By Will Barlow
Biochemistry and Evolution
• Common misconceptions with evolution
• General framework of evolution
• Modern evolutionary theory
Common misconceptions with evolution
Misconception #1: “It’s just a theory!”
• Often, opponents of evolution will state that it is a theory (and use that term pejoratively)
• However, evolution does account for much of the scientific evidence and has made many successful predictions
Definition of “theory”
“A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles, or causes of something known or observed.”
-Richard Dawkins, The Greatest Show of Earth, pg. 9
Common misconceptions with evolution
Misconception #2: It means to explain how life began
• Often, opponents of evolution attack the beginning of life problem
• However, evolution does not attempt to account for the beginning of life; this is the theory of abiogenesis
Misconception #3: Evolution says that humans evolved from apes
• This is a vast over-simplification of the theory
• Evolution teaches that all life came evolved from a single organism, so apes and humans share an ancestor
Misconception #4: Evolution is a progression from simpler organisms to more complex organisms
• This is another over-simplification of the theory
• No particular animal alive is more advanced than any prior animal in history
• Current animals are simply better suited to survive than their ancestors
General framework of evolution
Thought experiment: Millions of years ago, there’s an animal named “tom” that is a mammal
• At one point, there is one population of “toms”
• However, some time later, the population splits in two due to a geographical issue (let’s say a mountain pass)
• On one side of the mountain, there is more rain
• On the other side of the mountain, there is less rain and more heat
• Since the populations have been split (and are not sharing genetic information), random mutations occur in each population
• Since the environments are different, the random mutations that lead to “better” alternatives are different
• Over time, these mutations build up into noticeable differences
• Eventually, two new species emerge: “tom a” and “tom b”
Predictions of evolution
Successful prediction #1: Scientists have demonstrated that DNA is more advanced as life is more advanced
• For example, human DNA is 96% similar to chimpanzee DNA
• Yet the number of protein-encoding genes is roughly the same for all animals and plants!
“Our complexity must arise not from the number of separate instruction packets, but from the way they are utilized.”
-Francis Collins, The Language of God, pg. 137
Predictions of evolution
The concept of the “tree of life” is another important prediction of evolution.
We should expect to see intermediate species in the fossil record and the genetic record as we study the world around us.
Support for the tree of life:
• Transition between fish and amphibians — we can find fish that could walk and breathe oxygen
• Genetic sequencing has mostly confirmed scientists’ predictions, with a few surprises!
“At the level of the genome as a whole, a computer can construct a tree of life based solely upon the similarities of the DNA sequences of multiple organisms…. Bear in mind that this analysis does not utilize any information from the fossil record, or from anatomical observations of current life forms. Yet its similarity to conclusions drawn from studies of comparative anatomy… is striking.”
Successful prediction #2: Breeders and agriculture experts have demonstrated “micro-evolution” countless times.
• Ex: dog breeds
• Ex: Hybrid crops
• Detractors of evolution sometimes say that micro-evolution is possible but “macro-evolution” is not
• Francis Collins argues that the distinction is an artificial one
Successful prediction #3: Accumulation of “junk DNA”
• Darwin’s theory predicts that mutations that do not affect function (located in “junk DNA”) will accumulate slowly over time
• We see this, as well as “silent” differences in the genetic code
What about man?
Does evolution successfully show that humans evolved?
• Richard Dawkins demonstrates that the fossil record is full of so-called “missing” links
• Perhaps even more powerful, Francis Collins gives evidence for human evolution from genetics
What is Francis Collins’ best piece of evidence?
What happens when we compare the human genome to other animals’ genomes?
What about genes that appear to be non-functional in humans but functional in multiple species?
Fact #1: Comparing human and mouse genomes
• The overall size of the genome is roughly the same
• The inventory of protein-encoding genes is remarkably similar
• The order of genes is generally the same over substantial stretches of DNA
• The existence of similar AREs (ancient repetitive elements)
“When one aligns sections of the human and mouse genomes, anchored by the appearance of gene counterparts that occur in the same order, one can usually also identify AREs in approximately the same location in these two genomes.”
“The process of transposition often damages the jumping gene. There are AREs throughout the human and mouse genomes that were truncated when they landed, removing any possibility of their functioning. In many instances, one can identify a decapitated and utterly defunct ARE in parallel positions in the human and mouse genome.”
Fact #2: Comparing human and chimpanzee chromosomal fusion
“Recently… it has become possible to look at the precise location where this proposed chromosomal fusion must have happened…. But they are found right where evolution would have predicted, in the middle of our second fused chromosome.”
Fact #3: Comparing human and chimpanzee genetic function
• Caspase-12 is a functional gene in chimpanzees (and many other mammals, including mice)
• The human version is found in the identical location as the chimp version, but lacks the function