What were the first animals?

by Matthew Cobb

I’ve just finished making a BBC World Service radio programme about the first animals. Anyone, anywhere in the world, can listen to it (it’s only 28 minutes long!) – you just have to register with the BBC (free, rapid and cost- and spam-free). Click on the pic to go to the BBC website:

The programme deals with two different ways that researchers are studying this question – by looking at fossils, and at DNA. In both cases I interview researchers and – in the case of the Ediacara – get to handle some fossils. I also ate some 600 million year embryos at Bristol University (to see what they tasted like, obviously), but we didn’t include that in the programme. . .

The fossil data relate to what are called the Ediacaran biota – strange fossils from before the Cambrian, around 570 million years ago. The fossils are very hard to interpret – they don’t look like much alive today – but an amazing technique for analysing cholesterol molecules in the rock, so organic molecules preserved for all that time, has confirmed that Dickinsonia, the thing in the picture above, was an animal. Other techniques involve looking at large numbers of Ediacaran fossils and seeing how their distribution relates to those of modern animals. All the data suggest that some of the Ediacaran weirdos were indeed animals, although we cannot know if they are the ancestors of any animal alive today.

The DNA data focuses on a different question, which DNA can answer – which of the groups of animals alive today was the first to branch off the tree of life? Traditionally there has been a straightforward answer to this: sponges, which are nerveless and tissueless. But 10 years ago comparative genomic studies dropped a bombshell – they suggested that the first group to branch off were the ctenophores or comb jellies. This has caused a huge row because it would mean either that nerves evolved twice – once in the ctenophores, and once in our ancestors, after the nerveless sponges branched off – or that the huge sponge group somehow lost the genes for producing nerves.

Many biologists (myself included) don’t like either of these options, and prefer the sponges as the first model, but the data are persistent. Or are they? I spoke to experts on both sides of this argument, which has caused quite a hoo-haa in the zoological community for the past decade.

Anyway, go ahead and have a listen – download it and listen to it on public transport or while you are exercising. NB: I made the programme with ace producer Andrew Luck-Baker.

If you are a teacher, especially if you teach animal evolution, please get your students to listen to it.

34 Comments

  1. Posted October 31, 2018 at 11:51 am | Permalink

    Reblogged this on The Logical Place.

  2. mikeyc
    Posted October 31, 2018 at 12:05 pm | Permalink

    I’ll listen, alright, but I what I really want to hear is the story behind eating 600 million year old embryos!

    Rock tasting?

    • Ken Kukec
      Posted October 31, 2018 at 12:41 pm | Permalink

      Wondering about the wine pairing.

      • James Walker
        Posted October 31, 2018 at 5:19 pm | Permalink

        A nice pre-Cambrian beaujolais.

        • Ken Kukec
          Posted October 31, 2018 at 6:24 pm | Permalink

          “Nouveau,” it’s not.

      • Posted November 2, 2018 at 11:39 am | Permalink

        When did grapes evolve? 🙂

  3. TJR
    Posted October 31, 2018 at 12:05 pm | Permalink

    What is the exact definition of “animal” you use? Wikipedia says heterotrophic, multicellular eukaryotes.

    I’m sure when I was at school we were told that non-photosynthesising and motile protozoa were called animals, but looks like only multicellular non-photosynthesisers are called that now.

    • keith
      Posted October 31, 2018 at 1:30 pm | Permalink

      Wikipedia is pretty much correct in the definition (description) of animals. The protozoa are animal-like protists. Really, under cladistic reasoning, the animals are all the descendant species of the most recent common ancestor species which gave rise to the things we recognize animals. Though animals are largely multicellular heterotrophs, some photosynthesize by incorporating symbionts and others by stealing chloroplasts from algae.

      Protozoa and protists aren’t formal taxonomic groups, but are used to describe certain eukaryotes which are neither plants, animals, nor fungi.

    • Posted November 11, 2018 at 7:05 pm | Permalink

      Most motile protozoa are very distantly related to multicellular animals. Their forward-protruding flagella betray them.

  4. ThyroidPlanet
    Posted October 31, 2018 at 12:06 pm | Permalink

    Sub

  5. Pierluigi Ballabeni
    Posted October 31, 2018 at 12:18 pm | Permalink

    I can listen to it without registering with the BBC. Too bad that it is in English since my understanding of spoken English has its limitations (I often do not recognise words that would I understand if read them 🙂 )

    • Pierluigi Ballabeni
      Posted October 31, 2018 at 12:20 pm | Permalink

      … that I would understand… I should re-read before I send.

    • Posted November 11, 2018 at 7:06 pm | Permalink

      Same with me. But if this is the new paradigm, we’ll read about it in the good old PubMed.

  6. Posted October 31, 2018 at 1:10 pm | Permalink

    If they are indeed the first animals, they would have to be ancestors, wouldn’t they?

    • mikeyc
      Posted October 31, 2018 at 1:45 pm | Permalink

      I think that means the first *in time*, not in sequence.

      • Posted October 31, 2018 at 3:00 pm | Permalink

        How can it be first in time but not sequence?

        • mikeyc
          Posted October 31, 2018 at 3:38 pm | Permalink

          If they left no descendants.

          • Posted October 31, 2018 at 4:26 pm | Permalink

            So that would mean there must be other animal species contemporaneous with Dickinsonia that have not been found, right? Thus, Dickinsonia and this other species must have a common ancestor, so Dickinsonia cannot be the first animal, just the first known animal.

            • Posted October 31, 2018 at 5:33 pm | Permalink

              Yes, so if there were sponges around at the same time – fossil record is poor – then they might be the ancestors of you and me, and not Dickinsonia. It’s very hard to tell because of the lack of fossils and the lack so diagnostic molecules.

          • Posted October 31, 2018 at 4:33 pm | Permalink

            I wouldn’t be confused if Dickinsonia were described as the earliest known animal, rather than “the first animal.”

            • GBJames
              Posted October 31, 2018 at 4:36 pm | Permalink

              This happens all the time in archaeology/paleontology/etc. The first known gets short-handed as “the first”. Drives me nuts, too. Given the extremely limited data points, we can pretty much never really know the first anything.

              (To say nothing of the arbitrary nature of drawing a line in a continuum and calling it where some first thing happened.)

            • mikeyc
              Posted October 31, 2018 at 5:12 pm | Permalink

              Yes. I think when they are saying “first” they mean “earliest”. We can’t actually know if these are the ancestors of life today. But we CAN (to some degree of precision) say that these are the “earliest known animals”.

  7. Debbie Coplan
    Posted October 31, 2018 at 1:53 pm | Permalink

    Thank you so much for posting and I look forward to listening later when I can catch some time. I enjoy your posts!

  8. Posted October 31, 2018 at 2:10 pm | Permalink

    First “animal” is a pretty slippery concept. It isn’t clear to me why multicellularity is necessary. I’ll put my money on the first prokaryote to incorporate mitochondria through endosymbiosis, and on the first plant having been the first prokaryote to incorporate chloroplasts through endosymbiosis. If in fact that’s what happened.

    • keith
      Posted October 31, 2018 at 9:05 pm | Permalink

      The first prokaryote to incorporate mitochondria is the first eukaryote, not the first animal. Plants also have mitochondria. If we use your definition, plants should be considered animals because they would be descended from animals, unless the eukaryote condition independently evolved in more than one lineage.

  9. Dave
    Posted October 31, 2018 at 2:10 pm | Permalink

    “they suggested that the first group to branch off were the ctenophores or sponge jellies”

    Minor slip here – should be “comb jellies”.

  10. David Hughes
    Posted October 31, 2018 at 2:12 pm | Permalink

    “they suggested that the first group to branch off were the ctenophores or sponge jellies”

    Minor correction: ctenophores are “comb jellies”.

  11. CAS
    Posted October 31, 2018 at 4:26 pm | Permalink

    Thanks Matthew!

  12. Otternaut
    Posted October 31, 2018 at 5:28 pm | Permalink

    Aren’t we assuming that the first animal still exists or left a fossil record. What we really are asking,seems to me to be, what is the most primitive existing Class of animal that descended from the KINGDOM OF ANIMALIA/

  13. Diane G
    Posted November 1, 2018 at 1:02 am | Permalink

    Very cool stuff!

  14. Posted November 11, 2018 at 7:09 pm | Permalink

    I recently joked with my colleagues that sponges are neotenic deuterostomes, because they lack a distinct mouth but have a distinct “anus”.


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