1. Evidence of Evolution cont’d

2. Embryology So what does this mean?
Embryo: organism at early stage of development
In the early 19th century, scientists noticed that embryos of many different embryos looked so similar that they were hard to tell apart.
So what does this mean?

3. Similar genes are at work
The genes that control the animal’s basic body plan (head, tail, position of limbs…) are all similar.
Hox cluster: group of genes that control the basic body pattern of an animal from head to toe
What does this tell us about these organisms?
They share a common ancestor
Why are there differences between the species?
Mutations: changes in the genetic blueprint of an organism’s DNA

4. Biochemestry
All organisms use DNA and/or RNA
ATP = energy carrier in all living systems
Many of the same proteins
Comparison of biochemical similarities matches the fossil record
If these organisms had arisen independently, there would be little chance that they would have similar structures and biochemistries
Life is too complex!

5. Natural selection
Lots of variation in plants and animals (height, colour, patterns, tail length, claw size…)
Many of these characteristics are inherited
Struggle for existence – high birth rate but constant population size
Individuals whose characteristics are well-suited to their environment survive.
Individuals whose characteristics are not well suited to their environment either die or leave fewer offspring

6. Peppered Moths
Spent much of their lives resting on the bark of trees in England
Beginning of the 19th century, most tree bark was light brown with speckles of green
Most of the moths were also light brown
But there were always a few dark moths too

7. Industrial revolution
Pollution (mostly soot from burning coal) stained the tree trunks dark brown
And more dark moths started appearing
Hypothesis: birds are the major predator, and it is harder to catch food that blends into its environment
As the bark darkened, the rarer, dark-coloured moths were now better camouflaged and harder for birds to spot and so survived better in that environment
Why was the population changing colour?
So the darker moths now have more what? (fitness)