Question: How does DNA help us define the classification of animals?

Oli Wilson answered on 8 Nov 2017:

Ooh, that’s a really good question! Without DNA we have to classify animals (and plants) on the basis of morphology – basically what shape their different bits are. So the difference between two similar species might come down to small differences in something like colour or skull shape or size. The thing is, animals can be quite variable and morphological differences don’t always show species-level differences – I bet you and I don’t look the same, but we’re 100% the same species.
DNA lets us get round these problems. You don’t necessarily have to catch (and maybe kill) animals you’re studying in order to study them, and you can more easily put numbers on DNA similarity/difference than body shape. Scientists at Kew Gardens have recently taken a gene sequencer up a mountain to work out which species some plants belong to – it saves lots of time, and if you have the DNA fingerprints or barcodes of lots of known species you can really easily work out if something you’ve found is new. This is especially useful if different species look really similar (DNA recently showed that there are actually 3 more giraffe species than we thought – they just all look the same! http://www.nature.com/news/dna-reveals-that-giraffes-are-four-species-not-one-1.20567), or if they change a lot – like this shrew which *shrinks its skull* every winter. What a weirdo. https://www.gizmodo.com.au/2017/10/shrews-shrink-their-heads-to-survive-winter/