Ape to human
Monkeys are close relatives to humans. Close... how close exactly? For an ape to become a homo sapiens it has to mutate one percent of its DNA (other institutions say its four percent, but one is enough for this article). This might sound as if apes and humans are practically the same, but "close" is a misleading relative term.
- How much DNA are we talking about?
- What is a mutation?
- When do mutations occur?
- What's the ape-to-human timeline?
- Do the numbers make sense?
- Another problem
- Maybe the variables were different millions of years ago?
- Apes are different
How much DNA are we talking about?
Almost every cell in our body has DNA molecules inside of them. These molecules are compressed libraries that contain the genetic blueprints for building, growing and maintaining all traits of our body. DNA molecules are composed of a series of smaller molecules which contain so called base pairs. The entire genome size for both humans and chimps is about 3 billion base pairs. One percent of 3 billion base pairs about 30 million base pairs.
What is a mutation?
The most basic mutation is a point mutation, this is when a single base pair is altered. A point mutation can be a deletion, a duplication, an inversion, an instertion, or a translocation. An alteration in DNA causes a change in a certain trait of the organism, this can be for for better or worse.
A difference of 30 million base pairs means a difference of 30 million point mutations.
When do mutations occur?
Mutations can be caused by high-energy sources such as radiation or by chemicals in the environment. These mutation are always destructive. I'm sorry, but the Fantastic Four, the Hulk, Daredevil, and Spider-Man are not real. Yes, I'm sad too.
Mutations also occur during the replication process of the DNA molecule.
What's the ape-to-human timeline?
The direct ancestors of current day humans are the "Homo erectus". They are described as: "the oldest known early humans to have possessed modern human-like bodies", already quite human for as far as we can tell. Their time range was between about 1.89 million and 110,000 years ago.
Before the Homo Erectus there were: Paranthropus boisei, Paranthropus robustus, Homo rudolfensis, Australopithecus sediba, Homo habilis. These, and all species before them, are all very much apes. So it's fair to say that humans as we know them now, started with the Homo Erectus, about 1.89 million years ago. Homo sapiens appeared about 300,000 years ago, so the total amount of time needed for the Homo Erectus to evolve into Homo sapiens was about 1.59 million years. (https://humanorigins.si.edu/evidence/human-evolution-interactive-timeline)
Do the numbers make sense?
- ScienceDirect says: "Mean age of reproduction: 25 years (Apes)" (https://www.sciencedirect.com/science/article/pii/S0959437X20300794)
- Science.org says: "The average age of reproduction was 25 years (Chimpanzees)" (https://www.science.org/content/article/generation-gaps-suggest-ancient-human-ape-split)
- ScienceDirect says: ∼100 new mutations per genome each generation (https://www.sciencedirect.com/science/article/pii/S0959437X20300794)
- Nature.com says: "Every time human DNA is passed from one generation to the next it accumulates 100–200 new mutations" (https://www.nature.com/articles/news.2009.864)
Our starting numbers
- 30 million point mutations needed
- 1.59 million years
- 25 years for one generation (on average)
- 150 mutations every generation (on average)
Were there enough mutations?
- 1.59 million years divided over 25 years would account for 63,600 generations.
- 63,600 generations multiplied by an average of 150 generational mutations equals to 9,540,000 point mutations.
- 30 million mutations minus 9.5 million mutations equals to 20.5 million too few mutations...
Was there enough time?
Same point, different angle:
- 30 million mutations divided by 150 mutations per generation equals to 200,000 generations actually needed.
- 200,000 generations minus 63,600 generations equals to 136,400 too few generations...
- Or: 200,000 multiplied by 25 years equals to 5,000,000 years needed...
- Or: 1.59 million years divided by 200,000 generations equals to a generation length of 7.95 years
All the above conclusions assume that all the 30 million mutations, inherited throughout all generations, were all perfectly beneficial to the organism. But most mutations aren't beneficial at all.
Rarity of beneficial mutations
Mutational effects can be neutral, beneficial, or harmful. So how are these three outcomes distributed across the total average of 150 mutations per generation?
- "Mutation rates are difficult to measure because the events are so rare …"(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2871823/)
- "more than 80 percent are probably harmful to us" (https://www.discovermagazine.com/the-sciences/most-mutations-in-the-human-genome-are-recent-and-probably-harmful)
- "999/1000 are harmful or fatal and the remainder may be beneficial" and "There are about 1/1000 beneficial mutations per individual per generation" (http://www.cs.unc.edu/~plaisted/ce/genetics.html)
- "only a small percentage of mutations cause genetic disorders—most have no impact on health or development. For example, some mutations alter a gene's DNA sequence but do not change the function of the protein made by the gene." (https://askinglot.com/are-all-mutations-harmful-or-beneficial)
Somehow its quite hard find confident statements with actual percentages...
Let's go with the 1/1000 beneficial mutations. In the average 150 mutations per generation, this would translate to 0.15 average beneficial mutations per generation.
- 30 million mutations divided by 0.15 beneficial mutations per generation equals to 200,000,000 generations actually needed for all mutations.
- 200,000,000 generations minus 63,600 generations equals to 199,936,400 too few generations...
- Or: 200,000,000 multiplied by 25 years equals to 5,000,000,000 years needed...
- Or: 1.59 million years divided by 200,000,000 generations equals to an ape generation length of 0.00795 years (or 2.9 days)
Maybe the variables were different millions of years ago?
One might say, that maybe, the generation lengths and evolutions per generation rates were more to our advantage (shorter and more). But that’s just something we don't know. Recent studies do claim that human evolution has been gathering speed for the past 50,000 years, human evolution is now faster than ever! So, frankly, while we hardly see anything beneficial, evolution is on a relative peak! (https://archive.archaeology.org/0803/etc/conversation.html)
Apes are different
One percent is not close, and the numbers aren't sensical. And they still won't be even if you loosely add another million years of time, or set generational length to 10 years, or assume 200 mutations per generation.
Giving those numbers a crank wouldn’t be very scientific. The number that is up for debate though, is the 1% base pair difference, try it with 2%, 3%, or even 4% and see how much sense it makes. It's about time the scientific world stops throwing around time ranges with margins in the millions...
Whether you believe every being on earth evolved out of a rock, or a divine six day creation week... the first one would've had just as much need for Gods handiwork than the latter.