Quid nos docet, elephanti dentem Evolution

What an elephant’s tooth teaches us about evolution

Ad probandum, quod non semper est motus evolutionary ad genes, ut aperiat os elephanti ...

Powered by Guardian.co.ukHic titulus “Quid nos docet, elephanti dentem Evolution” scriptum per dictam Aliciam Cicero, observatori die 31 Jan. 2016 07.00 UTC

iam pridem, forsan etiam ad nobilissima nebulae de tempore,, animalia in magna familia Africa. Fabula incipit aliquid 10 et de cognatione abhinc annorum crescebat, et multiplicabatur. Circa tres decies annos,, ramus ejus effundetur in Europa quaeque in Asia. Novos motus et animalia agri, et accommodata ad laté. tandem, pontem quidam transgressi Beringia, Europe Asiam migrandi ab aestivo solis ortu.

Fabula sonat familiare. Nonne omnia maiorum - originem in Africae Miocene, antiquis visi sunt cum clavis fossilium sediments in Kenya; hoc coetus colonizing ex Europa et Asia,; iter ad novum terrarum. Hoc autem non solum historiam hominins: de australopithecines, et paranthropines Homo. Hæ autem elephantines: mammoths, Rattus norvegicus atque Elephas.

Vivendi rationes magis insigne elephantorum - truncis aduncis - gomphothere apparuit patribus suis 20 decies annis ago. Quia animal magnum collum breve, truncus eget erat magno usui, ut haec proboscideans foliis capere de ore ejus, et adducet eos ad, sic præstetur uti evolutionis.

Progressus in trunco ​​et mutation dentes anteriores capitis figura mutationem calonum. Intra os,, dentes quoque mutatis. A maxilla enim parvum spatium a plena statuto de molaribus, cum dentibus opus valeat sustinere gravi labore longa aetate. Si commode ad solutionem problematis tam Evolution. Potius quam totius Materiae premolars ore simul et commandit molaribus inculcata - in os - uno iusto, molarem dentem in maxilla superiore et inferiore parte situ aliquando. Sicut erat in hoc dente, aliud enim est esse post crescens, dens ad illabi contigit dum obsoletae, dum animali vita ad sex summa dentibus.

An artifex impressionem gomphotherium
An artifex impressionem gomphotherium, tusked pater quattuor elephantis, et semen eius,. Photograph: Alamy

The teeth of fossil gomphotheres and elephants preserve a signal of their diets. The ratio of different isotopes of carbon in the tooth enamel shows whether a particular individual was focusing more on browsing on leaves or eating grass. The grasslands of Africa first began to spread around 10 million years ago and isotope analysis reveals that late gomphotheres and early elephants switched to eating mainly grass around eight million years ago. In elephants, this switch is reflected in another change to their chewing teeth, which became three times as tall, with a proliferation of enamel ridges. But these adaptations to an abrasive diet appeared around five million years ago, three million years after that switch from soft leaves to tough grasses. With the degree of resolution we can achieve when looking far back into the past, it’s often difficult to know what came first – a change in behaviour or in anatomy. But in this case, it’s very clear: the changes to teeth lagged millions of year after the change in diet.

In our evolutionary narratives, the organism itself often seems to play a passive role: a powerless victim, fere, of changes to its environment or mutations in its genes. But the tale of the elephant’s tooth is somehow different, mutatio in moribus esse praecedit mutari fabrica (and the underlying genetic instructions for tooth development). Perhaps we shouldn’t be surprised by this: developmental plasticity means that the final shape of an animal’s body is determined not only by DNA but also by external factors. And animals are more flexible in the way they interact with their environments than we sometimes assume. As elephants show, the source of novelty in evolution can come from behaviour rather than from genes.

Teeth in an African elephant skull.
Teeth in an African elephant skull. Photograph: Images of Africa Photobank/Alamy

It’s just possible that this type of change, originating with a change in behaviour, played an important role in human evolution. Around two million years ago, there was a large shift in body shape away from short legs, which first appears in Homo erectus. It’s likely that many of the new anatomical features, from longer legs to enlarged gluteal muscles and chunkier achilles tendons, are related to increased efficiency in running. If a group of humans began to run regularly, perhaps allowing them to hunt or scavenge more effectively, anatomical changes would follow, especially among the still-developing youngsters. Once running became an important part of behaviour, any mutations that enhanced it would be favoured. But the real source of novelty, forte, was that change in behaviour and not a genetic mutation.

The great proboscideans that roamed the African landscapes where our own ancestors evolved remind us that evolutionary novelty doesn’t always originate in the genes.

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