early beliefs ♦ each species had been created separately and “placed” on the earth ♦ these...
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EARLY BELIEFSEARLY BELIEFS
♦ each species had been created separately and “placed” on the Earth
♦ these created species were unchanging– they exist today in the same form as they did at the beginning
of the world
In the 1700’s and 1800’s, several scientific fields developed which
challenged this view of how species exist through time & how they relate to
each other
1) BIOGEOGRAPHY
biology geography
an examination of the world distribution of organisms and the similarities and
differences among organisms from different geographic locations
Naturalists accompanied sailing expeditions to other continents and observed the numerous plant and animal
species that existed in these “new” areas
2) comparative morphology
comparing the form and structure of organisms
morphology = the form and structure of organisms
As more and more organisms were observed and described, scientists began comparing their body plans:
they found that many body parts of seemingly different organisms (e.g. whales, bats, and humans) were clearly
modifications of a single basic plan.
3. Study of fossils:
geologists began to map the layers of the Earth’s crust
fossils found in these layers showed changes in organisms through time ه
many of the fossilized organisms that had existed in the past were no longer ه present and…
many present-day organisms were not found in ancient fossils
*** the study of geologic layers also showed that the age of the planet was millions (now known to be billions) of years old rather than thousands of years old as previously thought
All of these scientific developments had a strong impacton scientists’ perceptions about the relationships
between species
The travels of several scientists led them to develop theories on how organisms change through time
1. Lamarck2. Wallace and Darwin
Lamarck traveled to Africa fascinated by the elongated necks of giraffes
Proposed that there was some type of substance that offspring inherit from parents that carried the codes fortraits–
-- called this substance “fluida”
-- idea: giraffes stretch their necks higher to reach leaves, then passed this “long neck” fluida to offspring
-- felt that organisms could change their fluida and pass these changes on to offspring
We now know that our genetic code is We now know that our genetic code is passed on through our germ cells passed on through our germ cells
(gametes)(gametes)&&
is not changed by changes that we make to is not changed by changes that we make to our bodies over the course of our lifetimeour bodies over the course of our lifetime
Wallace and Darwin were both naturalists from England traveled to other continents & studied the flora and fauna
Darwin Wallace
Their ideas would become known as NATURAL SELECTION – a mechanism that became widely accepted for explaining evolution
They simultaneously came up with very similar theories on how organisms change through time
??
Wallace- traveled to South America (Amazon)for 11 years as a naturalist
lost all his collections when ship sank on trip back
bored in England, went to Malaysia for 8 years
during a bout with malaria, came up with ideas on natural selection
Darwin- grew up playing with bugs in the back yard
parents wanted him to go to med school, but he dropped out-- his folks said- you can’t stay at home! …so he went to theology school
he got his degree in theology, but he spent a lot of time studying natural history with hisbiology and botany professors
so… when an a spot opened up on the Beagle, Darwin was recommended by his prof. to go as the naturalist
5 yrs sailing around S. America
eventually published The Origin of Species by Means of Natural Selection
Conditions for Natural Selection:
3. Some of these variable, heritable traits will affect an organisms fitness
FITNESS = SURVIVAL & REPRODUCTION = an organism’s contribution of genetic information to
future generations (the amount of genetic information passed, in terms of offspring, to the future)
1. Not all organisms that are born will survive to the age of reproduction
2. Organisms vary in many ways & much of this variation is heritable (passed from parent to offspring in genetic code)
4. (the kicker) Those traits that increase an organism’s fitness (survival and reproduction) will tend to be passed on to future generations more often than those traits that decrease an organism’s fitness.
Natural selection acts on the variations in traits among organisms… … where does this variation in traits come from?
Only mutations create new gene forms– all others simply shuffle existing gene forms, creating different combinations of genes!
2. mutations:
a. gene mutationsb. chromosome mutations
1. sexual reproduction- mixes alleles from 2 parents
Sources of genetic variation:
a. crossing over in meiosis
b. independent assortment in meiosis (mixing maternal and paternal chromosomes in the formation of gametes
evolution = change in allele frequencies over time ه e.g. the change in the frequency of the allele that codes for long vs. short tails in tulus
alleles (gene forms) are not necessarily “good” or “bad”, whether an هallele has a positive effect on an organisms fitness often depends on the environmental conditions at the time! -- e.g. fur color in tulus
natural selection can act on an individual organism, but ** هevolution acts on a population!
ADAPTATION:
adaptations are traits (or characters) that have been subjected to natural selection
This means that the trait has "evolved" (been modified during its evolutionary history) in ways that have contributed to the FITNESS of the organism
e.g. spines on a cactus -- prevent predation
-- reflect light