasping
 Despite this diversity of function, the internal
anatomy is remarkably similar
 These internally similar structures are called

homologous structures
Examples of homologous structures
Figure 3.1.1. Comparison of the forelimbs of various relatives of modern birds. Forelimbs of (A) Ornitholestes, a theropod dinosaur,
(B) Archaeopteryx, (C) Sinornis, an archaic bird from the lower Cretaceous,
and (D) the wing of a modern chicken (modified from Carroll 1988, p. 340;
Vestigial structures
 These are structures that serve NO
apparent purpose
 examples include: molar teeth in vampire
bats, pelvic bones in whales and snakes,
the appendix, wings on ants
Embryology
It was observed, in the 1800’s, that vertebrate
embryos look quite similar to each other in early
development
 All vertebrates have gill slits at some point in
their development. Only fish retain them in
adulthood
 The plausible explanation is that early forms had
these traits and passed the genes on but in some
forms the genes get masked or turned off during
development

Homework
 Read 255-269
 do applying concepts 1-6
 do key terms pg 270
Eeewwwww, where are your
lysosomes?
Biochemistry and genetics
 These two fields reveal striking evidence
for the evolutionary relatedness of all
organisms
 At the most fundamental levels, ALL living
cells are very similar
Examples
 ALL use DNA as the carrier of genetic
information
 ALL use RNA, ribosomes and approximately
the same genetic code to translate genetic
information into proteins
 ALL use the same 20 amino acids to build
proteins
 ALL use ATP as the intracellular energy
carrier
Some evidence that populations
evolve by natural selection
 Artificial Selection: The breeding of
domestic plant and animal species to
produce specific, desirable features
 The reasoning is this, if humans can
produce such a wide variety of, say, dog
breeds in a few hundred or thousand years.
 It stands to reason that nature could
produce a wide variety of organisms in
several billion years
Natural Selection is Occurring
RIGHT NOW!!!
 Evolution did NOT ONLY happen in the past
 There is still competition for space,
resources and mating right now
 We already discussed the palmerus longus
tendon
 The classic example is the peppered moths
(Biston betularia) of England
The Peppered Moth
 Before the Industrial Revolution most
peppered moths were white with scattered
specks of black pigment
 They blended in very well with the lichen
that grew on the sides of trees
 This camouflage was helpful in preventing
predation by birds
 There were, however, mutant all black
individuals
The mutants...





…were easily seen against the lichen and were eaten by
predators
During the Industrial Revolution, industries in England
burned lots of coal
pollution from the smokestacks covered the lichen
causing it to die off and left the trees covered in black
soot
This led to heavier predation of the light colored moths
and there was an increase in the dark moth population
By the end of the 19th century, 98% of the peppered moths
were black
1 more example
In the 1990’s in Florida a rare mutation in
cockroaches was an agent of natural selection
 The mutation caused the roaches to dislike
glucose
 glucose was used as bait in roach poison
 the individuals with the mutation did not eat the
poison, the ones that did died
 now the once rare mutation is part of the
widespread genome of that roach population

Three points to understand
 1. Mutations arise spontaneously
 2. Selection does not necessarily produce
well-adapted species. In some cases it
causes extinction
• other moth species in England went extinct
because there was no mutation to cause a
black variant
 Natural Selection selects for organisms
that are best adapted to a particular