Transcript Speciation - Fulton County Schools

Unit 5 – Lecture 5
Speciation
 Speciation – creation of a new species
 could occur when organisms of the same species can
no longer interbreed in their natural environment
 explains how tigers and lions can interbreed but
are not of the same species – not in same
environment
Speciation
 Causes for speciation:
 geographic isolation – physical separation of
populations lead to each changing separately
Speciation
 Causes for speciation:
 reproductive isolation – caused by:


fertilization prevention
creation of sterile hybrids [mule/hinny]
Speciation
 Causes for speciation:
 reproductive isolation – caused by:


behavioral differences
 nocturnal/diurnal, blooming seasons, mating
rituals or choices, etc
simple physical incompatibilities.
Change over Time
 Two ways of hypothesized evolutionary change:
 gradualism – gradual changes [microevolution]
which would slowly build to change org.
 believed to be the major form of evolutionary
change
 transitions are rarely seen in the fossil record
Change over Time
 Two ways of hypothesized evolutionary change:
 punctuated equilibrium – long periods of little
change followed by short periods of intense change
 because of very “incomplete” fossil record
according to the theory of gradualism, created by
Stephen J Gould
Comparing Traits
 Comparing organisms from an evolutionary viewpoint,
they can be said to exhibit convergence or divergence.
 Convergent Evolution
 organisms in similar environments
have similar traits
 makes sense –similar adaptations
needed to function
Comparing Traits
 Comparing organisms from an evolutionary viewpoint,
they can be said to exhibit convergence or divergence.
 Convergent Evolution
 organisms which show convergence have
analogous structures
 analogous structures – different structures
with the same use
Comparing Traits
 Comparing organisms from an evolutionary viewpoint,
they can be said to exhibit convergence or divergence.
 Divergent Evolution
 states that organisms which were once closely
related become less similar over time because of
geographic or reproductive isolation
Comparing Traits
 Comparing organisms from an evolutionary viewpoint,
they can be said to exhibit convergence or divergence.
 Divergent Evolution
 adaptive radiation – states that this change
between species happens in a short amount of
time
 believed to occur because of change in location
Comparing Traits
 Comparing organisms from an evolutionary viewpoint,
they can be said to exhibit convergence or divergence.
 Divergent Evolution
 homologous structures – similar structures have a
different use
 assumed to be caused by evolutionary ancestry
Comparing Traits
 Comparing organisms from an evolutionary viewpoint,
they can be said to exhibit convergence or divergence.
 Divergent Evolution
 homologous structures – similar structures have a
different use
 DNA evidence doesn’t always support this
theory
 similar structures are sometimes coded for by
very different genetic information
Comparing Traits
 Vestigial Structures – multiple definitions:
 previously – structures which no longer are thought
to provide any benefit to organisms
 list of nearly 200 useless structures in late 1800s to
almost none now, leading to a re-vamping of the
definition according to an evolutionary
standpoint
Comparing Traits
 Vestigial Structures – multiple definitions:
 previously – structures which no longer are thought
to provide any benefit to organisms
 list of nearly 200 useless structures in late 1800s to
almost none now, leading to a re-vamping of the
definition according to an evolutionary
standpoint
Comparing Traits
 Vestigial Structures – multiple definitions:
 previously – structures which no longer are thought
to provide any benefit to organisms
 list of nearly 200 useless structures in late 1800s to
almost none now, leading to a re-vamping of the
definition according to an evolutionary
standpoint
Comparing Traits
 Vestigial Structures – multiple definitions:
 currently – structure which no longer serve in their
capacity it is assumed that they had
 based off of comparing organs in organisms
comparing their uses to their hypothesized
evolutionary ancestors
Vestigial…or not?
 Appendix – breaks down cellulose in plants
 serves as part of the immune system in humans to
make white blood cells and antibodies to fight
infection
Vestigial…or not?
 Coccyx [tailbone] – continues into tail in other orgs
 helps anchor muscles so that we can sit and walk
correctly – including the gluteus maximus
 btw – humans born with “tails”
do not have tails in the sense of
typical orgs, they are just fleshy
growths.
Vestigial…or not?
 Pineal gland – secretes melatonin, an important
chemical to our sleep/wake cycles [what makes you
feel sleepy]
Vestigial…or not?
 Tonsils – part of immune system
 minimizes
respiratory
infections,
produces
antibodies
 first line
of defense
Vestigial…or not?
 Wings in flightless birds – not for flying…
 but often used for balance or for sexual selection
Vestigial…or not?
 “Junk” DNA – does not code for any traits…
 found to have important functions
in embryonic development, possibly
for social functions, controlling
expression of other genes
Vestigial…or not?
 Eyes in blind cave animals like fish & salamanders
Vestigial…or not?
 Sexual organs in dandelions –
dandelions reproduce asexually
 vegetative reproduction
 seeds are asexually formed too
Vestigial…or not?
 Wisdom teeth
 human mouths now smaller than those even a few
hundred years ago
Vestigial…or not?
 Male nipples – certainly don’t nurse children
 ALL humans are female during the first six weeks of
development
 around 6 weeks, certain hormones are dispersed
which lead to further development of a certain sex.
Vestigial…or not?
 There is no way to scientifically determine the
uselessness of an organ just that no function has been
found – Darwin agreed.
 As always, science can only work with available info
and revise as necessary, which again stresses what
science truly IS – the pursuit of knowledge about our
world.