DARwinism

Predictions From Darwinism1. Natural Selection is the only significant

mechanism of evolution

2. Evolutionary change is slow and gradual

3. All evolutionary change is adoptive

4. Macroevolution is the same as microevolution

Criticisms

1. Relative absence in fossil record of any transition types

• Punctuated Equilibrium (Steven Jay Gould) proposed as an alternative

2. Possible limits to genetic variation• Only so much could be contributed to

random, small change in genes

3. 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

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

Comparative Embryology

Work by Ernst Haeckel provided support

Idea behind similar embryos lead to understanding of homologous structures

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

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

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

1. Very large population size2. Isolation from other populations3. No net mutations4. Random mating5. No natural selection

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

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

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

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?

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

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

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?