Liberal Arts Blog — The Tree of Life — A Lesson in Humility and Gratitude
Liberal Arts Blog — Wednesday is the Joy of Science, Engineering, and Technology Day
Today’s Topic — The Tree of Life — A Lesson in Humility and Gratitude
Did you know that “Eight percent of our DNA consists of remnants of ancient viruses, and another 40 percent is made up of repetitive strings of genetic letters that is also thought to have a viral origin. Those extensive viral regions are much more than evolutionary relics: They may be deeply involved with a wide range of diseases including multiple sclerosis, hemophilia, and amyotrophic lateral sclerosis (ALS), along with certain types of dementia and cancer”? I had no clue until this morning. I found out as I poked around looking for the perfect graphic that if it does not exist could be constructed if the right folks got together and would, once constructed, be the coolest graphic ever — a tree of life with each identified life form having underneath it two numbers: first, the absolute number of genes, and second the percentage shared with humans. The closest thing I’ve found so far is the third graphic below but it is stunningly lacking in visual appeaI. Experts — please chime in. Correct, elaborate, elucidate.
NB: “Similarity” here is defined by genes. If “similarity” is defined by letters of the genetic alphabet, the number is 100%. Does that not blow your mind? Which is the more outrageous hypothesis: God or no God?
HUMANS AND BANANAS — 60% gene overlap
MORE COMPREHENSIVE LISTING — HUMANS AND YEAST 43%; CUCUMBERS “only” 37.7%
Strangely omitted from this graphic: a weed at 18%,
GRAPHIC WITH TIME ADDED — but what about dinosaurs? (a little fun math from Quora starting with the premise that birds are descended from dinosaurs)
1. “Chickens have ~17,000 genes while we have ~22,000*. That’s 23% we don’t share right off the bat. .. 40% of the chicken genome has no homologs in humans, removing another 31%, for a total of 46% of human genes with chicken homologs. We share 75% amino acid identity in those genes, so that’s 34%.
2. But that’s amino acids, not DNA. Each amino acid in a protein is coded for by three nucleotides (called a codon or triplet). Since there are four nucleotides, there are 4*4*4 = 64 possible codons. Three are used to signal the end of a protein, so 61 code for the 20 possible amino acids. This means that most amino acids can be represented by any of a number of DNA codons. So the actual percent in common with chickens is lower than 34%. Because most of the codons for a given amino acid start with the same letter, it’s almost certainly higher than 11%, though.”
3. “Now for the difference between chickens and the extinct dinosaurs you were presumably talking about. Let’s assume that gene loss and substitution has been mostly uniform over the last half eon. The most recent common ancestor of humans and birds lived about 350 million years ago. That means 350 million years of evolution on our side and 350 million years on theirs, for a total of 700 million. The most recent common ancestor of birds and T. rex lived a bit more than 65 million years ago, so there was 10% less evolution between T. rex and humans than between humans and chickens. If we go back to the earliest dinosaurs, about 240 million years ago, that cuts off 33% of the evolution.”
NB: “So if we cut off 10% of what we don’t share with chickens, we get between 20% and 40% similarity. If we cut off 33%, we get between 40% and 55% similarity.”
A LINK TO THE LAST FOUR YEARS OF POSTS ORGANIZED BY THEME:
ATTACHMENT BELOWS -
Please share the coolest thing you learned this week related to science, engineering, or technology. Or, even better, the coolest or most important thing you learned in your life related to science and engineering.
This is your chance to make someone else’s day. Or to cement in your mind something that you might otherwise forget. Or to think more deeply about something dear to your heart. Continuity is key to depth of thought.