This is part two of a series on evolution and why it matters. In this part, we present more evidence for evolution. You can find part one here.
If you compare any living organism with any other, you will find genetic similarities. But, first, let us look at human and ape DNA.
No matter how you measure the similarities between human and chimpanzee or bonobo DNA, the results are the same: Humans, chimpanzees and bonobos are more closely related to each other than any of them are to gorillas or other primates.
You will find many similarities even if you compare human DNA between very different groups of organisms.
For instance, humans, cows, chimps and chickens all share a similar gene for insulin production. They inherited this from their last common ancestor.
If you study that gene in humans and chimps, that gene is about 98% identical. But if you compare that gene between humans and chickens, that gene is only about 64% similar. That is because humans and chickens are much more distantly related.
They have a common ancestor far further back in time. Since that time the genes for insulin production have diverged far more than is the case with chimps and humans.
We know that humans and other apes have a broken gene for vitamin C production. As a result, we must derive vitamin C solely from our food. Why would this broken gene exist? Because at some point, our ancestors had a functioning version of this gene.
If you edit the genes for birds you can cause them to be born with teeth! This is because they retain the genes to produce teeth that they inherited from their non-avian dinosaur ancestors! Although, this gene is normally disabled in birds.
Humans are on occasion born with short monkey-like tails! We have genes that allow this, but the development of this tail is normally suppressed. For some people that suppression mechanism does not function.
As a result, they are born with short tails! Indicating that we evolved from monkeys and are still monkeys.
It turns out that we may contain a lot of DNA from our evolutionary ancestors. Although much of it is regulated and disabled or modified by regulatory genes.
There is countless other genetic evidence that indicates ancestral links between all groups of life. No matter how distantly related those groups might be. Or which indicates closer relationships between certain groups of organisms.
In the early stages of embryonic development, the species of most embryos look almost identical. In fact, if you look at the early embryonic states of all vertebrates you see a common pattern. Whether they develop into fish, amphibians, birds or humans.
All vertebrate embryos start out with a long tail, well-developed gill slits and many other fish-like features.
In the case of fish, the tails and gills develop further. But in humans, they are lost during further development. As is the case for other non-fish embryos.
For humans and other apes, the tail shrinks during later stages of embryonic development, leaving only the vestigial tailbone.
Species share a great many common structural similarities which specialize and diverge from this common design during later stages of embryonic development.
If you look at the very early embryos of different species, you might find it very different to tell them apart. Even if you looked at the embryos of three species which look very different when they are born. Say if you looked at the embryos of a frog, a hippo and a rabbit.
Not only do these common features exist, they typically develop in the same order. But are absorbed or adapted during later stages of development.
What does this indicate? That all these species have common ancestry and genetic code, which influences early embryonic development. But that each species also has specialized genetic code which controls the development of specialized features during later stages of development.
If we look at the anatomy of various organisms, we can see evidence of clear developmental relationships.
For instance, all chordates possess the following: a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail .
In fish, the slits develop into gills. But for birds and mammals, they develop into the jaw and inner ear.
In humans and other apes, the post-anal tail is vestigial. But some other species make use of it for balance.
Why do all chordates have these? Why do they have all these features, even if for some species they are vestigial? And why have these features developed differently in later organisms and taken on different functions?
Because these are features which the common ancestor of all chordates possessed and thus all chordates continue to possess. Over time these features have evolved and some of them have taken on different roles as different groups evolved separately from each other.
In some cases, these features became vestigial once they no longer served any purpose. Or as is often the case, these vestigial organs have been adapted for different purposes.
Yes, humans have tails! During embryonic development, this tail is highly visible. But during later embryonic development it is absorbed almost entirely without a trace. The only remnant of it is our tailbone.
Consider the fact that so many vertebrates have five digits. Including many creatures without a distinct hand or who have returned to the sea!