DARwinism

1. DARwinism

2. Predictions From Darwinism • Natural Selection is the only significant mechanism of evolution • Evolutionary change is slow and gradual • All evolutionary change is adoptive • Macroevolution is the same as microevolution

3. Criticisms • Relative absence in fossil record of any transition types • Punctuated Equilibrium (Steven Jay Gould) proposed as an alternative • Possible limits to genetic variation • Only so much could be contributed to random, small change in genes • Blended inheritance • Favorable variation “swamped out” by backcrossing with “ordinaries”

4. Non-adaptive traits • Example: peacock’s tail - more energy to make, attractive to predators, etc • Darwin’s response was sexual selection

5. Evidence • Darwin had a multitude of evidence he could point to • Initially, it answered most questions critics had • However, over time it wasn’t enough Fossil Record • Observed many extinct species similar to those that were alive then

6. Comparative Embryology • Work by Ernst Haeckel provided support

8. Idea behind similar embryos lead to understanding of homologous structures

9. Minor Geographic Variation • Galapagos Islands very important here • Noted that each island had distinct species of finches, tortoises etc. • Each variant was best suited for its unique environment Mendelian Genetics • Available at the time, but not connected until 1930’s

10. What Darwin Didn’t Know… • Basically DNA • Key idea was variation in offspring – mechanism unknown • Today, we understand concepts of gamete formation, random mutation of germ line, “switches”, HOX genes etc. • The more data that is gathered, the more evidence is provided for natural selection

11. Causes of Microevolution The Hardy-Weinberg principle states that there are five requirements for stability Any deviation from the requirements below indicates the population is evolving • Very large population size • Isolation from other populations • No net mutations • Random mating • No natural selection

12. Monitoring • So now the question becomes, how do we watch for changes • Recall the Hardy-Weinberg principle • There is also an equation which can predict the relative frequencies of alleles in a gene pool

13. Example • Imagine a wildflower population of 500 plants • In this, there are pink alleles A, completely dominant over white alleles a • 20 are white, so they would be aa • 320 are AA • 160 are Aa

14. Since they are dipliod, the pink allele accounts for 800 of the 1000, and white 200 of the 1000 • We can use math to determine relative frequencies in the population • Any deviation from that means the population is evolving

15. Example Batten disease is a rare recessive neurodegenerative disease, affecting 3 out of every 100 000 people in North America. Based on this knowledge, what percentage of people are carriers and could pass it onto their offspring?

16. Answer • We define the dominant, normal allele as B, and the recessive as b • Since occurrence is 3 out of 100 000, b2=0.00003 • So, frequency of recessive allele is b=√0.00003 = 0.005 • The frequency of the dominant allele is B = 1-b = 1-0.005 = 0.995

17. The frequency of carriers would be 2Bb=2 x 0.995 x 0.005 = 0.0095 • So, approximately 1% of the population are carriers for this disease

18. Example (try on your own) It is believed that approximately 4% of Canadians of South American decent are carriers for the recessive condition sickle cell anemia. If 98% of the alleles in this population are dominant, what should the prevalence of sickle cell anemia be?