Bit geeky but important for understanding how mammal/primate/human minds work.
- An improved ability to suss out scents in our 200-million-year old ancestors may have laid the groundwork for the bulging brains of humans and all other mammals
- Brain areas involved in smell, or olfaction, catalysed brain growth in the evolutionary branch that gave rise to mammals.
With this foundation in place, later mammals could have siphoned off some of those resources for colour vision, echolocation and even, in the case of the platypus, the ability to sense electric currents. “The olfactory system was the thing that drove the expansion of the brain in the first place, and once you’ve got a big brain you can do all kinds of things with it,”
The evolutionary branch that spawned mammals took shape during the late Permian, about 260 million years ago. Known as cynodonts, these not-yet-mammals resembled reptiles, with small brains relative to their body size and puny olfactory bulbs — the brain structures that pass sensory information about smells on to other parts of the brain — Rowe says. “They had bad eyes, bad ears and a poor sense of smell, and from the structure of their brain it doesn’t look like they were very coordinated.”
One of the fossilized creatures, Morganucodon oehleri, had a puny head — just 1.3 centimetres long — but Rowe says it probably resembled animals such as opossums, with a fur coat and long tail. “If you were to look at it today you’d say: oh that’s a mammal or that’s almost a mammal. It would look very familiar to you,” he says.
Brain areas involved in detecting and processing smells, which lie near the front of the skull, explain much of this growth, Rowe’s team concludes. A region called the neocortex, which may have processed sensory information from the skin and hairs, also swelled in Morganucodon, as did the cerebellum, which coordinates movement.
The first true mammals may have gained even better senses of smell by developing additional nasal tissue to support the neurons that detect different odours and ferry them to the brain, Rowe says. Mammals have about 10 times as many odour-sensing genes as other vertebrates.
Rowe speculates that an improved sense of smell would have been useful because they would, by necessity, have become creatures of the night. “They were after insects and grubs and other things that were active at night. Dinosaurs were picking up on food sources active during the day and mammals took over the night shift.”
…our ancestors grew larger cerebellums — essential for coordinating movement — than did their predecessors. Smells, after all, are useless if you can’t act on them, Barton points out. “Ultimately, the function of the brain is to mediate adaptive behaviour, it’s not to reflect on the mysteries of the Universe, much as we like to think that’s what our brains evolved for.”