History of Conflict

History of Conflict

Explore the constant debate about animal relationships
through the changing animal trees over the last 100 years.

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Relationships

How are we related to each other?

...I know we are related,
but how?

...I know we are related,
but how?

umm...
our mothers are not sisters.

umm...
our mothers are not sisters.

Yes, but...
our grand-fathers are brothers.

Yes, but...
our grand-fathers are brothers.

And we have the same
great-grand parents!

And we have the same
great-grand parents!

But...sometimes I wonder,
how are we related to our cat?

Or....even a starfish?

But...sometimes I wonder,
how are we related to our cat?

Or....even a starfish?

ARGUMENTS

Scientists have been arguing about the relationships between animals for a long, long time.

ARGUMENTS

Over the last two centuries, they have put forward their arguments by creating trees, called Phylogenetic trees, which illustrate the relationship between animals.

ARGUMENTS

Let's see how our understanding of animal relationships has changed by looking at phylogenetic trees over the last 100 years.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

This tree was created by comparing the physical appearances and behaviours of the animals.

The more characteristics two organisms share, the closer they are placed on the tree and hence, the more they are related to each other.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

The Jellyfish hangs out by itself, away from the other animals.

Hence, the jellyfish is least related to all other animals in this tree.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

These animals are grouped together because they all have a left and right side that mirror each other.

We, therefore, call this group
the Bilaterian species.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

Within this group, there is another split into two groups.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

These animals are grouped together as they develop from their mouth first. We will therefore call them “mouth-first animals”.

Their scientific name is Protostomes.”

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

On the other hand, these animals develop from their anus-first.

These “anus-first animals” are called Deuterostomes – this is where you find us! Humans!

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

These two distinct groups form the accepted structure by most for the following century and still to this day.

Why was this strange feature used to group animals?


At some point in the past two different groups evolved out of a “clump of cells with a hole”. One group used the opening to form their anus, and the other group used the opening to form their mouth.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

Over the next 80 years, scientists continuously refined their understanding of the tree.

The quality and quantity of physical characteristics improved and the tree became more detailed.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

Some of the relationships, however, remained obscure.

Scientists were unsure about the position of the Arrow worms. It looked very similar to other “anus-first animals”, such as the Lancelets.

Hence was loosely positioned in this group.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

In the case of the arrow worm and other loosely positioned species, tracing the evolutionary relationship between animals by looking at their physical appearances has many pitfalls.

Similarity in physical traits does not always equal evolutionary similarity!

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

In the late 80s, scientists started to construct trees by comparing the genes of animals.

The more alike the genes of the animals are, the more they are related.

For this tree, a very specific type of gene called 18s RNA was used.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

By comparing genes instead of physical characteristics scientists became increasingly unsure of certain groupings.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

In this tree, we see Lake and Field are continuing to view the tree as a split between anus-first and mouth-first development.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

With the use of genetic materials scientists became more unsure about the position of the arrow worms in the anus-first group. So they began to be loosely placed within the mouth-first animals.

If this was correct, then an animal known to develop from the anus-first would now be placed within the mouth-first animals.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

Computer technology and the models for analyzing data increasingly improved.

By 2006, scientists found evidence that humans are more closely related to sea squirts than the lancelets!

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

With new and improved data, scientists were finally able to place the arrow worms!

After quite an interesting journey it now forms a group within the mouth-first animals and moves further away from us.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

This placement contradicts the defined split of anus and mouth first animals.

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

Today we still argue about what the correct tree looks like and recently asked if an anus-first animal grouping actually exists?

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

Did this idea of a split between the two groups influence the way we constructed the trees all these years?

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

Have we manipulated ourselves into this perspective?

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

The tree might, rather, look like this...

Earthworm
Fruit Fly
Arrow Worm
Starfish
Seasquirt
Lancelet
Human
Jellyfish

Or it might look like this.

This would have huge implications on our understanding of early animal evolution.

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