I’ve said before that humans are amazing creatures.
(Picture
from here.)
We are
incredibly smart—so smart that we forget how smart we are when we do stupid
things or find minimal common ground with other animals. “Well, if a myna bird
can use tools, they must be on a par with us. Therefore, tool using isn’t such
a great thing.” Forgetting, for the moment, that while a myna bird might use a
stick or a chimp might solve a maze, neither has built computers, sky scrapers,
trains, or managed to get off earth into space.
You can
argue the value of these things but you can’t argue we did it.
Every
now and then we outdo ourselves. The Zoonomia
Project is an example.
Mammals arose 200 million years ago, around
the same time dinosaurs began taking off. The two groups do have a stem
ancestor long ago but very few of the traits that dinosaurs, crocodilians,
birds, etc., have any shared origin with mammals.
However, mammals do have a lot of shared
ancestry with each other. Mammals died back, diversified, radiated, rinse
and repeat, over tens of millions of years. But many of the ancient
lineages died during the Cretaceous extinction along with other animals. This
means that modern animals derive from a lot of common stock. Primates, bats, cows,
dogs, and cats, all originated either just before the extinction event or
somewhat after. By examining the differences, it could be possible to tease out
how any individual group pulled their physical characteristics from the
originating material.
The Zoonomia Project, carried out jointly at
MIT and Harvard, took 240 diverse animals
and fully sequenced their genes. Then, they compared the codes against each
other. That this was done at all is a terrific achievement. That this was done now is especially interesting. The Human Genome Project finished
over twenty years ago but at that time not much was known about the sequences.
Then, sequencing techniques improved enormously, gene roles began to be
understood, and genetic alterations became an established scientific operation.
We don’t know all that much—there is a lot to know—but we know a whole lot more
than we did then. Enough to perhaps understand what we’re seeing.
And we’re seeing a lot.
The April 28 2023 issue of Science
has several papers
released from Zoonomia, all of which are exciting.
The first order of business is pure
accounting: what changed between these lineages and how much? Evolution is a
constant tug-of-war between innovation and conservation. Innovation introduces
new genetic behavior. This could be sequences moved, changed, or deleted. All
of which could have an effect but could also be deleterious
or result in no change at all.
Conservation, however, prevents change. There’s no point in improving an existing system. This is
especially true for very important systems since innovating involves the risk
of losing the behavior that makes the sequence important in the first place. Hemoglobin is a good example for
this. Hemoglobin is extremely efficient in capturing and releasing oxygen
appropriately. It is highly conserved.
Therefore, seeing which sequences have been
innovated vs sequences that have been conserved across species gives us an
insight into what is important to mammals as a whole.
Innovation and conservation aren’t just
common to mammals, thought. This is also important to individual groups of
mammals. One group might innovate in a sequence that another group might
conserve.
Analyzing this is the province of the Christmas,
and others, paper.
Innovation reflects selection across a set of sequences. Sequences that show a
great deal of change over time reflect rapid evolution. Sequences that show
little change (highly conserved or constrained) within a group should reflect those qualities
that evolution has shaped in the lineage. Knowing the nature of cats, we might
expect a fair amount of conservation of those genes that reflect their behavior
and their indicative collective traits.
Because we are who we are, we looked first
to those traits we like about ourselves: brain size. They also looked at sense
of smell, and hibernation.
One of the interesting results the Christmas
paper is that many conserved sequences had no known function. In addition, they
discovered that at least 10% of the genome is functional. Since about 1%
actually codes for proteins, a whole lot of the genome is bent around the task
of regulating expression rather than actual expression.
It is very clear this comparator tool is
extremely useful.
The Zoonomia data is already serving up
interesting papers outside the project. One is Katie
Pollard’s work with human accelerated regions (HARs) in the human genome.
Pollard has been working the HARs for some
time. Pollard’s HARs are enhancers, dialing gene expression up or down during
development—especially during brain development. Working on concert with the
Project, Pollard has been examining why HARs happened in the first place. She found
that about a third of the HARs between humans and chimps involved how DNA was
folded. This seems to suggest that the structural nature of DNA
might have something to do with brain development.
They hypothesis is that by changing the
structural folding of DNA within the cell, HARs were brought into closer
proximity to genes responsible for brain development. I.e., the genetic sequence
responsible for brain development is brought close to an HAR that enhances its
activity.
Pollard’s work suggests that a random
sequence mutation might have been the originating impulse for our brain
development.
This doesn’t surprise me: this is exactly where randomness usually appears. Consider that humans derive from
primates, animals with two eyes pointing forward, the perceive color, with very
nice hands, and a fair starting brain. This was fertile ground to take
advantage of increasing brain capability. Once that variation in capability was
available, evolution jumped right on it. Chimps haven’t changed much in the
last few million years since we split from them but we have.
Another paper, lead author Foley,
attempts to build a timeline of mammalian evolution. This timeline suggests a significant
increase in diversity prior to the Cretaceous extinction that was
exacerbated after the dinosaurs were taken out of the way.
There are eleven papers in that Science issue. Every one of them is gold.
Nice to feel good about being human once in
a while.