EVOLUTION

* a process of change through time
* evolution explains the differences in structures, function, and behavior among all life forms

EVOLUTION IS A UNIFYING PRINCIPLE FOR BIOLOGY

* evolution and molecular genetics help explain the change of characteristics of populations through generations

I. SUPPORTING EVIDENCE FOR EVOLUTION

A) fossils

* direct or indirect remains of organisms preserved in rock, amber, ice, or tar
* some fossils are over 3 billion years old; we can tell this by radioactive dating, which looks at the amounts of radioactive elements in the substance
* by the fossil record, we have discovered that the earth is between 4 1/2 and 5 billion years old
* the deeper down fossils are found in SEDIMENTARY ROCK (the layers), the older they are

* upper layers of rock have more complex and relatively newer organisms than the lower layers
* fossils that resemble each other in different layers show COMMON ANCESTRY (also shown by the following)

B) comparative cytology

* remember the cell theory, cells are the basic unit for all living things
* organelles such as:
plasma membrane
ribosomes
mitochondria
structure of the nucleus of eukaryotes

...are very similar in all organisms

C) comparative biochemistry

* nucleic acids (DNA and RNA) are in EVERY organism
* many different organisms have similar genetic makeups...
* ...therefore they have similar enzymes and proteins

ex. pig insulin was used for treatment for
people that suffer from diabetes

* the closer the genetic code matches up between organisms, the closer they are related...

humans and chimpanzees
DNA is 98.5% the SAME

below are chromosomes from a human (left) and a bonobo chimpanzee (right)--note the similarirties!

D) comparative anatomy
* some anatomical structures are similar in living things

homologous structures- parts of organisms that are similar in structure but may have different functions

ex. homologous bones in forelimbs (forearms)
in frogs, birds, bats, horses, whales, humans

E) comparative embryology

* during early stages of development, embryos of many different members of the animal kingdom (vertebrates) are almost indistinguishable from each other
* this is believed to be a carryover from the development pattern of a common ancestor

Evolution

take a look at the different eras of life on planet earth
watch how footprint fossils from early hominids were found
look at the Toumai Skull

II. EARLY THEORIES OF EVOLUTION

A) spontaneous generation

* the belief that living organisms could arise spontaneously (naturally) from nonliving matter

* example of "proof":

1) leave out a piece of meat
2) watch maggots grow from meat
3) maggots came from meat

THIS IS NOT PROOF!
you must carry out a controlled experiment

* Francesco Redi disproved spontaneous generation in the mid-1600 by using a control--some meat was placed in an open jar, other meat was placed in a covered jar (one variable--easy to study)...RESULTS:

1) flies landed on the uncovered meat--then maggots
2) no flies on covered meat--no maggots, flies could
not land on meat to lay eggs!


other theories were based on ADAPTATIONS--features (structural behavioral, of functional) which make a species better able to live and reproduce in its environment

B) Lamarck's Theory of Evolution (mid 1800's)
* explained the changing of species over time with two principles:
1) USE AND DISUSE

* new organs will arise according to the needs of a particular organism
* the size of the organ depends on how much they are used

2) TRANSMISSION OF ACQUIRED TRAITS

* useful characteristics were acquired by an individual organism during its lifetime and were passed on to its offspring

* Lamarck was disproved by Weismann
* Weismann removed the tails of several generations of mice and found that this trait was not passed on to the offspring!


C) Darwin's Theory of Evolution

* explained the changing of species over time with the principle of NATURAL SELECTION (mid 1800's)
* natural selection has many parts:

1) OVERPRODUCTION
* more offspring are born in a population than can possibly survive

2) COMPETITION
* because of the large amount of organisms, there is a struggle to survive
* limited resources such as space, food, water, light, minerals keep populations at bay

3) VARIATIONS
* due to genetic recombination (crossing over and sexual reproduction) and mutations, members of a population show variations
* these can possibly help or hurt an organism to survive its respective environment

4) SURVIVAL OF THE FITTEST
* those individuals who do survive are the ones that have the variations that are best adapted to its environment

ex. in the woods, brown fur is helpful for hiding and
white fur is not helpful...brown lives!

5) REPRODUCTION
* the individuals that do survive in a population will pass their variations (genes) to their offspring
* those that had unfavorable adaptations do not survive and do not pass on their traits

6) SPECIATION
* over time...a LONG PERIOD OF TIME, these adaptations will result in a new species; called SPECIATION


Because Darwin (19th century) didn't know what DNA/genes/chromosomes were, he could not explain the genetic basis for variation!

COMPARING LAMARCK AND DARWIN
The ancestor of the modern day giraffe had a short neck, as seen by fossils.

LAMARCK would have explained the change in the giraffe's neck by saying that the giraffe's ancestor was a grass-eating, short-necked animal. When the grass became scarce, the giraffes needed to stretch their necks to reach for food. Each generation had to stretch more to reach their food. The longer neck then was passed on to the next generation and each following generation had a longer and longer neck.

DARWIN would have said that the giraffe's ancestors had different neck lengths. Through natural selection, the giraffes with the longer necks could reach food and survived, while the giraffes with short necks starved and died. Long necked giraffes would survive to reproduce and pass along their traits to the next generation.

 

Evolution

see what is meant by spontaneous generation--and why it has been shown wrong

III. MODERN EVOLUTIONARY THEORY
* supports and explains the genetic basis for Darwin's concepts of variation and natural selection

A) Supporting Variation

1) MUTATIONS
* are changes in DNA
* are spontaneous cause for change!

2) SEXUAL REPRODUCTION
* the sorting out and recombination of genes during meiosis and fertilization
* forms new combinations of genes!

B) Natural Selection

* traits which are beneficial to survival of an organism will be passed to new generations and will increase in gene frequency
* traits which are not beneficial will not be passed on and will decrease in gene frequency

IF THE ENVIRONMENT CHANGES...
...some traits not beneficial may
become so--or vice versa!

ex. moths during the industrial revolution,
bugs becoming resistant to insecticide,
bacteria becoming resistant to
anti-biotics such as penicillin

C) Extinction

* throughout history, species have evolved together
* not all species survive...99% of all species that have existed on earth are no longer present
* you can track different species using the "tree model"
* some branches change over time, some remain the same, some do not survive


Evolution

one of our early relatives is shown here:

A. Afarensis

a nice review of Darwin and the social impact of his theory
nice brief clip showing primate evolution
when good asteroids go bad; extinction level event!

IV. TYPES OF NATURAL SELECTION

A) Geographic Isolation

* when members of a species are physically separated from one another
* they can evolve (change) separately according to their new environement

 

B) Reproductive Isolation

* groups that are separated can become so different over time that they no longer can produce offspring that can survive (genetic drift)
* so now, you have two separated species

C) Time Frame for Evolution

* there are two separate theories that attempt to explain how long evolution takes
* based on fossil record

1) GRADUALISM
* evolutionary change is a slow, gradual, continuous process

2) PUNCTUATED EQUILIBRIUM
* species remain stable (no changes) for a long period of time, then a big change happens in a brief time... meteors? volcanoes?
* the fossil record show that most invertebrate species only last between 5-10 million years

Evolution

read up on how an environmental shift can lead towards evolution; a simple way to see natural selection at work
a nice review of Darwin and the social impact of his theory

V. HOW DID LIFE BEGIN ON EARTH

THE HETEROTROPH HYPOTHESIS
(the following is based off of years of human experiments, observations, analyses, and conclusions)

A long, long time ago...

* the earth was a hot place filled with inorganic material
* as the planet cooled down, water condensed and collected into the seas carrying dissolved gases (NH3 H2O H2 methane) and minerals
* energy from lightning, cosmic rays (no ozone layer yet) , and radioactive material provided an energy rich environment

* from these conditions, simple organic molecules formed! (proven in the Miller/Urey experiments)

* in time, these simple organic molecules aggregated (clumped) to form larger, more complex organic molecules

WHAT HAPPENED NEXT IS COOL...and took a very long time...
* as these molecules became more advanced, they gained the capability to take in other molecules (nutrition) as well as being able to make copies of themselves (reproduction) by trial and error of code

* meanwhile, there is no oxygen O2 gas

* the simple life forms got their energy through simpler anaerobic (no oxygen) respiration and released carbon dioxide (CO2) into the atmosphere

* soon, some life forms were able to use CO2 to carry out photosynthesis--which releases oxygen!

* others then gained the ability to use the oxygen to carry out aerobic (using oxygen) respiration...lots more energy released...evolution speeds up!


SUMMARY OF HETEROTROPHIC HYPOTHESIS


SIMPLE MOLECULES

COMPLEX MOLECULES
(Heterotrophic nutrition)

SIMPLE ORGANISMS
(heterotrophic nutrition)
(anaerobic respiration--releases CO2)

SIMPLE ORGANISMS
(autotrophic nutrition--releases O2)
(anaerobic respiration)

SIMPLE ORGANISMS
(aerobic respiration--uses O2
lots of energy!!!)

COMPLEX ORGANISMS

Evolution

some history of the Miller/Urey experiment
cell evolution review