Tiny Vessels

This Father’s Day give your dad a gift to remember – an understanding of the evolution of his gametes

With Father’s Day quickly approaching, I think it’s time we had a little talk about the evolution of dad’s gametes. Before you get creeped out, don’t think of this as being just about your dad, but rather any dad or male of an organism that reproduces sexually (sorry, bacteria!).

While not all dads are the same across the animal or plant kingdoms, they do all share one common feature – sperm. The production of this gamete type is what defines the male within every species. What defines females is their ability to produce eggs. The most important distinction between these two gamete types is their investment in size; sperm are small, eggs are large. It is their union into a zygote that characterizes sexual reproduction. But how did these two gamete types come to be?


A sperm cell fertilizing an egg cell. <WikiCommons>

It all starts with parasitism. Ah, the romance.

One theory is that before females or males existed, all gametes were of the same type and size. Size is an important trait for gametes because being large translates into more nutrition for a developing zygote, which assures it higher survival. Such survival is highly favored by natural selection and, thus, larger gametes also came to be favored. But might there be a cost if gametes are all under the same selective pressure to become large?

Consider a vast ocean with a single target – a giant ocean liner. Your goal is to reach this easy-to-spot target, which you can achieve through building one of two vessels given a set amount of materials: you can either invest your resources into producing a few more giant ocean liners, or you can take these resources and parse them into a large fleet of torpedo-like mini-submarines ready to divide and conquer. Finding a large vessel with another large vessel will prove a difficult task. For one, they’re less maneuverable. Moreover, they’re less likely to encounter one another since they cover less area. But time is of the essence, and a bunch of smaller vessels all working toward a common goal will more frequently encounter their target and, ultimately, will win the race.

Renegade at Dutch Wikipedia

Underwater attack by frogmen on manned torpedoes. <Renegade at Dutch Wikipedia>

In the gamete world, slow and steady will never win the race either. Large gametes are less efficient at finding their target precisely because their strategy of being large constrains them to be fewer in number. On the other hand, by not investing resources into their size, the smaller gametes are freed up to be more abundant. Occurring in greater numbers means they are much more likely to encounter their larger counterparts – an excellent racing strategy if you’re a gamete.

Now, let’s imagine the potential pairings of these different gamete types from the perspective of natural selection. The important rules of the race are two-fold: the more zygotes the better, and enhanced survival of the zygote is key.

In a remarkable feat, suppose two large gametes finally do find one another.



Sure, the fusion of their genetic material will result in a few mighty-super-survivor zygotes because of their equal investments in being large and nutritious. Unfortunately for them, however, their big investments will come at the expense of being rare, so their union will result in fewer zygotes.

Likewise, though the union of two small gametes would be more probable given their abundance, neither gamete can provide sufficient nutrition for zygote survival.


Consequently, neither of these unions between like-gametes would be favored by selection over time.

It’s these unfortunate pairings that help explain how natural selection additionally came to favor the evolution of a smaller gamete, sperm. What remained and became the evolutionary norm was the most productive and efficient strategy – the fusion of two disparate gamete types – large and small. Now, where there were once only ocean liners, there were also millions of torpedo-like mini-submarines.

And now for the unsettling part. In addition to representing a trade-off between quality and quantity, gamete size also embodies a trade-off in offspring investment. While large gametes evolved for nourishment of the zygote, small gametes evolved to be cheats. They downsized to be better able to find the large gamete, which was then entrapped into providing all of the sustenance for the zygote. So here is the rub that necessitated parasitism. By favoring both egg and sperm, selection actually ensured their unequal contributions to the zygote.

Hence, the very reason sperm likely evolved was to exploit the resources of eggs. And it is ultimately the selection of these two very different investment strategies that led to the origin of females and males, moms and dads.

So this Father’s Day, when you’re having trouble finding the right words to say, keep it simple. Thank him for his parasitic little sperm cell. It made all the difference.



Totally Enormous Extinct Dinosaurs

Just as I’m sure watching movies involving *your* profession is annoying because they can never quite get it right in the film biz, it’s excruciating for scientists to watch movies with bad science in it. Case in point: I came across this funny blog advertisement for an entomologist (a person who studies insects) for the new Jurassic World movie set to come out in June of 2015.

And this is completely irrelevant to the science in it, but here is a funny comic of the original Jurassic Park with a slight twist in perspective. Enjoy!

Kelly Watch The Stars

Chances are that if you are reading my blog, you like science. But you don’t need to be a scientist to contribute to scientific research.

You can contribute through citizen science, which is a collaborative form of scientific research that involves the voluntary participation of public citizens (i.e. YOU). Citizen science projects can be done by individuals or by teams, and they’re often under the direction of a leading scientist or institution.

Do you think that one or two scientists alone could follow the entire fall migration of the Monarch butterfly from the US and Canada all the way down to Mexico, across thousands of miles?

Photograph of a Monarch butterfly (Photo Credit: Kenneth Dwain Harrelson) – Wiki Commons

Well, they certainly could.

But how long would it take for only a few individuals to collect data on the Monarch’s population size and travel patterns? And how much funding would that require? With citizen science butterfly counts, you can have many participants living in the migration corridor volunteer to collect data based on their observations. Such wildlife-monitoring programs are not only cheap, but they allow for large-scale data collection. Quite efficient they are.

So for the scientist, citizen science is a very powerful way to improve scientific research because it can greatly improve the sheer quantity of data that is collected, and it’s a great solution to a shrinking science budget.

But what’s in it for you?

Citizen science makes research a more democratic process, which means you get a say. Also, a fresh set of eyes on an old problem can lead to creative innovations. Isn’t it wonderful to think that you can discover something new and contribute to our scientific knowledge? Plus, it’s a nifty way to engage with the world (for more, read this).

Everyone wins!

There are a large number of projects and online outlets for you to share and contribute to science, so I am including links to them below. Some of them are regional. But no matter your interests, there is likely to be a perfect project for you. So get on out there and start collecting!







Enemies Like This

Yesterday had a theme, and it was this: mimicry.

Mimicry is the similarity between one species and another. And there are just as many flavors of mimicry as there are means for animals to sense the world around them, referred to as modalities. As animals, we humans have several of these as well. We perceive the world through our senses, which includes the visual modality, chemical (smell/taste) modality, or auditory modality. Of course there are others.

But what I want to convey here is that mimicry can exist within any one of these modalities.

The Titan Arum I wrote about yesterday is a great example of chemical mimicry. It mimics the putrid smell of rotting flesh to attract its carrion-eating pollinators. It benefits from this mimicry by being pollinated. As for the pollinator? It’s been duped into responding to the deceptive signal because that chemical scent mostly means a meal or site for laying eggs is close by.

There’s also auditory mimicry, for which the superb lyrebird is the master dj. I saw a talk on these magnificent birds yesterday, and I learned that they can incorporate into their calls a remix of over a dozen different songbirds, not to mention opossums!

In the cuckoo-host system I mentioned in a previous post, the colorful egg mimics of the cuckoos are a form of visual mimicry.

Here’s another:

Planthopper, Siphanta acuta, mimics a leaf (Wiki Commons)

Got predators? Not a problem – just mimic a leaf to avoid being perceived and subsequently eaten!

Sure, plant-mimicking animals seem silly (albeit effective), but what happens when the tables are turned?

Ophrys speculum, the Mirror Bee Orchid; photo taken in Portugal, Algarve, in March 2004 by Carsten Niehaus (Wiki Commons)

This orchid mimics a female bee, which is not so silly if you’re a male bee. He’ll think he’s landed on the sexiest female on the flower patch, only to discover that not only is she not a female, she’s not even an animal!

Never you mind though. The male bee will be duped into mating with it. While this kinky, plant-animal mating will go nowhere for the bee, it will serve as a way for the orchid to be able to mate (not with the bee, but by spreading its pollen when the bee moves to the next deceptive orchid).

There are countless other cool examples of mimicry. It abounds in nature. The question for you to think about is this: what have you mistaken lately?


Here’s a puzzling argument that a philosopher introduced me to yesterday:

Global climate change* is a phenomenon that will undoubtedly have devastating long-term effects on the earth and its inhabitants. We (the 97%) believe that these changes are caused by humans. One simple thing we humans can do to curb climate change is reduce greenhouse gas emissions. Or, we could simply go on as we currently are, doing nothing.

Wiki Commons – License: CC by 2.0 User: Joost J. Bakker IJmuiden Joost J. Bakker

The decision is moral. If we do not curb greenhouse gas emissions, we will harm future generations of people. So, you might think, we should curb emissions. However, if we curb emissions, then those people — the people we will supposedly harm, if we do nothing — will not exist.

Wait, what?

That’s right. If we change our behavior in such a way that catastrophic climate change does not occur, then the people we would have harmed, had we done nothing, will not exist. Different policies will lead to different consequences will lead to different genetic combinations will lead to different human beings. So, one might ask, how can we harm future people by not curbing emissions when curbing emissions results in those very same people not existing?

Makes your brain twisty, doesn’t it?

This is an example of the nonidentity problem. You can read more about it here.

Is something wrong with the argument? If so, what?

*Side note: Climate change is a better term to use than ‘global warming’ because it encompasses all of the possible climatic changes that can (and are) globally occurring, including surface temperatures changes (i.e. global warming), precipitation pattern changes, and sea level changes.

Art vs. Science

I was given a great piece of advice today by a philanthropist. One that I hadn’t been given in a long while. Simply this: express yourself.

When you get home from a long day, and I mean long, tap into the creative side.

Write poetry. Paint. Sing. Play guitar. Take photos.

Wing scales of a butterfly (Photo credit: Tom Eisner)

Wing scales of a butterfly (Photo credit: Tom Eisner)

Take a break to be a whole, well-rounded person.

There are two things one can gain from this approach: 1) sanity and 2) a fresh perspective upon return to work

You can also be inspired by science and nature. Here are some examples of this intersection between art and science. Or find your inspiration in one of these animal sound recordings. Or this nearly indecipherable poem about grasshoppers. Or listen to artists who master science music geekery.

Many people don’t realize a) that scientists are highly creative people and b) there is a surprising connection between scientists and music. Just ask one, and she or he will likely know how to play at least one instrument.

An old professor from my department is rumored to have once said, “Never trust a scientist that doesn’t have a love of music.”

I’m inclined to agree.

All this to say: it’s time to remove the “vs”.

Networking (Theory)

I take pleasure in coincidences. One of my favorite coincidences happened just a week ago. At the anniversary weekend of my department, I met an alumna who is currently a professor at a small liberal arts college in Pennsylvania. It just so happens that one of my former students back from my Teach for America days in Brooklyn goes to this very college now. I asked the alumna if she knows my former student (then in 7th and 8th grade), and lo and behold, this student is currently in her neuroscience class! Wow – mind blown!

Then there’s the time that out of a crowd of 60,000 people at a concert in London one summer, I spotted a random guy that I had casually chatted with once at the breakfast table of a hostel in Argentina six months earlier. (Side note: incredible memory for faces apparently IS a thing). Or that time a decade ago that I randomly talked to a stranger in Fiji to learn that he (at the time) lived in my hometown AND we knew someone in common! Not to mention Facebook friend adds that result in the realization that we have random friends in common, not just locally, but globally.

I could go on and on. But I have met people that are not impressed by these stories. They have come to expect them. One such person is Steve Strogatz, a mathematician at Cornell that I had the pleasure to see speak on campus this past Friday. The topic was his co-authored work on small-world networks. By networks, we mean to say associations between individuals – be they humans, birds, or even neurons in the brain. Based on this modeling work, such coincidences as I’ve described above shouldn’t come as a surprise at all.

From Wiki Commons

From Wiki Commons

How do networks behave, and how do you get a small-world phenomenon to arise out a seemingly giant network (aka, the human population)? All it takes are a few key properties. One such property is the average shortest path between the nodes. If we were to play the Kevin Bacon game, this would be the smallest number of steps it takes to get from Kevin Bacon to the actor of your choice. In reality, this takes less than six degrees of separation, it’s more on the order of three or four.

Another property is the degree to which the nodes cluster. There tends to be more clustering within networks than is predicted by random chance, with nodes creating tightly-knit groups. With high connectivity between nodes and some nodes more connected than others (so called, hubs), it’s easy to see how small-world networks arise.

From neural networks in the brain to web pages on the internet, there’s growing evidence that real networks, though complex, are actually small-world networks.

So it IS a small world after all. Yet despite rationally knowing this, I know I will still be in awe of the next coincidence, no matter how probable it is.

For more from Strogatz, read his 15-part series on mathematics in the New York Times.