This article has 6 strong pieces of evidence for why evolution is true. Scientists need evidence to know something is true, a fact. Evolution is hard proven undeniable fact. There is lots of evidence for it. Here is a round up of most (but not all) different point which prove that evolution exists:
DINOSAURS!!! No seriously, fossils are remains of preserved organisms. Digging can uncover the existence of extinct species. As you start at the top the fossils are very similar to animals today but as you go deeper, through different strata (layers of rock corresponding to geological eras) you see gradual changes. These changes allow relationships to be formed and for us to understand how the web of life is connected. It can explain why big cats are found on different continents and what the world was like million years ago. The oldest fossils are found in the deepest rock.
There are issues with fossil evidence. The fossil record (a list of fossils found, dated, in order) is incomplete as not all organisms have been preserved or could be preserved. One of the most special things about the Cambrian Explosion was appearance of soft bodied animals. They may have existed before but it was the unique preservation in the burgess shale which allows us to try and reconstruct the animals of 560 years ago!
Another issue is that the fossils may be destroyed or not yet discovered. Mining can often destroy fossils but also big diasters like volcanos can bury fossils further underground. A lot of areas are have not be excavated yet so the record is incomplete. A huge number of interesting fossils are coming out of there at the moment due to the easier access (politics/war etc) and there is more freedom in academic sharing. The growth of the internet has made it easier to take pictures and create 3D maps of fossils so you can study they on the other side of the world
If you look at the distribution of organisms relative to geological activity you can identify similar organisms and examples of convergent and divergent evolution.
Comparative anatomy is look at the structure or appearance of animal and noting similarities or differences due to environment and selection pressures. This is particularly interesting when looking at the skeleton of mammals and seeing how things are shorten/lengthen to adapt to different niches.
- Homologous Structures – appears superficially different but has the same underlying structure, so evidence for common ancestors, divergent evolution and the effect of selection pressures
- Analogous structures – show effect of selection pressures on superficially similar structures but different origins = convergent/parallel evolution e.g. fins in sharks/whales
Molecular evidence is primarily how we work out when two species became separate using cladistics. The most important molecules, such as cytochrome C (respiration), are highly preserved with subtle silent differences because of they mutated the animal would not survive.
Evolution is gradual changes in base sequence, so you can compare amino acids sequence in proteins to see how they vary in different animals. A really interesting database is the IBOL which collects DNA barcoding. The aim is to have every species one record so you can take a sample and barcode it to find the species it is. It was devised by Paul Herbet in 2003. It focuses on the mitochondrial gene cytochrome-C oxidase 1 or CO1 (to be sensible). Mitochondrial DNA or mtDNA is highly conserved but does have mutations between species. It is short, so quicker and cheaper to sequence but long enough to be significantly different. The more similar the code the more closely related as less time for neutral mutations to occur
The differences in the colours is a difference in the code. You can see which fish are more similar and which are more different. The website to check out is here. The process of collecting samples is shown below:
Intriguingly if you look more closely at the development of (let’s be biased here) animals, you can see which animals are closely related to each other by looking at their development. If you look at each stage and what happens in gestation you can see how the evolutionary tree split – especially if you understand the homeodomain and the role of sonic the hedgehog. No, thats not a joke but a real biological term.
A new body plan is often created due to a couple of genes changing. This is what causes the great variety of limb numbers and fingers and toes in different species.
Adaptations are characteristics that increase an organisms chance of survival. These features can show whether evolution is convergent or divergent (to a point in history) and how closely it may be related. If you look at mammalian teeth they all used to follow the same dental formula and have either lost or changed to their environment.
Convergent evolution is when two unrelated species look very similar. This is because similar environments have similar selection pressures so traits appear similar. e.g. Aloe vs Agave or Placental vs Marsupial Mammals
Divergent evolution is when two completely different species are very closely related.
If you think of sea horses, they look look pretty similar so they must be related. But they are also different – as a result of evolution and selection.
Anatomical adaptations are physical features that provide evidence for convergent evolution. This includes:
- Body coverings such as hair, scales, fur to help to fly, stay warm, offer protection.
- Teeth – related to diet
- Mimicry – pretending to look dangerous when you’re not.
Look at those seahorses and how well they blend into the coral?! An excellent example of camouflage.
Physical adaptations seem very similar to anatomical but they are how the body performs – how it functions, not it’s features. This provides evidence for divergent evolution – as metabolic activity is unlikely to evolve twice. Bioluminescence, for example, is usually a defence mechanism but the chemical pathway is the same and likely to have evolved once.
- Water storage in Cacti
- Specific poison production i.e. the nightshade family
- Antibiotic production
Behavioural adaptations are how an animal acts, or, funnily enough, behaves. This can be innate or instinctive and inherited through genes or learnt through experience. Examples of this include courtship rituals or seasonal behaviour like migration or hibernation.
Examples and Questions
To finish off looking at evidence for evolution, what better way then to look at examples! Simply tracing the history of human evolution is a fascinating journey of detective work, and involves looking at all these different areas.
One question which always comes up is “Can we observe evolution?”. The answer, I think, is yes. If you look at pesticide resistance or antibiotic resistance you can easily watch it occurring it. Sometimes evolution affects behaviour and this is much more noticeable – such as these crows in Japan. Check out this article for more.
You may be wondering now that you know what evolution is and the evidence which proves it, how new species are formed. After all, evolution is just stating that populations change over time but not how they form new species. On to speciation!