Recently, I started following @TakeThatDarwin on Twitter, assuming he would provide some funny parodies of creationism. Boy was I wrong. As it turns out, he retweets tweets that ask “If humans evolved from monkeys, why do we still have monkeys?”, and there’s a mind-blowing number of them. Seriously, creationists? I thought this matter was settled.
All right, let’s tallk about what evolution is. Take a population of organisms – animals, plants, fungi, amoebae, protozoa, algae, bacteria, archaea, you name it. All these organisms have DNA, which is used to make messenger RNA, acts like an instruction tape for the ribosome, a naturally-occurring Turing machine that reads the code on the mRNA and assembles amino acids to make proteins. So far so good; everybody agrees on this basic principle (well, some new agers will probably invoke ‘vital energy‘ or some such, but that’s a topic for another post). DNA is bundled together in structures called chromosomes; animals, fungi, amoebae, protozoa, and algae each have two copies of each chromosome per cell nucleus, while plants can have a bunch of copies of each, and bacteria and archaea only have one chromosome each.
Anyway, fungi are made of at least one cell; plants and animals of lots of cells; bacteria, archaea, amoeba, protozoa, and algae of one cell each; and viruses don’t have cells, though they do have a protein coat. When a single-celled organism reproduces, it divides in two; when it does so, it copies all its DNA. Multicellular organisms grow by having their cells reproduce in much the same manner as single-celled organisms. Viruses replicate by injecting their nucleic acid into host cells, where it is copied.
Nucleic acid replication is not 100% faithful; occasionally, the wrong base gets inserted by accident. This is called a mutation. Because most amino acids have a few different codons that code for them, the majority of mutations make no difference one way or the other. When a mutation does make a difference, it is often just a matter of changing how often a given protein is made; occasionally, the mutation actually changes the structure of the protein.
Most animals and plants, as well as some fungi, reproduce sexually. When special sex cells, called gametes (it eggs and sperm), split in two, each daughter cell only gets half the DNA. The male’s sperm combines with the female’s egg to form a new cell with the full complement of DNA, and each chromosome then swaps chunks with its partner from the other half, which induces more variance in the genetic code. This is why different people look different, and why police can identify you by matching your DNA to DNA taken from a crime scene. Identical twins have the same DNA, which is why they look the same.
Due to this mutation, all the organisms in a population will differ from each other a bit. Some of them will be better able to find food, survive without food, make the best use of available food, outrun predators, find a mate, cooperate with others for mutual benefit, etc. These organisms will survive better than others, and will mate more often; thus, they will pass their advantageous DNA. Hence, over time, the average ability of the population as a whole to survive will improve – that’s evolution.
What I have just described is popularly known as survival of the fittest, but it’s not quite the whole story. There is also the matter of sexual selection, a process by which certain organisms, most especially animals, possess qualities that allow them to mate more often and thus pass on these qualities to their offspring. The classic example is peacocks – it is well known that peahens choose their mates based on how impressive the males’ tails are, meaning that the males with the biggest, fanciest tails mate most often and thus the average tail fanciness of the population as a whole tends to increase.
For another example, consider the female orgasm. New agers sometimes claim it serves no biological role, and thus is evidence of some sort of sex-loving deity who supports gay marriage, abortion, universal healthcare, use of Apple products, organic food, homeopathy, anti-vaccination, and whatever else is popular among modern neo-hippies. However, the female orgasm actually does serve a valuable role in evolution – it makes women enjoy sex. A woman who enjo;y sex will have sex more often, and the more she has sex, the more babies she will have. As a result of women who enjoy sex reproducing more than women who don’t, the frequency of sex-liking women will increase in a population until they become standard. It has also been suggested that the reason women have a harder time achieving orgasm than men is to encourage mating with caring and attentive partners.
It is important to remember that evolution is exclusively a process of a population gradually adapting to become better suited to its ecological niche – this may involve losing body parts which are not necessary. For a simple example, humans first appeared in Africa. The first humans were black because they produced large quantities of melanin, a protein that protects against ultraviolet light. Some groups of humans later migrated via the Middle East and into Europe, where there is much less sunlight than in Africa. As a result, lots of melanin was no longer an advantage for these people – in fact, lack of melanin was actually an advantageous trait, as one with a lower rate of melanin production expended less energy on melanin and could better utilise what sunlight was available to make vitamin D. Thus, a white person is more suited than a black person to surviving in Europe – but if you stuck that same white person into Africa, he would be much less suited to survival due to lack of melanin to protect him from sunburn.
This example also helps illustrate another point. Just because one population of an organism evolves into a different form, it does not automatically follow that all other populations of the same organism will. As we saw, while it was advantageous for humans in Europe to evolve paler skin, the same adaptation would have been harmful for humans in Africa, and so they stayed as they were. This also shows that it is meaningless to speak of one population or organism as being ‘more evolved’ than another – all we can say is that one is better adapted for a given environment.
Related to this, it is entirely possible for two different adaptations to arise in different populations that are both descended from a common ancestor. For example, consider an arboreal rodent in a forest. One day, there is an earthquake, and a chasm opens right in the middle of the forest cutting the rodent population in half. In the east forest, wolves move in from afar; since the ground is a dangerous place, the rodents will tend to spend more time in trees, and thus will tend to evolve adaptations better suited for a life in the trees. Meanwhile, in the west forest, eagles appear and start catching and eating rodents from the trees. For the rodents in the forest, life in the trees is more dangerous, and so mutations that allow them to survive better on the ground will be selected for. Thus we see that, by dividing two populations of an organism, it is possible for both of them to evolve into different forms depending on what survival pressures are present.
Creationists have not had a problem with any of the foregoing since it was pointed out that Noah could never have fitted two of every animal on the ark. The issue arises when they are asked to accept change above the minor variation that can be readily seen in selective breeding, as when a farmer makes sure that the trees which produce the most fruit exchange pollen to increase her overall average yield. One of the most common arguments is “If humans evolved from monkeys and apes, why are there still monkeys and apes? Shouldn’t they have evolved into humans by now?” This is also sometime seen from someone who honestly misunderstands evolution due to persistent misrepresentation in popular media.
First of all, this argument compares apples to fruits. Today, there is only one human species extant, cro-magnons (Homo sapiens), though at one point there was another, the neanderthal (Homo neanderthalensis). Ape, by contrast, refers to a variety of primates with only vestigial tails – specifically, it includes, gibbons, orangutans, gorillas, bonobos, chimpanzees, and humans. Yes, humans are in fact apes.
Now, you may be wondering “OK, so if we’re apes, which ones did we evolve from, and why did some of them get left behind?” As a matter of fact, humans didn’t evolve from any other living species of ape. All apes extant today, as well as the extinct ones, ultimately evolved from a common ancestor millions of years ago.
OK, here’s how it works. About 600,000 years ago, a human species named Homo heidelbergensis lived. At some point around 400,000 years ago, this species divided into at least two populations. On one of these, selection pressure resulted in a tougher, stronger population – the neanderthals. The other population became somewhat taller and more spindly than the neanderthals, with a less flat face – these were the cro-magnons, modern humans. For some unknown reason, the neanderthals later went extinct, leaving the cro-magnons free to take over the world. I have to wonder if creationists would keep making the argument I am refuting if neanderthals had survived, thus giving us two human species.
Anyway, H. heidelbergensis evolved from Homo antecessor, which evolved from Homo erectus, an early human that lived 1.8 million years ago. H. erectus was shorter than H. heidelbergensis and had a smaller brain; thus, height and brain size are traits that were selected for in H. erectus.
H. erectus and a related human species, Homo habilis, evolved from Australopithecus afarensis, a small human ancestor with a brain about 1/3 the size of cro-magnons which lived about 3.6 million years ago. A afarendid evolved from another ape, Ardipithecus, that lived 4.4 million years ago.
Ardipithecus in turn evolved from Sahelanthropus tchadensis, an ape that lived around 7 million years ago in Chad. Ardipithecus was not the only descendent of S. tchadensis; another population, faced with different selection pressures, evolved longer limbs for a more arboreal lifestyle – this is the group that gave rise to the Pan genus, which evolved along its own path at the same time as humans were evolving. The original Pan species split further, with those that lived in a kinder environment evolving into the smaller, gentler bonobos, while those in a harsher environment evolved into the slightly larger, more aggressive chimpanzees.
Thus, as you can plainly see, bonobos and chimpanzees did not evolve from each other, but both evolved from a Pan species at some time in the past. Before that species evolved, there was S. tchadensis, which ultimately gave rise to bonobos, chimpanzees, and humans independently of each other. Humans did not evolve from chimpanzees or bonobos – all three evolved from a common ancestor 7 million years ago.
But let’s go back further. 10 million years ago, there lived an as yet unnamed primate whose population split into two groups. One one group, selection pressure led to considerably increased size and strength, resulting in gorillas. The other population did not receive selection pressure for such great size, and evolved into bonobos, chimpanzees, and humans as already described.
13 million years ago, an ape called Pierolapithecus catalaunicus lived in trees. It, too, split into two populations. In one population, selection pressure led to improved adaptations for living in trees, giving rise to orangutans. The other population survived by gaining adaptations to spending more time on the ground, and were the ancestors of gorillas, bonobos, chimpanzees, and humans.
About 17 million years ago, an ape by the name of Proconsul africanus was living in Africa. It, too, split into two populations. One population evolved into Pierolapithecus catalaunicus, whose evolutionary lineage I have just spent several paragraphs discussing. The other was served by mutations leading to a smaller, more gracile form and also monogamy, giving rise to gibbons.
P africanus‘ ancestor was probably a primate called Aegyptopithecus, known to have lived in northeast Africa around 33 million years ago. It, too, split into two populations at some point. One of these populations ended up losing their tails, growing quite large, and gaining various other mutations, and gave rise to the apes. The other stayed smaller and retained their tails, and went on to evolve into the various African and Asian monkey species.
Around 40 million years ago, Africa was home to various monkeys, one species of which was ancestral to Aegypticus. Some of these monkeys managed to cross over to South America, perhaps via land bridges or on vegetation rafts (the Atlantic was much narrower back then). These monkeys adapted to their new environment, developing prehensile tails among other things, and various populations from among this initial grouping gave rise to the American monkeys. The other group remained in Africa and, faced with different challenges to survival, evolved along different lines, giving rise to the various monkeys and apes I’ve just talked about.
And that, dear friends, is why we still have monkeys and apes.
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