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EARLY BELIEFS ♦ each species had been created separately and “placed” on the Earth ♦ these created species were unchanging– they exist today in the same.

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Presentation on theme: "EARLY BELIEFS ♦ each species had been created separately and “placed” on the Earth ♦ these created species were unchanging– they exist today in the same."— Presentation transcript:

1 EARLY 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

2 1) BIOGEOGRAPHY biology  geography an examination of the world distribution of organisms and the similarities and differences among organisms from different geographic locations

3 Naturalists accompanied sailing expeditions to other continents and observed the numerous plant and animal species that existed in these “new” areas


5 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.


7 3. Study of fossils: geologists began to map the layers of the Earth’s crust ﻬ 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 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

8 All of these scientific developments had a strong impact on scientists’ perceptions about the relationships between species The travels of several scientists led them to develop theories on how organisms change through time 1.Lamarck 2.Wallace and Darwin

9 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 for traits– -- 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

10 We now know that our genetic code is passed on through our germ cells (gametes) & is not changed by changes that we make to our bodies over the course of our lifetime

11 Wallace and Darwin were both naturalists from England  traveled to other continents & studied the flora and fauna DarwinWallace 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 ?

12 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

13 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

14 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.

15 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 mutations b. 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

16 ﻬ evolution = change in allele frequencies over time e.g. the change in the frequency of the allele that codes for long vs. short tails in tulus ﻬ alleles (gene forms) are not necessarily “good” or “bad”, whether an allele has a positive effect on an organisms fitness often depends on the environmental conditions at the time! -- e.g. fur color in tulus ﻬ ** natural selection can act on an individual organism, but evolution acts on a population!

17 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

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