Origins of Us: S01E02: Guts

Tonight’s episode is about guts. Well food and how we digest it. The search for food and how we behave because of food. The Sea Squirt, we see, is a distant relative of ours. With no arms, eyes, or legs; it can be a bit hard to see how we are related. It’s the gut that we’re looking at. Food in, waste out. And so the digestive system begins…

The digestive system that we have today, the digestive system that can get the best even out of junk food, has evolved over millions of years. Propliopithecoidea, an ancient primate ancestor lived off fruit and leaves. It couldn’t tell the difference between the colours of different food. 40 million years ago we started to see some variation in colour with 2 types of colour receptor. 30 Million years ago an adaptation opened up reds and greens – the third receptor – the adaptation that we still use today. This helps us to see when fruit is ripe and therefore, more likely to survive, as we can see up to 1 million colours.

From around 3 million years ago the world was becoming drier, forests shrinking and grasslands expanding. Apes adapted to this as we saw in the last episode. Around 6 different types of Apes were able to walk on 2 legs to embrace this new habitat – even though we don’t know how they relate to each other: or to us. The nut cracker man fed on nuts and seeds, as seen due to the massive muscle going through his skull to power some mighty snappers.

Lions were the predators that our ancestor has to share our environment with, in the grasslands. Why are we looking at Lions? Tapeworm larvae of course. We see that the lions eat animals with parasites and the tapeworm grows within the Lion and eats the Lion’s food. It seems that we have the same tapeworm since around 1.7 million years ago. This happened due to us eating the same food as the Lions – big game. Homo Erectus is the likely candidate hunting big game. His body was similar to ours and therefore deserved the name Homo, they also used tools to butcher their kills. 

We see that our changing diet affected our faces and teeth. As herbivores we had big teeth and chewing muscles. As Omnivores we developed smaller teeth and a flatter face shape. An experiment shows that our new narrow teeth are well adapted to cutting through meat, whereas the bigger teeth weren’t able to cut through the meat. We also see some teeth mapping from the pits and scratches on the teeth from the things it ate during its’ lifetime. Looking at the images we see that Homo Erectus had a massively varied diet of meat along with nuts, grasses and fruit.

Chimpanzee saliva, like ours, is packed with enzymes that start to digest the food as we eat it. The differences are in the amount of amylase, we have a lot and it breaks starchy foods down, showing that at some point it became a really important food type for us.

Alice then visits the Hadza People, a tribe that Ray Mears has previously camped with and learnt from. They are hunter gatherer nomadic people, hunting most days. The Hadza men usually hunt on their own, however today they hunt with Alice. Although with only 1 in every 29 hunts being successful, Alice goes back to camp empty handed to head out with the women to gather. Finding berries and tubers (probably a sweet yam) we see that plants provide a more reliable food source – with about 60% being from these sources and 40% from meat sources in calorific content. This means that our ancestors weren’t reliant on one particular type of food and could populate wide areas.

Chewing and digesting raw food can take 25 calories for 100 calories. The human capability to create and control fire with the ability to cook food allowed us digest food with fewer calories – we even unlock calories, sometimes 35% more calories, with cooking them.

Finally we look at behaviour. A hunter gatherers way of life shaped society, with the men hunting for meat and honey and the women gathering fruit, berries and tubers. We see with the Hadzas that men and women normally pair for life for the reason of coupling their collective resources.  We see that the women wear a bracelet to show that they are married. Typically having around 5 children and it taking 13 million calories from birth to weaning means that choosing the right husband is the most important decision a Hadza woman makes. With the woman having the decider on this means that testosterone can jump 40% when women are around, making us ‘show off’ or take risks to show our prowess as hunters. Even when there is nothing to actually hunter. In the programme this is shown by males skateboarders taking risks to complete tricks that they were struggling to get right. When women, rather than men, were watching, they took many more risks to stick with the trick and try to get it right. 

When we moved to farming, which enabled a population explosion and changed the face of our planet. A third of our land is taken over by farming. Enabling us to find food anywhere - because, as Alice puts it, we put it there.

From Homo Erectus expanding out and evolving to Homo Heidelbergensis with a larger brain, which in turn probably evolved into Homo Sapiens covering a large part of the globe. Over time our dietary flexibility, along with the ability to create fire and to cook food has allowed us to populate the desolate places of the world from some of the coldest in the Artic, to the hottest at the equator, as well as the temperate regions of the world.While this is an amazing feat, it is one that we are now coming to realise requires us to be responsible.