Test 2 Flashcards
Explain common descent, common ancestor, and what we now realize it’s due to
Darwin saw evidence that all organisms had similar anatomical structures. This was because they all had a common ancestor. Today we realize that this is specifically due to shared DNA which is a result of a common ancestor.
Give an example of common descent
Pentadactyl limb-adapted by modification. 5 fingered limb.
Monkeys being able to grasp
The difference in shape and function of the mammalian limb bones is due to gradual modifications that made the organism better able to survive in a particular environment. Environmental factors naturally select for or against variations in the basic shape of bones-gives evolutionary advantage. There is a genetic basis to this (Darwin didn’t know in his time)
Descent with Modification
Natural selection selects among whatever genetic variations arise due to ___
Random mutation
Why is natural selection not random?
The genetic variation that occurs in a population because of mutation is random, but selection is not because selection acts on that variation in a very non-random way: genetic variants that aid survival and reproduction are much more likely to become common than variants that don’t.
Summarize Darwin’s theory
Individuals with the variations/adaptations best suited to their environment will survive and reproduce. Those not suited will be less likely to breed (survival of the fittest). There is a
genetic basis! These variations are due to random genetic mutation. * Species change over time by passing on their useful (and harmful?) traits to their offspring*
All species alive today have ___ from ancient ancestors. Ultimately, all organisms on earth are united into a single ___
Descended with modifications; tree of life
The concept that a group of closely related species are all descended with some modifications from the same ancestor
Common ancestry
Idea that living species have descended with changes due to adaptations and natural selection from species that lived before them
Descent with modification
What is one piece of evidence for common ancestry/descent with modification?
Fossils are evidence that the world was much older than once thought. They show how organisms have changed over time. 99% of species that once lived are now extinct.
Preserved remains or traces of ancient organisms
Fossils
Fossil record: when comparing fossils found in rock layers, the ___ the layer the ___ the fossil
Deeper; older
What is more evidence of evolution?
Biogeography. Shows how closely related species change in different environments/selection pressures and shows how distantly related groups have evolved similar traits under similar selection pressures
The study of where species live now and where species and their ancestors lived in the past. Shows common ancestry in two ways: 1) how closely related species change in different environments/selection pressures; 2) how distantly related groups have evolved similar traits under similar selection pressures
Biogeography
The study of similar characteristics between organisms. Three major branches: anatomical, embryological, molecular
Homology
