I checked 'How to Clone a Mammoth' (by Beth Shapiro, 2015, Princeton U. Press) out from the library and have been slowly reading it the last few weeks. There's lots of interesting stuff in there. I'm going to use this thread to post about things that caught my eye.
The Species Concept (p. 28).
"A species tends to be defined as an evolutionary lineage that is reproductively isolated from all other evolutionary lineages... Individuals belonging to different species cannot mate. Or if they do, the offspring that are born either do not survive into adulthood or cannot have offspring themselves."
This definition is apparently fairly recent, originating with Ernst Mayr in 1942. It's found in most textbooks. But it doesn't always work that way in real life.
Shapiro points out that polar bears and brown bears are considered separate species, but they can mate and produce fertile offspring. Dogs, wolves and coyotes are considered separate species but they frequently interbreed. Cows, bison and yaks can all interbreed and produce fertile offspring.
Genome Dimensions (p. 41)
Quantities of DNA are typically measured in terms of base-pairs (the rungs on the DNA double-helix ladder). The human genome has about 3.2 billion base pairs, organized into 23 chromosomes.
Compare that to the loblolly pine genome, which has roughly 22.2 billion base pairs in 12 huge chromosomes. Or the carp genome which has 1.7 billion base pairs in 100 little chromosomes.
So my take-away is that the number of chromosomes isn't really an indicator of how much DNA is present, nor is the amount of DNA proportional to the complexity of the organism. (These pine trees have 7x as much DNA as a human? Why? What's it doing?)
The Species Concept (p. 28).
"A species tends to be defined as an evolutionary lineage that is reproductively isolated from all other evolutionary lineages... Individuals belonging to different species cannot mate. Or if they do, the offspring that are born either do not survive into adulthood or cannot have offspring themselves."
This definition is apparently fairly recent, originating with Ernst Mayr in 1942. It's found in most textbooks. But it doesn't always work that way in real life.
Shapiro points out that polar bears and brown bears are considered separate species, but they can mate and produce fertile offspring. Dogs, wolves and coyotes are considered separate species but they frequently interbreed. Cows, bison and yaks can all interbreed and produce fertile offspring.
Genome Dimensions (p. 41)
Quantities of DNA are typically measured in terms of base-pairs (the rungs on the DNA double-helix ladder). The human genome has about 3.2 billion base pairs, organized into 23 chromosomes.
Compare that to the loblolly pine genome, which has roughly 22.2 billion base pairs in 12 huge chromosomes. Or the carp genome which has 1.7 billion base pairs in 100 little chromosomes.
So my take-away is that the number of chromosomes isn't really an indicator of how much DNA is present, nor is the amount of DNA proportional to the complexity of the organism. (These pine trees have 7x as much DNA as a human? Why? What's it doing?)