The Meaning of it All
If there is one fundamental principle in biology it is this: every living thing on the planet had parents.
Even more fundamentally, and this is obvious to anyone who observes humanity for more than a few minutes, every living thing is slightly (sometimes a lot) different from their parents. This is true even if you go all the way back to the chemical reactions that are the precursors for organic molecules that are the precursor for living things. In this way, there is no difference between:
mom + dad = baby
3O2 + 4Fe –> 2Fe2O3
When taken over millions and billions of years it is quite easy to see how new, novel features appear in populations. There are dozens (if not hundreds or thousands) of examples of this. Everything from Scottish fold cats to Lenski’s Escherichia coli developing the ability to utilize citrate. We can point to people that are immune to HIV and those with unique abilities to not have heart trouble with high cholesterol.
These are novel traits that appeared in the human population. Due to selection (note the lack of ‘natural’ and ‘artificial’), over time, those traits will become more and more prevalent in the population.
As Shubin does in Your Inner Fish, and I’ve tried to capture here, the structure of the human body is not random. Any attempts to determine the odds of human hemoglobin appearing out of a pile of random amino acids, is doomed to being ridiculous. Our bodies are not random assemblages of material.
Likewise, any attempt to attribute our bodies to an Intelligent Designer, is doomed to failure as well. There are too many very poor design decisions that DO make sense if you consider that our bodies are just heavily modified fish.
That change over time and relatedness (i.e. more closely related species are more similar and have a more recent last common ancestor) are both predicted by and can be used to make other predictions. Tiktaalik is a perfect example of this.
Shubin makes it very clear in this chapter (suggesting that someone commenting on this blog didn’t actually read the book as claimed) that
Tiktaalik is a wonderful intermediate between fish and their land living descendants, but the odds of it being our exact ancestor are very remote. It is more of a cousin than an ancestor. No sane paleontologist would ever claim that he or she had discovered “The Ancestor.”
This is obvious to anyone who thinks about the rarity of the event of fossilization and the chance of that fossil being intact and found after hundreds of millions of years.
Another interesting point that Shubin makes is that much of the relationships and knowledge about basic evolution are so strong, that for all intents and purposes, they are facts. This is why you don’t find recent works talking about common descent or natural selection. There are hundreds to thousands of papers, reports, and experiments that support these claims. Many of them are a hundred years old or more.
Just like modern engineers have to show the evidence for the acceleration due to gravity or the conductivity of pure copper, biologists don’t have to show evidence for common descent anymore. It’s not accepted as fact without evidence. It’s that the evidence is so conclusive and has been for so long that it doesn’t have to be supported in every paper anymore.
Until a significant (hundreds of thousands) of papers sow that every single one of the pieces of evidence that support common descent is proven to be wrong in a very fundamental way, common descent, for all practical purposes is a fact. There is no avoiding it and those that deny it either don’t understand it or refuse to accept it for reasons other than logic and science.
Humans are unique forms of hominids (others of which are just as unique as we are). We are in the larger group of primates, sharing many of the characters of primates, including some mistakes in our genes (the inability to manufacture vitamin C for example). We are mammals and anyone who denies this is just being silly. There is no fundamental difference between our hair and the hair on dogs or whales. We are chordates. Again, this is a fundamental feature of our anatomy. We are animals. We are multicelled, without cell walls, and cannot manufacture our own food. We are a living thing, and like every other living thing on the planet, we respire, we use chemical energy, we respond to our environment, we are made of cells, we have information stored in nucleic acids, etc. etc. etc.
This is but a tiny sampling of the thousands of characteristics that are used to group organisms (including humans) into smaller and smaller groups. This isn’t guesswork either. There are dozens of very complicated statistical analysis tools that can be used to examine every measurable character (including genetic information). These tools produce estimates of the family tree that these organisms exist in and estimates of their relatedness. These tools can be used for a single small group or everything so far discovered on the planet.
For example, here’s one for cats. The estimated ages of the last common ancestor are shown for each group. (from: http://www.sciencemag.org/content/311/5757/73.abstract)
And here’s one for everything. Obviously, the resolution isn’t as good, but you get the picture. Click on it to go to the website and get the big version.
Shubin ends with a large list of the faults of the human body, from swollen knees to hernias. There are many, many more besides what he lists in the book to. These are all things that are easily explained by common descent. They are not ‘just so stories’ either. There is solid evidential support for every one of them.
Why do men get some really nasty hernias? Because we have a hole in the pad of muscle and tissue that holds our guts up. Why do we have the hole, because our sperm are the relics of our fish past. Our sperm needs to be at a very specific temperature to survive and the human body is just too hot. So we store sperm outside of the body, but to get to the penis, the sperm travels this torturous route through the hole in our gut, loops over the pelvis, then back out of the body.
Sometimes, parts of our guts slip through that hole and we men get a nasty hernia. Oops.
It would make a lot of sense for our male plumbing to not have that hole and reside almost entirely outside of the body. At least from a design perspective. But the reason we are set up that way is understandable if you consider that we came from sharks.
Just like in sharks, gonads develop near the liver. In males, they for testes and have to get outside of the body to produce viable sperm. To get out, they need to make a hole in the gut lining… that’s the hole that causes some hernias. Unfortunately, it takes the ‘wrong’ path outside and loops the sperm cord over the pelvis (testes on one side and penis on the other). Oops. Reminds me of an old Chrysler I had. Bloody stupid design, where one of the drive belts, went between the two tubes for the air conditioner.
I could go on (and Shubin does).
This has been a long journey and one that was fairly difficult for me, but (judging by the number of hits this series is getting) one well worth the effort.
I do hope that you will pick up and read Your Inner Fish. Shubin goes into much more detail than I do and there are some great stories and insites in the book that I didn’t touch upon. I also hope that my additions and explanations have helped to make things easier.
I’m still looking for another book to review and have found a few candidates. We’ll see what happens over the next week or so.
If you have enjoyed this, please let me and Dr. Shubin know.
 The reason to not talk about the difference between natural selection and artificial selection is simple. There is no difference in the resulting organism. No one has ever been able to tell the difference between the results of natural selection and artificial selection without knowing the history of the organism in question. The only difference is what environment is doing the selecting; the wild plains of Africa or a little old lady picking the cutest kitten in the litter. Selection simply is, there is no need for types.