Adaptation Rewound - a thought experiment for Facebook debate.

The other day a good friend of mine posted a link about the discovery of hybrid black tip sharks. It caused a little bit of back and forth on the subject of evolution and a fairly common argument was put forward, that adaptation occurs and could be called "micro-evolution," but "macro-evolution" is something entirely different which can not be proved.

I'm sure you have heard something along these lines before, and if you are anything like me, they never become easier to swallow. The claim seems always to stand alongside the fallacious assertion that evolution means a dog giving birth to a cat, or some similarly absurd leap that makes the theory appear ridicules to those who can not be bothered to look into even the most simple legitimate explanation.

Attempting provide evidence of large scale change or speciation over and over to no effect can start to wear on you after a while, so it's fun to mix things up a bit from time to time. Prior to my contribution the OP shared an image to help show how micro and macro evolution were very much two sides of the same coin.

This inspired me to come up with my own unique approach to the issue. Please note that this argument was designed in part to be persuasive by leaving out the more abstract molecular components of evolutin (though a shout out is given toward the bottom to everyone's favorite human chromosome #2), but mostly for mine own amusement. Here's hoping it gives some of you cause to smile as well.

"Adaptation over time is evolution, much as in Chris's red-purple-blue example, gradual change over time eventually leaves us with something completely different. It may be hard to draw the line where the change has become macro, but it's clear eventually that it is.

Just for fun, think of a human. Now we are going to gradually alter this human through a series of adaptations that we know, via their vestigial remnants, have occurred.

Firstly we have the Coccyx, or “tail bone.” We call it the tail bone because it is exactly that, the bone that provided structural support to the tail of an earlier version of us. Humans have been born with tails though, it's odd, but not inhuman.

So let's go a step further, humans have ear muscles that for the vast majority are completely functionless. If we couldn't move our head horizontally without turning our whole upper body (as is the case in many mammals including lower primates) then these muscles would be very useful in allowing us to listen in a specific direction for things like threat detection. As it stands though, we can swivel our neck about and most of our ears stay in place, even though we have (under-formed) muscles for moving them. But of course again, there are people able to move their ears about, so we are still looking at a human.

The plantaris muscle in our leg was thought for a long time to be a tendon, and is often confused as being a nerve by freshman med students. It is however, another under-formed muscle that serves nearly no function in human beings, it is often surgically removed when muscle tissue is needed elsewhere, and in fact roughly 9% of humans are born without it, to no real detriment. Humans have very specialized feet for bipedal motion, we don't really grab things with our feet (save the odd coin off the carpet). Other primates however have feet that look much more like hands than do ours, and they are used for gripping things regularly. They do this with the help of a larger version of the same plantaris muscle. So we have a muscle that some version of us used to grab things with our feet. Look at a human foot and imagine the toes are just a bit longer and the “palm” just a bit shorter. A pretty minor adaptation by itself. But our imagined human is starting to look pretty odd.

Another minor adaptation, we know some earlier version of us was quite a bit hairier. I'm sure there are plenty of ways to show this to be true, but again, for fun, let's take a vestigial behavior (rather than body part or gene (of which there are many, that would do little for building our picture)) as evidence. When humans are cold or experiencing emotions such as fear a common involuntary response is the formation of “goosebumps.” This reaction does not serve to help humans at all in either of these cases. We do see the same reaction in mammals with considerably more hair than us, and the benefit in either case is clear. In response to temperature, the goosing causes an extra layer of air to be trapped between the skin and the atmosphere, helping to keep warm. In response to emotions like fear, the puffing out of the fur causes the animal to appear slightly larger which can serve to help deter a threat. The fact that we have this behavior strongly suggests that it was at some point useful, meaning we were a good bit hairier. Again, some of us are hairier than others, so it's not hard to imagine a state prior to an adaptation where we were on average much more covered in body hair.

Each of these changes on its own is a very minor adaptation that we have very strong reason to believe has occurred. Now try really hard to picture a human with all of these differences at once. It's hard to say for sure what you are seeing is human, your at the very least half way to purple. And this is a very small sample size of physical adaptations that have left behind visible remnants, I could go on, though I see little reason to. And while these vestigial structures (and behavior) are overall less convincing than the DNA evidence (human chromosome #2 for example, or the presence of an inhibited L-gulonolactone oxidase gene), it was a good deal more entertaining I think."