I read an article claiming that our ancestors were taller than us. their reasoning can be summarized as:
The smaller the planet, the lesser its gravity and the bigger and taller its creatures will be.
The earth was much smaller and it keeps expanding.
No, according to the fossil record, most past human species were similar heights or shorter than modern humans, research suggests that:
suggests that the height of the Homo genus remained more or less stable for 2 million years until the appearance of a "ground-breaking species in this sense" in Africa just 200,000 years ago. These were the Homo sapiens, who were initially significantly taller than any other species that existed at the time.
Image and quote source: Homo heidelbergensis was only slightly taller than the Neanderthal (2012)
A couple more examples are in the diagram below:
Image source: Blog of Michael J. Ryan, Ph.D. Head of Vertebrate Paleontology, Cleveland Museum of Natural History
In fact, according to the article Why are we getting taller as a species? (1998), we, as a species are getting taller, due to:
Most geneticists believe that the improvement in childhood nutrition has been the most important factor in allowing humans to increase so dramatically in stature.
But importantly, they state:
the trend toward increasing height has largely leveled off, suggesting that there is an upper limit to height beyond which our genes are not equipped to take us, regardless of environmental improvements.
As for the basis of this notion, the theory that the Earth was smaller in the past, explained in the answer here.
Some further references:
José-Miguel Carretero, Laura Rodríguez, Rebeca García-González, Juan-Luis Arsuaga, Asier Gómez-Olivencia, Carlos Lorenzo, Alejandro Bonmatí, Ana Gracia, Ignacio Martínez, Rolf Quam. Stature estimation from complete long bones in the Middle Pleistocene humans from the Sima de los Huesos, Sierra de Atapuerca (Spain). Journal of Human Evolution, 2012; 62 (2): 242 DOI: 10.1016/j.jhevol.2011.11.004
. Wu, X. Collilieux, Z. Altamimi, B. L. A. Vermeersen, R. S. Gross, I. Fukumori. Accuracy of the International Terrestrial Reference Frame origin and Earth expansion. Geophysical Research Letters, 2011; 38 (13) DOI: 10.1029/2011GL047450
