Evolution is still a theory, that’s true. Whether the moon travels around the earth is also still technically a theory. When you say “theory” in a scientific context it doesn’t mean “wild stab in the dark”, it means it’s a very good idea that’s been shown to work under lots of circumstances and in loads of different ways. It’s not like when you say “my theory is that Spurs will win the Global Sports Cup” – that’s guesswork. A theory in the scientific sense means not just an idea, but something with some weight behind it and some thorough evidence. For a theory to remain as popular and largely unchallenged as evolution means that it’s incredibly solid.
Oftentimes anti-evolutioners will bring up the fact that evolutionary scientists still argue about how evolution panned out. That’s true, we don’t have all of the answers, and the whole idea of science is that you constantly test theories and discuss how they can be bettered or even possibly overturned. Arguments between evolutionary scientists, however, are about the mechanisms of evolution and it’s timescales, not whether or not it happened at all.
This post sets out to mention a few vestigial organs, or evolutionary left-overs. They aren’t evidence for evolution on their own, but they’re yet another stitch in the tapestry of life. Before we crack on, I thought it might be nice to summarise some of the lines of evidence we already have for evolution:
Often touted as being an incomplete record with loads of gaps and no “missing links”, the fossil record is in fact truly amazing. Not every animal that dies is fossilised, it takes pretty special circumstances for it to take place, and the fact that we have so many species and so many “missing links” is testament in itself. Whole family trees can be written in the bones.
Homologies are the similarities between species. It’s easy for us to go “wow, look at the variation in life” and that certainly is a fair comment. But when you stop to think you realise that variation between animals is kind of skin deep to a certain extent.
For instance, all mammal hair is made of the same stuff, all mammal skin works in a similar way. Every single living thing has DNA coded in the same kind of way using similar sorts of mechanisms. There are molecules in plants that are also found in humans and insects and reptiles (e.g. cryptochrome). We’re not so different after all, roundworms share 25% of their genome with humans.
All higher animals have two eyes, one head, four limbs, hair, one nose, bones, stomachs, hearts… You get my point.
People often worry that carbon dating and using strata in rocks aren’t 100% accurate, and they aren’t. That’s a fact, there’s always areas of doubt when delving backwards so far. But carbon dating agrees with what’s found in geological strata and tree ring studies. All of the strings line up and match with a wonderful degree of accuracy. What they find is that less complex animals came first and then gradually over time more and more complex critters evolved.
Nowadays embryology isn’t considered particularly strong evidence for evolution, but it’s still worth a mention. The embryo of a chick, or a whale, or a human or a sloth all start off in startlingly similar ways. It doesn’t really count as proof, but it’s just another lovely description of how species have solved the same sorts of problems in the same sorts of ways with the same sorts of tools.
Animals evolved in a similar way initially, but then once they were on land, and that land they stood on split apart and separated, things got interesting. Animals from one part of the world developed in different ways to those in other parts of the world. For instance, you pretty much only get marsupials in Australasia because it split from the rest of Gondwanaland so early on.
Places like Madagascar and Sri Lanka have been island nations for an incredibly long time and as such, their flora and fauna are more distinct than say Europe, where we’ve been attached to each other for ever. New Zealand’s birds all evolved to live on the ground because they had no mammals around to eat them.
The Galapagos islands that helped Darwin crystallize his theory of evolution showed him a great deal. The Galapagos are a string of islands miles from anywhere, they’re even miles away from each other. The animals there are different, and even the animals on different islands have become specialised for the slightly different challenges that each island presents.
The five points above aren’t the only lines of evidence for evolution of course, but it gives you a general feel for the vast array of strings that make up the bow of evolutionary theory.
And now on with the task at hand. What have you got in you that points back to our distant cousins?..
Although none of the following vestigial anatomical things prove evolution has definitely occurred, they do add further strands of information supporting the other findings in the field of evolutionary biology.
The most famous of all the vestigial organs in the human body is of course the appendix, that tiny-weeny bag that hangs off the large intestine. In animals that have to digest cellulose the appendix is much larger in comparison and entirely vital for survival.
There are some lines of thought that say the appendix may serve some other minor roles in modern humans, but not the one it first evolved to do.
It’s obviously not too vital, hence the reason it’s so small compared to herbivore versions and around 8% of people in the Western world get along without it just fine.
The coccyx, otherwise known as the tail bone, is indeed a little left over nubbin where our tails used to be. All mammals have a tail at some point in their development, whether they keep it or not. For humans the tail can be seen for about 4 weeks during our time as an embryo, it appears most prominently when the foetus is 31-35 days old.
Why has it hung around? It now serves as an attachment point for muscles, so despite having all but gone, it’s developed a secondary use.
Most people will know what a pain in the arse these guys can be. They turn up late for the party when there’s only standing room left and often have to be forcibly ejected from the premises.
It’s commonly postulated that ancient human jaws were longer to aid in the breakdown of more rough plant material. As diets changed jaw length shortened. Interestingly, not all humans have wisdom teeth anymore, no indigenous Tasmanian Aborigines have wisdom teeth, but 100% of indigenous Mexicans do.
This odd little organ, otherwise known as the vomeronasal organ (VNO), serves some pretty vital roles in non-human animals. It’s situated at the base of the nasal cavity and detects pheromones. The VNO is part of the accessory olfactory system, so it’s like a second smell, but instead of a rabbit sniffing the air and thinking “wow, fresh cut grass, let’s go!” it smells the air and goes “wow, I’m feeling frisky today”.
Hamsters with their VNO removed have a hard time even determining the gender of other hamsters in the vicinity, let alone responding correctly.
In humans the VNO does appear sometimes, but not always and the jury is divided as to how widespread it is. What is agreed is that even when the VNO is present in humans it’s not wired up properly to the brain so is effectively useless.
The VNO is present in pretty much all other mammal species, and is found in all the reptile and amphibian species that have ever been searched. Read more about Jacobson’s organ and the flehmen response here.
Many animals have the ability to move their ears around to better hear the sinister footsteps of potential predators from all angles. Humans still have remnants of these muscles, and some, with a bit of training, can flick their ears up and down a degree or two. When primates evolved the ability to move their heads in the horizontal plane, the ear muscles weren’t such a big deal any more. Over countless generations of not being positively selected by survival they slowly shrivelled away.
In many humans the muscle is attached to the ear but has literally no purpose whatsoever. There are actually a fair few of these redundant muscles in humans, including the Occipitalis Minor, the palmaris longus muscle, the levator claviculae muscle and the pyramidalis.
The nictitating membrane is a clear membrane that many species can move across their eye ball to either clean it or protect it. In humans the plica semilunaris, a small fold of tissue on the inside corner of the eye, is the leftover vestigial remnant of this organ.
The plica semilunaris is by no means useless though. The plica helps maintain tear drainage via the lacrimal lake, and permits greater rotation of the globe.
When humans were much hairier the goose bump reaction would raise the body’s hair. This would have the function of making us look bigger if we were under attack from a predator (that’s why you get goose bumps when you’re scared). The other bonus of the goose bumps is to increase the amount of insulating air next to the skin when the temperature is a little nippy.
Now that we’re almost bald, goose bumps aren’t much use at all, unless you’re particularly hairy, and even then it will only help you in the latter of the two situations really.
The palmar grasp reflex in babies describes their natural propensity to grab your finger if you touch their palm. According to a study done in 1932, 37% of infants could support their own weight from a rod.
You might have also noticed that when seated a baby’s feet will curl in like a chimp’s feet at rest. In our evolutionary past these responses would have caused the little ones to clasp tightly onto our adequate hair. Nowadays it’s no longer necessary or possible to hang onto a mother’s body hair. Thankfully.
Those are just a handful of the vestigial bits and bobs that us humans cling onto. Like I said earlier, they’re not evidence for evolution themselves, but personally I find them intriguing. I hope you did too.
