Why drinking milk isn’t natural

Possibly contrary to what you’d expect, drinking milk is only a very recent development in our evolution. Despite it being completely natural for the young of animals to drink their mother’s milk, after a period of weening these animals will never drink milk again, and that used to be the same for us. But why is this the case?

Milk from animals such as cows and humans (but not monotremes like the duck-billed platypus, or the pinnidae (saltwater clams called pen shells)) contains the sugar lactose. In order to digest lactose, we need the enzyme lactase, which breaks the beta-glycosidic bond between glucose and galactose. Without this enzyme the milk passes through the body largely undigested, and the sugar content then has an osmotic effect in the colon, so instead of water being absorbed, water travels by osmosis into the colon, making the contents more liquified. The lactase is also repired by bacteria in the intesetines, producind hydrogen gas. This is how it can be discovered if you have the enzyme lactase in your body – if the amount of hydorgen in you breath is above that in the atmosphere it means bacteria are respiring lactose, and therefore you don’t produce any lactase. Even though we are capable of producing lactase at birth, the production of this enzyme decreases rapidly, and is essentially non-existant by the time we reach adulthood. Is this true for all of us thhough?

Lactase persistant (where lactase enzyme production does not decline with age) is common in europe – for example in Ireland over 60% of the population have this ability, yet in areas such as asia it’s very uncommon, except umong pastoralists.

The cause of lactase persistance? It’s thought that a mutation of a gene neighbouring the lactase gene, -13,910*T, increases the chances f developing lactase persistance. To determine when this mutation first occurrerd, microsatellites were analysed. As they mutate fast, the greater their variation, the longer the gene has existed in the mutated form. From this information a link was made between the mutation and the domestication of livestock. Until this point, it would have  been hard for our hunter-gatherer ancestors to collect milk. This theory was then backed up by archaeological evidence showing the existance of fatty acids specific to animal milk such as goat’s milk on pottery from the neolithic period. However the study of DNA from neolithic bones found no mutation of this gene.

The distribution of the gene mutations linked to lactase are also somewhat of a mystery as it is much higher in north-west europe despite the fist farmers, including members of the Linearbandkeramik culture, being from much further south. Furthermore, the first mutation occured only about 10,000 years ago, yet the mutation has spread rapidly, so instead of genetic drift, extremely strong natural selection of between 10 and 15% has occured – an asonishingly high rate. This is were the calcium assimilation hypothesis comes in – it suggests that in high latitude regions there is not enough sunlight to get the daily vitamin D requirement and the vitamin D in milk supplemented this defficiency. Drinking milk would also be a much safer, regular soucre of fluids and proteins, in much the same way as beer can be thought of as liquid bread.

All this is very well, but it is not always true that where a gene is most abundant is where it’s origin lies. Computer simmulations have suggested allele surfing is the cause of the gene’s unusual distribution, which began in central europe (it’s not known exactly where). The way a population spreads can effect the distribution of genes and is a gene appears near the edge of a wave of population expansion, the gene can essentially surf on the population expansion and get pushed far away from it’s origin.

I hope you’ve found this interesting, and I’d like to thank Mark Thomas for his recent lecture at the London IOE on the evolution and origins of milk drinking, which inspired me to write this post. To find out more about his research in this area click here.

Word Dissection: Chemistry

Although some words in chemistry are obvious at a glance as to why they are what they are e.g. hydrocarbons are called hydrocarbons because they contain simply carbon and hydrogen, where do we get the chemical words with a less obvious meaning from?

 

Monomer: the simplest repaet unit.      

Mono means one and the Greek meros means part.

 

Atmosphere: The gases surrouding a planet.

From the Greek where Atmos, meaning Steam/vapor, and spharia meaning spherical.

 

Aldehyde: an oxidised primary alcohol, it contains the -CHO group.

Abbreviation of modern Latin name alcohol dehydrogenatum.

 

Ester: the product of the reaction between carboxylic acids and alcohols.

Possibly an abbreviation of the german word Essigäther (ethyl acetate), where Essig means vinegar and Äther means ether.

 

Titration: a method of chemical analysis

From the french titrer meaning title or standard.

 

Alkali: a water-soluble base

From the Arabic al-qaliy meaning ashes

 

Elements: the different types of atom

From the latin elementum which means a matter in its most basic form           .

 

Equation: a formula which equates the reactants in a reaction with the products.

From the latin aequationem which means a community or equal distribution.

 

Oxygen:

A combination of the greek oxys, meaning sharp or acid, and genes, meaning formation or creation. French chemist Antoine-Laurent Lavoisier invented the name oxygène as at the time it was thought that oxygen was vital when it came to forming acids.

Potassium, Bromine and Potassium Bromide

Here is some notes about Group 1, Group 7 and Ionic Bonding, using K, Br and KBr as examples:

Potassium

  • Potassium is in group 1 – the alkali metals – meaning it has one electron in its outer shell, and in the fourth period, so it has four shells.
  • This makes potassium very reactive because the first ionisation energy is only 418.8 kJ/mol as the outer electron is far from the nucleus so potassium easily loses this electron in reactions to form a K+1 ion.
  • The electron arrangement is 2, 8, 8, 1.
  •  The electron configuration for potassium is: 1s2 2s2 2p6 3s2 3p6 4s1. 
  • As potassium isn’t very dense, at room temperature it is a soft silvery solid that can easily be cut with a knife.
  • Potassium has a low melting point – 63°C and a boiling point of 759°C.
  • In a flame test potassium emits a lilac colour flame.
  • Potassium reacts with water in an exothermic reaction to produce potassium hydroxide and hydrogen gas. The metal floats of the water’s surface and ignites the escaping hydrogen.

 

Bromine

  • Bromine is in group 7 – the halogens – so it has 7 electrons in its outer shell, and is also in the fourth period so has four shells.
  • Elemental bromine exists as a diatomic molecule, Br2 and it is a dense, red-brown liquid at room temperature, and gives an orange vapour when heated.
  • It can form ionic bonds with metals as it becomes a -1 ion, but it can also form covalent bonds with non-metals. It is very reactive with metals forming a salt (metal bromide).
  • Reactivity decreases down the group as the outer electrons are further away from the nucleus so are less attracted to it so it becomes harder to attract an extra electron. This property means that Fluorine and Chlorine will both displace bromine, but bromine can displace iodine.
  • The electron arrangement is 2, 8, 18, 7.
  • The electron configuration is 1s2 2s2 2p6 3s2 3p6 4s3d10  4p5.
  • Bromine has a low melting point of -7°C and a low boiling point of 59°C.
  • Bromine can be used to test for saturation in hydrocarbons as the bromine solution will turn colourless if the other solution is unsaturated.
  • Bromine does dissolve in water but it is highly soluble in organic solvents such as carbon disulfide as it is a non-polar molecule.

 

Potassium Bromide

  • It is a white crystalline powder and easily dissolves in water as it is an ionic molecule and so dissociates, with potassium attracting the slightly negative oxygen atoms while bromine attracts the slightly positive hydrogen atoms.
  • It has a high melting point of 734 °C and a boiling point of 1435 °C due to its strong ionic bonds.
  • It can be reacted with silver nitrate to form silver bromide which is used in photographic film.

Jokes for Chemists

After a stressful day at school, including not arriving home until 8 due to parents’ evening, I rewatched the vlogbrother’s video 31 Jokes for Nerds, and despite having watched it on numerous occasions it still made me smile, so I thought I would make a post about the best nerdy jokes I’ve found on the internet, this time focusing on chemistry – enjoy!

I told a chemist a joke. There was no reaction.

How often do I enjoy chemistry jokes? Periodically.

A man walks into a bar and orders some H2O. His freinds says “That sounds good, I’ll have some H2O too”. The freind died.

The name’s Bond, Ionic Bond. Taken, not shared.

A neutron walks into a bar and orders a pint. The bartender says “For you, no charge”.

Did you hear that Oxygen and Potassium went on a date? It went OK.

Argon walks into a bar. The bartender says “We don’t serve Noble Gases in here!” Argon doesn’t react.

Have you got any Sodium Hypobromite? NaBrO.

I blew up my chemistry experiment. Oxidants happen.

My chemistry teacher always told me, if you’re not part of the solution, you’re part of the precipitate.

A small piece of ice fell in love with a Bunsen burner. “Bunsen! my flame! I melt whenever I see you” said the ice. The Bunsen burner replied :”It’s just a phase you’re going through”.

Why did the white bear dissolve in water? Because it was Polar.

What do you call a tooth in a glass of water? A one molar solution.

What do you do with dead chemists? Barium.

What ghosts haunt chemistry labs? Methylated spirits.

The Silver Surfer and Iron Man would make great alloys.

Know any jokes about sodium? Na.

What do you call a benzene ring if the carbon atoms are replaced with iron atoms? A ferris wheel.

Why did the chemist cover his shoes in silicone? To reduce his carbon footprint.

What emotional disorder does a gas chromatograoh suffer from? Seperation anxiety.

What did the mass spectrometer say to the gas chromatograph? Breaking up is hard to do.

Sorry for all the groan-worthy jokes, but all the good ones argon!