Have you seen this famous image? VERY COMMON MISCONCEPTION
Proof of Similar Ancestry How do we know an organism is related to another?
How can we find proof of similar ancestry? • Embryology • Homologous Body Structures • Analogous Body Structures • Vestigial Body Structures • Genetic Similarities (DNA)
Embryology • The early stages of vertebrate development are all very similar. Vertebrates start to diverge into chimp, chicken, & lizard form in the later stages of development! What does this say about the relationship between vertebrates?
Does this provide evidence that vertebrates share a common ancestor? YES!
Larvae are the immature stage of an organism that looks different from the adult form. For example, a caterpillar is the larva of a butterfly. The larvae of modern sea stars, which are invertebrates, resemble some simple vertebrate larvae. This similarity may suggest that simple vertebrates… • Share a common ancestor with sea stars. • Evolved from sea stars. • Evolved before sea stars. • Belong to the same species of sea stars. Simple vertebrates share a common ancestor with sea stars!
Homologous Body Structures • Structures derived from a common ancestor or the same evolutionary or developmental origin
Homologous Body Structures Developmentally, a human arm, whale fin, cat leg, & bat wing share the same bones! Due to different selective pressures & occupying different niches, these bones can have dramatically different functions!
What can you say about the relationship between species who share homologous structures? Species who share homologous structures share a common ancestor – they are related!
Homologous Structures • Come from the same embryonic tissue • Similar structure • May have different functions • Provide evidence of close evolutionary relationship • Recent common ancestor!
Analogous Structures • Structures that seem similar, but they DO NOTshare a recent common ancestor! Compare the wing of the bird to the wing of the moth. What do they have in common? What are some differences?
Analogous Structures • The wing of the bird & the wing of the insect are similar in function (flight), but are different in structure (bones vs. no bones) & embryonic origin! These wings evolved separately to perform a similar function (due to similar selective pressures acting on the species)!
What can you say about the relationship between species who share analogous structures? Species who share analogous structures DO NOT share a recent common ancestor – they are NOT related!
Analogous Structures • Similar functions • Similar external form • Different internal structure & development • Different origin • No evolutionary relationship! Don’t be fooled by their looks! Solving a similar problem with a similar solution…
Which type of structures do the dinosaur & bird wings share? • Homologous • Analogous • Both • Neither From left to right: insect, dinosaur, bird, bat. Homologous Structures!
Which type of structures do the bat & insect wings share? • Homologous • Analogous • Both • Neither From left to right: insect, dinosaur, bird, bat. Analogous Structures!
Vestigial Structures • Structures that have become reduced in size, because they do not have a true contributing function or role in survival Whales have the remains of pelvis & leg bones from their walking ancestors!
Vestigial Structures • If you take an x-ray of a snake, you will find pelvic & femur (thigh) bones! What do these vestigial structures mean? Snakes evolved from an ancestor that had legs!
Basically… • Homologous Structures: similar structures, used for different functions • Shows that the species share a common ancestor & are related • Analogous Structures: different structures, used for similar functions • Shows that the species do NOT share a common ancestor & are NOT related • Vestigial Structures: no longer have function or use • Shows that the species evolved from another species that used the structure
Dolphins (mammals) & fish both have similar body shapes adapted for moving in water. • Homologous • Analogous • Vestigial Analogous Structures! Similar functions (swimming), but mammals & fish are not closely related!
This species of cave-dwelling salamander has eyebuds, but is completely blind. • Homologous • Analogous • Vestigial Vestigial! The fact that this blind salamander still has eyebuds shows that, though blind, has evolved from an ancestor who had eyes & was not blind!
Humans, whales, & giraffes all have 7 neck bones. • Homologous • Analogous • Vestigial Homologous! Similar neck structures, different functions!
The ear muscles, appendix, & tailbone in humans. • Homologous • Analogous • Vestigial Vestigial!
Indicates that 2 organisms probably have a common ancestor. • Homologous • Analogous • Vestigial Homologous Structures!
Genetic Data • We can compare DNA sequences between species to see how similar or different they are. Here is a short section of DNA. What do the A, T, G, and C represent?
Now compare the DNA to a close ancestor: Living organism: Ancestor: On which nucleotide(s) do the sequences differ? What is this difference called?
You try it! • You have 9 nitrogen base sequences from a section of DNA similar to what you might find in a human. Look for the sequence labeled “living DNA”. • Find the closest ancestor to the living DNA and place it below the living DNA • Place the rest of the sequences in the correct order, from present (living) to oldest ancestor.
What did you use to make your decision? Were you correct in your order? Assume the rate of mutation is 1 mutation for every 10,000 years. How many years separate the “living DNA” from its oldest ancestor?
The table below shows chemicals found in certain bacteria. Each capital letter represents a different chemical. Which 2 bacteria are most closely related? • Bacteria 1 & 2 • Bacteria 2 & 3 • Bacteria 2 & 4 • Bacteria 3 & 4 Bacteria 2 & 4!