1. Next Time
Bring a deck of cards

4. How Does Evolution Work?SO
How Does Evolution Work?

5. LAMARCK’S View
The French Biologist Lamarck argued that characteristics acquired during the life time of an organism could be passed on to its offspring=
Evolution by Acquired Characteristics
Use and Disuse

6. LAMARCK’S VIEW Inheritance of Acquired Characteristics
ENVIRONMENT
“NEED”
USE & DISUSE
HEREDITY
NEW SPECIES

7. How did the giraffe get its long neck?

8. His classical answer

9. If giraffes needed wings to fly, would they appear?
How could the “need” for long necks actually cause long necks to appear?
If giraffes needed wings to fly, would they appear?

10. Enter Mr. Charles Darwin

11. DARWIN’S VIEW expressed in modern terms
MUTATION
SEX
Fertilization
CROSSOVER
Genetic recombination
HEREDITY
NEW
SPECIES
NATURAL
SELECTION
VARIATION

12. How did the giraffe get it’s long neck?

13. Darwin argument was that a giraffe’s ancestors had variable neck lengths and the ones with the longest neck had a selective advantage.
And they were the ones that were most likely to leave offspring behind.
So the average giraffe neck progressively grew longer over time because the ones with the longest necks in a given generation were always at an advantage.

14. Both Lamarck & Darwin Had a Problem
How could they explain why a trait appears?
Lamarck said “need” & “use and disuse” does it. But how do these factors prompt the development of the trait to be passed on?
Darwin said that chance variations come along. But how does that happen & why?

15. But no matter which hypothesis is correct this still doesn’t resolve the question of what the mechanism of evolution exactly is. Is it Use and Disuse leading to Acquired Characteristics ? or Is it Variation followed by Natural Selection? Or……

16. Weismann’s experiments
August Weismann was a famous German scientist in the early 1900’s. He believed passionately that natural selection was the only driving force of evolution.

17. Weismann’s experiments
Weismann argued that the inheritance of acquired characteristics could not occur on theoretical grounds, saying that the germ cells (sperm and eggs) were totally isolated from the body cells.
so any environmental influence acting on the body could not affect the heredity.
(Today we argue something similar when we say that any mutation in a body cell does not affect the genes of the sex cells.)

18. Weismann’s experiments
Weismann’s ideas were published in 1912 in a book entitled “The Germ Plasm: A Theory of Heredity.”
He argued that the germ plasm is continuous from generation to generation and that bodies are merely vehicles for transmitting the germ plasm from place to place.

19. Weismann’s experiments
Samuel Butler said something similar when he said, “A hen is only an egg’s way of making another egg.”
Or as E.O. Wilson has put it,
“People are DNA’s way of making more DNA.”

20. Weismann’s Experiments
Weismann decided to test Lamarck’s ideas by cutting off the tails of mice. He knew that two short tailed cats had been exhibited at a recent scientific meeting with the claim they were the progeny of cats with amputated tails.
Could this claim be true? Weismann decided to amputate the tails of 20 generations of mice, always breeding together the short-tailed animals with each other, carefully measuring their tails all along.

21. Weismann found that there was no shortening.
The data do not support Lamarck’s hypothesis.

22. It’s not that cut & dried
Interestingly,
Darwin also accepted that acquired characteristics was also part of evolution. But Natural Selection was most important.
There were some things that he could not explain such as how variation was caused—(Remember he knew nothing about genetics)—
So he believed that the environment could stimulate variation— (one of Lamarck’s ideas)—and this would be inheritable.

23. Paul Kammerer’s Experiments
Paul Kammerer was a well known scientist in Vienna in the early 1900’s.
He believed in the Inheritance of Acquired Characteristics.

24. Paul Kammerer’s Experiments
Frog’s and toads generally breed in water. The males grab a female that is about to lay eggs from behind. He mounts her and clings to her back until she releases her eggs. Then he discharges his sperm on them as they emerge from her cloaca. To help him hold onto the wet slippery female he has roughened places on his forelegs called callosities.
The Midwife Toad is an exception; it breeds on land and the males lack the callosities.

25. And I did find that the young toads developed callosities !

26. Critics Attack
But Kammerer was supported by many well-known scientists.
He defended his work
People had difficulty repeating his work because of the difficulty in working with the toads.
The Soviet Union praised his work and

27. Confusion
Paul Kammerer was invited to the Soviet Union to take over the chairmanship at the University of Moscow.
While he was away a committee of scholars visited his laboratory and examined one of the toads that remained from his experiment. They concluded that black India ink had been applied to the toad’s legs to enhance the visibility and the callosities appeared artificial.

28. Confusion
When Kammerer heard this he was offended and deeply hurt.

29. Confusion
Kammerer returned to pack his belongings to go to the Soviet Union and he heard about the committee’s conclusion.
He promptly walked into the woods and put a bullet through his brain.

30. Lysenko’s Wheat
Trofim Lysenko was a Russian agricultural specialist with strong political leanings toward the ruling Bolshevik party run by President Stalin and based on the philosophical basis of Marx, Engels and Lenin.
They came to power in the 1917 Russian revolution determined to improve the lot of the peasant farmers.

31. Converting Wheat to Feed the People
Lysenko was able to convince Stalin that the Lamarckian principles could be applied to Soviet agriculture.
He believed that elements of both Darwinism and Lamarckism were correct. Many of his experiments were directed toward converting winter to spring wheat, causing seeds to germinate earlier.

32. Lysenko’s Experiments
Lysenko’s experiments were based upon an old peasant farmer practice known as vernalization—applying cold temperatures to seeds.

33. Lysenko’s Experiments
The seeds were treated with cool spring temperatures and the ones that germinated and developed their seeds were collected and treated again. This was repeated over several years. Progressively, he developed good varieties of wheat that possessed a frost resistance and could be grown earlier than normal.

34. Conclusion?
Lysenko argued that answers (A) and (C) were correct. He stated that there are two methods for the vernalization of wheat.
The first is to moisten and chill the winter seeds at 0-10° C
for days and this stimulates early growth in the spring but does not change the heredity.

35. Conclusion?
Lysenko said, “The second method is to change the nature of the winter plants, whereupon they will cease to be winter plants in respect to their heredity.” He used this method
Winter seeds were given not 0° C but only cool spring temperatures.
The seeds that germinated were used for the next generation; this was repeated over and over to get the desired effect changing winter wheat into spring varieties. These trials, he believed, had disrupted their heredity.

36. Today’s View
Today we think that Lysenko was doing a simple artificial selection experiment:
choosing the seeds that germinated early and using them for the next generation throwing the others seeds out.
But maybe epigenisis was involved.

37. The Tragedy
The tragedy of Lysenko’s rise to power was that he stifled any opposition to his interpretation of genetics. He argued that anyone working on theoretical genetics (e.g. Drosophila) was not doing the practical work needed by the Soviet economy.
He argued that only Lamarckian principles were compatible with the stated goals of the revolution.

38. The Tragedy Lysenko’s view was that
Darwinism left evolution to chance;
Lamarckism meant that we are not bound to our genetic destinies but can change things for the better.

39. The End of Soviet Genetics
Prior to the Lysenko period, the Soviets were the leaders in the field of genetics. During the period from1925—1965, Lysenko’s opponents were systematically jailed, removed from power, or just disappeared. All opposition was silenced and the field of basic genetics largely disappeared

40. Science & Politics don’t
Mix
Or Do They?

41. Climate Change Research
Anyone?

43. Coda DNA is the genetic blueprint of the organism.
2) All cells of a multicellular organism carry the same set of instructions, i.e. the same DNA
3) Yet the cells of the different organs in the body act differently because different parts of the DNA are active;
half of the proteins are the same in all cells and half are different.

44. Control is achieved 4) Control of the DNA is achieved by chemicals
in the cell controlling
which genes turn on
and which turn off.
These chemicals include
histone proteins,
different kinds of RNA,
and chemical tags
like methyl groups.

46. Environment effects Epigenesis
5) Organisms accumulate these tags as they age and are exposed to different environmental factors.
Even identical twins
who have the same DNA,
progressively become more
different as they accumulate
these epigenetic tags

48. Environment matters
6) The kinds of environmental factors that have an epigenetic impact include nutrition, chemicals such as cigarette smoke, stress, social factors, exercise.

49. It appears that the environment can induce heritable epigenetic changes
So maybe Paul Kammerer was innocent

50. Maybe Lysenko was right
Epigenetics = changes in the expression of a genes that occur without changing the DNA sequence
Maybe Lysenko was right

51. So maybe Lamarck was right

54. Epigenesis & Evolution
7. Epigenetic effects can be passed on to the next generations.
The environment
of your grandmother
has influenced you.
And you are now
accumulating tags
that can last
generations

55. Live Wisely