One of the things that has a great potential to irritate is the denial of basic and proven scientific truths. A lot of confusion can come from the fact that a theory in science is something very different from the regular understanding of the word “theory”. We touched upon this already.
A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed, preferably using a written, pre-defined, protocol of observations and experiments. Scientific theories are the most reliable, rigorous, and comprehensive form of scientific knowledge.
So, to cut through this confusion, here’s a MEME to show what evolution is:
First of all, I am not a scientist, but I do know how to read and how to think for myself. Also, when something matters to me, I will take the time to study it, to read about it, to make myself at least a bit more familiar with it than I would have been if I relied on my education alone. The sad fact is, education in my time (and even today) is not focused on teaching critical thinking, but memorizing facts, which makes students more robots than educated citizens. But I digress.
So, how do scientists know that evolution really happened?
By Zephyris at the English language Wikipedia, CC BY-SA 3.0, Link
When you think about potential evidence for evolution, you immediately think FOSSILS. But, as we shall see, fossils are actually only extra, bonus, icing on the cake … however you wish to call it. The case for evolution would be air-tight without any fossil evidence whatsoever!!
How? Well, let’s just see.
First thing you should know, is that there is not only Evidence, there are GROUPS of evidence, with TONS of examples in each group. So, what are these groups?
- Fossil evidence
- Evidence from physical similarities between species (anatomy)
- Evidence from biogeography – Geographical distribution of species
- Genetic evidence
- Natural selection directly observed
It is also worth noting that for example speciation is shown also in the fossil evidence, which makes all groups basically interconnected to point to the same conclusion: Common Descent.
1. Fossil evidence
Not much needs to be said about fossil evidence. This is one type of evidence everybody’s familiar with, more or less. Basically, it is possible to show how life evolved by arranging and showing the fossils that have been found in order.
This is possible because fossils are found in layers and as layers are added on top of each other, this means that the oldest fossils are found in the lowest layers and youngest fossils are in the highest layers of the rock.
By Jillcurie (Own work) [CC BY-SA 3.0], via Wikimedia Commons
This also allowed scientists to see that the fossils which appeared earlier disappeared later.
In the past, scientists could only more or less estimate the age of these layers, but now this can be determined much more accurately using radiometric dating.
2. Evidence from anatomy
This group of evidence is easily overlooked, when thinking about evolution, yet it is very very obvious when you are made aware of it.
When plants and animals are closely inspected, both scientists and also common people can see that although various species of animals and plants are different, they are really, really similar.This is easiest to see in flowers.
For example, the basic structure of all flowers consists of sepals, petals, stigma, style and ovary; yet the size, colour, number of parts and specific structure are different for each individual species. (Wikipedia)
Other things mentioned a lot when discussing evidence from anatomy are the skeletons. When skeletons are examined, they are, of course, different, but also same in a way, meaning they contain the same bones.
By Волков Владислав Петрович (Own work) [CC BY-SA 4.0], via Wikimedia Commons
Another beautiful example which Richard Dawkins uses in the book “The Greatest Show On Earth: The Evidence For Evolution” is the bat skeleton where he points out the similarities between human hands and bat’s wings. Bat’s wing and a human hand are two versions of the same thing. He even mentions our and bat similarities to pterodactyl!
There are other forms of common traits in modern animals and they all point to one thing – common descent and evolution over millions of years. Examples of this evidence can also be remnants of the eyes in animals that lost their sight due to adaptations to environment. Various insect mouths have the same structure … There are countless examples. And this group of evidence is supported by the previous group of evidence – the fossils. See how it all fits together?
3. Evidence from geographical distribution of species
Evolution is driven by mutation and natural selection. The most successful organisms are those that do NOT get eliminated – meaning they are optimal to survive and reproduce. This means that those with the best camouflage, or those that are fastest, for example, generally survive to reproduce.
So when looking naively, you could assume that the animals would be the same where environmental conditions are the same. However, this is not the case. And this is strong evidence for evolution.
The most used example is Australia. Australia is home to the most marsupials on the planet, but other species found elsewhere in the World are missing in Australia. This indicates that evolution occurred on this place on Earth separately … and that is the reason why for example kangaroos evolved only there – this is the “path” that evolution “took” there and this couldn’t spread anywhere else.
Four of the 13 finch species found on the Galápagos Archipelago, have evolved by an adaptive radiation that diversified their beak shapes to adapt them to different food sources. (Wikipedia)
Quote about Australia:
Australia has an abundance of endemic species (those found nowhere else) which is typical of islands whose isolation by expanses of water prevents species from migrating. Over time, these species diverge evolutionarily into new species that look very different from their ancestors that may exist on the mainland. The marsupials of Australia, the finches on the Galápagos, and many species on the Hawaiian Islands are all unique to their one point of origin, yet they display distant relationships to ancestral species on mainlands.
“The biological distribution of species is based on the movement of tectonic plates over a period of time" by boundless.com is licensed under CC BY-SA 4.0
Also, Africa and South America are not that different with regard to climate, yet for example Africa has giraffes, while South America has Llamas & sloths.
This line of evidence is reinforce by previous group, where it can be shown that “basics” for now similar, yet different species on different continents evolved when everything was one supercontinent and later different continents drifted apart.
4. Genetic evidence
One of the most strongest groups of evidence for evolution is this. Genetic evidence. What does genetic evidence mean? Well, we humans have the technology to study gene sequences, yes?
And scientists did study them. Genetic evidence for evolution can be found in the similarities between genetic markup of various species. Basically what scientists do is: they take gene samples from animals and compare how similar they are. They do this comparison across the species and this enables them to form a tree of cousinship – similarities in those gene samples between species let them know how “related” species are. This is what showed them that, for example, humans and chimpanzees are very closely related.
David Hillis's 2008 plot of the tree of life, based on completely sequenced genomes.
By Ivica Letunic: Iletunic. Retraced by Mariana Ruiz Villarreal: LadyofHats [Public domain], via Wikimedia Commons
In short, the number of similarities shows the scientists how close are the species related. And the most beautiful thing is that the data obtained from DNA evidence mateches the data from previous groups. It all fits together.
5. Natural selection directly observed
Natural selection is the process where organisms that have traits that are favourable for them to survive are more likely to reproduce and pass those traits to their offspring. This is a driving force of evolution.
When natural selection occurs and the organisms with favourable traits survive to reproduce this makes those traits more widely spread in the population. The new generation of animals comes from the most successful ones, ones that do survive. Others are eliminated.
Now, this process has been directly observed both in nature and laboratory.
Perhaps the most famous widely known example of natural selection is the bacteria that has developed antibiotic resistance.
The concept is rather simple, which makes you wonder how people can believe it0s not true. What antibiotics do – they kill bacteria, meaning they apply evolutionary pressure. Now, if a genetic mutation occurs in the bacteria which enables them to survive the effects of antibiotics – this is the bacteria that will survive in the environment. In effect, bacteria is evolving and natural selection is directly observed.
Watch this video:
Terrifying. Let this be a lesson to you: do NOT abuse antibiotics.
Anyway, there are also other examples where natural selection is directly observed, for example lizards that were moved to Croatian islands and evolutionary change was directly observed in their descendants:
In 1971, ten adult specimens of Podarcis sicula (the Italian wall lizard) were transported from the Croatian island of Pod Kopište to the island Pod Mrčaru (about 3.5 km to the east).
In the 1990s, scientists returned to Pod Mrčaru and found that the lizards currently occupying Mrčaru differ greatly from those on Kopište. While mitochondrial DNA analyses have verified that P. sicula currently on Mrčaru are genetically very similar to the Kopište source population, the new Mrčaru population of P. sicula was described as having a larger average size, shorter hind limbs, lower maximal sprint speed and altered response to simulated predatory attacks compared to the original Kopište population.
So, basically, this all goes to show that not only the EFFECTS of evolution have been proven, but the very mechanism of evolution has been directly observed. There really should not be any doubt: Evolution is true.
6. Additional: Evidence from mathematic modeling
IF scientists can use computers to simulate the amounts of dark matter in the galaxy, it only stands to reason that complex systems and processes such as evolution can be simulated as well.
A simulation has been made where the basic concepts of evolution have been programmed into a computer. Random “mutations” were added and the ability to preserve those that are beneficial to the simulated environment.
As the simulation was turned on, “life” has reproduced and adapted to the “environment” in the same manner as in the “real” evolution, with beneficial traits surviving and those without them disappearing.
You can read more about it in “Avida” Wikipedia article, and there’s even a version for you to download and check for yourself. The source code is available on GitHub, so if you understand the details and code, you can check it for yourself.
If you have just a bit of time on your hands, you can examine the evidence and discover for yourself that evolution is true and that it really happened. You do not have to be a scientist, as the evidence is so strong that it just makes sense. So, really, only things you need are free time, common sense and an open mind.
- Dawkins, Richard - The Greatest Show On Earth - Evidence for Evolution
- Dawkins, Richard - The Blind Watchmaker
- Darwin, Charles – The Origin Of Species
- Evidence of common descent – Wikipedia