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Evolution is change.

The American cockroach (Periplaneta americana) is a common visitor to our house. This visitor is very difficult to keep away and comes uninvited like the guest in the film “Atithi Tum Kab Jaoge”. One day, as I was seated on my toilet doing my morning ritual, I spotted one that was upside down. I wondered what had brought upon such an unfortunate position. And I pondered about something. Why couldn’t the cockroach turn itself right?

I could see it struggle and wiggle and beat its legs about as if it were asking someone to lend a hand. I felt bad. Most of the times, cockroaches flip over because they ingest neurotoxins such as ivermectin1,2 in insecticides that mess with their muscle coordination and cause spasms. They start kicking and a wrong kick flips them over. Once they are, they cannot turn themselves right. 3,4

But, there is another side to this story.

Credit:, A Visual Guide to Evolution Strategies

One, of evolution. Evolution is change, over time. These cartoon lemmings teach us about adaptation. They jump off the cliff. The fall is fatal. Not all lemmings survive the fall, but once in a while some develop capabilities that help them safely reach the bottom. Few lemmings in the herd “adapt”, or atleast try to. The lemmings that survive, have offspring that have these adaptations which help the offspring survive the fall. As species change, they adapt to their environment to survive better to that environment. Adaptations develop as generations of members of a species live and die, and can happen very slowly or quickly depending on the species. Fruits borne by parents are passed to offspring. The body of P.americana is more or less flat on dorsal side and that makes it harder for it to flip back up. In the wilderness where the surface is uneven, it finds some rock or some other material as support. But there is no such support on the bathroom floor. It simply has not adapted to this environment. Excavations near the Caspian Sea revealed floors covered with mats made of sheep wool that were dated to 6000 BC. Mosaic tiles were used in 400 BC Greece and

Credit: Allen Hoof,

smoother floors came into existence from 1860s after the invention of linoleum. Very smooth tiles cannot be expected before the 18th or 19th century, in England.5,6

The crux of the argument here is that P.americana ‘s common ancestor with sister taxa P.lateralis (rusty red) and P. fuliginosa (smokybrown) was 10 MY ago7 Literature so far shows no evidence of any significant morphological change occurring in the species, also with respect to its dorsal region. So, our roach has pretty much remained the same for the last 10 million years.

This made me think - wasn’t there enough time to adapt, because smooth tiles only came about 200 years ago? Or maybe there was. Perhaps there wasn’t enough “selective pressure” and tiles really haven’t killed that many cockroaches. Insecticides make a deadly combination with tiles and present-day cockroaches may be experiencing more pressure than their ancestors.

Whatever be the reason, it will be interesting to wait, to witness them change as time passes.

18th century English Second century Roman bathroom. Lawrence OP, flickr.


1. LIN, Y. Cockroach killing bait. (2009).

2. Turner, M. J. & Schaeffer, J. M. Mode of Action of I vermectin. (1989).

3. Ask a Scientist: Why do roaches die lying on their backs? | Raleigh News & Observer. Available at: (Accessed: 20th May 2021)

4. entomology - Why do cockroaches flip over when they die? - Biology Stack Exchange. Available at: 20th May 2021)

5. A Lesson on the History of Tiles. Available at: (Accessed: 20th May 2021)

6. Floor covering | Britannica. Available at:

covering. (Accessed: 20th May 2021)

7. Evangelista, D. A. et al. An integrative phylogenomic approach illuminates the evolutionary history of cockroaches and termites (Blattodea). Proc. R. Soc. B Biol. Sci. 286, (2019).

- Rahul Keshav (

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