I sometimes get email from people asking, in one way or another, whether our long-term evolution experiment (LTEE) with E. coli provides evidence of evolution writ large – new species, new information, or something of that sort. I try to answer these questions by providing some examples of what we’ve seen change, and by putting the LTEE into context. Here’s one such email:
Hi Professor Lenski,
I have a quick question. I’m asking because I am having a discussion with someone who is skeptical of evolution. The question is: Over the 50,000 generations of e-coli has any of the e-coli evolved into something else or is it still e-coli?
I am a non-religious person who likes to think of myself as an adherent to science but I am not sure how to respond to my skeptic-friend.
And here’s my reply:
50,000 generations, for these bacteria, took place in a matter of ~25 years. They have changed in many (mostly small) ways, and remained the same in many other respects, just as one expects from evolutionary theory. Although these are somewhat technical articles, I have attached 3 PDFs that describe some of the changes that we have seen.
Wiser et al. (2013) document the process of adaptation by natural selection, which has led to the improved competitive fitness of the bacteria relative to their ancestors.
Blount et al. (2012) describe the genetic changes that led one population (out of the 12 in the experiment) to evolve a new capacity to grow on an alternative source of carbon and energy.
Tenaillon et al. (2016) describe changes that have occurred across all 12 populations in their genomes (DNA sequences), which have caused all of them to become more and more dissimilar to their ancestor as time marches on.
Although these articles were written for other scientists, they make three big points that I hope almost anyone with an open mind can understand.
- We see organisms adapting to their environment, as evidenced by increased competitiveness relative to their ancestors.
- Against this backdrop of more or less gradual improvement, we occasionally see much bigger changes.
- And at the level of their genomes, we see the bacteria becoming more and more different from their ancestors.
In these fundamental respects, evolution in these flasks works in much the same way that evolution works in nature. Of course, the scales of time and space are vastly greater in nature than they are in the lab, and natural environments are far more complex and variable than is the simple one in the LTEE. But the core processes of mutation, drift, and natural selection give rise to evolution in the LTEE, just as they do (along with sex and other forms of gene exchange) in nature.
2 responses to “Asking for a Skeptic Friend”
That’s one thing that I have always discovered when talking to people who do not accept evolution. That is, they expect “proof” it’s a new species. Like Chicken egg will hatch a turkey or a dog will give birth to cats.
I explain it, occasionally, like this. A person and his cousin are related through their mutual grandparents. Many times, first cousins like this are close. They grow up together, see each other frequently and are friends. But they grow old, have children and probably move. Some go off to college and never come back to their hometown. Others stay in that hometown forever.
The two cousin’s children may see each other once every year, or less frequently, once every couple of years for a wedding or funeral.
The two cousin’s grandchildren probably don’t even know that they are related through an ancestor a mere 4 generations back. Some family names have changed. Some are rich, some are poor. Some are liberal, some are conservative. They may live thousands of miles from where that common ancestor started.
By the next generation, all the stories of that common ancestor are gone. There is only information that someone interested in genealogy will find and care about. But even then, it’s exceedingly difficult to trace other branches of the tree forward along another branch. My dad, only found his family by someone who studied the records very carefully.
That’s 5 generations, maybe 100 years more or less. Those common ancestors (the original grandparents) have spawned many offspring that were successful. And some that were not. Some families have few branches, few offspring. Some have hundreds by the 5th generation.
But that’s all it takes. The same thing happens in species. And, more importantly, that’s all that happens. Bigger changes are just artifacts of missing chunks of the fossil record and other forms of incomplete information. Just like I have no idea who my actual grandfather is, because my dad was adopted. Doesn’t mean that I don’t exist or didn’t have a grandfather.
Anyway, I think that helps some people get the concept.
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