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Are humans evolving?

In 2005, Stefasson et al. reported the fascinating discovery of an allele in humans whose presence is associated with increased fertility in Icelandic and European populations. Females with at least one copy of the allele have approximately 3.5%, and males 2.9%, more children on average than non-carriers. The exact mechanism by which the allele affects fertility is unknown.

1. Predict: Consider what you know about evolution. Do you think these populations are likely to be evolving with respect to this allele? Why or why not? Please make sure your response illustrates your understanding of evolution.

2. Test: Describe one way you could test your prediction quantitatively . What data would enable you to conclude that these human populations are evolving? What results would support the contention they are not?

Differential survival and reproduction underpin evolution

The fascinating discovery above should have called to mind the key causes, a.k.a. 'agents', of evolution

  • natural selection
  • sexual selection
  • genetic drift (including bottle necks and founder effects)
  • immigration/emigration
  • mutation

and their consequences. All cause a population to evolve by altering the frequency with which particular phenotypes, their underlying genotypes and most importantly the responsible alleles, occur. This quantitative description of the genetic consequences of these evolutionary mechanisms is encapsulated by the population geneticists definition of evolution:

  • Evolution is a change in the allele frequencies observed in a population over time (i.e. over generations).

Agents of evolution cause allele frequencies to change because they result in differential survival and reproduction. That is, not every individual has an equal chance of surviving, reproducing and contributing surviving offspring to the next generation. (The survival of offspring is key; if you reproduce but your kids don't survive to reproduce then you are evolutionarily inconsequential in terms of your allelic contribution to future generations.) Instead, for reasons that vary with the agent, some phenotypes, and their responsible genotypes, are more likely to survive or to reproduce and thus, to leave behind offspring than other phenotypes (genotypes). As a result, alleles of reproductively successful individuals become more common, and those associated with relatively unsuccessful individuals become less common, in subsequent generations. This change in allele frequencies is, of course, evolution.

Conversely, a population will not evolve if every phenotype (genotype) has an equal probability of surviving and producing surviving offspring. To imagine this, conjure a population in which all of the following conditions are simultaneously met:

  • all phenotypes are equally likely to survive and to reproduce surviving offspring; there is no natural selection.
  • all phenotypes are equally attractive or have equal access to potential mates; there is no sexual selection.
  • no phenotypes leave behind more offspring than others just by chance; the population must be very large as there is no genetic drift.
  • breeding individuals (and their genotypes) are not leaving or entering the population; there is no emigration or immigration.

The genetic consequence of all this equality is that the same allele frequencies are maintained from one generation to the next so the population does not evolve.

Of course, not all organisms reproduce sexually but the point is that a population will not evolve if all genotypes are equally likely to leave behind offspring with their alleles, even if reproduction occurs asexually.

3. Consider these definitions as you reflect your answers to questions 1 and 2 in the "Are Humans Evolving?" scenario above. Have you learned anything that would encourage you to modify your answers? If so, please do. If not, explain why your responses are appropriate.

    Definitions

  • frequency - the number of times an event or observation, for example a particular measurement or condition like blue eyes, is observed in a collection of events or observations like those comprising a sample, population or study. In this statistical sense, a frequency is equivalent to a proportion. For example, the frequency of a particular allele is equal to the number of times that allele is observed in a population over the total number of alleles for that locus in the population. Can be expressed as a fraction, a percentage, a decimal, or a probability.

    Works cited

  • Stefansson, H., Helgason, A., Thorleifsson, G. et al. 2005. A common inversion under selection in Europeans. Nature Genetics . 37:129-137.

Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Understanding the hardy-weinberg equation. OpenStax CNX. Oct 22, 2007 Download for free at http://cnx.org/content/col10472/1.1
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