What is a tree of life?

A phylogeny? An evolutionary tree? A cladogram? We see the branching lines of these diagrams in many museum displays and science articles, but what do they tell us and why are they helpful?

Duncan Murdock, research fellow, explains. 

You are a fish.

Starfish, jellyfish and cuttlefish are not fish.

Actually, no, there’s no such thing as a fish. Let’s take a step back…

The Jackson 5 – the ultimate singing family tree?
Credit: Wikimedia Commons

It all comes down to common ancestry. All life is related, and we can think of it in terms of a family tree (or ‘phylogeny’): Jackie, Tito, Jermaine, Marlon and Michael were all Jacksons. United not only by a collective inability to control their feet, but also by common descent – they are all their parent’s children*.

By tracing further and further back in MJs family tree we could define ever larger groups united by common ancestors, first cousins (grandparents), second cousins (great-grandparents), all the way to every human, every mammal, every animal, and eventually all life – we are family (ok, that was Sister Sledge, but you get the point).

In the case of the tree of life, species are at the tips of branches and their common ancestors are where branches meet. A true biological group consists of a common ancestor and all its descendants, and we can use characteristics common between two species to imply common descent. Siblings look a lot like each other because they have inherited much of their appearance via common ancestry (i.e. their parents). In a similar way, two closely related species will share lots of inherited characteristics.

However, things are not quite that simple. Wings of bats, birds and insects are not inherited from a common ancestor but independently evolved for the same purpose, in this case flight. To complicate things further, as species evolve they may lose features inherited from their ancestors that other descendants retain. Snakes have lost their limbs, but still sit in the same group as lizards. These problems can be overcome by looking at many characteristics at once, using genetic information to test predicted relationships, and adding fossils to the tree to track change or loss through time (as in snakes).

Birds, insects and bats have all evolved wings for flight, but did not inherit this feature from a common ancestor. This is a good example of convergent evolution.

So, what about fish? ‘Fish’ is used to refer to pretty much anything that swims in water, but this lifestyle in animals like starfish (a relative of crinoids and sea urchins), jellyfish (a relative of corals) and cuttlefish (a relative of squid and octopus) evolved independently from more familiar fish like cod and carp. So, they’re not really ‘fish’ at all. With that in mind, how can we be fish? Well, the last common ancestor of, say, hagfish, salmon, shark and lungfish, is also the common ancestor of frogs, lizards, cats and us! All four-limbed animals with backbones descend from a fish-like ancestor. To complicate things further some have adapted to life back into the water and look much more like a ‘fish’ again, like dolphins, seals and the extinct ichthyosaur. Without a tree of life, we could not begin to unravel the evolutionary path that lead to all the diversity of life we see today.

The Blue Fin Tuna on display in the Museum is definitely a fish… right?!

You are closer to a chimp than a monkey, closer to a starfish than a snail, and closer to a mushroom than a tree. And, of course, there’s no such thing as a fish, but they still go well with chips.

*Joseph Jackson and Katherine Scruse had ten children, including the members of the Jackson 5, twenty-six grandchildren and several great-grandchildren.


Is it real? – Taxidermy

One of the most common questions asked about our specimens, from visitors of all ages, is ‘Is it real?’. This seemingly simple question is actually many questions in one and hides a complexity of answers. 

In this FAQ mini-series we’ll unpack the ‘Is it real?’ conundrum by looking at different types of natural history specimens in turn. We’ll ask ‘Is it a real animal?’, ‘Is it real biological remains?’, ‘Is it a model?’ and many more reality-check questions.

First up: Taxidermy, by Mark Carnall

The Museum is well-known for its touchable taxidermy. As of today, we have two large bears, a Black Bear and a Brown Bear, greeting visitors as they enter the main court, as well as taxidermy specimens on our Sensing Evolution touch-tables. For children and adults alike, this close encounter with a taxidermy animal prompts the question – is it real?

Taxidermy, or ‘stuffed’ animals, are specimens that have been specially prepared, preserved and posed to show what the creature may have looked like in life, but real and not real here is tricky. The animal itself is, or was, a real animal – there are no taxidermy unicorns, for example. But the biologically real parts may only be the skin, the skull, and the skeleton inside the paws and feet, depending on the type of animal.

The touchable taxidermy Brown Bear greets visitors to the museum.

Inside taxidermy specimens there may be sculpted statues over which the skin is stretched; for older specimens, a wire and wood framework with paper, wood wool, straw and seeds may be used to fill out the skin. The animal’s squishy parts, which are not easy to preserve –such as eyes, lips and tongues – are normally made of glass or plaster.

Animals that have skins and skeletons that are relatively easy to preserve – including mammals, reptiles, and birds – are generally better suited to taxidermy. Marine mammals such as whales and dolphins, amphibians such as frogs and salamanders, and fish are all less common as taxidermy because their skins are harder to treat and keep stable.

Dogfish and piranha taxidermy which have been painted and varnished in an attempt to make them resemble the living animals. Note the comedic eyes on the shark.

The hard parts of skin, such as crests, wattles and skin patterns in reptiles, are susceptible to discolouring and fading in light, so these areas may be repainted to show what the animals look like in life. This introduces another ‘non-real’ element: paint.

So although there are certainly real parts used in taxidermy, there’s yet another complication in answering the question: the animals are usually posed by a human, so even their posture and appearance could be considered ‘subjective’ and perhaps therefore not quite ‘real’.

In fact, some of our older taxidermy may have been prepared by taxidermists who hadn’t ever even seen a living example of the animal they were working on. This can lead to inaccurate positioning and posing, as in the taxidermy kiwi on display in our main court.

So, is it real? You decide.

Next time… Skeletons and bones