1. There’s something you need to know…
Chapter 23
The Origin of Species
Mom, Dad…
There’s something you need to know…
I’m a MAMMAL!

2. “That mystery of mysteries…”
Darwin never actually tackled how new species first arose…
Both in space and time, we seem to be brought somewhat near to that great fact —that mystery of mysteries— the first appearance of new beings on this Earth.

3. So…what is a species? Biological species concept defined by Ernst Mayr
population whose members can interbreed & produce viable, fertile offspring
reproductively compatible
Distinct species: songs & behaviors are different enough to prevent interbreeding
Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species.
Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding
Eastern Meadowlark
Western Meadowlark

4. “Evolution is so overwhelmingly established that it has become irrational to call it a theory.”
Born in 1904 in Germany, Mayr trained as a medical student but realized he had a greater passion for studying birds and biology. Emigrating to the United States, he became a curator at the American Museum of Natural History, working on bird classification while formulating his key ideas about evolution. In 1942 he published his most important work, Systematics and the Origin of Species. Mayr moved to Harvard University in 1953 and served as director of the school's Museum of Comparative Zoology from 1961 to Since then, he has published a number of books and chapters and received the prestigious Japan Prize for Biology in 1983.
In his landmark 1942 book, Mayr proposed that Darwin's theory of natural selection could explain all of evolution, including why genes evolve at the molecular level. On the stubborn question of how species originate, Mayr proposed that when a population of organisms becomes separated from the main group by time or geography, they eventually evolve different traits and can no longer interbreed.
It's this isolation or separation that creates new species, said Mayr. The traits that evolve during the period of isolation are called "isolating mechanisms," and they discourage the two populations from interbreeding.
Moreover, Mayr declared that the development of many new species is what leads to evolutionary progress. "Without speciation, there would be no diversification of the organic world, no adaptive radiation, and very little evolutionary progress. The species, then, is the keystone of evolution."
Ernst Mayr What Evolution Is 2001
Professor Emeritus, Evolutionary Biology
Harvard University
( )

5. How and why do new species originate?
Species are created by a series of evolutionary processes
populations become isolated
geographically isolated
reproductively isolated
isolated populations evolve independently
Types of Isolation
allopatric
geographic separation
sympatric
still live in same area
AP Link—Ch 23: Speciation Mechanisms—TSOB

6. Pre-reproduction Barriers
Obstacle to mating or to fertilization if mating occurs
geographic isolation
ecological isolation
temporal isolation
behavioral isolation
mechanical isolation
gametic isolation

7. Geographic Isolation Species occur in different areas physical barrier
allopatric speciation
“other country”
Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel.
AP Link—Ch 23: Speciation Mechanisms—TSOB

8. lions & tigers could hybridize, but they live in different habitats:
Ecological Isolation
Species occur in same area, but occupy different habitats so rarely encounter each other
lions & tigers could hybridize, but they live in different habitats:
lions in grasslands
tigers in rainforest
2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial

9. Temporal Isolation
Species that breed during different times of day, different seasons, or different years cannot mix gametes
sympatric speciation
“same country”
Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

10. Behavioral Isolation
Unique behavioral patterns & rituals isolate species
identifies members of species
attract mates of same species
courtship rituals, mating calls
AP Movie—Ch 23: Blue-Footed Boobie Courtship
AP Movie—Ch 23: Giraffe Courtship
The most comedic species of the Galapagos Islands is the Blue Footed Booby, what a ridiculous outfit and expression! Their name is in fact taken from the Spanish 'bobo' which means clown.
The Blue Footed Boobies above display part of their humorous courtship ritual whereby they raise their feet one at a time and then swivel their heads away from the prospective mate looking to the sky.
Other interesting Booby features are the highly evolved airbag systems in their skulls which allow them to dive bomb into the sea for fish from great height, and the egg and hatchling nesting boundaries they make which are rings of Boobie poop. They aren't the only Booby on the island — there are also Masked and Red Footed Boobies about.
Blue footed boobies mate only after a courtship display unique to their species
sympatric speciation?

11. Recognizing your own species…
What can you say? I guess some people think this look is AWESOME!
courtship songs of sympatric species of lacewings
courtship display of Gray-Crowned Cranes, Kenya
firefly courtship displays

12. Mechanical Isolation
sympatric speciation?
Morphological differences can prevent successful mating
Plants
Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen.

13. Mechanical Isolation Animals
For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer
lack of “fit” between sexual organs: hard to imagine for us… but a big issue for insects with different shaped genitals!
The selection is intense because it directly affects offspring production -- it is affecting sex itself
I can’t even imagine!
Damsel fly penises

14. Gametic Isolation
sympatric speciation?
Sperm of one species may not be able to fertilize eggs of another species
mechanisms
biochemical barrier so sperm cannot penetrate egg
receptor recognition: lock & key between egg & sperm
chemical incompatibility
sperm cannot survive in female reproductive tract
Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species are unable to fuse.

15. Post-reproduction Barriers
Prevent hybrid offspring from developing into a viable, fertile adult
reduced hybrid viability
reduced hybrid fertility
hybrid breakdown
zebroid

16. Reduced Hybrid Viability
Genes of different parent species may interact & impair the hybrid’s development
Different pecies of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.
sympatric speciation?

17. Reduced Hybrid Fertility
Even if hybrids are vigorous they may be sterile
chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes
Mules are vigorous, but sterile
What’s wrong with having 63 chromosomes?
Odd number! Cannot pair up in meiosis.
Horses have 64 chromosomes
(32 pairs)
Donkeys have 62 chromosomes
(31 pairs)
Mules have 63
chromosomes!

18. Hybrid Breakdown
sympatric speciation?
Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile
In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. ‘Parents’ on path to separate species.

19. Rate of Speciation Current debate:
Does speciation happen gradually or rapidly?
Gradualism
Charles Darwin
Charles Lyell
Punctuated equilibrium
Stephen Jay Gould
Niles Eldredge
Niles Eldredge
Curator
American Museum
of Natural History

20. Stephen Jay Gould ( )
Harvard paleontologist & evolutionary biologist
punctuated equilibrium
prolific author
popularized evolutionary thought
Stephen Jay Gould (September 10, 1941 – May 20, 2002) was a New York-born American paleontologist, evolutionary biologist, and historian of science. He was the most influential and widely read writer of popular science of his generation. He served as a member of the faculty at Harvard University beginning in Toward the end of his life he served as the Alexander Agassiz Professor of Zoology at that university. He helped Niles Eldredge develop Eldredge's theory of punctuated equilibrium 1972, wherein evolutionary change occurs relatively rapidly in comparatively brief periods of environmental stress, separated by longer periods of evolutionary stability. According to Gould, this overthrew a key tenet of neo-Darwinism; according to most evolutionary biologists, the theory was an important insight but merely modified neo-Darwinism in a way fully compatible with what had been known before. Gould became widely known through his popular science essays in Natural History magazine, collections of essays like The Panda's Thumb and The Flamingo's Smile, and extended studies like Wonderful Life and others.Gould was an emphatic advocate of evolution and wrote prolifically on the subject, trying to communicate his understanding of contemporary evolutionary theory to a wide audience. A recurring theme in his writings is the history and development of evolutionary (and pre-evolutionary) thinking. His early research involved the study of the fossil record of snails (detailed in one of his essays). He was also an enthusiastic baseball fan and made frequent references to the sport (including an entire essay) and a very wide range of other topics.

21. Gradualism Gradual divergence over long spans of time
assume that big changes occur as the accumulation of many small ones

22. Punctuated Equilibrium
Rate of speciation is not constant
rapid bursts of change
long periods of little or no change
species undergo rapid change when they 1st bud from parent population
Time

23. Evolution is not goal-oriented!
An evolutionary trend does not mean that evolution is goal-oriented.
Surviving species do NOT represent the peak of perfection. There is compromise & random chance involved as well
Remember that for humans as well!

24. Excerpt from “Why Darwin Matters”
Any Questions??
Excerpt from “Why Darwin Matters”
In the legendary debate over evolution at Oxford University in June 1860, Archbishop Samuel Wilberforce sardonically inquired of his debate opponent, Thomas Henry Huxley (“Darwin’s Bulldog”), whether he was descended from an ape on his grandfather’s or grandmother’s side. The legend of the debate is that Huxley followed with his stinging rejoinder: “If question is put to me: Would I rather have a miserable ape for a grandfather or a man highly endowed by nature and possessed of great means of influence and yet who employs these faculties and that influence for the mere purpose of introducing ridicule into a grave scientific discussion, I unhesitatingly affirm my preference for the ape.”
Excerpt from “Why Darwin Matters”.
In the legendary debate over evolution at Oxford University in June 1860, Archbishop Samuel Wilberforce sardonically inquired of his debate opponent, Thomas Henry Huxley (“Darwin’s Bulldog”), whether he was descended from an ape on his grandfather’s or grandmother’s side. The legend of the debate is that Huxley followed that his his stinging rejoinder: “If then, said I, the question is put to me would I rather have a miserable ape for a grandfather or a man highly endowed by nature and possessed of great means of influence and yet who employs these faculties and that influence for the mere purpose of introducing ridicule into a grave scientific discussion, I unhesitatingly affirm my preference for the ape.”