More on this book
Community
Kindle Notes & Highlights
Read between
September 23 - November 16, 2019
Archaeology suggests that something very special began to happen to our species around 50,000 years ago.
I like Jared Diamond’s name for it, the Great Leap Forward.
Some authorities are so impressed by the Great Leap Forward that they think it coincided with the origin of language.
Nobody thinks writing goes back more than a few thousand years,
hunch, supported by the authority of linguists such as Steven Pinker, is that language is older than the Leap.
Certain authorities use the name ‘Archaic Homo sapiens’ right back to about 900,000 years ago where they grade into an earlier species, Homo erectus
Each one of your genes must have come from either your mother or your father, from one and only one of your four grandparents, from one and only one of your eight great-grandparents, and so on.
Males have only one X chromosome which they inherit from their mother. Females have two X chromosomes, one inherited from each parent.
Prince Charles has blue eyes, which means, since blue is recessive, that he has two blue-eyed genes.
Like a surname, the (male-specific portion of the) Y chromosome always passes through men only.
Mitochondrial DNA, on the other hand, passes exclusively down the female line (although in this case it is not responsible for making the embryo develop as a female: males have mitochondria, it is just that they don’t pass them on).
If we compare your mitochondrial DNA with mine, we can tell how long ago they shared an ancestral mitochondrion.
Outside Africa, the indigenous mitochondria always seem to belong to one of two main branches or ‘haplogroups’: M (predominantly Asian) and N (found throughout Eurasia).
Human and chimpanzee mitochondria differ by not 30, but about one and a half thousand mutations.
the difference between M and N must have taken roughly 50,000 to 90,000 years of evolution.
The Y chromosome contains several thousand times more DNA than the mitochondrion.
The pattern over time reveals a feature typical of all non-Africans: a dramatic drop in population size about 60,000 years ago.
Most Eurasians have a few per cent of their DNA
that has been passed from Neanderthals or other ancient humans.
over 95 per cent of the DNA of a typical non-African traces back to Africa within the most recent 100,000 years, but even that DNA has probably come through a few different routes.
Because we have so many ancestors in so many different places, it is impossible to trace human diversity back to a single population (let alone a single breeding pair!).
Whenever we have two types, the rarer of which is favoured because it is rare, it is a recipe for polymorphism: the positive maintenance of variety for variety’s sake.
This feature of evolution is called trans-specific polymorphism, and it shows conclusively that differences between humans can trace back to before humans themselves existed.
An itinerant selfish gene Said ‘Bodies a-plenty I’ve seen. You think you’re so clever But I’ll live for ever. You’re just a survival machine.’
The longer the intact sequence, the fewer generations undergone since interbreeding
The Neanderthals certainly didn’t die out entirely. And it is hard now to think of them as a separate species to ourselves.
The Denisovans’ whole genome is generally more Neanderthal-like than their mitochondrial DNA, although it still supports the idea that they were a separate subspecies.
today the greatest density of Denisovan DNA is found in native Australians, New Guineans and Filipinos, and to a lesser extent in Polynesians and west Indonesian islanders.
FOXP2. This gene encodes a ‘transcription factor’:
FOXP2 is not simply a ‘gene for language’, as it is sometimes touted in the press.
Although humans and chimpanzees usually show rather few differences in their protein sequences, FOXP2 is an exception.
more visible change has occurred along the human line of descent from the common ancestor, than along the lines leading to the chimpanzees.
The very phrase ‘missing link’ is suggestive of this misunderstanding. You still hear people saying things like, ‘Well, if we are descended from chimpanzees, why are there still chimpanzees around?’
Concestor 1, the most recent common ancestor of humans and chimpanzees, probably lived around 6 million years ago.
The DNA passed on to us from our parents contains novel changes—mutations—which were not present in the DNA that they inherited from their parents.
How many DNA letters can be copied, on average, before an uncorrected typo slips in? We don’t know for sure, but biochemical observations suggest a range of once every 1 billion to once every 100 billion letters copied.
No longer would we propose a 6-million-year-split between humans and chimpanzees. Instead the split should be more like 12 million years. Other dates are pushed back too. For example, it was originally thought that Neanderthals split from Archaics around 350,000 years ago. The new estimates of mutation rate suggest more like 700,000 years.
In fact it implies that our 6 billion DNA letters experience, on average, around 80 new copying errors each generation.
