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.

Unit 5 – Lecture 5

SpeciationSpeciation – creation of a new species

could occur when organisms of the same species can no longer interbreed in their natural environmentexplains how tigers and lions can

interbreed but are not of the same species – not in same environment

SpeciationCauses for speciation:

geographic isolation – physical separation of populations lead to each changing separately

SpeciationCauses for speciation:

reproductive isolation – caused by:fertilization prevention creation of sterile hybrids [mule/hinny]

SpeciationCauses for speciation:

reproductive isolation – caused by:behavioral differences

nocturnal/diurnal, blooming seasons, mating rituals or choices, etc

simple physical incompatibilities.

Change over TimeTwo 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 TimeTwo ways of hypothesized evolutionary

change:punctuated equilibrium – long periods of

little change followed by short periods of intense changebecause of very “incomplete” fossil record

according to the theory of gradualism, created by Stephen J Gould

Comparing TraitsComparing 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 TraitsComparing organisms from an evolutionary

viewpoint, they can be said to exhibit convergence or divergence.Convergent Evolution

organisms which show convergence have analogous structuresanalogous structures – different

structures with the same use

Comparing TraitsComparing 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 TraitsComparing 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 timebelieved to occur because of change in

location

Comparing TraitsComparing organisms from an evolutionary

viewpoint, they can be said to exhibit convergence or divergence.Divergent Evolution

homologous structures – similar structures have a different useassumed to be caused by evolutionary

ancestry

Comparing TraitsComparing organisms from an evolutionary

viewpoint, they can be said to exhibit convergence or divergence.Divergent Evolution

homologous structures – similar structures have a different useDNA evidence doesn’t always support

this theorysimilar structures are sometimes coded

for by very different genetic information

Comparing TraitsVestigial Structures – multiple definitions:

previously – structures which no longer are thought to provide any benefit to organismslist 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 TraitsVestigial Structures – multiple definitions:

previously – structures which no longer are thought to provide any benefit to organismslist 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 TraitsVestigial Structures – multiple definitions:

previously – structures which no longer are thought to provide any benefit to organismslist 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 TraitsVestigial Structures – multiple definitions:

currently – structure which no longer serve in their capacity it is assumed that they hadbased 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 orgshelps 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 asexuallyvegetative reproductionseeds 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.